Immunogenetics, sylvatic plague and its vectors: insights from the pathogen reservoir Mastomys natalensis in Tanzania.

Yersinia pestis is a historically important vector-borne pathogen causing plague in humans and other mammals. Contemporary zoonotic infections with Y. pestis still occur in sub-Saharan Africa, including Tanzania and Madagascar, but receive relatively little attention. Thus, the role of wildlife reservoirs in maintaining sylvatic plague and spillover risks to humans is largely unknown. The multimammate rodent Mastomys natalensis is the most abundant and widespread rodent in peri-domestic areas in Tanzania, where it plays a major role as a Y. pestis reservoir in endemic foci. Yet, how M. natalensis' immunogenetics contributes to the maintenance of plague has not been investigated to date. Here, we surveyed wild M. natalensis for Y. pestis vectors, i.e., fleas, and tested for the presence of antibodies against Y. pestis using enzyme-linked immunosorbent assays (ELISA) in areas known to be endemic or without previous records of Y. pestis in Tanzania. We characterized the allelic and functional (i.e., supertype) diversity of the major histocompatibility complex (MHC class II) of M. natalensis and investigated links to Y. pestis vectors and infections. We detected antibodies against Y. pestis in rodents inhabiting both endemic areas and areas considered non-endemic. Of the 111 nucleotide MHC alleles, only DRB*016 was associated with an increased infestation with the flea Xenopsylla. Surprisingly, we found no link between MHC alleles or supertypes and antibodies of Y. pestis. Our findings hint, however, at local adaptations towards Y. pestis vectors, an observation that more exhaustive sampling could unwind in the future.

When Viruses Don't Go Viral: The Importance of Host Phylogeographic Structure in the Spatial Spread of Arenaviruses.

Many emerging infections are RNA virus spillovers from animal reservoirs. Reservoir identification is necessary for predicting the geographic extent of infection risk, but rarely are taxonomic levels below the animal species considered as reservoir, and only key circumstances in nature and methodology allow intrinsic virus-host associations to be distinguished from simple geographic (co-)isolation. We sampled and genetically characterized in detail a contact zone of two subtaxa of the rodent Mastomys natalensis in Tanzania. We find two distinct arenaviruses, Gairo and Morogoro virus, each spatially confined to a single M. natalensis subtaxon, only co-occurring at the contact zone's centre. Inter-subtaxon hybridization at this centre and a continuum of quality habitat for M. natalensis show that both viruses have the ecological opportunity to spread into the other substaxon's range, but do not, strongly suggesting host-intrinsic barriers. Such barriers could explain why human cases of another M. natalensis-borne arenavirus, Lassa virus, are limited to West Africa.

Polymorphism in vkorc1 Gene of Natal Multimammate Mice, Mastomys natalensis, in Tanzania.

Resistance of rodents to anticoagulant rodenticides has emerged in several areas across the world. Single nucleotide mutations in the vkorc1 gene have been shown to elicit various levels of anticoagulant resistance, and these mutations are prevalent in several Rattus and Mus musculus populations. In sub-Saharan Africa, the Natal multimammate mouse, Mastomys natalensis, is one of the most damaging pests to crops, and anticoagulant poisons such as bromadiolone are frequently used to control these rodents in agricultural fields. Here, we investigate if vkorc1 shows any polymorphism in natural populations of M. natalensis. We sequenced the third exon of vkorc1 of 162 M. natalensis captured from 14 different agricultural sites in Morogoro Region, Tanzania. In addition to 6 SNPs in the noncoding flanking region, we detected 3 nonsynonymous SNPs in this exon: 10 animals (6.2%) carried a Leu108Val variant, 2 animals (1.2%) an Ala140Thr variant, and 1 animal (0.6 %) an Arg100His variant, all 3 in heterozygous form. Ala140Thr is just one residue from a mutation known to be involved in anticoagulant resistance in Rattus and Mus. While in vitro or in vivo experiments are needed to link vkorc1 genetic polymorphisms to level of VKOR activity and anticoagulant susceptibility, our results suggest that M. natalensis individuals may vary in their response to anticoagulant rodenticides. This is the first vkorc1 sequence data from a species outside the Rattus or Mus genera, and for the first time from a rodent species endemic to Africa.

