Japanese encephlu emergence in Australia: the potential population at risk

Japanese encephalitis virus (JEV), an RNA virus transmitted by Culex mosquitoes, primarily cycles between aquatic birds and mosquitoes with pigs as amplifying hosts, posing a significant global encephalitis threat. The emergence and spread of the JEV in new epidemiological regions, such as recent cases in Australia and nonendemic areas like Pune, India, raise significant concerns. With an estimated 68 000 clinical cases and 13 600 to 20 400 deaths annually, JEV poses a substantial global health threat. The virus primarily affects children, with a case-fatality ratio of 20-30% and long-term neurological sequelae in survivors. The changing epidemiology, influenced by factors like bird migration, climate change, and increased urbanization, contributes to the geographic expansion of JEV. The recent outbreaks underscore the potential for the virus to establish itself in nonendemic regions, posing a threat to populations previously considered at low-risk. With limited treatment options and high rates of neurological complications, continued surveillance, traveler vaccination, and research into treatments are crucial to mitigate the impact of JEV on human health. The evolving scenario necessitates proactive measures to prevent and control the spread of the virus in both endemic and newly affected areas.

Transmission Cycle of Shimokoshi-Type Orientia tsutsugamushi in Shimane Prefecture, Japan

To demonstrate the transmission cycle of Shimokoshi-type Orientia tsutsugamushi in Shimane Prefecture, field rodents were captured from areas where four human infections caused by the pathogen have been reported. The rodents were investigated for the transmission cycle of the pathogen based on the pathogen's genome, antibodies against the pathogen, and the vector of the pathogen (Leptotrombidium palpale). In addition, the vector was captured from the soil in the study area. A total of 44 rodents were captured. No O. tsutsugamushi DNA was detected in the blood or spleen samples by real-time polymerase chain reaction. However, a specific antibody against the pathogen was detected in 2 out of 44 (4.5%) rodents using the indirect immunoperoxidase method, indicating the presence of the pathogen in the study area. Although 29 L. palpale were identified, DNA detection was not performed because of the insufficient number of vectors, based on the DNA detection rate in previous studies. However, the identification of the vector, as well as the specific antibody in rodents, suggests the presence of the transmission cycle of Shimokoshi-type O. tsutsugamushi in Shimane Prefecture.

Diversity and Epidemiology of Bat Trypanosomes: A One Health Perspective

Bats (order Chiroptera) have been increasingly recognised as important reservoir hosts for human and animal pathogens worldwide. In this context, molecular and microscopy-based investigations to date have revealed remarkably high diversity of Trypanosoma spp. harboured by bats, including species of recognised medical and veterinary importance such as Trypanosoma cruzi and Trypanosoma evansi (aetiological agents of Chagas disease and Surra, respectively). This review synthesises current knowledge on the diversity, taxonomy, evolution and epidemiology of bat trypanosomes based on both molecular studies and morphological records. In addition, we use a One Health approach to discuss the significance of bats as reservoirs (and putative vectors) of T. cruzi, with a focus on the complex associations between intra-specific genetic diversity and eco-epidemiology of T. cruzi in sylvatic and domestic ecosystems. This article also highlights current knowledge gaps on the biological implications of trypanosome co-infections in a single host, as well as the prevalence, vectors, life-cycle, host-range and clinical impact of most bat trypanosomes recorded to date. Continuous research efforts involving molecular surveillance of bat trypanosomes are required for improved disease prevention and control, mitigation of biosecurity risks and potential spill-over events, ultimately ensuring the health of humans, domestic animals and wildlife globally.

Metagenomic Analysis of the Gut Microbiota of Wild Mice, a Newly Identified Reservoir of Campylobacter

