Patterns of host specificity and transmission among parasites of wild primates

Predicting host range expansion in parasitic mites using a global mammalian-acarine dataset

Multi-host parasites pose greater health risks to wildlife, livestock, and humans than single-host parasites, yet our understanding of how ecological and biological factors influence a parasite's host range remains limited. Here, we assemble the largest and most complete dataset on permanently parasitic mammalian mites and build a predictive model assessing the probability of single-host parasites to become multi-hosts, while accounting for potentially unobserved host-parasite links and class imbalance. This model identifies statistically significant predictors related to parasites, hosts, climate, and habitat disturbance. The most important predictors include the parasite's contact level with the host immune system and two variables characterizing host phylogenetic similarity and spatial co-distribution. Our model reveals an overrepresentation of mites associated with Rodentia (rodents), Chiroptera (bats), and Carnivora in the multi-host risk group. This highlights both the potential vulnerability of these hosts to parasitic infestations and the risk of serving as reservoirs of parasites for new hosts. In addition, we find independent macroevolutionary evidence that supports our prediction of several single-host species of Notoedres, the bat skin parasites, to be in the multi-host risk group, demonstrating the forecasting potential of our model.

Assessing the role of individual foxes in environmental contamination with Echinococcus multilocularis through faecal samples

Key parasite transmission parameters are difficult to obtain from elusive wild animals. For Echinococcus multilocularis, the causative agent of alveolar echinococcosis (AE), the red fox is responsible for most of the environmental contamination in Europe. The identification of individual spreaders of E. multilocularis environmental contamination is crucial to improving our understanding of the ecology of parasite transmission in areas of high endemicity and optimising the effectiveness of prevention and control measures in the field. Genetic faecal sampling appears to be a feasible method to gain information about the faecal deposition of individual animals. We conducted a 4 year faecal sampling study in a village that is highly endemic for E. multilocularis, to assess the feasibility of individual identification and sexing of foxes to describe individual infection patterns. Individual fox identification from faecal samples was performed by obtaining reliable genotypes from 14 microsatellites and one sex locus, coupled with the detection of E. multilocularis DNA, first using captive foxes and then by environmental sampling. From a collection of 386 fox stools collected between 2017 and 2020, tested for the presence of E. multilocularis DNA, 180 were selected and 124 samples were successfully genotyped (68.9%). In total, 45 unique individual foxes were identified and 26 associated with at least one sample which tested positive for E. multilocularis (Em(+)). Estimation of the population size showed the fox population to be between 29 and 34 individuals for a given year and 67 individuals over 4 years. One-third of infected individuals (9/26 Em(+) foxes) deposited 2/3 of the faeces which tested positive for E. multilocularis (36/60 Em(+) stools). Genetic investigation showed a significantly higher average number of multiple stools for females than males, suggesting that the two sexes potentially defecated unequally in the studied area. Three partially overlapping clusters of fox faeces were found, with one cluster concentrating 2/3 of the total E. multilocularis-positive faeces. Based on these findings, we estimated that 12.5 million E. multilocularis eggs were produced during the study period, emphasizing the high contamination level of the environment and the risk of exposure faced by the parasite hosts.

A combined amplicon approach to nematode polyparasitism occurring in captive wild animals in southern China

BACKGROUND

Gastrointestinal tract (GIT) nematodes prefer to live in the intestines of wild animals, causing damage and even death, and posing a zoonotic risk. The polyparasitism of GIT nematodes results in the complex dynamics of the nematode communities that occur naturally in wild animals. However, the nematode community in captive wild animals is poorly understood.

METHODS

We combined  microscopic examination and amplicon sequencing for community diversity.

RESULTS

We characterized GIT nematode assemblages to one order, one family, four genera, and ten species, in 512 fecal samples of 121 species from captive wild animals in southern China. The positive rate of GIT nematodes was 20.7% (106/512), including 42.3% (11/26) in reptiles, 26.5% (39/147) in herbivores, 25.0% (25/100) in non-human primates, 20.0% (5/25) in omnivores, 12.2% (9/74) in carnivores, and 12.1% (17/140) in avians. The dominant nematodes were Haemonchus contortus in herbivores and Trichuris species in primates. The nematode communities of arboreal primates differed from their terrestrial counterparts, reflecting both host phylogeny and ecological constraints. Soil-transmitted Strongyloides species were widespread throughout the herbivore, primate, avian, and carnivore communities, and tended to infect omnivorous primates and terrestrial herbivores. In addition, new Trichuris and Heterakis species were found in the nematode communities of captive porcupines and peafowls.

CONCLUSION

This study highlights the variation in the composition of the GIT nematode community and strengthens the attention to the harms induced by zoonotic nematodes and co-infective nematodes with low species richness.

Diversity and prevalence of zoonotic infections at the animal-human interface of primate trafficking in Peru

Wildlife trafficking creates favorable scenarios for intra- and inter-specific interactions that can lead to parasite spread and disease emergence. Among the fauna affected by this activity, primates are relevant due to their potential to acquire and share zoonoses - infections caused by parasites that can spread between humans and other animals. Though it is known that most primate parasites can affect multiple hosts and that many are zoonotic, comparative studies across different contexts for animal-human interactions are scarce. We conducted a multi-parasite screening targeting the detection of zoonotic infections in wild-caught monkeys in nine Peruvian cities across three contexts: captivity (zoos and rescue centers, n = 187); pet (households, n = 69); and trade (trafficked or recently confiscated, n = 132). We detected 32 parasite taxa including mycobacteria, simian foamyvirus, bacteria, helminths, and protozoa. Monkeys in the trade context had the highest prevalence of hemoparasites (including Plasmodium malariae/brasilianum, Trypanosoma cruzi, and microfilaria) and enteric helminths and protozoa were less common in pet monkeys. However, parasite communities showed overall low variation between the three contexts. Parasite richness (PR) was best explained by host genus and the city where the animal was sampled. Squirrel (genus Saimiri) and wooly (genus Lagothrix) monkeys had the highest PR, which was ~2.2 times the PR found in tufted capuchins (genus Sapajus) and tamarins (genus Saguinus/Leontocebus) in a multivariable model adjusted for context, sex, and age. Our findings illustrate that the threats of wildlife trafficking to One Health encompass exposure to multiple zoonotic parasites well-known to cause disease in humans, monkeys, and other species. We demonstrate these threats continue beyond the markets where wildlife is initially sold; monkeys trafficked for the pet market remain a reservoir for and contribute to the translocation of zoonotic parasites to households and other captive facilities where contact with humans is frequent. Our results have practical applications for the healthcare of rescued monkeys and call for urgent action against wildlife trafficking and ownership of monkeys as pets.

Using phylogeographic link-prediction in primates to prioritize human parasite screening

Objectives

The ongoing risk of emerging infectious disease has renewed calls for understanding the origins of zoonoses and identifying future zoonotic disease threats. Given their close phylogenetic relatedness and geographic overlap with humans, non-human primates (NHPs) have been the source of many infectious diseases throughout human evolution. NHPs harbor diverse parasites, with some infecting only a single host species while others infect species from multiple families.

Materials and Methods

We applied a novel link-prediction method to predict undocumented instances of parasite sharing between humans and NHPs. Our model makes predictions based on phylogenetic distances and geographic overlap among NHPs and humans in six countries with high NHP diversity: Columbia, Brazil, Democratic Republic of Congo, Madagascar, China and Indonesia.

Results

Of the 899 human parasites documented in the Global Infectious Diseases and Epidemiology Network (GIDEON) database for these countries, 12% were shared with at least one other NHP species. The link prediction model identified an additional 54 parasites that are likely to infect humans but were not reported in GIDEON. These parasites were mostly host generalists, yet their phylogenetic host breadth varied substantially.

Discussion

As human activities and populations encroach on NHP habitats, opportunities for parasite sharing between human and non-human primates will continue to increase. Our study identifies specific infectious organisms to monitor in countries with high NHP diversity, while the comparative analysis of host generalism, parasite taxonomy, and transmission mode provides insights to types of parasites that represent high zoonotic risk.

