Species interactions in a parasite community drive infection risk in a wildlife population

Ectoparasitic fungi of Myrmica ants alter the success of parasitic butterflies

Exploitation of organisms by multiple parasite species is common in nature, but interactions among parasites have rarely been studied. Myrmica ants are rich in parasites. Among others, the ectoparasitic Rickia wasmannii fungus and the parasitic caterpillars of myrmecophilous Phengaris butterflies often infect the same Myrmica colonies. In this study, we examined the effects of R. wasmannii on the adoption, long-term development, and survival of P. alcon. In laboratory conditions, caterpillars introduced into nests of Myrmica scabrinodis uninfected with R. wasmannii survived significantly longer compared to caterpillars introduced into infected nests. In the field, joint infection was less common than expected if both parasites exploited M. scabrinodis colonies independently. Pre-pupal caterpillars of P. alcon were somewhat larger in nests infected with R. wasmannii than those found in uninfected nests. Based on these results it seems that R. wasmannii infection of M. scabrinodis affects the survival and development of P. alcon caterpillars, suggesting competition between these two ant parasites.

Predictors of parasite and pathogen infections in urban rodents of central Argentina

Urban rodents are associated with parasites and pathogens, which present health risks for humans, but information on factors related to parasite and pathogen infection in rodents in cities of Latin America is scarce. This study analyzes the hosts, host community structure and environmental characteristics of parasite and pathogen fauna present in the three species of urban rodents in an urban area of South America. Rodents were captured seasonally in seven different neighborhoods. Digestive tracts were dissected under stereoscopic microscopy and feces were processed using a sedimentation technique. Protozoa and bacteria were detected through polymerase chain reaction and indirect immunofluorescence techniques. In Rattus norvegicus, Rattus rattus and Mus musculus, ten helminths, three protozoa and two bacteria were found. Six were zoonotic: Toxoplasma gondii; Hymenolepis diminuta; Rodentolepis nana; Strobilocercus fasciolaris; Leptospira borgpetersenii; and Leptospira interrogans. The parasite and pathogen infections were influenced by the host species, the host community structure, the season, and the presence of streams in the neighborhood. Urban rodents may be the infection source of many zoonotic diseases and it is important to generate public policies for this problem. This study is one example of the situation of many cities of Latin America, where peripheral neighborhoods are growing dramatically.

Context-Dependent Host-Symbiont Interactions: Shifts along the Parasitism-Mutualism Continuum

AbstractSymbiotic interactions can shift along a mutualism-parasitism continuum. While there are many studies examining dynamics typically considered to be mutualistic that sometimes shift toward parasitism, little is known about conditions underlying shifts from parasitism toward mutualism. In lake populations, we observed that infection by a microsporidian gut symbiont sometimes conferred a reproductive advantage and other times a disadvantage to its Daphnia host. We hypothesized that the microsporidian might benefit its host by reducing infection by more virulent parasites, which attack via the gut. In a laboratory study using field-collected animals, we found that spores of a virulent fungal parasite were much less capable of penetrating the guts of Daphnia harboring the microsporidian gut symbiont. We predicted that this altered gut penetrability could cause differential impacts on host fitness depending on ecological context. Field survey data revealed that microsporidian-infected Daphnia hosts experienced a reproductive advantage when virulent parasites were common while resource scarcity led to a reproductive disadvantage, but only in lakes where virulent parasites were relatively rare. Our findings highlight the importance of considering multiparasite community context and resource availability in host-parasite studies and open the door for future research into conditions driving shifts along parasitism to mutualism gradients.

Ecological and evolutionary perspectives on tick-borne pathogen co-infections

Tick-borne pathogen co-infections are common in nature. Co-infecting pathogens interact with each other and the tick microbiome, which influences individual pathogen fitness, and ultimately shapes virulence, infectivity, and transmission. In this review, we discuss how tick-borne pathogens are an ideal framework to study the evolutionary dynamics of co-infections. We highlight the importance of inter-species and intra-species interactions in vector-borne pathogen ecology and evolution. We also propose experimental evolution in tick cell lines as a method to directly test the impact of co-infections on pathogen evolution. Experimental evolution can simulate in real-time the long periods of time involved in within-vector pathogen interactions in nature, a major practical obstacle to cracking the influence of co-infections on pathogen evolution and ecology.

Synzootics

Ecologists increasingly recognise coinfection as an important component of emergent epidemiological patterns, connecting aspects of ecoimmunology, behaviour, ecosystem function and even extinction risk. Building on syndemic theory in medical anthropology, we propose the term 'synzootics' to describe co-occurring enzootic or epizootic processes that produce worse health outcomes in wild animals. Using framing from syndemic theory, we describe how the synzootic concept offers new insights into the ecology and evolution of infectious diseases. We then recommend a set of empirical criteria and lines of evidence that can be used to identify synzootics in nature. We conclude by exploring how synzootics could indirectly drive the emergence of novel pathogens in human populations.

Linking Behavior, Co-infection Patterns, and Viral Infection Risk With the Whole Gastrointestinal Helminth Community Structure in Mastomys natalensis

Infection probability, load, and community structure of helminths varies strongly between and within animal populations. This can be ascribed to environmental stochasticity or due to individual characteristics of the host such as their age or sex. Other, but understudied, factors are the hosts' behavior and co-infection patterns. In this study, we used the multimammate mouse (Mastomys natalensis) as a model system to investigate how the hosts' sex, age, exploration behavior, and viral infection history affects their infection risk, parasitic load, and community structure of gastrointestinal helminths. We hypothesized that the hosts' exploration behavior would play a key role in the risk for infection by different gastrointestinal helminths, whereby highly explorative individuals would have a higher infection risk leading to a wider diversity of helminths and a larger load compared to less explorative individuals. Fieldwork was performed in Morogoro, Tanzania, where we trapped a total of 214 individual mice. Their exploratory behavior was characterized using a hole-board test after which we collected the helminths inside their gastrointestinal tract. During our study, we found helminths belonging to eight different genera: Hymenolepis sp., Protospirura muricola, Syphacia sp., Trichuris mastomysi, Gongylonema sp., Pterygodermatites sp., Raillietina sp., and Inermicapsifer sp. and one family: Trichostrongylidae. Hierarchical modeling of species communities (HMSC) was used to investigate the effect of the different host-related factors on the infection probability, parasite load, and community structure of these helminths. Our results show that species richness was higher in adults and in females compared to juveniles and males, respectively. Contrary to our expectations, we found that less explorative individuals had higher infection probability with different helminths resulting in a higher diversity, which could be due to a higher exposure rate to these helminths and/or behavioral modification due to the infection.

Single-cell genome sequencing of protozoan parasites

Despite considerable genetic variation within hosts, most parasite genome sequencing studies focus on bulk samples composed of millions of cells. Analysis of bulk samples is biased toward the dominant genotype, concealing cell-to-cell variation and rare variants. To tackle this, single-cell sequencing approaches have been developed and tailored to specific host-parasite systems. These are allowing the genetic diversity and kinship in complex parasite populations to be deciphered and for de novo genetic variation to be captured. Here, we outline the methodologies being used for single-cell sequencing of parasitic protozoans, such as Plasmodium and Leishmania spp., and how these tools are being applied to understand parasite biology.