Spatio-temporal home range of the dominant rodent species in Mabira central forest reserve, Uganda.

BACKGROUND: Rodents form the largest order among mammals in terms of species diversity, and home range is the area where an individual normally moves during its normal daily activities. Information about rodent home ranges is paramount in the development of effective conservation and management strategies. This is because rodent home range varies within species and different habitats. In Uganda, tropical high altitude forests such as the Mabira Central Forest Reserve are experiencing continuous disturbance. However, information on rodent home range is lacking. Therefore, a two year Capture-Mark-Release (CMR) of rodents was conducted in the intact forest habitat: Wakisi, regenerating forest habitat: Namananga, and the depleted forest habitat: Namawanyi of Mabira Central Forest Reserve in order to determine the dominant rodent species, their home ranges, and factors affecting these home ranges. The home ranges were determined by calculating a minimum convex polygon with an added boundary strip of 5 m. RESULTS: Overall, the most dominant rodent species were: Lophuromys stanleyi, Hylomyscus stella, Praomys jacksoni Mastomys natalensis, Lophuromys ansorgei, and Lemniscomys striatus. H. stella dominated the intact forest habitat, while L. stanleyi was the most dominant both in the regenerating and the depleted forest habitats. L. stanleyi had a larger home range in the depleted forest, and the regenerating forest habitats, respectively. In the regenerating forest habitat, M. natalensis had a larger home range size, followed by L. stanleyi, and L. striatus. While in the intact forest habitat, H. stella had the largest home range followed by P. jacksoni. H. stella, L. striatus, L. stanleyi, M. natalensis, and P. jacksoni were most dominant during the wet season while L. ansorgei was relatively more dominant during the dry season. L. ansorgei, and P. jacksoni had a larger home range in the dry season, and a lower home range in the wet season. H. stella, L. stanleyi, M. natalansis and L.striatus had larger home ranges in the wet season, and lower home ranges in the dry season.   The home ranges of the dominant rodent species varied across the three habitats in Mabira central forest reserve ([Formula: see text], [Formula: see text]). CONCLUSION: The significant variation in home ranges of the dominant rodent species in Mabira Central Forest Reserve depending on the type of habitat presupposes that the rodent management strategies in disturbed forest reserves should focus on the type of habitat.

Arthropod Ectoparasites of Two Rodent Species Occurring in Varied Elevations on Tanzania's Second Highest Mountain.

Climate change causes organisms, including species that act as parasite reservoirs and vectors, to shift their distribution to higher altitudes, affecting wildlife infestation patterns. We studied how ectoparasite distributions varied with altitude using two rodent species, Montemys delectorum and Rhabdomys dilectus, at different elevations (1500-3500 m). The ectoparasites infesting the two rodent species were influenced by the host sex, species, and temperature. We expected host density to predict parasite infestation patterns, because hosts in higher densities should have more parasites due to increased contact between individuals. However, temperature, not host density, affected ectoparasite distribution. Since temperatures decrease with elevation, parasite prevalences and abundances were lower at higher elevations, highlighting that the cold conditions at higher elevations limit reproduction and development-this shows that higher elevation zones are ideal for conservation. The rodents and ectoparasite species described in this study have been reported as vectors of diseases of medical and veterinary importance, necessitating precautions. Moreover, Mount Meru is a refuge for a number of endemic and threatened species on the IUCN Red List. Thus, the parasitic infection can also be an additional risk to these critical species as well as biodiversity in general. Therefore, our study lays the groundwork for future wildlife disease surveillance and biodiversity conservation management actions. The study found a previously uncharacterized mite species in the Mesostigmata group that was previously known to be a parasite of honeybees. Further investigations may shed light into the role of this mite species on Mount Meru.

Twenty-nine years of continuous monthly capture-mark-recapture data of multimammate mice (Mastomys natalensis) in Morogoro, Tanzania.