Multi-Species Host Use by the Parasitoid Fly Ormia lineifrons

Antagonistic species relationships such as parasitoid/host interactions lead to evolutionary arms races between species. Many parasitoids use more than one host species, requiring the parasitoid to adapt to multiple hosts, sometimes being the leader or the follower in the evolutionary back-and-forth between species. Thus, multi-species interactions are dynamic and show temporary evolutionary outcomes at a given point in time. We investigated the interactions of the multivoltine parasitoid fly Ormia lineifrons that uses different katydid hosts for each of its fly generations sequentially over time. We hypothesized that this fly is adapted to utilizing all hosts equally well for the population to persist. We quantified and compared the fly's development in each of the four Neoconocephalus hosts. Cumulative parasitism rates ranged between ~14% and 73%, but parasitoid load and development time did not differ across host species. Yet, pupal size was lowest for flies using N. velox as a host compared to N. triops and other host species. Successful development from pupa to adult fly differed across host species, with flies emerging from N. triops displaying a significantly lower development success rate than those emerging from N. velox and the other two hosts. Interestingly, N. triops and N. velox did not differ in size and were smaller than N. robustus and N. nebrascensis hosts. Thus, O. lineifrons utilized all hosts but displayed especially low ability to develop in N. triops, potentially due to differences in the nutritional status of the host. In the multi-species interactions between the fly and its hosts, the poor use of N. triops may currently affect the fly's evolution the most. Similarities and differences across host utilization and their evolutionary background are discussed.

Predicting primate-parasite associations using exponential random graph models

Ecological associations between hosts and parasites are influenced by host exposure and susceptibility to parasites, and by parasite traits, such as transmission mode. Advances in network analysis allow us to answer questions about the causes and consequences of traits in ecological networks in ways that could not be addressed in the past. We used a network-based framework (exponential random graph models or ERGMs) to investigate the biogeographic, phylogenetic and ecological characteristics of hosts and parasites that affect the probability of interactions among nonhuman primates and their parasites. Parasites included arthropods, bacteria, fungi, protozoa, viruses and helminths. We investigated existing hypotheses, along with new predictors and an expanded host-parasite database that included 213 primate nodes, 763 parasite nodes and 2319 edges among them. Analyses also investigated phylogenetic relatedness, sampling effort and spatial overlap among hosts. In addition to supporting some previous findings, our ERGM approach demonstrated that more threatened hosts had fewer parasites, and notably, that this effect was independent of hosts also having a smaller geographic range. Despite having fewer parasites, threatened host species shared more parasites with other hosts, consistent with loss of specialist parasites and threat arising from generalist parasites that can be maintained in other, non-threatened hosts. Viruses, protozoa and helminths had broader host ranges than bacteria, or fungi, and parasites that infect non-primates had a higher probability of infecting more primate species. The value of the ERGM approach for investigating the processes structing host-parasite networks provided a more complete view on the biogeographic, phylogenetic and ecological traits that influence parasite species richness and parasite sharing among hosts. The results supported some previous analyses and revealed new associations that warrant future research, thus revealing how hosts and parasites interact to form ecological networks.

Preliminary Survey of Pathogens in the Asian Honey Bee (Apis cerana) in Thailand

Widespread parasites, along with emerging threats, globalization, and climate change, have greatly affected honey bees' health, leading to colony losses worldwide. In this study, we investigated the detection of biotic stressors (i.e., viruses, microsporidian, bacteria, and fungi) in Apis cerana by surveying the colonies across different regions of Thailand (Chiang Mai in the north, Nong Khai and Khon Kaen in the northeast, and Chumphon and Surat Thani in the south, in addition to the Samui and Pha-ngan islands). In this study, we detected ABPV, BQCV, LSV, and Nosema ceranae in A. cerana samples through RT-PCR. ABPV was only detected from the samples of Chiang Mai, whereas we found BQCV only in those from Chumphon. LSV was detected only in the samples from the Samui and Pha-ngan islands, where historically no managed bees are known. Nosema ceranae was found in all of the regions except for Nong Khai and Khon Kaen in northeastern Thailand. Paenibacillus larvae and Ascosphaera apis were not detected in any of the A. cerana samples in this survey. The phylogenetic tree analysis of the pathogens provided insights into the pathogens' movements and their distribution ranges across different landscapes, indicating the flow of pathogens among the honey bees. Here, we describe the presence of emerging pathogens in the Asian honey bee as a valuable step in our understanding of these pathogens in terms of the decline in eastern honey bee populations.

A framework for testing the impact of co-infections on host gut microbiomes

Parasitic infections disturb gut microbial communities beyond their natural range of variation, possibly leading to dysbiosis. Yet it remains underappreciated that most infections are accompanied by one or more co-infections and their collective impact is largely unexplored. Here we developed a framework illustrating changes to the host gut microbiome following single infections, and build on it by describing the neutral, synergistic or antagonistic impacts on microbial α- and ß-diversity expected from co-infections. We tested the framework on microbiome data from a non-human primate population co-infected with helminths and Adenovirus, and matched patterns reported in published studies to the introduced framework. In this case study, α-diversity of co-infected Malagasy mouse lemurs (Microcebus griseorufus) did not differ in comparison with that of singly infected or uninfected individuals, even though community composition captured with ß-diversity metrices changed significantly. Explicitly, we record stochastic changes in dispersion, a sign of dysbiosis, following the Anna-Karenina principle rather than deterministic shifts in the microbial gut community. From the literature review and our case study, neutral and synergistic impacts emerged as common outcomes from co-infections, wherein both shifts and dispersion of microbial communities following co-infections were often more severe than after a single infection alone, but microbial α-diversity was not universally altered. Important functions of the microbiome may also suffer from such heavily altered, though no less species-rich microbial community. Lastly, we pose the hypothesis that the reshuffling of host-associated microbial communities due to the impact of various, often coinciding parasitic infections may become a source of novel or zoonotic diseases.

Improving mathematical modeling of interventions to prevent healthcare-associated infections by interrupting transmission or pathogens: How common modeling assumptions about colonized individuals impact intervention effectiveness estimates

Mathematical models are used to gauge the impact of interventions for healthcare-associated infections. As with any analytic method, such models require many assumptions. Two common assumptions are that asymptomatically colonized individuals are more likely to be hospitalized and that they spend longer in the hospital per admission because of their colonization status. These assumptions have no biological basis and could impact the estimated effects of interventions in unintended ways. Therefore, we developed a model of methicillin-resistant Staphylococcus aureus transmission to explicitly evaluate the impact of these assumptions. We found that assuming that asymptomatically colonized individuals were more likely to be admitted to the hospital or spend longer in the hospital than uncolonized individuals biased results compared to a more realistic model that did not make either assumption. Results were heavily biased when estimating the impact of an intervention that directly reduced transmission in a hospital. In contrast, results were moderately biased when estimating the impact of an intervention that decolonized hospital patients. Our findings can inform choices modelers face when constructing models of healthcare-associated infection interventions and thereby improve their validity.

Gastrointestinal parasites of Leontopithecus chrysomelas in the Atlantic Forest, Brazil

We performed coproparasitological testing of free-living golden-headed lion tamarins, Leontopithecus chrysomelas, using the Hoffmann-Pons-Janner method. In total, we collected 118 samples from ten groups: four living in Federal Protected Area and six living in Non-Protected Areas of cocoa farms. Eggs from parasites of the Acanthocephala phylum and Spiruridae, Ancylostomatidae, Ascarididae and Oxyuridae families were identified, as well as the genus Strongyloides (Nematode: Strongyloididae) and phylum Apicomplexa. This is the first description of infection with coccidian, Trichuridae family and Strongyloides spp. in L. chrysomelas. A total of 48% (n= 57) of the animals were infected and the highest prevalence (37.2±SD 8.72, n = 44) was for Acanthocephalidae, followed by Spiruridae (8.5±SD 5.03, n = 10). There was no difference in parasite prevalence by age classes or sex. However, we found higher diversity and prevalence of parasites in animals living in the Federal Protected Area. These results suggest that intestinal parasites may be influenced by environmental factors, such as the management of the areas where the animals live, in addition to the feeding behavior of L. chrysomelas and distinct transmission strategies of parasites. The combination of ecological and demographic data combined with parasitological studies may contribute to conservation programs for this species.