Linking Zoonosis Emergence to Farmland Invasion by Fluctuating Herbivores: Common Vole Populations and Tularemia Outbreaks in NW Spain

The expansion and intensification of agriculture are driving profound changes in ecosystems worldwide, favoring the (re)emergence of many human infectious diseases. Muroid rodents are a key host group for zoonotic infectious pathogens and frequently invade farming environments, promoting disease transmission and spillover. Understanding the role that fluctuating populations of farm dwelling rodents play in the epidemiology of zoonotic diseases is paramount to improve prevention schemes. Here, we review a decade of research on the colonization of farming environments in NW Spain by common voles (Microtus arvalis) and its public health impacts, specifically periodic tularemia outbreaks in humans. The spread of this colonizing rodent was analogous to an invasion process and was putatively triggered by the transformation and irrigation of agricultural habitats that created a novel terrestrial-aquatic interface. This irruptive rodent host is an effective amplifier for the Francisella tularensis bacterium during population outbreaks, and human tularemia episodes are tightly linked in time and space to periodic (cyclic) variations in vole abundance. Beyond the information accumulated to date, several key knowledge gaps about this pathogen-rodent epidemiological link remain unaddressed, namely (i) did colonizing vole introduce or amplified pre-existing F. tularensis? (ii) which features of the “Francisella—Microtus” relationship are crucial for the epidemiology of tularemia? (iii) how virulent and persistent F. tularensis infection is for voles under natural conditions? and (iv) where does the bacterium persist during inter-epizootics? Future research should focus on more integrated, community-based approaches in order to understand the details and dynamics of disease circulation in ecosystems colonized by highly fluctuating hosts.

Borrelia afzelii Infection in the Rodent Host Has Dramatic Effects on the Bacterial Microbiome of Ixodes ricinus Ticks

The microbiome of blood-sucking arthropods can shape their competence to acquire and maintain infections with vector-borne pathogens. We used a controlled study to investigate the interactions between Borrelia afzelii, which causes Lyme borreliosis in Europe, and the bacterial microbiome of Ixodes ricinus, its primary tick vector. We applied a surface sterilization treatment to I. ricinus eggs to produce dysbiosed tick larvae that had a low bacterial abundance and a changed bacterial microbiome compared to those of the control larvae. Dysbiosed and control larvae fed on B. afzelii-infected mice and uninfected control mice, and the engorged larvae were left to molt into nymphs. The nymphs were tested for B. afzelii infection, and their bacterial microbiome underwent 16S rRNA amplicon sequencing. Surprisingly, larval dysbiosis had no effect on the vector competence of I. ricinus for B. afzelii, as the nymphal infection prevalence and the nymphal spirochete load were the same between the dysbiosed group and the control group. The strong effect of egg surface sterilization on the tick bacterial microbiome largely disappeared once the larvae molted into nymphs. The most important determinant of the bacterial microbiome of I. ricinus nymphs was the B. afzelii infection status of the mouse on which the nymphs had fed as larvae. Nymphs that had taken their larval blood meal from an infected mouse had a less abundant but more diverse bacterial microbiome than the control nymphs. Our study demonstrates that vector-borne infections in the vertebrate host shape the microbiome of the arthropod vector. IMPORTANCE Many blood-sucking arthropods transmit pathogens that cause infectious disease. For example, Ixodes ricinus ticks transmit the bacterium Borrelia afzelii, which causes Lyme disease in humans. Ticks also have a microbiome, which can influence their ability to acquire and transmit tick-borne pathogens such as B. afzelii. We sterilized I. ricinus eggs with bleach, and the tick larvae that hatched from these eggs had a dramatically reduced and changed bacterial microbiome compared to that of control larvae. These larvae fed on B. afzelii-infected mice, and the resultant nymphs were tested for B. afzelii and for their bacterial microbiome. We found that our manipulation of the bacterial microbiome had no effect on the ability of the tick larvae to acquire and maintain populations of B. afzelii. In contrast, we found that B. afzelii infection had dramatic effects on the bacterial microbiome of I. ricinus nymphs. Our study demonstrates that infections in the vertebrate host can shape the tick microbiome.

Indirect interactions among co-infecting parasites and a microbial mutualist impact disease progression

Interactions among parasites and other microbes within hosts can impact disease progression, yet study of such interactions has been mostly limited to pairwise combinations of microbes. Given the diversity of microbes within hosts, indirect interactions among more than two microbial species may also impact disease. To test this hypothesis, we performed inoculation experiments that investigated interactions among two fungal parasites, Rhizoctonia solani and Colletotrichum cereale, and a systemic fungal endophyte, Epichloë coenophiala, within the grass, tall fescue (Lolium arundinaceum). Both direct and indirect interactions impacted disease progression. While the endophyte did not directly influence R. solani disease progression or C. cereale symptom development, the endophyte modified the interaction between the two parasites. The magnitude of the facilitative effect of C. cereale on the growth of R. solani tended to be greater when the endophyte was present. Moreover, this interaction modification strongly affected leaf mortality. For plants lacking the endophyte, parasite co-inoculation did not increase leaf mortality compared to single-parasite inoculations. By contrast, for endophyte-infected plants, parasite co-inoculation increased leaf mortality compared to inoculation with R. solani or C. cereale alone by 1.9 or 4.9 times, respectively. Together, these results show that disease progression can be strongly impacted by indirect interactions among microbial symbionts.

The rise of ecological parasitology: twelve landmark advances that changed its history

In the five decades since the first publication of the International Journal for Parasitology, ecological parasitology has grown from modest beginnings to become a modern discipline with a strong theoretical foundation, a diverse toolkit, and a multidisciplinary approach. In this review, I highlight 12 advances in the field that have spurred its growth over the past 50 years. Where relevant, I identify pivotal contributions that have altered the course of research, as well as the influence of developments in other fields such as mainstream ecology and molecular biology. The 12 key advances discussed are in areas including parasite population dynamics and community assembly, the regulation of host population abundance and food web structure, parasites as agents of natural selection, the impacts of biodiversity and anthropogenic changes on host-parasite interactions, the biogeography of parasite diversity, and the evolutionary genetics of parasites. I conclude by identifying some challenges and opportunities lying ahead, which need to be met for the future growth of ecological research on host-parasite interactions.

A comparative study of single Theileria lestoquardi and mixed infections with Theileria ovis

Background

Epidemiological surveys in Oman have revealed a high prevalence of the co-occurrence of the pathogenic Theileria lestoquardi and the non-pathogenic Theileria ovis among sheep in the Barka region, Oman. Our most recent data illustrated an interaction and reduced mortality risk in animals co-infected with T. lestoquardi and T. ovis, suggesting that the latter confers protection against pathogenicity of T. lestoquardi. The present study extends the above findings and examines disease outcomes; clinical markers, hematological parameters, and parasite density in mixed and single T. lestoquardi infections.

Methods

A total of 390 blood samples were collected from 16 sheep pens located in Barka, Oman between July and November 2019. Theileria spp. were detected and quantified using qPCR assay targeting 18S rRNA, and the extent of genetic diversity was estimated by a panel of T. lestoquardi specific micro- and mini-satellites. The association of some disease markers with the presence of Theileria spp. and genetic diversity was tested.

Results

Theileria spp. were detected in 75 (19.2%) sheep; of these 65 (86.7%) had mixed infections (T. lestoquardi plus T. ovis), 8 (10.6%) were infected with T. lestoquardi alone, and 2 (2.7%) with only T. ovis. Exotic breeds had a higher risk for Theileria spp. infection. The density (18S rRNA gene copies) of both parasites was higher in single infection against mixed infection, and there was a relatively lower density of T. lestoquardi in mixed infections. However, there was no difference in hematological indices between single T. lestoquardi and mixed infections. High genetic diversity was observed among T. lestoquardi in Barka, with no differences of T. lestoquardi in single and mixed infections. The extent of diversity seen in Barka was higher (He = 0.772) than that reported in Oman in 2019 (He = 0.582), with distinct T. lestoquardi genotypes.