The multimammate mice (Mastomys natalensis) is the most-studied rodent species in sub-Saharan Africa, where it is an important pest species in agriculture and carrier of zoonotic diseases (e.g. Lassa virus). Here, we provide a unique dataset that consists of twenty-nine years of continuous monthly capture-mark-recapture entries on one 3 ha mosaic field (MOSA) in Morogoro, Tanzania. It is one of the most accurate and long-running capture-recapture time series on a small mammal species worldwide and unique to Africa. The database can be used by ecologists to test hypotheses on the population dynamics of small mammals (e.g. to test the effect of climate change), or to validate new algorithms on real long-term field data (e.g. new survival analyses techniques). It is also useful for both scientists and decision-makers who want to optimize rodent control strategies and predict outbreaks of multimammate mice.

Impact of contraceptive hormones on the reproductive potential of male and female commensal black rats (Rattus rattus).

The black rat is considered one of the world's top pests. With increased restrictions on rodenticides, new alternatives to manage rats are urgently needed. Research on the use of contraceptive hormones, levonorgestrel (LE), and quinestrol (QU), have been evaluated against some rodent species, and this research is the first study to assess these on black rats. Hormones were incorporated into rodent bait at 10 and 50 ppm concentrations singly and in combination (EP-1). Groups of 10 animals of each sex were fed the baits over 7 days. Lower bait consumption was observed with slight body mass reductions. On dissection, it was observed that the uterus was in a state of edema and male reproductive organs weighed less with reduced sperm counts/motility. The 2 most promising baits, 50 ppm QU and EP-1, were used to assess impact on pregnancy and litter size. Pregnancy was reduced from 70% success when both males and females consumed untreated bait, down to 30% when males had consumed contraceptive bait but females had not, and down to 0% when females had consumed contraceptive bait, regardless of whether they had paired with a treated or untreated male. Litter size in the untreated pairs was 8 pups, but only 4 pups in those cases where the male only had consumed the contraceptive. Further studies should investigate how long the effect lasts and its reversibility. Field studies at the population level may also shed light on the practicality of using contraceptive baits for black rats in different habitats.

Plague in Tanzania: first report of sylvatic plague in Morogoro region, persistence in Mbulu focus, and ongoing quiescence in Lushoto and Iringa foci.

Objectives: Plague has been a threat to human health in Tanzania since 1886. This zoonotic disease has established several endemic foci in the country, posing a risk of outbreaks. This study was conducted to investigate the presence of Yersinia pestis in small mammals in five districts. These districts were selected because of recent (Mbulu), past (40-18 years ago: Lushoto) and historic (>100 years ago: Iringa and Kilolo) human cases of plague. In addition, one region that has not had any reported human cases of plague was included (Morogoro-Mvomero). Methods: Blood from 645 captured small mammals was screened for antibodies against the fraction 1 (F1) antigen of Y. pestis using indirect enzyme-linked immunosorbent assay (ELISA) and competitive-blocking ELISA. Results: Specific antibodies against Y. pestis F1 antigens were detected in six (0.93%) animals belonging to Mastomys natalensis. Of these, four animals were captured in the active focus in Mbulu, and two animals were captured from an area with no history of human plague (Morogoro-Mvomero). Conclusion: These results provide evidence of the circulation of Y. pestis in small mammals in Tanzania. Furthermore, evidence of the circulation of Y. pestis in Morogoro-Mvomero highlights the importance of carrying out plague surveillance in areas with no history of human plague, which can help to predict areas where future outbreaks may occur.

Effects of forest disturbance on the fitness of an endemic rodent in a biodiversity hotspot.