Primate malarias as a model for cross-species parasite transmission

Parasites regularly switch into new host species, representing a disease burden and conservation risk to the hosts. The distribution of these parasites also gives insight into characteristics of ecological networks and genetic mechanisms of host-parasite interactions. Some parasites are shared across many species, whereas others tend to be restricted to hosts from a single species. Understanding the mechanisms producing this distribution of host specificity can enable more effective interventions and potentially identify genetic targets for vaccines or therapies. As ecological connections between human and local animal populations increase, the risk to human and wildlife health from novel parasites also increases. Which of these parasites will fizzle out and which have the potential to become widespread in humans? We consider the case of primate malarias, caused by Plasmodium parasites, to investigate the interacting ecological and evolutionary mechanisms that put human and nonhuman primates at risk for infection. Plasmodium host switching from nonhuman primates to humans led to ancient introductions of the most common malaria-causing agents in humans today, and new parasite switching is a growing threat, especially in Asia and South America. Based on a wild host-Plasmodium occurrence database, we highlight geographic areas of concern and potential areas to target further sampling. We also discuss methodological developments that will facilitate clinical and field-based interventions to improve human and wildlife health based on this eco-evolutionary perspective.

Forecasting parasite sharing under climate change

Species are shifting their distributions in response to climate change. This geographic reshuffling may result in novel co-occurrences among species, which could lead to unseen biotic interactions, including the exchange of parasites between previously isolated hosts. Identifying potential new host-parasite interactions would improve forecasting of disease emergence and inform proactive disease surveillance. However, accurate predictions of future cross-species disease transmission have been hampered by the lack of a generalized approach and data availability. Here, we propose a framework to predict novel host-parasite interactions based on a combination of niche modelling of future host distributions and parasite sharing models. Using the North American ungulates as a proof of concept, we show this approach has high cross-validation accuracy in over 85% of modelled parasites and find that more than 34% of the host-parasite associations forecasted by our models have already been recorded in the literature. We discuss potential sources of uncertainty and bias that may affect our results and similar forecasting approaches, and propose pathways to generate increasingly accurate predictions. Our results indicate that forecasting parasite sharing in response to shifts in host geographic distributions allow for the identification of regions and taxa most susceptible to emergent pathogens under climate change. This article is part of the theme issue 'Infectious disease macroecology: parasite diversity and dynamics across the globe'.

Post COVID-19: a solution scan of options for preventing future zoonotic epidemics

The crisis generated by the emergence and pandemic spread of COVID-19 has thrown into the global spotlight the dangers associated with novel diseases, as well as the key role of animals, especially wild animals, as potential sources of pathogens to humans. There is a widespread demand for a new relationship with wild and domestic animals, including suggested bans on hunting, wildlife trade, wet markets or consumption of wild animals. However, such policies risk ignoring essential elements of the problem as well as alienating and increasing hardship for local communities across the world, and might be unachievable at scale. There is thus a need for a more complex package of policy and practical responses. We undertook a solution scan to identify and collate 161 possible options for reducing the risks of further epidemic disease transmission from animals to humans, including potential further SARS-CoV-2 transmission (original or variants). We include all categories of animals in our responses (i.e. wildlife, captive, unmanaged/feral and domestic livestock and pets) and focus on pathogens (especially viruses) that, once transmitted from animals to humans, could acquire epidemic potential through high rates of human-to-human transmission. This excludes measures to prevent well-known zoonotic diseases, such as rabies, that cannot readily transmit between humans. We focused solutions on societal measures, excluding the development of vaccines and other preventive therapeutic medicine and veterinary medicine options that are discussed elsewhere. We derived our solutions through reading the scientific literature, NGO position papers, and industry guidelines, collating our own experiences, and consulting experts in different fields. Herein, we review the major zoonotic transmission pathways and present an extensive list of options. The potential solutions are organised according to the key stages of the trade chain and encompass solutions that can be applied at the local, regional and international scales. This is a set of options targeted at practitioners and policy makers to encourage careful examination of possible courses of action, validating their impact and documenting outcomes.

The Context-Dependent Effects of Host Competence, Competition, and Pathogen Transmission Mode on Disease Prevalence

AbstractBiodiversity in communities is changing globally, including the gain and loss of host species in host-pathogen communities. Increased host diversity can cause infection prevalence in a focal host to increase (amplification) or decrease (dilution). However, it is unclear what general rules govern the context-dependent effects, in part because theories for pathogens with different transmission modes have developed largely independently. Using a two-host model, we explore how the pathogen transmission mode and characteristics of a second host (disease competence and competitive ability) influence disease prevalence in a focal host. Our work shows how the theories for pathogens with environmental transmission, density-dependent direct transmission, and frequency-dependent direct transmission can be unified. Our work also identifies general rules about how host and pathogen characteristics affect amplification/dilution. For example, higher-competence hosts promote amplification, unless they are strong interspecific competitors; strong interspecific competitors promote dilution, unless they are large sources of new infections; and dilution occurs under frequency-dependent direct transmission more than density-dependent direct transmission, unless interspecific host competition is sufficiently strong. Our work helps explain how the characteristics of the pathogen and a second host affect disease prevalence in a focal host.

Using sensitivity analysis to identify factors promoting higher versus lower infection prevalence in multi-host communities

Relationships between host species richness and levels of disease in a focal host are likely to be context-dependent, depending on the characteristics of which particular host species are present in a community. I use a multi-host epidemiological model with environmental transmission to explore how the characteristics of the host species (e.g., competence and competitive ability), host density, and the pathogen transmission mechanism affect the proportion of infected individuals (i.e., infection prevalence) in a focal host. My sensitivity-based approach identifies the indirect pathways through which specific ecological and epidemiological processes affect focal host infection prevalence. This in turn yields predictions about the context-dependent rules governing whether increased host species richness increases (amplifies) or decreases (dilutes) infection prevalence in a focal host. For example, in many cases, amplification and dilution are predicted to occur when added host species are sources or sinks of infectious propagules, respectively. However, if the added host species have strong and asymmetric competitive effects on resident host species, then amplification and dilution are predicted to occur when the added host species have stronger competitive effects on resident host species that are sources or sinks of infectious propagules, respectively. My results also predict that greater dilution and less amplification is more likely to occur under frequency-dependent direct transmission than density-dependent direct transmission when (i) the added hosts have lower competence than resident host species and (ii) interspecific competition between the added host species and resident host species is lower; the opposite conditions promote greater amplification and less dilution under frequency-dependent direct transmission. This work helps identify and explain the mechanisms shaping the context-dependent relationships between host species richness and disease in multi-host communities.

Intestinal parasites of dogs (Canis lupus familiaris) in Svalbard (Norway): low prevalence and limited transmission with wildlife

Domesticated dogs (Canis lupus familiaris Linnaeus, 1758) are widely kept on all continents and could share parasites with free-living animals. To understand the transmission of intestinal parasites between dogs kept on the four dog stations and wildlife in Svalbard, 170 faecal samples from dogs and 203 faecal samples from wildlife, including Arctic fox (Vulpes lagopus (Linnaeus, 1758); n = 62), Svalbard reindeer (Rangifer tarandus platyrhynchus (Vrolik, 1829); n = 106), sibling vole (Microtus levis Miller, 1908; n = 63), Pink-footed Goose (Anser brachyrhynchus Baillon, 1834; n = 30), Little Auk (Alle alle (Linnaeus, 1758); n = 49), and Black-legged Kittiwake (Rissa tridactyla (Linnaeus, 1758); n = 18), were individually screened for the presence of intestinal parasites using microscopy and PCR and nucleotide sequencing methods. Additionally, the results of the study were compared with previous studies performed in the same area. The roundworm Toxascaris leonina (Linstow, 1902) was found microscopically and by PCR in a dog (n = 1). The specific DNA of three species of parasitic protists was detected in dogs from different yards. Phylogenetic analyses revealed the presence of Cryptosporidium canis Fayer, Trout, Xiao, Morgan, Lal and Dubey, 2001 (n = 1), Encephalitozoon cuniculi Levaditi, Nicolau and Schoen, 1923 genotype II (n = 4), and dog-specific Enterocytozoon bieneusi Desportes, Le Charpentier, Galian, Bernard, Cochand-Priollet, Lavergne, Ravisse and Modigliani, 1985 genotypes (n = 12). This study showed overall a low prevalence of intestinal parasites in dogs in Svalbard and possible but minimal transmission with wildlife.