Conclusion

The lower density of T. lestoquardi as mixed infection with T. ovis compared to single infection supports the hypothesis that T. ovis confers protection against lethal T. lestoquardi infection. However, there were no differences in disease correlations (clinical markers, hematological parameters, and density of parasites) or the extent of diversity of T. lestoquardi between the two types of infection. The presence of distinct T. lestoquardi genotypes in Barka, compared to that reported earlier in Oman, likely reflects movement of carrier animals and highlights the need for further analysis of the parasite populations to inform novel approaches for controlling malignant ovine theileriosis.

Graphical Abstract

Spatial epidemiology of diabetes: Methods and insights

Diabetes mellitus (DM) is a growing epidemic with global proportions. It is estimated that in 2019, 463 million adults aged 20-79 years were living with DM. The latest evidence shows that DM continues to be a significant global health challenge and is likely to continue to grow substantially in the next decades, which would have major implications for healthcare expenditures, particularly in developing countries. Hence, new conceptual and methodological approaches to tackle the epidemic are long overdue. Spatial epidemiology has been a successful approach to control infectious disease epidemics like malaria and human immunodeficiency virus. The implementation of this approach has been expanded to include the study of non-communicable diseases like cancer and cardiovascular diseases. In this review, we discussed the implementation and use of spatial epidemiology and Geographic Information Systems to the study of DM. We reviewed several spatial methods used to understand the spatial structure of the disease and identify the potential geographical drivers of the spatial distribution of DM. Finally, we discussed the use of spatial epidemiology on the design and implementation of geographically targeted prevention and treatment interventions against DM.

Soil-transmitted helminth infections in free-ranging non-human primates from Cameroon and Gabon

BACKGROUND

Zoonotic diseases are a serious threat to both public health and animal conservation. Most non-human primates (NHP) are facing the threat of forest loss and fragmentation and are increasingly living in closer spatial proximity to humans. Humans are infected with soil-transmitted helminths (STH) at a high prevalence, and bidirectional infection with NHP has been observed. The aim of this study was to determine the prevalence, genetic diversity, distribution and presence of co-infections of STH in free-ranging gorillas, chimpanzees and other NHP species, and to determine the potential role of these NHP as reservoir hosts contributing to the environmental sustenance of zoonotic nematode infections in forested areas of Cameroon and Gabon.

METHODS

A total of 315 faecal samples from six species of NHPs were analysed. We performed PCR amplification, sequencing and maximum likelihood analysis of DNA fragments of the internal transcribed spacer 2 (ITS2) nuclear ribosomal DNA to detect the presence and determine the genetic diversity of Oesophagostomum spp., Necator spp. and Trichuris spp., and of targeted DNA fragments of the internal transcribed spacer 1 (ITS1) to detect the presence of Ascaris spp.

RESULTS

Necator spp. infections were most common in gorillas (35 of 65 individuals), but also present in chimpanzees (100 of 222 individuals) and in one of four samples from greater spot-nosed monkeys. These clustered with previously described type II and III Necator spp. Gorillas were also the most infected NHP with Oesophagostomum (51/65 individuals), followed by chimpanzees (157/222 individuals), mandrills (8/12 samples) and mangabeys (7/12 samples), with O. stephanostomum being the most prevalent species. Oesophagostomum bifurcum was detected in chimpanzees and a red-capped mangabey, and a non-classified Oesophagostomum species was detected in a mandrill and a red-capped mangabey. In addition, Ternidens deminutus was detected in samples from one chimpanzee and three greater spot-nosed monkeys. A significant relative overabundance of co-infections with Necator and Oesophagostomum was observed in chimpanzees and gorillas. Trichuris sp. was detected at low prevalence in a gorilla, a chimpanzee and a greater spot-nosed monkey. No Ascaris was observed in any of the samples analysed.

CONCLUSIONS

Our results on STH prevalence and genetic diversity in NHP from Cameroon and Gabon corroborate those obtained from other wild NHP populations in other African countries. Future research should focus on better identifying, at a molecular level, the species of Necator and Oesophagostomum infecting NHP and determining how human populations may be affected by increased proximity resulting from encroachment into sylvatic STH reservoir habitats.

Towards an ecosystem model of infectious disease

Increasingly intimate associations between human society and the natural environment are driving the emergence of novel pathogens, with devastating consequences for humans and animals alike. Prior to emergence, these pathogens exist within complex ecological systems that are characterized by trophic interactions between parasites, their hosts and the environment. Predicting how disturbance to these ecological systems places people and animals at risk from emerging pathogens-and the best ways to manage this-remains a significant challenge. Predictive systems ecology models are powerful tools for the reconstruction of ecosystem function but have yet to be considered for modelling infectious disease. Part of this stems from a mistaken tendency to forget about the role that pathogens play in structuring the abundance and interactions of the free-living species favoured by systems ecologists. Here, we explore how developing and applying these more complete systems ecology models at a landscape scale would greatly enhance our understanding of the reciprocal interactions between parasites, pathogens and the environment, placing zoonoses in an ecological context, while identifying key variables and simplifying assumptions that underly pathogen host switching and animal-to-human spillover risk. As well as transforming our understanding of disease ecology, this would also allow us to better direct resources in preparation for future pandemics.

Prevalence and intensity of avian malaria in a quail hybrid zone

Hybrid zones have been described as natural laboratories by researchers who study speciation and the various mechanisms that may affect gene flow. The evolutionary consequences of hybridization depend not only on reproductive compatibility between sympatric species, but also on factors like vulnerability to each other's predators and parasites. We examined infection patterns of the blood parasite Haemoproteus lophortyx, a causative agent of avian malaria, at a site in the contact zone between California quail (Callipepla californica) and Gambel's quail (C. gambelii). Controlling for the potential influence of sex and year, we tested whether species identity predicted infection status and intensity. We found that infection prevalence was lower in California and hybrid quail compared with Gambel's quail. However, infected California and hybrid quail had higher infection intensities than Gambel's quail. California and hybrid quail exhibited no significant differences in prevalence or intensity of infection. These findings suggest that infection by H. lophortyx has the potential to influence species barrier dynamics in this system; however, more work is necessary to determine the exact evolutionary consequences of this blood parasite on hybridization.

Host exposure history and priority effects impact the development and reproduction of a dominant parasite

Within a single organism, numerous parasites often compete for space and resources. This competition, together with a parasite's ability to locate and successfully establish in a host, can contribute to the distribution and prevalence of parasites. Coinfection with trematodes in snail intermediate hosts is rarely observed in nature, partly due to varying competitive abilities among parasite taxa. Using a freshwater snail host (Biomphalaria glabrata), we studied the ability of a competitively dominant trematode, Echinostoma caproni, to establish and reproduce in a host previously infected with a less competitive trematode species, Schistosoma mansoni. Snails were exposed to S. mansoni and co-exposed to E. caproni either simultaneously or 1 week, 4 weeks, or 6 weeks post S. mansoni exposure. Over the course of infection, we monitored the competitive success of the dominant trematode through infection prevalence, parasite development time, and parasite reproductive output. Infection prevalence of E. caproni did not differ among co-exposed groups or between co-exposed and single exposed groups. However, E. caproni infections in co-exposed hosts took longer to reach maturity when the timing between co-exposures increased. All co-exposed groups had higher E. caproni reproductive output than single exposures. We show that although timing of co-exposure affects the development time of parasite transmission stages, it is not important for successful establishment. Additionally, co-exposure, but not priority effects, increases the reproductive output of the dominant parasite.