Campylobacter, the most common etiologic agent of zoonotic gastroenteritis in humans, is present in many reservoirs including livestock animals, wildlife, soil, and water. Previously, we reported a novel Campylobacter jejuni strain SCJK02 (MLST ST-8388) from the gut of wild mice (Micromys minutus) using culture-dependent methods. However, due to fastidious growth conditions and the presence of viable but non-culturable Campylobacter spp., it is unclear whether M. minutus is a Campylobacter reservoir. This study aimed to: 1) determine the distribution and proportion of Campylobacter spp. in the gut microbiota of wild mice using culture-independent methods and 2) investigate the gut microbiota of wild mice and the relationship of Campylobacter spp. with other gut microbes. The gut microbiota of 38 wild mice captured from perilla fields in Korea and without any clinical symptoms (18 M. minutus and 20 Mus musculus) were analyzed. Metagenomic analysis showed that 77.8% (14 of 18) of the captured M. minutus harbored Campylobacter spp. (0.24–32.92%) in the gut metagenome, whereas none of the captured M. musculus carried Campylobacter spp. in their guts. Notably, 75% (6 of 8) of M. minutus determined to be Campylobacter-negative using culture-dependent methods showed a high proportion of Campylobacter through metagenome analysis. The results of metagenome analysis and the absence of clinical symptoms suggest that Campylobacter may be a component of the normal gut flora of wild M. minutus. Furthermore, linear discriminant analysis (LDA) showed that Campylobacter was the most enriched genus in the gut microbiota of M. minutus (LDA score, 5.37), whereas Lactobacillus was the most enriched genus in M. musculus (LDA score, −5.96). The differences in the presence of Campylobacter between the two species of wild mice may be attributed to the differential abundance of Campylobacter and Lactobacillus in their respective gut microbiota. In conclusion, the results indicate that wild M. minutus may serve as a potential Campylobacter reservoir. This study presents the first metagenomics analysis of the M. minutus gut microbiota to explore its possible role as an environmental Campylobacter reservoir and provides a basis for future studies using culture-independent methods to determine the role of environmental reservoirs in Campylobacter transmission.

The Absence of Yellow Fever in Asia: History, Hypotheses, Vector Dispersal, Possibility of YF in Asia, and Other Enigmas

Since the recent epidemics of yellow fever in Angola and Brazil as well as the importation of cases to China in 2016, there has been an increased interest in the century-old enigma, absence of yellow fever in Asia. Although this topic has been repeatedly reviewed before, the history of human intervention has never been considered a critical factor. A two-stage literature search online for this review, however, yielded a rich history indispensable for the debate over this medical enigma. As we combat the pandemic of COVID-19 coronavirus worldwide today, we can learn invaluable lessons from the historical events in Asia. In this review, I explore the history first and then critically examine in depth major hypotheses proposed in light of accumulated data, global dispersal of the principal vector, patterns of YF transmission, persistence of urban transmission, and the possibility of YF in Asia. Through this process of re-examination of the current knowledge, the subjects for research that should be conducted are identified. This review also reveals the importance of holistic approach incorporating ecological and human factors for many unresolved subjects, such as the enigma of YF absence in Asia, vector competence, vector dispersal, spillback, viral persistence and transmission mechanisms.

Tripartite Interactions among Ixodiphagus hookeri, Ixodes ricinus and Deer: Differential Interference with Transmission Cycles of Tick-Borne Pathogens

For the development of sustainable control of tick-borne diseases, insight is needed in biological factors that affect tick populations. Here, the ecological interactions among Ixodiphagus hookeri, Ixodes ricinus, and two vertebrate species groups were investigated in relation to their effects on tick-borne disease risk. In 1129 questing ticks, I. hookeri DNA was detected more often in I. ricinus nymphs (4.4%) than in larvae (0.5%) and not in adults. Therefore, we determined the infestation rate of I. hookeri in nymphs from 19 forest sites, where vertebrate, tick, and tick-borne pathogen communities had been previously quantified. We found higher than expected co-occurrence rates of I. hookeri with deer-associated Anaplasma phagocytophilum, and lower than expected rates with rodent-associated Borrelia afzelii and Neoehrlichia mikurensis. The prevalence of I. hookeri in nymphs varied between 0% and 16% and was positively correlated with the encounter probability of ungulates and the densities of all life stages of I. ricinus. Lastly, we investigated the emergence of I. hookeri from artificially fed, field-collected nymphs. Adult wasps emerged from seven of the 172 fed nymphs. From these observations, we inferred that I. hookeri is parasitizing I. ricinus larvae that are feeding on deer, rather than on rodents or in the vegetation. Since I. hookeri populations depend on deer abundance, the main propagation host of I. ricinus, these wasps have no apparent effect on tick populations. The presence of I. hookeri may directly interfere with the transmission cycle of A. phagocytophilum, but not with that of B. afzelii or N. mikurensis.