Gastro-intestinal parasites in two subspecies of toque macaque (Macaca sinica) in Sri Lanka and their zoonotic potential

Gastro-intestinal (GI) parasites of primates have a greater potential of becoming zoonotic. This potential may vary in different primates based on multiple factors such as proximity to human settlements and the climate of their habitat. We examined the GI parasites in two subspecies of toque macaque: Macaca sinica sinica (confined to the dry zone) and Macaca sinica aurifrons (confined to the wet zone) of Sri Lanka. Fresh faecal samples were collected and analysed following a modified Sheather's sucrose floatation method. A total of 90.8% (89/98) macaques were infected with one or more parasite species. There was no difference in the overall prevalence of GI parasites between the two subspecies, M. s. aurifrons (95.9%) and M. s. sinica (85.7%; χ²;χ = 3.059, p = 0.080). Sixteen parasite species were recorded including, 15 species in the M. s. sinica and 12 species in the M. s. aurifrons. Among the helminths identified, Anatrichosoma sp., Ancylostoma spp., Capillaria spp., Oesophagostomum /Bunostomum spp. and Physaloptera spp. are known to be zoonotic while Ascaris spp., Enterobius sp., Strongyloides spp. and Trichuris spp. have both zoonotic and anthroponotic potential. Among the protozoans, Balantidium coli and Buxtonella sp. are known to be zoonotic, while Entamoeba spp. and Cryptosporidium spp. have both anthroponotic and zoonotic potential. This study provides the first record of Anatrichosoma sp. and Buxtonella sp. in Sri Lanka and the first record of Cryptosporidium spp. in M. s. aurifrons. The molecular data allowed further identification and differentiation of Entamoeba nuttalli and E. coli that are known to be zoonotic and anthroponotic, respectively. The two subspecies of macaques have close interactions with humans; hence, in-depth epidemiological studies are required to understand the potential public-health risks to humans and conservation implications for macaque populations.

Epidemiological transitions in human evolution and the richness of viruses, helminths, and protozoa

BACKGROUND AND OBJECTIVES

In absolute terms, humans are extremely highly parasitized compared to other primates. This may reflect that humans are outliers in traits correlated with parasite richness: population density, geographic range area, and study effort. The high degree of parasitism could also reflect amplified disease risk associated with agriculture and urbanization. Alternatively, controlling for other variables, cultural and psychological adaptations could have reduced parasitism in humans over evolutionary time.

METHODOLOGY

We predicted the number of parasites that would infect a nonhuman primate with human phenotypic characteristics and phylogenetic position, and then compared observed parasitism of humans in eight geopolitical countries to the predicted distributions. The analyses incorporated study effort, phylogeny, and drivers of parasitism in 33 primate species.

RESULTS

Analyses of individual countries were not supportive of either hypothesis. When analyzed collectively, however, human populations showed consistently lower than expected richness of protozoa and helminths, but higher richness of viruses. Thus, human evolutionary innovations and new parasite exposures may have impacted groups of parasites in different ways, with support for both hypotheses in the overall analysis.

CONCLUSIONS AND IMPLICATIONS

The high level of parasitism observed in humans only applies to viruses, and was not extreme in any of our tests of individual countries. In contrast, we find consistent reductions in protozoa and helminths across countries, suggesting reduced parasitism by these groups during human evolution. We propose that hygienic and technological advances might have extinguished fecal-orally or indirectly transmitted parasites like helminths, whereas higher human densities and host-shifting potential of viruses have supported increased virus richness.

LAY SUMMARY

Vastly more parasite species infect humans than any other primate host. Controlling for factors that influence parasite richness, such as the intensity of study effort and body mass, we find that humans may have more viruses, but fewer helminths and protozoa, than expected based on evolutionary analyses of parasitism in other primates.

Pliant pathogens: Estimating viral spread when confronted with new vector, host, and environmental conditions

Pathogen spread rates are determined, in part, by the performance of pathogens under altered environmental conditions and their ability to persist while switching among hosts and vectors.To determine the effects of new conditions (host, vector, and nutrient) on pathogen spread rate, we introduced a vector-borne viral plant pathogen, Barley Yellow Dwarf Virus PAV (BYDV-PAV) into hosts, vectors, and host nutrient supplies that it had not encountered for thousands of viral generations. We quantified pathogen prevalence over the course of two serial inoculations under the new conditions. Using individual-level transmission rates from this experiment, we parameterized a dynamical model of disease spread and projected spread across host populations through a growing season.A change in nutrient conditions (increased supply of phosphorus) reduced viral transmission whereas shifting to a new vector or host species had no effect on infection prevalence. However, the reduction in the new nutrient environment was only temporary; infection prevalence recovered after the second inoculation. Synthesis. These results highlight how robust the pathogen, BYDV-PAV, is to changes in its biotic and abiotic environment. Our study also highlights the need to quantify longitudinal infection information beyond snapshot assessments to project disease risk for pathogens in new environments.

Comparing the Indirect Effects between Exploiters in Predator-Prey and Host-Pathogen Systems

AbstractIn multipredator and multipathogen systems, exploiters interact indirectly via shared victim species. Interspecific prey competition and the degree of predator specialization are known to influence whether predators have competitive (i.e., (-,-)) or noncompetitive (i.e., (-,+) or (+,+)) indirect interactions. Much less is known about the population-level indirect interactions between pathogens that infect the same populations of host species. In this study, we use two-predator-two-prey and two-host-two-pathogen models to compare the indirect effects between predators with the indirect effects between pathogens. We focus on how the indirect interactions between pathogens are affected by the competitive abilities of susceptible and infected hosts, whether the pathogens are specialists or generalists, and the transmission pathway (direct vs. environmental transmission). In many cases, indirect effects between pathogens and predators follow similar patterns, for example, more positive indirect effects with increased interspecific competition between victim species. However, the indirect effects between pathogens can qualitatively differ, for example, more negative indirect effects with increased interspecific host competition. These contrasting patterns show that an important mechanistic difference between predatory and parasitic interactions (specifically, whether interactions are immediately lethal) can have important population-level effects on the indirect interactions between exploiters.

Effects of seasonality and previous logging on faecal helminth-microbiota associations in wild lemurs

Gastrointestinal helminth-microbiota associations are shaped by various ecological processes. The effect of the ecological context of the host on the bacterial microbiome and gastrointestinal helminth parasites has been tested in a number of ecosystems and experimentally. This study takes the important step to look at these two groups at the same time and to start to examine how these communities interact in a changing host environment. Fresh faecal samples (N = 335) from eight wild Eulemur populations were collected over 2 years across Madagascar. We used 16S ribosomal RNA gene sequencing to characterise the bacterial microbiota composition, and faecal flotation to isolate and morphologically identify nematode eggs. Infections with nematodes of the genera Callistoura and Lemuricola occurred in all lemur populations. Seasonality significantly contributed to the observed variation in microbiota composition, especially in the dry deciduous forest. Microbial richness and Lemuricola spp. infection prevalence were highest in a previously intensely logged site, whereas Callistoura spp. showed no such pattern. In addition, we observed significant correlations between gastrointestinal parasites and bacterial microbiota composition in these lemurs, with 0.4-0.7% of the variation in faecal bacterial microbiota composition being explained by helminth infections. With this study, we show effects of environmental conditions on gastrointestinal nematodes and bacterial interactions in wild lemurs and believe it is essential to consider the potential role of microbiome-parasite associations on the hosts' GI stability, health, and survival.

DNA Footprints: Using Parasites to Detect Elusive Animals, Proof of Principle in Hedgehogs

Simple Summary

Nocturnal and elusive animals are notoriously difficult to count—hedgehogs being a prime example. Therefore, any reliable way to demonstrate the presence of a particular animal, within a given area, would be a valuable addition to many ecologists’ tool kits. The proposed method is based upon the idea that you can find a parasite, specific to a vertebrate animal of interest that has a life stage within an invertebrate host. Molecular detection of these parasites is then carried out in the more abundant and easily collected invertebrate intermediate host. The key to this proposed method is the specificity of the parasite to the vertebrate animal and its detection in the invertebrate intermediate hosts. Crenosoma striatum is specific to hedgehogs and was chosen as the parasite to develop the molecular survey tool for hedgehogs, an elusive nocturnal species of considerable interest at present. Results revealed the presence of the nematode only at a site known to be inhabited by hedgehogs confirming the potential of this method to improve the accuracy of recording hedgehog populations.