Coinfection and infection duration shape how pathogens affect the African buffalo gut microbiota

Changes in the gut microbiota during pathogen infection are often predicted to influence disease outcomes. However, studies exploring whether pathogens induce microbiota shifts have yielded inconsistent results. This suggests that variation in infection, rather than the presence of infection alone, might shape pathogen-microbiota relationships. For example, most hosts are coinfected with multiple pathogens simultaneously, and hosts vary in how long they are infected, which may amplify or diminish microbial shifts expected in response to a focal pathogen. We used a longitudinal anthelmintic treatment study of free-ranging African buffalo (Syncerus caffer) to examine whether (i) coinfection with bovine tuberculosis (Mycobacterium bovis, TB) and gastrointestinal nematodes, and (ii) the duration of TB infection, modified effects of single pathogens on the gut microbiota. By accounting for the interaction between TB and nematodes, we found that coinfection affected changes in microbial abundance associated with single infections. Furthermore, the duration of TB infection predicted more microbiota variation than the presence of TB. Importantly, coinfection and infection duration had nearly as much influence on microbial patterns as demographic and environmental factors commonly examined in microbiota research. These findings demonstrate that acknowledging infection heterogeneities may be crucial to understanding relationships between pathogens and the gut microbiota.

Predictors of helminth parasite infection in female chacma baboons (Papio ursinus)

Helminth parasite infection can impose major consequences on host fitness. Several factors, including individual characteristics of hosts, environmental conditions, and patterns of coinfection, are thought to drive variation in parasite risk. Here, we report on four key drivers of parasite infection-phase of reproduction, steroid hormone profiles, rainfall, and patterns of coinfection-in a population of wild female chacma baboons (Papio ursinus) in South Africa. We collected data on reproductive state and hormone profiles over a 3-year span, and quantified helminth parasite burdens in 2955 fecal samples from 24 female baboons. On a host level, we found that baboons are sensitive to parasite infection during the costliest phases of the reproductive cycle: pregnant females harbored higher intensities of Protospirura eggs than cycling and lactating females; lactating and cycling females had a higher probability of Oesophagostomum infection than pregnant females; and cycling females exhibited lower Trichuris egg counts than pregnant and lactating females. Steroid hormones were associated with both immunoenhancing and immunosuppressive properties: females with high glucocorticoid concentrations exhibited high intensities of Trichuris eggs but were at low risk of Oesophagostomum infection; females with high estrogen and progestagen concentrations exhibited high helminth parasite richness; and females with high progestagen concentrations were at high risk of Oesophagostomum infection but exhibited low Protospirura egg counts. We observed an interaction between host reproductive state and progestagen concentrations in infection intensity of Protospirura: pregnant females exhibited higher intensities and non-pregnant females exhibited lower intensities of Protospirura eggs with increasing progestagen concentrations. At a population level, rainfall patterns were dominant drivers of parasite risk. Lastly, helminth parasites exhibited positive covariance, suggesting that infection probability increases if a host already harbors one or more parasite taxa. Together, our results provide a holistic perspective of factors that shape variation in parasite risk in a wild population of animals.

Infected juvenile salmon can experience increased predation during freshwater migration

Predation risk for animal migrants can be impacted by physical condition. Although size- or condition-based selection is often observed, observing infection-based predation is rare due to the difficulties in assessing infectious agents in predated samples. We examined predation of outmigrating sockeye salmon (Oncorhynchus nerka) smolts by bull trout (Salvelinus confluentus) in south-central British Columbia, Canada. We used a high-throughput quantitative polymerase chain reaction (qPCR) platform to screen for the presence of 17 infectious agents found in salmon and assess 14 host genes associated with viral responses. In one (2014) of the two years assessed (2014 and 2015), the presence of infectious haematopoietic necrosis virus (IHNv) resulted in 15-26 times greater chance of predation; in 2015 IHNv was absent among all samples, predated or not. Thus, we provide further evidence that infection can impact predation risk in migrants. Some smolts with high IHNv loads also exhibited gene expression profiles consistent with a virus-induced disease state. Nine other infectious agents were observed between the two years, none of which were associated with increased selection by bull trout. In 2014, richness of infectious agents was also associated with greater predation risk. This is a rare demonstration of predator consumption resulting in selection for prey that carry infectious agents. The mechanism by which this selection occurs is not yet determined. By culling infectious agents from migrant populations, fish predators could provide an ecological benefit to prey.

Hantavirus-Leptospira coinfections in small mammals from central Germany

European orthohantaviruses (Puumala orthohantavirus (PUUV); Dobrava-Belgrade orthohantavirus (DOBV), genotype Kurkino; Tula orthohantavirus (TULV)), and Leptospira spp. are small mammal-associated zoonotic pathogens that cause diseases with potentially similar symptoms in humans. We investigated the frequency of Leptospira spp. and hantavirus single and double infections in small mammals from 22 sites in Thuringia, central Germany, during 2017. TULV infections were detected at 18 of 22 sites (mean prevalence 13.8%, 93/674). PUUV infections were detected at four of 22 sites (mean prevalence 1.5%, 7/471), and respective PUUV sequences formed a novel phylogenetic clade, but DOBV infections were not detected at all. Leptospira infections were detected at 21 of 22 sites with the highest overall prevalence in field voles (Microtus agrestis) with 54.5% (6/11) and common voles (Microtus arvalis) with 30.3% (205/676). Leptospira–hantavirus coinfections were found in 6.6% (44/671) of common voles but only in two of 395 bank voles. TULV and Leptospira coinfection probability in common voles was driven by individual (age) and population-level factors. Coinfections seemed to be particularly associated with sites where Leptospira spp. prevalence exceeded 35%. Future investigations should evaluate public health consequences of this strong spatial clustering of coinfections.

Abundance data applied to a novel model invertebrate host shed new light on parasite community assembly in nature

Understanding how environmental drivers influence the assembly of parasite communities, in addition to how parasites may interact at an infracommunity level, are fundamental requirements for the study of parasite ecology. Knowledge of how parasite communities are assembled will help to predict the risk of parasitism for hosts, and model how parasite communities may change under variable conditions. However, studies frequently rely on presence-absence data and examine multiple host species or sites, metrics which may be too coarse to characterise nuanced within-host patterns. We utilised a novel host system, the freshwater mussel Anodonta anatina, to investigate the drivers of community structure and explore parasite interactions. In addition, we aimed to highlight consistencies and inconsistencies between PA and abundance data. Our analysis incorporated 14 parasite taxa and 720 replicate infracommunities. Using Redundancy Analysis, a joint species distribution model and a Markov random field approach, we modelled the impact of both host-level and environment-level characteristics on parasite structure, as well as parasite-parasite correlations after accounting for all other factors. This approach was repeated for both the presence and abundance of all parasites. We demonstrated that the regional species pool, individual host characteristics (mussel length and gravidity) and predicted parasite-parasite interactions are all important but to varying degrees across parasite species, suggesting that applying generalities to parasite community construction is too simplistic. Furthermore, we showed that PA data fail to capture important density-dependent effects of parasite load for parasites with high abundance, and in general performs poorly for high-intensity parasites. Host and parasite traits, as well as broader environmental factors, all contribute to parasite community structure, emphasising that an integrated approach is required to study community assembly. However, care must be taken with the data used to infer patterns, as presence-absence data may lead to incorrect ecological inference.