Landmarks of the Knowledge and Trypanosoma cruzi Biology in the Wild Environment

Trypanosomatids are ancient parasitic eukaryotes that still maintain prokaryotic characteristics. Trypanosoma cruzi, a primarily wild mammal parasite, infected humans already long before European colonization of the Americas. T. cruzi heterogeneity remains an unsolved question, and until now, it has still not been possible to associate T. cruzi genotypes with any biological or epidemiological feature. One of the first biochemical attempts to cluster the T. cruzi subpopulations recognized three main subpopulations (zymodemes) that have been associated with the transmission cycles in the wild (Z1; Z3) and in the domestic environment (Z2). The description of wild mammal species harboring Z2 two decades later challenged this assemblage attempt. Currently, the genotypes of T. cruzi are assembled in seven discrete typing units (DTUs). The biology of T. cruzi still shows novelties such as the description of epimastigotes multiplying and differentiating to metacyclic trypomastigotes in the lumen of the scent glands of Didelphis spp. and the capacity of the true meiosis in parallel to clonal reproduction. The study of the transmission cycle among wild animals has broken paradigms and raised new questions: (i) the interaction of the T. cruzi DTUs with each of its mammalian host species displays peculiarities; (ii) the impact of mixed genotypes and species on the transmissibility of one or another species or on pathogenesis is still unknown; (iii) independent T. cruzi transmission cycles may occur in the same forest fragment; (iv) the capacity to act as a reservoir depends on the peculiarities of the host species and the parasite genotype; and (v) faunistic composition is a defining trait of the T. cruzi transmission cycle profile. The development of models of environmental variables that determine the spatial distribution of the elements that make up T. cruzi transmission by spatial analysis, followed by map algebra and networking, are the next steps toward interpreting and dealing with the new profile of Chagas disease with its many peculiarities. There is no way to solve this neglected disease once and for all if not through a multidisciplinary look that takes into account all kinds of human and animal activities in parallel to environmental variations.

The Wild Mouse (Micromys minutus): Reservoir of a Novel Campylobacter jejuni Strain

Campylobacter jejuni is one of the most common zoonotic pathogens worldwide. Although the main sources of human C. jejuni infection are livestock, wildlife can also affect C. jejuni transmission in humans. However, it remains unclear whether wild mice harbor C. jejuni and are involved in the "environment-wildlife-livestock-human" transmission cycle of C. jejuni in humans. Here, we characterized C. jejuni from wild mice and identified genetic traces of wild mouse-derived C. jejuni in other hosts using a traditional approach, along with comparative genomics. We captured 115 wild mice (49 Mus musculus and 66 Micromys minutus) without any clinical symptoms from 22 sesame fields in Korea over 2 years. Among them, M. minutus were typically caught in remote areas of human houses and C. jejuni was solely isolated from M. minutus (42/66, 63.6%). We identified a single clone (MLST ST-8388) in all 42 C. jejuni isolates, which had not been previously reported, and all isolates had the same virulence/survival-factor profile, except for the plasmid-mediated virB11 gene. No isolates exhibited antibiotic resistance, either in phenotypic and genetic terms. Comparative-genomic analysis and MST revealed that C. jejuni derived from M. minutus (strain SCJK2) was not genetically related to those derived from other sources (registered in the NCBI genome database and PubMLST database). Therefore, we hypothesize that C. jejuni from M. minutus is a normal component of the gut flora following adaptation to the gastro-intestinal tract. Furthermore, M. minutus-derived C. jejuni had different ancestral lineages from those derived from other sources, and there was a low chance of C. jejuni transmission from M. minutus to humans/livestock because of their habitat. In conclusion, M. minutus may be a potential reservoir for a novel C. jejuni, which is genetically different from those of other sources, but may not be involved in the transmission of C. jejuni to other hosts, including humans and livestock. This study could form the basis for further studies focused on understanding the transmission cycle of C. jejuni, as well as other zoonotic pathogens originating from wild mice.

Lack of Evidence of Sylvatic Transmission of Dengue Viruses in the Amazon Rainforest Near Iquitos, Peru

Dengue viruses (DENV) are currently responsible for more human morbidity and mortality than any other known arbovirus, and all four DENV are known to exist in sylvatic cycles that might allow these viruses to persist if the urban (Aedes aegypti) cycle could be controlled. To determine whether DENV were being maintained in a sylvatic cycle in a forested area about 14 km southwest of Iquitos, Peru, a city in which all 4 serotypes of DENV circulate, we placed 20 DENV seronegative Aotus monkeys in cages either in the canopy or near ground level for a total of 125.6 months. Despite capturing >66,000 mosquitoes in traps that collected some of the mosquitoes attracted to these monkeys, blood samples obtained once a month from each animal were tested and found to be negative by an enzyme-linked immunosorbent assay for IgM and IgG antibodies to dengue, yellow fever, Venezuelan equine encephalitis, Oropouche, and Mayaro viruses. Although all four DENV serotypes were endemic in nearby Iquitos, the findings of this study did not support a DENV sylvatic maintenance and transmission cycle in a selected area of the Amazon rainforest in northeastern Peru.