Praomys delectorum occurs abundantly in both disturbed and intact forests in the Ukaguru Mountains within the Eastern Arc Mountains (EAM), Morogoro, Tanzania. While previous studies have reported that anthropogenic disturbances such as grazing, wood cutting, and harvesting have a positive effect on the population density of P. delectorum, the impact of habitat disturbance on its demographic traits is still unknown. We performed a capture-mark-recapture study in both disturbed and intact forests from June 2018 to February 2020 in order to investigate the effects of habitat disturbance on abundance and two demographic traits: survival and maturation of P. delectorum in the Ukaguru Mountains. We found no variation in abundance or maturation between intact and disturbed forests, but habitat type did affect survival. However, this effect was sex-dependent since female survival was higher in disturbed forests, while male survival remained similar across the two forest types potentially due to differences in predation pressure or food availability between the two habitats. Continuous demographic monitoring of P. delectorum in EAM is necessary given that the increasing human population surrounding the landscape is leading to higher deforestation rates and expansion of the pine plantation in the forest reserve.

Molecular detection and genomic characterization of diverse hepaciviruses in African rodents.

Hepatitis C virus (HCV; genus Hepacivirus) represents a major public health problem, infecting about three per cent of the human population. Because no animal reservoir carrying closely related hepaciviruses has been identified, the zoonotic origins of HCV still remain unresolved. Motivated by recent findings of divergent hepaciviruses in rodents and a plausible African origin of HCV genotypes, we have screened a large collection of small mammals samples from seven sub-Saharan African countries. Out of 4,303 samples screened, eighty were found positive for the presence of hepaciviruses in twenty-nine different host species. We, here, report fifty-six novel genomes that considerably increase the diversity of three divergent rodent hepacivirus lineages. Furthermore, we provide strong evidence for hepacivirus co-infections in rodents, which were exclusively found in four sampled species of brush-furred mice. We also detect evidence of recombination within specific host lineages. Our study expands the available hepacivirus genomic data and contributes insights into the relatively deep evolutionary history of these pathogens in rodents. Overall, our results emphasize the importance of rodents as a potential hepacivirus reservoir and as models for investigating HCV infection dynamics.

Sympatric occurrence of 3 arenaviruses, Tanzania.

To determine the specificity of Morogoro virus for its reservoir host, we studied its host range and genetic diversity in Tanzania. We found that 2 rodent species other than Mastomys natalensis mice carry arenaviruses. Analysis of 340 nt of the viral RNA polymerase gene showed sympatric occurrence of 3 distinct arenaviruses.

Host use of Bactrocera latifrons, a new invasive tephritid species in Tanzania.

Bactrocera latifrons (Hendel) is a pest of Asian origin, first detected in Africa in 2006. We assessed the host utilization of this quarantine pest in Morogoro region, eastern central Tanzania, by collecting a wide range of cultivated and wild host plants of species belonging to Solanaceae and Cucurbitaceae from April 2007 to April 2008. Fruit were collected from 29 plant species and varieties (16 Solanaceae and 13 Cucurbitaceae) in all agroecological zones of Morogoro region. Twelve solanaceous fruit species yielded B. latifrons of which four are new host records: Capsicum annuum L. cov. longum A. DC., Capsicum chinense Jacq., Solanum sodomeum L., and Solanum scabrum Mill. Similarly, three cucurbitaceous fruit species provided positive rearings and are new host records: Citrullus lanatus (Thunb.) Matsum & Nakai, Cucumis dipsaceus L., and Momordica cf trifoliata L. The infestation rate and incidence of the pest was mainly high in the solanaceous hosts of nightshades (Solanum nigrum L. and Solanum scabrum) and African eggplants (Solanum aethiopicum Lam. and Solanum anguivi). In a host preference study involving limited number of cultivated solanaceous crops, S. scabrum was recorded as the most preferred host. The pest has been found to outnumber Bactrocera invadens (Drew et al.), Bactrocera cucurbitae (Coquillett), and Ceratitis capitata (Wiedemann) in most of the common solanaceous hosts.

Comparative assessment on rodent impacts and cultural perceptions of ecologically based rodent management in 3 Afro-Malagasy farming regions.