Co-infection best predicts respiratory viral infection in a wild host

The dynamics of directly transmitted pathogens in natural populations are likely to result from the combined effects of host traits, pathogen biology, and interactions among pathogens within a host. Discovering how these factors work in concert to shape variation in pathogen dynamics in natural host-multi-pathogen systems is fundamental to understanding population health. Here, we describe temporal variation in incidence and then elucidate the effect of hosts trait, season and pathogen co-occurrence on host infection risk using one of the most comprehensive studies of co-infection in a wild population: a suite of seven directly transmitted viral and bacterial respiratory infections from a 4-year study of 200 free-ranging African buffalo Syncerus caffer. Incidence of upper respiratory infections was common throughout the study-five out of the seven pathogens appeared to be consistently circulating throughout our study population. One pathogen exhibited clear outbreak dynamics in our final study year and another was rarely detected. Co-infection was also common in this system: The strongest indicator of pathogen occurrence for respiratory viruses was in fact the presence of other viral respiratory infections. Host traits had minimal effects on odds of pathogen occurrence but did modify pathogen-pathogen associations. In contrast, only season predicted bacterial pathogen occurrence. Though a combination of environmental, behavioural, and physiological factors work together to shape disease dynamics, we found pathogen associations best determined infection risk. Our study demonstrates that, in the absence of very fine-scale data, the intricate changes among these factors are best represented by co-infection.

Determinants of Eimeria and Campylobacter infection dynamics in UK domestic sheep: the role of co-infection

Coccidiosis caused by Eimeria species is a well-recognized disease of livestock. Enteric Eimeria infections are common, but disease usually only manifests when infection intensity is abnormally high. Campylobacter species are important zoonotic enteric bacterial pathogens for which livestock are important reservoir hosts. The diversity and epidemiology of ovine Eimeria and Campylobacter infections on two farms in north-western England were explored through a 24-month survey of shedding in sheep feces. Most animals were infected with at least one of 10 different Eimeria species, among which E. bakuensis and E. ovinoidalis were most common. An animal's age and the season of sampling were associated with the probability and intensity of Eimeria infection. Season of sampling was also associated with the probability of Campylobacter infection. Interestingly, higher intensities of Eimeria infections were significantly more common in animals not co-infected with Campylobacter. We explored the determinants of E. bakuensis and E. ovinoidalis infections, observing that being infected with either significantly increased the likelihood of infection with the other. The prevalence of E. ovinoidalis infections was significantly lower in sheep infected with Campylobacter. Recognition that co-infectors shape the dynamics of parasite infection is relevant to the design of effective infection control programmes.

Habitat type and interannual variation shape unique fungal pathogen communities on a California native bunchgrass

The role of infectious disease in regulating host populations is increasingly recognized, but how environmental conditions affect pathogen communities and infection levels remains poorly understood. Over 3 y, we compared foliar disease burden, fungal pathogen community composition, and foliar chemistry in the perennial bunchgrass Stipa pulchra occurring in adjacent serpentine and nonserpentine grassland habitats with distinct soil types and plant communities. We found that serpentine and nonserpentine S. pulchra experienced consistent, low disease pressure associated with distinct fungal pathogen communities with high interannual species turnover. Additionally, plant chemistry differed with habitat type. The results indicate that this species experiences minimal foliar disease associated with diverse fungal communities that are structured across landscapes by spatially and temporally variable conditions. Distinct fungal communities associated with different growing conditions may shield S. pulchra from large disease outbreaks, contributing to the low disease burden observed on this and other Mediterranean grassland species.

Patterns of flea infestation in rodents and insectivores from intensified agro-ecosystems, Northwest Spain

BACKGROUND

Fleas frequently infest small mammals and play important vectoring roles in the epidemiology of (re)emerging zoonotic disease. Rodent outbreaks in intensified agro-ecosystems of North-West Spain have been recently linked to periodic zoonotic diseases spillover to local human populations. Obtaining qualitative and quantitative information about the composition and structure of the whole flea and small mammal host coexisting communities is paramount to understand disease transmission cycles and to elucidate the disease-vectoring role of flea species. The aims of this research were to: (i) characterise and quantify the flea community parasiting a small mammal guild in intensive farmlands in North-West Spain; (ii) determine and evaluate patterns of co-infection and the variables that may influence parasitological parameters.

METHODS

We conducted a large-scale survey stratified by season and habitat of fleas parasitizing the small mammal host guild. We report on the prevalence, mean intensity, and mean abundance of flea species parasitizing Microtus arvalis, Apodemus sylvaticus, Mus spretus and Crocidura russula. We also report on aggregation patterns (variance-to-mean ratio and discrepancy index) and co-infection of hosts by different flea species (Fager index) and used generalized linear mixed models to study flea parameter variation according to season, habitat and host sex.

RESULTS

Three flea species dominated the system: Ctenophthalmus apertus gilcolladoi, Leptopsylla taschenbergi and Nosopsyllus fasciatus. Results showed a high aggregation pattern of fleas in all hosts. All host species in the guild shared C. a. gilcolladoi and N. fasciatus, but L. taschenbergi mainly parasitized mice (M. spretus and A. sylvaticus). We found significant male-biased infestation patterns in mice, seasonal variations in flea abundances for all rodent hosts (M. arvalis, M. spretus and A. sylvaticus), and relatively lower infestation values for voles inhabiting alfalfas. Simultaneous co-infections occurred in a third of all hosts, and N. fasciatus was the most common flea co-infecting small mammal hosts.

CONCLUSIONS

The generalist N. fasciatus and C. a. gilcolladoi dominated the flea community, and a high percentage of co-infections with both species occurred within the small mammal guild. Nosopsyllus fasciatus may show higher competence of inter-specific transmission, and future research should unravel its role in the circulation of rodent-borne zoonoses.

Experimental parasite community perturbation reveals associations between Sin Nombre virus and gastrointestinal nematodes in a rodent reservoir host

Individuals are often co-infected with several parasite species, yet measuring within-host interactions remains difficult in the wild. Consequently, the impacts of such interactions on host fitness and epidemiology are often unknown. We used anthelmintic drugs to experimentally reduce nematode infection and measured the effects on both nematodes and the important zoonosis Sin Nombre virus (SNV) in its primary reservoir (Peromyscus spp.). Treatment significantly reduced nematode infection, but increased SNV seroprevalence. Furthermore, mice that were co-infected with both nematodes and SNV were in better condition and survived up to four times longer than uninfected or singly infected mice. These results highlight the importance of investigating multiple parasites for understanding interindividual variation and epidemiological dynamics in reservoir populations with zoonotic transmission potential.

Infectious disease and sickness behaviour: tumour progression affects interaction patterns and social network structure in wild Tasmanian devils

Infectious diseases, including transmissible cancers, can have a broad range of impacts on host behaviour, particularly in the latter stages of disease progression. However, the difficulty of early diagnoses makes the study of behavioural influences of disease in wild animals a challenging task. Tasmanian devils (Sarcophilus harrisii) are affected by a transmissible cancer, devil facial tumour disease (DFTD), in which tumours are externally visible as they progress. Using telemetry and mark-recapture datasets, we quantify the impacts of cancer progression on the behaviour of wild devils by assessing how interaction patterns within the social network of a population change with increasing tumour load. The progression of DFTD negatively influences devils' likelihood of interaction within their network. Infected devils were more active within their network late in the mating season, a pattern with repercussions for DFTD transmission. Our study provides a rare opportunity to quantify and understand the behavioural feedbacks of disease in wildlife and how they may affect transmission and population dynamics in general.