Abstract

The Western European Hedgehog (Erinaceous europaeus) is a nocturnal animal that is in decline in much of Europe, but the monitoring of this species is subjective, prone to error, and an inadequate basis for estimating population trends. Here, we report the use of Crenosoma striatum, a parasitic nematode specific to hedgehogs as definitive hosts, to detect hedgehog presence in the natural environment. This is achieved through collecting and sampling the parasites within their intermediate hosts, gastropoda, a group much simpler to locate and sample in both urban and rural habitats. C. striatum and Crenosoma vulpis were collected post-mortem from the lungs of hedgehogs and foxes, respectively. Slugs were collected in two sessions, during spring and autumn, from Skomer Island (n = 21), which is known to be free of hedgehogs (and foxes); and Pennard, Swansea (n = 42), known to have a healthy hedgehog population. The second internal transcribed spacer of parasite ribosomal DNA was used to develop a highly specific, novel, PCR based multiplex assay. Crenosoma striatum was found only at the site known to be inhabited by hedgehogs, at an average prevalence in gastropods of 10% in spring and autumn. The molecular test was highly specific: One mollusc was positive for both C. striatum and C. vulpis, and differentiation between the two nematode species was clear. This study demonstrates proof of principle for using detection of specific parasite DNA in easily sampled intermediate hosts to confirm the presence of an elusive nocturnal definitive host species. The approach has great potential as an adaptable, objective tool to supplement and support existing ecological survey methods.

The topology and drivers of ant-symbiont networks across Europe

Intimate associations between different species drive community composition across ecosystems. Understanding the ecological and evolutionary drivers of these symbiotic associations is challenging because their structure eventually determines stability and resilience of the entire species network. Here, we compiled a detailed database on naturally occurring ant-symbiont networks in Europe to identify factors that affect symbiont network topology. These networks host an unrivalled diversity of macrosymbiotic associations, spanning the entire mutualism-antagonism continuum, including: (i) myrmecophiles - commensalistic and parasitic arthropods; (ii) trophobionts - mutualistic aphids, scale insects, planthoppers and caterpillars; (iii) social parasites - parasitic ant species; (iv) parasitic helminths; and (v) parasitic fungi. We dissected network topology to investigate what determines host specificity, symbiont species richness, and the capacity of different symbiont types to switch hosts. We found 722 macrosymbionts (multicellular symbionts) associated with European ants. Symbiont type explained host specificity and the average relatedness of the host species. Social parasites were associated with few hosts that were phylogenetically highly related, whereas the other symbiont types interacted with a larger number of hosts across a wider taxonomic distribution. The hosts of trophobionts were the least phylogenetically related across all symbiont types. Colony size, host range and habitat type predicted total symbiont richness: ant hosts with larger colony size, a larger distribution range or with a wider habitat range contained more symbiont species. However, we found that different sets of host factors affected diversity in the different types of symbionts. Ecological factors, such as colony size, host range and niche width predominantly determined myrmecophile species richness, whereas host phylogeny was the most important predictor of mutualistic trophobiont, social parasite and parasitic helminth species richness. Lastly, we found that hosts with a common biogeographic history support a more similar community of symbionts. Phylogenetically related hosts also shared more trophobionts, social parasites and helminths, but not myrmecophiles. Taken together, these results suggest that ecological and evolutionary processes structure host specificity and symbiont richness in large-scale ant-symbiont networks, but these drivers may shift in importance depending on the type of symbiosis. Our findings highlight the potential of well-characterized bipartite networks composed of different types of symbioses to identify candidate processes driving community composition.

Ecological and evolutionary drivers of haemoplasma infection and bacterial genotype sharing in a Neotropical bat community

Most emerging pathogens can infect multiple species, underlining the importance of understanding the ecological and evolutionary factors that allow some hosts to harbour greater infection prevalence and share pathogens with other species. However, our understanding of pathogen jumps is based primarily around viruses, despite bacteria accounting for the greatest proportion of zoonoses. Because bacterial pathogens in bats (order Chiroptera) can have conservation and human health consequences, studies that examine the ecological and evolutionary drivers of bacterial prevalence and barriers to pathogen sharing are crucially needed. Here were studied haemotropic Mycoplasma spp. (i.e., haemoplasmas) across a species-rich bat community in Belize over two years. Across 469 bats spanning 33 species, half of individuals and two-thirds of species were haemoplasma positive. Infection prevalence was higher for males and for species with larger body mass and colony sizes. Haemoplasmas displayed high genetic diversity (21 novel genotypes) and strong host specificity. Evolutionary patterns supported codivergence of bats and bacterial genotypes alongside phylogenetically constrained host shifts. Bat species centrality to the network of shared haemoplasma genotypes was phylogenetically clustered and unrelated to prevalence, further suggesting rare-but detectable-bacterial sharing between species. Our study highlights the importance of using fine phylogenetic scales when assessing host specificity and suggests phylogenetic similarity may play a key role in host shifts not only for viruses but also for bacteria. Such work more broadly contributes to increasing efforts to understand cross-species transmission and the epidemiological consequences of bacterial pathogens.

Genetic diversity of primate strongylid nematodes: Do sympatric nonhuman primates and humans share their strongylid worms?

The close phylogenetic relationship between humans and nonhuman primates (NHPs) can result in a high potential for pathogen exchange. In recent decades, NHP and human interactions have become more frequent due to increasing habitat encroachment and ecotourism. Strongylid communities, which include members of several genera, are typically found in NHPs. Using optimized high-throughput sequencing for strain-level identification of primate strongylids, we studied the structure of strongylid communities in NHPs and humans co-habiting a tropical forest ecosystem in the Central African Republic. General taxonomic assignment of 85 ITS-2 haplotypes indicated that the studied primates harbour at least nine genera of strongylid nematodes, with Oesophagostomum and Necator being the most prevalent. We detected both host-specific and shared strongylid haplotypes. Skin-penetrating Necator gorillaehaplotypes were shared between humans and gorillas but Necator americanus were much more restricted to humans. Strongylid communities of local hunter-gatherers employed as trackers were more similar to those of gorillas compared to their relatives, who spent more time in villages. This was due to lower abundance of human-origin N. americanus in both gorillas and trackers. Habituated gorillas or those under habituation did not show larger overlap of strongylids with humans compared to unhabituated. We concluded that the occurrence of the human-specific strongylids in gorillas does not increase with direct contact between gorillas and humans due to the habituation. Overall, our results indicate that the degree of habitat sharing between hosts, together with mode of parasite transmission, are important factors for parasite spillover among primates.

The changing ecology of primate parasites: Insights from wild-captive comparisons

Host movements, including migrations or range expansions, are known to influence parasite communities. Transitions to captivity-a rarely studied yet widespread human-driven host movement-can also change parasite communities, in some cases leading to pathogen spillover among wildlife species, or between wildlife and human hosts. We compared parasite species richness between wild and captive populations of 22 primate species, including macro- (helminths and arthropods) and micro-parasites (viruses, protozoa, bacteria, and fungi). We predicted that captive primates would have only a subset of their native parasite community, and would possess fewer parasites with complex life cycles requiring intermediate hosts or vectors. We further predicted that captive primates would have parasites transmitted by close contact and environmentally-including those shared with humans and other animals, such as commensals and pests. We found that the composition of primate parasite communities shifted in captive populations, especially because of turnover (parasites detected in captivity but not reported in the wild), but with some evidence of nestedness (holdovers from the wild). Because of the high degree of turnover, we found no significant difference in overall parasite richness between captive and wild primates. Vector-borne parasites were less likely to be found in captivity, whereas parasites transmitted through either close or non-close contact, including through fecal-oral transmission, were more likely to be newly detected in captivity. These findings identify parasites that require monitoring in captivity and raise concerns about the introduction of novel parasites to potentially susceptible wildlife populations during reintroduction programs.