Identification of Wild Boar-Habitat Epidemiologic Cycle in African Swine Fever Epizootic

The African swine fever epizootic in central and eastern European Union member states has a newly identified component involving virus transmission by wild boar and virus survival in the environment. Insights led to an update of the 3 accepted African swine fever transmission models to include a fourth cycle: wild boar–habitat.

Gongylonema infection of wild mammals in Japan and Sardinia (Italy)

The gullet worms, classical Gongylonema pulchrum and newly differentiated Gongylonema nepalensis, are prevalent in various mammals in Japan and Sardinia, Italy, respectively. The former species is cosmopolitan in distribution, dwelling in the mucosa of the upper digestive tract of a variety of domestic and wild mammals, and also humans. At present, the geographical distribution of G. nepalensis is known in Nepal and Sardinia, with the nematode having been recorded from the oesophagus of water buffaloes (Nepal), cattle, sheep, goats and wild mouflon (Sardinia). To clarify their natural transmission cycles among domestic and wild mammals, the present study analysed the ribosomal RNA gene (rDNA) and mitochondrial cytochrome c oxidase subunit 1 gene (cox1) of worms of various origins: G. pulchrum worms from sika deer, wild boars, Japanese macaques, and feral alien Reeves's muntjacs in Japan, and G. nepalensis worms from a red fox and a wild boar in Sardinia. Although the internal transcribed spacer (ITS) regions of rDNA and partial cox1 nucleotide sequences of G. pulchrum from native wild mammals in Japan were distinct from those of the worms in cattle, the worms from feral alien Reeves's muntjacs showed the cattle-type ITS genotype and cox1 cattle-I and II haplotypes. The rDNA and cox1 nucleotide sequences of G. nepalensis from a red fox in Sardinia were almost identical to those of the worms from domestic and wild ruminants on the island. The ecological interaction between domestic and wild mammals and their susceptibility to different Gongylonema spp. must be considered when trying to elucidate this spirurid's transmission dynamics in nature.

Impact of transmission cycles and vector competence on global expansion and emergence of arboviruses

Arboviruses are transmitted between arthropod vectors and vertebrate host. Arboviral infection in mosquitoes is initiated when a mosquito feeds on a viremic host. Following ingestion of a viremic blood meal by mosquitoes, virus enters midgut along with the blood, infects and replicates in midgut epithelial cells, and then escapes to the hemocoel, from where it disseminates to various secondary organs including salivary glands. Subsequently, when mosquito bites another host, a new transmission cycle is initiated. The midgut and salivary glands act as anatomical barriers to virus infection and escape. These complex interactions between the virus and vector dictate the vector competence. Thus, vector competence reflects the success in overcoming different barriers within the vector. Along with these, other intrinsic factors like midgut microbiota and immune responses, extrinsic factors like temperature and humidity, and genetic factors like vector genotype and viral genotype have been discussed in this review. Recent advancement on novel molecular tools to study vector competence is also included. Different modes of arboviral transmission like horizontal, vertical, and venereal and how these play role in sustenance and emergence of arboviruses in nature are also discussed. These factors can be exploited to reduce the susceptibility of vectors for the viruses, so as to control arboviral diseases to certain extent.

INFECTION BY Rickettsia felis IN OPOSSUMS (Didelphis sp.) FROM YUCATAN, MEXICO

Rickettsia felis is an emergent pathogen and the causative agent of a typhus-like rickettsiosis in the Americas. Its transmission cycle involves fleas as biological vectors (mainly Ctenocephalides felis) and multiple domestic and synanthropic mammal hosts. Nonetheless, the role of mammals in the cycle of R. felis is not well understood and many efforts are ongoing in different countries of America to clarify it. The present study describes for the first time in Mexico the infection of two species of opossum (Didelphis virginiana and D. marsupialis) by R. felis. A diagnosis was carried out from blood samples by molecular methods through the gltA and 17 kDa genes and sequence determination. Eighty-seven opossum samples were analyzed and 28 were found to be infected (32.1%) from five out of the six studied localities of Yucatan. These findings enable recognition of the potential epidemiological implications for public health of the presence of infected synanthropic Didelphis in households.

Chagas disease in a domestic transmission cycle, southern Texas, USA

After three dogs died from acute Chagas cardiomyopathy at one location, an investigation was conducted of the home, garage, and grounds of the owner. A serologic study was conducted on stray dogs, and an ecologic niche model was developed to predict areas where the vector Triatoma gerstaeckeri might be expected.