Evolutionary Genetics of Borrelia

The genus Borrelia consists of evolutionarily and genetically diverse bacterial species that cause a variety of diseases in humans and domestic animals. These vector-borne spirochetes can be classified into two major evolutionary groups, the Lyme borreliosis clade and the relapsing fever clade, both of which have complex transmission cycles during which they interact with multiple host species and arthropod vectors. Molecular, ecological, and evolutionary studies have each provided significant contributions towards our understanding of the natural history, biology and evolutionary genetics of Borrelia species; however, integration of these studies is required to identify the evolutionary causes and consequences of the genetic variation within and among Borrelia species. For example, molecular and genetic studies have identified the adaptations that maximize fitness components throughout the Borrelia lifecycle and enhance transmission efficacy but provide limited insights into the evolutionary pressures that have produced them. Ecological studies can identify interactions between Borrelia species and the vertebrate hosts and arthropod vectors they encounter and the resulting impact on the geographic distribution and abundance of spirochetes but not the genetic or molecular basis underlying these interactions. In this review we discuss recent findings on the evolutionary genetics from both of the evolutionarily distinct clades of Borrelia species. We focus on connecting molecular interactions to the ecological processes that have driven the evolution and diversification of Borrelia species in order to understand the current distribution of genetic and molecular variation within and between Borrelia species.

Scale-dependent effects of host patch traits on species composition in a stickleback parasite metacommunity

A core goal of ecology is to understand the abiotic and biotic variables that regulate species distributions and community composition. A major obstacle is that the rules governing species distributions can change with spatial scale. Here, we illustrate this point using data from a spatially nested metacommunity of parasites infecting a metapopulation of threespine stickleback fish from 34 lakes on Vancouver Island, British Columbia. Like most parasite metacommunities, the composition of stickleback parasites differs among host individuals within each host population, and differs between host populations. The distribution of each parasite taxon depends, to varying degrees, on individual host traits (e.g., mass, diet) and on host-population characteristics (e.g., lake size, mean host mass, mean diet). However, in most cases in this data set, a given parasite was regulated by different factors at the host-individual and host-population scales, leading to scale-dependent patterns of parasite-species co-occurrence.

Anaplasma and Theileria Pathogens in Cattle of Lambwe Valley, Kenya: A Case for Pro-Active Surveillance in the Wildlife-Livestock Interface

Tick-borne pathogens (TBPs) are major constraints to livestock production and a threat to public health in Africa. This cross-sectional study investigated the risk of infection with TBPs in cattle of Lambwe Valley, Kenya. Blood samples of 680 zebu cattle from 95 herds in six geospatial clusters within 5 km of Ruma National Park were screened for bacterial and protozoan TBPs by high-resolution melting analysis and sequencing of PCR products. We detected Anaplasma bovis (17.4%), Anaplasma platys (16.9%), Anaplasma marginale (0.6%), Theileria velifera (40%), and Theileria mutans (25.7%), as well as an Anaplasma sp. (11.6%) that matched recently reported Anaplasma sp. sequences from Ethiopia. Babesia, Rickettsia, and Ehrlichia spp. were not detected. The animal and herd-level prevalences for TBPs were 78.5% (95% confidence intervals (CI): 75.3, 81.5) and 95.8% (95% CI: 91.8, 99.8), respectively. About 31.6% of cattle were co-infected with 13 combinations of TBPs. The prevalence of TBPs differed between clusters and age, but the risk of infection was not associated with sex, herd size, or the distance of homesteads from Ruma. This study adds insight into the epidemiology of TBPs around Ruma and highlights the need for proactive surveillance of TBPs in livestock–wildlife interfaces.

Microhabitat distributions and species interactions of ectoparasites on the gills of cichlid fish in Lake Victoria, Tanzania

Heterogeneous exposure to parasites may contribute to host species differentiation. Hosts often harbour multiple parasite species which may interact and thus modify each other's effects on host fitness. Antagonistic or synergistic interactions between parasites may be detectable as niche segregation within hosts. Consequently, the within-host distribution of different parasite taxa may constitute an important axis of infection variation among host populations and species. We investigated the microhabitat distributions and species interactions of gill parasites (four genera) infecting 14 sympatric cichlid species in Lake Victoria, Tanzania. We found that the two most abundant ectoparasite genera (the monogenean Cichlidogyrus spp. and the copepod Lamproglena monodi) were non-randomly distributed across the host gills and their spatial distribution differed between host species. This may indicate microhabitat selection by the parasites and cryptic differences in the host-parasite interaction among host species. Relationships among ectoparasite genera were synergistic: the abundances of Cichlidogyrus spp. and the copepods L. monodi and Ergasilus lamellifer tended to be positively correlated. In contrast, relationships among morphospecies of Cichlidogyrus were antagonistic: the abundances of morphospecies were negatively correlated. Together with niche overlap, this suggests competition among morphospecies of Cichlidogyrus. We also assessed the reproductive activity of the copepod species (the proportion of individuals carrying egg clutches), as it may be affected by the presence of other parasites and provide another indicator of the species specificity of the host-parasite relationship. Copepod reproductive activity did not differ between host species and was not associated with the presence or abundance of other parasites, suggesting that these are generalist parasites, thriving in all cichlid species examined from Lake Victoria.

Intraspecific host variation plays a key role in virus community assembly

Infection by multiple pathogens of the same host is ubiquitous in both natural and managed habitats. While intraspecific variation in disease resistance is known to affect pathogen occurrence, how differences among host genotypes affect the assembly of pathogen communities remains untested. In our experiment using cloned replicates of naive Plantago lanceolata plants as sentinels during a seasonal virus epidemic, we find non-random co-occurrence patterns of five focal viruses. Using joint species distribution modelling, we attribute the non-random virus occurrence patterns primarily to differences among host genotypes and local population context. Our results show that intraspecific variation among host genotypes may play a large, previously unquantified role in pathogen community structure.

Evolutionary ecology of Lyme Borrelia

The bacterial genus, Borrelia, is comprised of vector-borne spirochete species that infect and are transmitted from multiple host species. Some Borrelia species cause highly-prevalent diseases in humans and domestic animals. Evolutionary, ecological, and molecular research on many Borrelia species have resulted in tremendous progress toward understanding the biology and natural history of these species. Yet, many outstanding questions, such as how Borrelia populations will be impacted by climate and land-use change, will require an interdisciplinary approach. The evolutionary ecology research framework incorporates theory and data from evolutionary, ecological, and molecular studies while overcoming common assumptions within each field that can hinder integration across these disciplines. Evolutionary ecology offers a framework to evaluate the ecological consequences of evolved traits and to predict how present-day ecological processes may result in further evolutionary change. Studies of microbes with complex transmission cycles, like Borrelia, which interact with multiple vertebrate hosts and arthropod vectors, are poised to leverage the power of the evolutionary ecology framework to identify the molecular interactions involved in ecological processes that result in evolutionary change. Using existing data, we outline how evolutionary ecology theory can delineate how interactions with other species and the physical environment create selective forces or impact migration of Borrelia populations and result in micro-evolutionary changes. We further discuss the ecological and molecular consequences of those micro-evolutionary changes. While many of the currently outstanding questions will necessitate new experimental designs and additional empirical data, many others can be addressed immediately by integrating existing molecular and ecological data within an evolutionary ecology framework.