Infection dynamics of gastrointestinal helminths in sympatric non-human primates, livestock and wild ruminants in Kenya

BACKGROUND

Gastrointestinal parasites are neglected infections, yet they cause significant burden to animal and human health globally. To date, most studies of gastrointestinal parasites focus on host-parasite systems that involve either a single parasite or a host species. However, when hosts share habitat and resources, they may also cross-transmit generalist gastrointestinal parasites. Here we explore multi-host-parasite interactions in a single ecosystem to understand the infection patterns, especially those linked to livestock-wildlife interfaces and zoonotic risk.

METHODS

We used both coprological methods (flotation and sedimentation; N = 1,138 fecal samples) and molecular identification techniques (rDNA and mtDNA; N = 18 larvae) to identify gastrointestinal parasites in nine sympatric host species (cattle, sheep, goats, wildebeest, Grant's gazelles, Thomson's gazelles, impala, vervet monkeys and baboons) in the Amboseli ecosystem, Kenya.

RESULTS

We found that the host community harbored a diverse community of gastrointestinal helminths, including 22 species and/or morphotypes that were heterogeneously distributed across the hosts. Six zoonotic gastrointestinal helminths were identified: Trichuris spp., Trichostrongylus colubriformis, Enterobius spp. Oesophagostomum bifurcum, Strongyloides stercoralis and Strongyloides fuelleborni. The dominant parasite was Trichuris spp, whose ova occurred in two morphological types. Baboons were co-infected with Strongyloides fuelleborni and S. stercoralis.

CONCLUSIONS

We found that the interface zone shared by wild ungulates, livestock and non-human primates is rich in diversity of gastrointestinal helminths, of which some are extensively shared across the host species. Closely related host species were most likely to be infected by the same parasite species. Several parasites showed genetic sub-structuring according to either geography or host species. Of significance and contrary to expectation, we found that livestock had a higher parasite richness than wild bovids, which is a health risk for both conservation and livestock production. The zoonotic parasites are of public health risk, especially to pastoralist communities living in areas contiguous to wildlife areas. These results expand information on the epidemiology of these parasites and highlights potential zoonotic risk in East African savanna habitats.

What factors explain the geographical range of mammalian parasites?

Free-living species vary substantially in the extent of their spatial distributions. However, distributions of parasitic species have not been comprehensively compared in this context. We investigated which factors most influence the geographical extent of mammal parasites. Using the Global Mammal Parasite Database we analysed 17 818 individual geospatial records on 1806 parasite species (encompassing viruses, bacteria, protozoa, arthropods and helminths) that infect 396 carnivore, ungulate and primate host species. As a measure of the geographical extent of each parasite species we quantified the number and area of world ecoregions occupied by each. To evaluate the importance of variables influencing the summed area of ecoregions occupied by a parasite species, we used Bayesian network analysis of a subset ( n = 866) of the parasites in our database that had at least two host species and complete information on parasite traits. We found that parasites that covered more geographical area had a greater number of host species, higher average phylogenetic relatedness between host species and more sampling effort. Host and parasite taxonomic groups had weak and indirect effects on parasite ecoregion area; parasite transmission mode had virtually no effect. Mechanistically, a greater number of host species probably increases both the collective abundance and habitat breadth of hosts, providing more opportunities for a parasite to have an expansive range. Furthermore, even though mammals are one of the best-studied animal classes, the ecoregion area occupied by their parasites is strongly sensitive to sampling effort, implying mammal parasites are undersampled. Overall, our results support that parasite geographical extent is largely controlled by host characteristics, many of which are subsumed within host taxonomic identity.

Small to modest impact of social group on the gut microbiome of wild Costa Rican capuchins in a seasonal forest

The horizontal transmission of pathogenic and beneficial microbes has implications for health and development of socially living animals. Social group is repeatedly implicated as an important predictor of gut microbiome structure among primates, with individuals in neighboring social groups exhibiting distinct microbiomes. Here we examine whether group membership is a predictor of gut microbiome structure and diversity across three groups of white-faced capuchins (Cebus capucinus imitator) inhabiting a seasonal Costa Rican forest. We collected 62 fecal samples from 18 adult females during four sampling bouts. Sampling bouts spanned the dry-to-wet-to-dry seasonal transitions. To investigate gut microbial composition, we sequenced the V4 region of the 16S rRNA gene. We used the DADA2 pipeline to assign amplicon sequence variants and the RDP database to classify taxa. Our findings are: 1) gut microbiomes of capuchins clustered by social group in the late dry season, but this pattern was less evident in other sampling bouts; 2) social group was a significant variable in a PERMANOVA test of beta diversity, but it accounted for less variation than season; 3) social group was not an important predictor of abundance for the ten most abundant microbial taxa in capuchins; 4) when examining log2-fold abundances of microbes between social groups, there were significant differences in some pairwise comparisons. While this is suggestive of group-wide differences, individual variation may have a strong impact and should be assessed in future studies. Overall, we found a minor impact of social group membership on the gut microbiota of wild white-faced capuchins. Future research including home range overlap and resource use, as well as fine-scale investigation of individual variation, will further elucidate patterns of socially structured microbes.

Detection of antibodies against Icoaraci, Ilhéus, and Saint Louis Encephalitis arboviruses during yellow fever monitoring surveillance in non-human primates (Alouatta caraya) in southern Brazil

BACKGROUND

Free-ranging non-human primates (NHPs) can host a variety of pathogenic microorganisms, such as arboviruses, which include the yellow fever virus (YFV). This study aimed to detect the circulation of YF and other arboviruses in three wild Alouatta caraya populations in forests in southern Brazil.

METHODS

We collected 40 blood and serum samples from 26 monkeys captured/recaptured up to four times from 2014 to 2016, searching for evidence of arboviruses by virus isolation, PCR, and neutralization tests.

RESULTS

Viral isolation and genome detection were negative; however, we detected neutralizing antibodies against the Saint Louis, Ilhéus, and Icoaraci viruses in three NHPs.

CONCLUSIONS

Saint Louis Encephalitis, Ilhéus, and Icoaraci viruses circulated recently in the region. Future studies should investigate the role of NHPs, other vertebrate hosts and wild vectors in the region's arbovirus circulation and the potential risks of the arboviruses to wildlife, domestic animals, and humans.

Host Specificity in Variable Environments

Host specificity encompasses the range and diversity of host species that a parasite is capable of infecting and is considered a crucial measure of a parasite's potential to shift hosts and trigger disease emergence. Yet empirical studies rarely consider that regional observations only reflect a parasite's 'realized' host range under particular conditions: the true 'fundamental' range of host specificity is typically not approached. We provide an overview of challenges and directions in modelling host specificity under variable environmental conditions. Combining tractable modelling frameworks with multiple data sources that account for the strong interplay between a parasite's evolutionary history, transmission mode, and environmental filters that shape host-parasite interactions will improve efforts to quantify emerging disease risk in times of global change.

Characterizing the phylogenetic specialism-generalism spectrum of mammal parasites

The distribution of parasites across mammalian hosts is complex and represents a differential ability or opportunity to infect different host species. Here, we take a macroecological approach to investigate factors influencing why some parasites show a tendency to infect species widely distributed in the host phylogeny (phylogenetic generalism) while others infect only closely related hosts. Using a database on over 1400 parasite species that have been documented to infect up to 69 terrestrial mammal host species, we characterize the phylogenetic generalism of parasites using standard effect sizes for three metrics: mean pairwise phylogenetic distance (PD), maximum PD and phylogenetic aggregation. We identify a trend towards phylogenetic specialism, though statistically host relatedness is most often equivalent to that expected from a random sample of host species. Bacteria and arthropod parasites are typically the most generalist, viruses and helminths exhibit intermediate generalism, and protozoa are on average the most specialist. While viruses and helminths have similar mean pairwise PD on average, the viruses exhibit higher variation as a group. Close-contact transmission is the transmission mode most associated with specialism. Most parasites exhibiting phylogenetic aggregation (associating with discrete groups of species dispersed across the host phylogeny) are helminths and viruses.