Influence of land use and host species on parasite richness, prevalence and co-infection patterns

Tropical forests are experiencing increasing impacts from a multitude of anthropogenic activities such as logging and conversion to agricultural use. These perturbations are expected to have strong impacts on ecological interactions and on the transmission dynamics of infectious diseases. To date, no clear picture of the effects of deforestation on vector-borne disease transmission has emerged. This is associated with the challenge of studying complex systems where many vertebrate hosts and vectors co-exist. To overcome this problem, we focused on an innately simplified system - a small oceanic island (São Tomé, Gulf of Guinea). We analyzed the impacts of human land-use on host-parasite interactions by sampling the bird community (1735 samples from 30 species) in natural and anthropogenic land use at different elevations, and screened individuals for haemosporidian parasites from three genera (Plasmodium, Haemoproteus, Leucocytozoon). Overall, Plasmodium had the highest richness but the lowest prevalence, while Leucocytozoon diversity was the lowest despite having the highest prevalence. Interestingly, co-infections (i.e. intra-host diversity) involved primarily Leucocytozoon lineages (95%). We also found marked differences between bird species and habitats. Some bird species showed low prevalence but harbored high diversity of parasites, while others showed high prevalence but were infected with fewer lineages. These infection dynamics are most likely driven by host specificity of parasites and intrinsic characteristics of hosts. In addition, Plasmodium was more abundant in disturbed habitats and at lower elevations, while Leucocytozoon was more prevalent in forest areas and at higher elevations. These results likely reflect the ecological requirements of their vectors: mosquitoes and black flies, respectively.

The impact of anthelmintic treatment on gut bacterial and fungal communities in diagnosed parasite-free sika deer Cervus nippon

The gut microbiota, including both bacterial and fungal communities, plays vital roles in the gut homeostasis of animals, and antibiotics can lead to disorders of these microbial communities. The use of anthelmintic treatment to control parasitic infection has long been a standard practice, although its impact on the gut microbiota of healthy sika deer is relatively unknown. This study used next-generation sequencing based on 16S/18S/ITS rRNA genes to investigate the shifts in fecal bacterial and fungal communities in parasite-free sika deer after treatment with fenbendazole and ivermectin tablets. The α-diversity of both bacterial and fungal communities was significantly decreased (P < 0.05) after treatment, as were the bacterial genus Bacteroides and fungal genus Candida (P < 0.05). The results of β-diversity, LEfSe analysis, core community's analysis, taxonomic composition, and functional prediction of fungal and bacterial communities confirmed the substantial impacts of anthelmintic treatment on the function and structure of the intestinal microbiota of sika deer. Nevertheless, many lines of evidence, including β-diversity, LEfSe analysis and functional prediction analysis, suggested that the anthelmintics exerted more significant influences on fungal communities than on bacterial communities, suggesting that more attention should be paid to the changes in fungal communities of sika deer under anthelmintic treatment. The present study provides evidence to support the assumption that anthelmintic drugs modify the gut microbiota of deer and serves as the first trial to test the potential effects of anthelmintics on mycobiota in ruminants using high-throughput sequencing techniques. Key Points • Anthelmintic treatment showed significant effects on the gut microbiota of sika deer. • Fungi were more strongly affected by anthelmintic treatment than bacteria. • The profile of mycobiota provides essential data that were previously absent.

Effects of life history stage and climatic conditions on fecal egg counts in plains zebras (Equus quagga) in the Serengeti National Park

In wildlife, endoparasite burden can be affected by host life history stage, environmental conditions, host abundance, and parasite co-infections. We tested the effects of these factors on gastrointestinal parasite infection in plains zebras (Equus quagga) in the Serengeti ecosystem, Tanzania, using fecal egg counts of two nematode families (Strongylidae and Ascarididae) and the presence/absence of cestode (Anoplocephalidae) eggs. We predicted higher egg counts of Strongylidae and Ascarididae, and increased likelihood of Anoplocephalidae infection in individuals (1) during energetically costly life history stages when resource allocation to immune processes may decrease and in young zebras after weaning because of increased uptake of infective stages with forage, (2) when climatic conditions facilitate survival of infective stages, (3) when large zebra aggregations increase forage contamination with infective stages, and (4) in individuals co-infected with more than one parasite group as this may indicate reduced immune competence. Strongylidae egg counts were higher, and the occurrence of Anoplocephalidae eggs was more likely in bachelors than in band stallions, whereas Ascarididae egg counts were higher in band stallions. Strongylidae and Ascarididae egg counts were not increased in lactating females. Strongylidae egg counts were higher in subadults than in foals. Regardless of sex and age, Ascarididae infections were more likely under wet conditions. Co-infections did not affect Strongylidae egg counts. Ascarididae egg counts in adult females were higher when individuals were co-infected with Anoplocephalidae. We present evidence that parasite burdens in plains zebras are affected by life history stage, environmental conditions, and co-infection.

Diversity in CRISPR-based immunity protects susceptible genotypes by restricting phage spread and evolution

Diversity in host resistance often associates with reduced pathogen spread. This may result from ecological and evolutionary processes, likely with feedback between them. Theory and experiments on bacteria-phage interactions have shown that genetic diversity of the bacterial adaptive immune system can limit phage evolution to overcome resistance. Using the CRISPR-Cas bacterial immune system and lytic phage, we engineered a host-pathogen system where each bacterial host genotype could be infected by only one phage genotype. With this model system, we explored how CRISPR diversity impacts the spread of phage when they can overcome a resistance allele, how immune diversity affects the evolution of the phage to increase its host range and if there was feedback between these processes. We show that increasing CRISPR diversity benefits susceptible bacteria via a dilution effect, which limits the spread of the phage. We suggest that this ecological effect impacts the evolution of novel phage genotypes, which then feeds back into phage population dynamics.

A negative covariation between toxoplasmosis and CoVID-19 with alternative interpretations

Coronaviruses may exert severely negative effects on the mortality and morbidity of birds and mammals including humans and domestic animals. Most recently CoVID-19 has killed about half million people (27th of June, 2020). Susceptibility to this disease appears to differ markedly across different societies but the factors underlying this variability are not known. Given that prevalence of toxoplasmosis in human societies may serve as a proxy for hygiene, and it also exerts both direct and immune-mediated antiviral effects, we hypothesize a negative covariation between toxoplasmosis and measures of the CoVID-19 pandemic across countries. We obtained aged-adjusted toxoplasmosis prevalence of pregnant women from the literature. Since the differences in the CoVID-19 morbidity and mortality may depend on the different timing of the epidemics in each country, we applied the date of first documented CoVID-19 in each country as a proxy of susceptibility, with a statistical control for population size effects. Using these two indices, we show a highly significant negative co-variation between the two pandemics across 86 countries. Then, considering that the wealth of nations often co-varies with the prevalence of diseases, we introduced GDP per capita into our model. The prevalence of toxoplasmosis co-varies negatively, while the date of first CoVID-19 co-varies positively with GDP per capita across countries. Further, to control for the strong spatial autocorrelation among countries, we carried out a Spatial Structure Analyses of the relationships between the date of first CoVID-19, prevalence of toxoplasmosis, and GDP per capita. Results of this analysis did not confirm a direct causal relationship between toxoplasmosis and susceptibility to the CoVID-19 pandemics. As far as an analysis of observational data let us to suggest, it appears that the interaction between CoVID-19 and toxoplasmosis is mediated by GDP per capita and spatial effects. This prompts the question whether the formerly known covariations of CoVID-19 and BCG vaccination or air pollution might have also emerged as spurious indirect effects.