Using physical contact heterogeneity and frequency to characterize dynamics of human exposure to nonhuman primate bodily fluids in central Africa

Emerging infectious diseases of zoonotic origin constitute a recurrent threat to global health. Nonhuman primates (NHPs) occupy an important place in zoonotic spillovers (pathogenic transmissions from animals to humans), serving as reservoirs or amplifiers of multiple neglected tropical diseases, including viral hemorrhagic fevers and arboviruses, parasites and bacteria, as well as retroviruses (simian foamy virus, PTLV) that are pathogenic in human beings. Hunting and butchering studies in Africa characterize at-risk human social groups, but overlook critical factors of contact heterogeneity and frequency, NHP species differences, and meat processing practices. In southeastern Cameroon, a region with a history of zoonotic emergence and high risk of future spillovers, we conducted a novel mixed-method field study of human physical exposure to multiple NHP species, incorporating participant-based and ecological methodologies, and qualitative interviews (n = 25). We find frequent physical contact across adult human populations, greater physical contact with monkeys than apes, especially for meat handling practices, and positive correlation of human exposure with NHP species abundance and proximity to human settlement. These fine-grained results encourage reconsideration of the likely dynamics of human-NHP contact in past and future NTD emergence events. Multidisciplinary social science and ecological approaches should be mobilized to generate more effective human and animal surveillance and risk communications around neglected tropical diseases. At a moment when the WHO has included "Disease X", a presumably zoonotic pathogen with pandemic potential, on its list of blueprint priority diseases as, new field-based tools for investigating zoonotic disease emergence, both known and unknown, are of critical importance.

Entamoeba histolytica infection in humans, chimpanzees and baboons in the Greater Gombe Ecosystem, Tanzania

Entamoeba histolytica is an enteric parasite that infects approximately 50 million people worldwide. Although E. histolytica is a zoonotic parasite that has the potential to infect nonhuman primates, such transmission is poorly understood. Consequently, this study examined whether E. histolytica is present among humans, chimpanzees and baboons living in the Greater Gombe Ecosystem (GGE), Tanzania. The primary aims were to determine patterns of E. histolytica infection in a system with human-nonhuman primate overlap and to test associations between infection status and potential risk factors of disease. Entamoeba spp. occurred in 60.3% of human, 65.6% of chimpanzee and 88.6% of baboon samples. Entamoeba histolytica occurred in 12.1% of human, 34.1% of chimpanzee and 10.9% of baboon samples. Human E. histolytica infection was associated with gastrointestinal symptoms. This was the first study to confirm the presence of E. histolytica in the GGE. The high sample prevalence of E. histolytica in three sympatric primates suggests that zoonotic transmission is possible and stresses the need for further phylogenetic studies. Interventions targeting better sanitation and hygiene practices for humans living in the GGE can help prevent E. histolytica infection in humans, while also protecting the endangered chimpanzees and other primates in this region.

Host allometry influences the evolution of parasite host-generalism: theory and meta-analysis

Parasites vary widely in the diversity of hosts they infect: some parasite species are specialists—infecting just a single host species, while others are generalists, capable of infecting many. Understanding the factors that drive parasite host-generalism is of basic biological interest, but also directly relevant to predicting disease emergence in new host species, identifying parasites that are likely to have unidentified additional hosts, and assessing transmission risk. Here, we use mathematical models to investigate how variation in host body size and environmental temperature affect the evolution of parasite host-generalism. We predict that parasites are more likely to evolve a generalist strategy when hosts are large-bodied, when variation in host body size is large, and in cooler environments. We then explore these predictions using a newly updated database of over 20 000 fish–macroparasite associations. Within the database we see some evidence supporting these predictions, but also highlight mismatches between theory and data. By combining these two approaches, we establish a theoretical basis for interpreting empirical data on parasites' host specificity and identify key areas for future work that will help untangle the drivers of parasite host-generalism.

This article is part of the themed issue ‘Opening the black box: re-examining the ecology and evolution of parasite transmission’.

Prevalence, molecular epidemiology, and zoonotic potential of Entamoeba spp. in nonhuman primates in China

Amebiasis is a major public-health concern. It has a global distribution, and is listed as the third leading parasitic cause of human mortality. To survey the prevalence and assess the potential zoonotic transmission of Entamoeba spp. in nonhuman primates (NHPs) in China, 2688 fresh fecal specimens were collected from NHPs reared in farms or zoos/parks or free ranging in 13 districts. The overall prevalence of Entamoeba spp. infection determined with microscopy analysis was 39.4% (1059/2688). Higher infection rates were detected in the free ranging group (41.1%, 169/411) and in animals <1year old (58.7%, 556/947). Gene fragments were successfully amplified 463 (87.2%) out of the 531 selected specimens (approximately half of the total microscopy-positive specimens). Polymerase chain reaction (PCR) amplification identified 386 (83.4%) Entamoeba dispar and 287 (62.0%) E. coli infections, and among these, 210 (45.4%) were mixed infections. And that the E. dispar and E. coli had also been detected in humans. In phylogenetic analysis, the E. dispar and E. coli sequences clustered with reference E. dispar and E. coli, respectively. In conclusion, nonhuman primates infected with Entamoeba species, with high prevalence and zoonotic potential, should be considered when evaluating the maintenance of Entamoeba spp. and its transmission between animal reservoirs and humans.

Phylogenetic Insight into Zika and Emerging Viruses for a Perspective on Potential Hosts

Global viral diversity is substantial, but viruses that contribute little to the public health burden or to agricultural damage receive minimal attention until a seemingly unimportant virus becomes a threat. The Zika virus (ZIKV) illustrated this, as there was limited information and awareness of the virus when it was identified as a public health emergency in February 2016. Predicting which virus may pose a future threat is difficult. This is in part because significant knowledge gaps in the basic biology and ecology of an emerging virus can impede policy development, delay decision making, and hinder public health action. We suggest using a phylogenetic framework of pathogens and their infected host species for insight into which animals may serve as reservoirs. For example, examining flaviviruses closely related to ZIKV, the phylogenetic framework indicates New World monkeys are the most likely candidates to be potential reservoirs for ZIKV. Secondarily, mammals that are in close proximity to humans should be considered because of the increased opportunity for pathogen exchange. The increase in human-mediated environmental change is accelerating the probability of another previously overlooked virus becoming a significant concern. By investing in basic science research and organizing our knowledge into an evolutionary framework, we will be better prepared to respond to the next emerging infectious disease.

Parasites and Their Social Hosts

The study of parasitism in socially living organisms shows that social group size correlates with the risk of infection, but group structure - and thus differences in contact networks - is generally more important. Also, genetic makeup or environmental conditions have effects. 'Social immunity' focuses on defence against parasites that are particular to social living. Recently, the role of socially transmitted microbiota for defence has become a focus, too. But whether and how parasites adapt to social organisms - beyond adaptation to solitary hosts - is poorly understood. Genomic and proteomic methods, as well as network analysis, will be tools that hold promise for many unsolved questions, but to expand our concepts in the first place is a much needed agenda.

An investigation of parasitic infections and review of molecular characterization of the intestinal protozoa in nonhuman primates in China from 2009 to 2015

Parasites are a well-known threat to nonhuman primate (NHP) populations, and potentially cause zoonotic diseases in humans. In this study, the basic data was provided of the parasites in NHPs and the molecular characterization of the Enterocytozoon bieneusi, Giardia duodenalis, Cryptosporidium spp., and Entamoeba spp. were reviewed, which were found in these samples. A total of 3349 fecal samples were collected from 34 species reared at 17 districts in zoos, farms, free-range, or research laboratories, and examined microscopically. Eleven genera of intestinal parasites were detected: five genera of protozoans (Isospora spp., Entamoeba spp., Giardia sp., Cryptosporidium spp., and Cyclospora spp.) and six genera of helminths (Trichuris spp., Strongyloides spp., Ascaris spp., Physaloptera spp., Ancylostoma spp., and Enterobius spp.). The overall sample prevalence of parasitic infection was 54.1% (1811/3349). Entamoeba spp. was the most prevalent (36.4%, 1218/3349). The infection rate was the highest in free-range animals (73.0%, 670/918) (P < 0.01) and Guangxi Zhuang autonomous region (64.8%, 566/873). Mixed infections were mostly detected for Entamoeba spp., Trichuris spp., and Strongyloides spp.. Molecular characterization was reviewed of Enterocytozoon bieneusi, Giardia duodenalis, Cryptosporidium spp., and Entamoeba spp., as these are zoonotic species or genotypes. This parasitological data for NHPs in China, provides important information for veterinarians and public health authorities for the elimination of such parasites and monitor the potential transmission of zoonotic infections from NHPs.

Detection of the mosquito-borne flaviviruses, West Nile, Dengue, Saint Louis Encephalitis, Ilheus, Bussuquara, and Yellow Fever in free-ranging black howlers (Alouatta caraya) of Northeastern Argentina

Several medically important mosquito-borne flaviviruses have been detected in Argentina in recent years: Dengue (DENV), St. Louis encephalitis (SLEV), West Nile (WNV) and Yellow Fever (YFV) viruses. Evidence of Bussuquara virus (BSQV) and Ilheus virus (ILHV) activity were found, but they have not been associated with human disease. Non-human primates can act as important hosts in the natural cycle of flaviviruses and serological studies can lead to improved understanding of virus circulation dynamics and host susceptibility. From July-August 2010, we conducted serological and molecular surveys in free-ranging black howlers (Alouatta caraya) captured in northeastern Argentina. We used 90% plaque-reduction neutralization tests (PRNT90) to analyze 108 serum samples for antibodies to WNV, SLEV, YFV, DENV (serotypes 1and 3), ILHV, and BSQV. Virus genome detection was performed using generic reverse transcription (RT)-nested PCR to identify flaviviruses in 51 antibody-negative animals. Seventy animals had antibodies for one or more flaviviruses for a total antibody prevalence of 64.8% (70/108). Monotypic (13/70, 19%) and heterotypic (27/70, 39%) patterns were differentiated. Specific neutralizing antibodies against WNV, SLEV, DENV-1, DENV-3, ILHV, and BSQV were found. Unexpectedly, the highest flavivirus antibody prevalence detected was to WNV with 9 (8.33%) monotypic responses. All samples tested by (RT)-nested PCR were negative for viral genome. This is the first detection of WNV-specific antibodies in black howlers from Argentina and the first report in free-ranging non-human primates from Latin-American countries. Given that no animals had specific neutralizing antibodies to YFV, our results suggest that the study population remains susceptible to YFV. Monitoring of these agents should be strengthened to detect the establishment of sylvatic cycles of flaviviruses in America and evaluate risks to wildlife and human health.

Relevance of Indirect Transmission for Wildlife Disease Surveillance

Epidemiological models of infectious diseases are essential tools in support of risk assessment, surveillance design, and contingency planning in public and animal health. Direct pathogen transmission from host to host is an essential process of each host–pathogen system and respective epidemiological modeling concepts. It is widely accepted that numerous diseases involve indirect transmission (IT) through pathogens shed by infectious hosts to their environment. However, epidemiological models largely do not represent pathogen persistence outside the host explicitly. We hypothesize that this simplification might bias management-related model predictions for disease agents that can persist outside their host for a certain time span. We adapted an individual-based, spatially explicit epidemiological model that can mimic both transmission processes. One version explicitly simulated indirect pathogen transmission through a contaminated environment. The second version simulated direct host-to-host transmission only. We aligned the model variants by the transmission potential per infectious host (i.e., basic reproductive number R₀) and the spatial transmission kernel of the infection to allow unbiased comparison of predictions. The quantitative model results are provided for the example of surveillance plans for early detection of foot-and-mouth disease in wild boar, a social host. We applied systematic sampling strategies on the serological status of randomly selected host individuals in both models. We compared between the model variants the time to detection and the area affected prior to detection, measures that strongly influence mitigation costs. Moreover, the ideal sampling strategy to detect the infection in a given time frame was compared between both models. We found the simplified, direct transmission model to underestimate necessary sample size by up to one order of magnitude but to overestimate the area put under control measures. Thus, the model predictions underestimated surveillance efforts but overestimated mitigation costs. We discuss parameterization of IT models and related knowledge gaps. We conclude that the explicit incorporation of IT mechanisms in epidemiological modeling may reward by adapting surveillance and mitigation efforts.

Incorporating the gut microbiota into models of human and non-human primate ecology and evolution

The mammalian gut is home to a diverse community of microbes. Advances in technology over the past two decades have allowed us to examine this community, the gut microbiota, in more detail, revealing a wide range of influences on host nutrition, health, and behavior. These host-gut microbe interactions appear to shape host plasticity and fitness in a variety of contexts, and therefore represent a key factor missing from existing models of human and non-human primate ecology and evolution. However, current studies of the gut microbiota tend to include limited contextual data or are clinical, making it difficult to directly test broad anthropological hypotheses. Here, I review what is known about the animal gut microbiota and provide examples of how gut microbiota research can be integrated into the study of human and non-human primate ecology and evolution with targeted data collection. Specifically, I examine how the gut microbiota may impact primate diet, energetics, disease resistance, and cognition. While gut microbiota research is proliferating rapidly, especially in the context of humans, there remain important gaps in our understanding of host-gut microbe interactions that will require an anthropological perspective to fill. Likewise, gut microbiota research will be an important tool for filling remaining gaps in anthropological research.

Multihost Bartonella parasites display covert host specificity even when transmitted by generalist vectors

Many parasites infect multiple sympatric host species, and there is a general assumption that parasite transmission between co‐occurring host species is commonplace. Such between‐species transmission could be key to parasite persistence within a disease reservoir and is consequently an emerging focus for disease control.

However, while a growing body of theory indicates the potential importance of between‐species transmission for parasite persistence, conclusive empirical evidence from natural communities is lacking, and the assumption that between‐species transmission is inevitable may therefore be wrong.

We investigated the occurrence of between‐species transmission in a well‐studied multihost parasite system. We identified the flea‐borne Bartonella parasites infecting sympatric populations of Apodemus sylvaticus (wood mice) and Myodes glareolus (bank voles) in the UK and confirmed that several Bartonella species infect both rodent species. However, counter to previous knowledge, genetic characterization of these parasites revealed covert host specificity, where each host species is associated with a distinct assemblage of genetic variants, indicating that between‐species transmission is rare.

Limited between‐species transmission could result from rare encounters between one host species and the parasites infecting another and/or host–parasite incompatibility. We investigated the occurrence of such encounter and compatibility barriers by identifying the flea species associated with each rodent host, and the Bartonella variants carried by individual fleas. We found that the majority of fleas were host‐generalists but the assemblage of Bartonella variants in fleas tended to reflect the assemblage of Bartonella variants in the host species they were collected from, thus providing evidence of encounter barriers mediated by limited between‐species flea transfer. However, we also found several fleas that were carrying variants never found in the host species from which they were collected, indicating some degree of host–pathogen incompatibility when barriers to encounter are overcome.

Overall, these findings challenge our default perceptions of multihost parasite persistence, as they show that despite considerable overlaps in host species ecology, separate populations of the same parasite species may circulate and persist independently in different sympatric host species. This questions our fundamental understanding of endemic transmission dynamics and the control of infection within natural reservoir communities.

Physiological and parasitological implications of living in a city: the case of the white-footed tamarin (Saguinus leucopus)

Among primates, the Neotropical Callitrichid monkeys (tamarins and marmosets) exhibit a particular ability to adapt to disturbed and urbanized environments. However, little is known about physiological and health status in contrasting ecological contexts. An example of adaptation to urban environments is the white-footed tamarin (Saguinus leucopus), an endangered species endemic to the central Andes in North West Colombia. This species was used as a model to contrast physical condition, physiological parameters and the parasite community of wild populations in rural and urban settings. Overall, the tamarins seemed to be in good body condition in both environments; however, urban tamarins exhibited overweight, elevated body mass, and higher cholesterol levels, while rural tamarins showed larger diversity and prevalence of parasites. Variation in several hematological parameters associated with altitude was also observed. Our data provide preliminary evidence of differential physiological responses to urban and rural environments in tamarins. These results may be attributed to nutritional factors, physical activity, and specific parasite-host ecological interactions in these two environments. Also, abundance and diversity of the parasite community in urban environments may be potentially constrained by habitat fragmentation and relatively fewer reservoirs. Finally, significant physiological and ecological disparities between white-footed tamarins occurring in urban and rural habitats as well as physiological response to hypoxia at higher altitudes were evidenced here. This study provides important preliminary information that will be useful to determine the ability of New World primate populations to cope with urban development and rapidly changing environments.