West Nile Virus: An Update on Pathobiology, Epidemiology, Diagnostics, Control and "One Health" Implications

West Nile virus (WNV) is an important zoonotic flavivirus responsible for mild fever to severe, lethal neuroinvasive disease in humans, horses, birds, and other wildlife species. Since its discovery, WNV has caused multiple human and animal disease outbreaks in all continents, except Antarctica. Infections are associated with economic losses, mainly due to the cost of treatment of infected patients, control programmes, and loss of animals and animal products. The pathogenesis of WNV has been extensively investigated in natural hosts as well as in several animal models, including rodents, lagomorphs, birds, and reptiles. However, most of the proposed pathogenesis hypotheses remain contentious, and much remains to be elucidated. At the same time, the unavailability of specific antiviral treatment or effective and safe vaccines contribute to the perpetuation of the disease and regular occurrence of outbreaks in both endemic and non-endemic areas. Moreover, globalisation and climate change are also important drivers of the emergence and re-emergence of the virus and disease. Here, we give an update of the pathobiology, epidemiology, diagnostics, control, and “One Health” implications of WNV infection and disease.

Timing and order of exposure to two echinostome species affect patterns of infection in larval amphibians

The study of priority effects with respect to coinfections is still in its infancy. Moreover, existing coinfection studies typically focus on infection outcomes associated with exposure to distinct sets of parasite species, despite that functionally and morphologically similar parasite species commonly coexist in nature. Therefore, it is important to understand how interactions between similar parasites influence infection outcomes. Surveys at seven ponds in northwest Pennsylvania found that multiple species of echinostomes commonly co-occur. Using a larval anuran host (Rana pipiens) and the two most commonly identified echinostome species from our field surveys (Echinostoma trivolvis and Echinoparyphium lineage 3), we examined how species composition and timing of exposure affect patterns of infection. When tadpoles were exposed to both parasites simultaneously, infection loads were higher than when exposed to Echinoparyphium alone but similar to being exposed to Echinostoma alone. When tadpoles were sequentially exposed to the parasite species, tadpoles first exposed to Echinoparyphium had 23% lower infection loads than tadpoles first exposed to Echinostoma. These findings demonstrate that exposure timing and order, even with similar parasites, can influence coinfection outcomes, and emphasize the importance of using molecular methods to identify parasites for ecological studies.

Parasite species co-occurrence patterns on Peromyscus: Joint species distribution modelling

Hosts are often infested by multiple parasite species, but it is often unclear whether patterns of parasite co-occurrence are driven by parasite habitat requirements or parasite species interactions. Using data on infestation patterns of ectoparasitic arthropods (fleas, trombiculid mites, cuterebrid botflies) from deer mice (Peromyscus maniculatus), we analyzed species associations using joint species distribution modelling. We also experimentally removed a flea (Orchopeas leucopus) from a subset of deer mice to examine the effect on other common ectoparasite species. We found that the mite (Neotrombicula microti) and botfly (Cuterebra sp.) had a negative relationship that is likely a true biotic species interaction. The flea had a negative association with the mite and a positive association with the botfly species, both of which appeared to be influenced by host traits or parasite life-history traits. Furthermore, experimental removal of the flea did not have a significant effect on ectoparasite prevalence of another species. Overall, these findings suggest that complex parasite species associations can be present among multiple parasite taxa, and that aggregation is not always the rule for ectoparasite communities of small mammals.

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A negative species interaction was identified between a mite and botfly species.

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Additional parasite associations appear to be influenced by host traits or parasite life-history traits.

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Removal of the flea species did not have an effect on prevalence of another species.

Spatio-temporal trends in richness and persistence of bacterial communities in decline-phase water vole populations

Understanding the driving forces that control vole population dynamics requires identifying bacterial parasites hosted by the voles and describing their dynamics at the community level. To this end, we used high-throughput DNA sequencing to identify bacterial parasites in cyclic populations of montane water voles that exhibited a population outbreak and decline in 2014-2018. An unexpectedly large number of 155 Operational Taxonomic Units (OTUs) representing at least 13 genera in 11 families was detected. Individual bacterial richness was higher during declines, and vole body condition was lower. Richness as estimated by Chao2 at the local population scale did not exhibit clear seasonal or cycle phase-related patterns, but at the vole meta-population scale, exhibited seasonal and phase-related patterns. Moreover, bacterial OTUs that were detected in the low density phase were geographically widespread and detected earlier in the outbreak; some were associated with each other. Our results demonstrate the complexity of bacterial community patterns with regard to host density variations, and indicate that investigations about how parasites interact with host populations must be conducted at several temporal and spatial scales: multiple times per year over multiple years, and at both local and long-distance dispersal scales for the host(s) under consideration.

Incapacitating effects of fungal coinfection in a novel pathogen system

As globalization lowers geographic barriers to movement, coinfection with novel and enzootic pathogens is increasingly likely. Novel and enzootic pathogens can interact synergistically or antagonistically, leading to increased or decreased disease severity. Here we examine host immune responses to coinfection with two closely related fungal pathogens: Batrachochytrium dendrobatidis (Bd) and Batrachochytrium salamandrivorans (Bsal). Both pathogens have had detrimental effects on amphibian populations, with Bd now largely enzootic, while Bsal is currently spreading and causing epizootics. Recent experimental work revealed that newts coinfected with Bd and Bsal had significantly higher mortality than those infected with either pathogen alone. Here we characterize host immunogenomic responses to chytrid coinfection relative to single infection. Across several classes of immune genes including pattern recognition receptors, cytokines, and MHC, coinfected host gene expression was weakly upregulated or comparable to that seen in single Bd infection, but significantly decreased when compared to Bsal infection. Combined with strong complement pathway downregulation and keratin upregulation, these results indicate that coinfection with Bd and Bsal compromises immune responses active against Bsal alone. As Bsal continues to invade naïve habitats where Bd is enzootic, coinfection will be increasingly common. If other Bd-susceptible species in the region have similar responses, interactions between the two pathogens could cause severe population and community-level declines.

Complex interactions between bacteria and haemosporidia in coinfected hosts: An experiment

Hosts are typically coinfected by multiple parasite species whose interactions might be synergetic or antagonistic, producing unpredictable physiological and pathological impacts on the host. This study shows the interaction between Plasmodium spp. and Leucocytozoon spp. in birds experimentally infected or not infected with Mycoplasma gallisepticum.In 1994, the bacterium Mycoplasma gallisepticum jumped from poultry to wild birds in which it caused a major epidemic in North America. Birds infected with M. gallisepticum show conjunctivitis as well as increased levels of corticosterone.Malaria and other haemosporidia are widespread in birds, and chronic infections become apparent with the detectable presence of the parasite in peripheral blood in response to elevated levels of natural or experimental corticosterone levels.Knowing the immunosuppressive effect of corticosterone on the avian immune system, we tested the hypothesis that chronic infections of Plasmodium spp. and Leucocytozoon spp. in house finches would respond to experimental inoculation with M. gallisepticum as corticosterone levels are known to increase following inoculation. Plasmodium spp. infection intensity increased within days of M. gallisepticum inoculation as shown both by the appearance of infected erythrocytes and by the increase in the number and the intensity of positive PCR tests. Leucocytozoon spp. infection intensity increased when Plasmodium spp. infection intensity increased, but not in response to M. gallisepticum inoculation. Leucocytozoon spp. and Plasmodium spp. seemed to compete in the host as shown by a negative correlation between the changes in their PCR score when both pathogens were present in the same individual.Host responses to coinfection with multiple pathogens measured by the hematocrit and white blood cell count depended on the haemosporidian community composition. Host investment in the leukocyte response was higher in the single-haemosporidia-infected groups when birds were infected with M. gallisepticum.A trade-off was observed between the immune control of the chronic infection (Plasmodium spp./Leucocytozoon spp.) and the immune response to the novel bacterial infection (M. gallisepticum).