Rodents generate negative consequences for smallholder farmers in Africa that directly impact household and livestock damage, food security, and public health. Ecologically Based Rodent Management (EBRM) seeks sustainable solutions for the mitigation of rodent damage through assessments of rodent population dynamics, agro-ecosystems, and socio-cultural contexts. We adopt a comparative approach across 3 rural Afro-Malagasy smallholder farming regions in South Africa, Tanzania, and Madagascar to assess the household impacts of rodent pests and current perceptions and preferences associated with several rodent control measures. We conducted focus group questionnaires and interviews in different study site locations. Rodents assert multiple impacts on Afro-Malagasy farmers demonstrating recurrent and emerging agricultural and household costs, and public health impacts. We identify a significant knowledge gap in educating communities about the application of different EBRM approaches in favor of acute poisons that are perceived to be more effective. Cultural issues and taboos also have a significant impact on the social acceptance of rodent hunting as well as biological control using indigenous predators. We advocate for an enhanced investigation of the socio-cultural beliefs associated with different rodent practices to understand the factors underlying social acceptance. A collaborative approach that integrates the perspectives of target communities to inform the design of EBRM initiatives according to the specific agro-ecosystem and socio-cultural context is necessary to ensure programmatic success.

Mopeia virus-related arenavirus in natal multimammate mice, Morogoro, Tanzania.

A serosurvey involving 2,520 small mammals from Tanzania identified a hot spot of arenavirus circulation in Morogoro. Molecular screening detected a new arenavirus in Natal multimammate mice (Mastomys natalensis), Morogoro virus, related to Mopeia virus. Only a small percentage of mice carry Morogoro virus, although a large proportion shows specific antibodies.

Species composition and community structure of small pest rodents (Muridae) in cultivated and fallow fields in maize-growing areas in Mayuge district, Eastern Uganda.

Pest rodents remain key biotic constraints to cereal crops production in the East African region where they occur, especially in seasons of outbreaks. Despite that, Uganda has scant information on rodents as crop pests to guide effective management strategies.A capture-mark-recapture (CMR) technique was employed to study the ecology of small rodents, specifically to establish the species composition and community structure in a maize-based agro ecosystem. Trapping of small rodents was conducted in permanent fallow land and cultivated fields, with each category replicated twice making four study grids. At each field, a 60 × 60 m grid was measured and marked with permanent trapping points spaced at 10 × 10 m, making a total of 49 trapping points/grids. Trapping was conducted monthly at 4-week interval for three consecutive days for two and half years using Sherman live traps.Eleven identified small rodent species and one insectivorous small mammal were recorded with Mastomys natalensis being the most dominant species (over 60.7%). Other species were Mus triton (16.1%), Aethomys hendei (6.7%), Lemniscomys zebra (5.2%), Lophuromys sikapusi (4.8%), Arvicanthis niloticus (0.9%), Gerbilliscus kempi (0.1%), Graphiurus murinus (0.1%), Steatomys parvus (0.1%), Dasymys incomtus (0.1%), and Grammomys dolichurus (0.1%). Spatially, species richness differed significantly (p = 0.0001) between the studied field habitats with significantly higher richness in fallow land compared with cultivated fields.Temporally, total species richness and abundance showed a significant interaction effect over the months, years, and fields of trapping with significantly (p = 0.001) higher abundances during months of wet seasons and in the first and third year of trapping. In terms of community structure, higher species diversity associated more with fallow field habitats but also with certain rare species found only in cultivated fields.Synthesis and applications. Based on these findings, management strategies can be designed to target the key pest species and the most vulnerable habitats thus reducing the impact they can inflict on field crops.

Does exploratory behavior or activity in a wild mouse explain susceptibility to virus infection?

Exploration and activity are often described as trade-offs between the fitness benefits of gathering information and resources, and the potential costs of increasing exposure to predators and parasites. More exploratory individuals are predicted to have higher rates of parasitism, but this relationship has rarely been examined for virus infections in wild populations. Here, we used the multimammate mouse Mastomys natalensis to investigate the relationship between exploration, activity, and infection with Morogoro virus (MORV). We characterized individual exploratory behavior (open field and novel object tests) and activity (trap diversity), and quantified the relationship between these traits and infection status using linear regression. We found that M. natalensis expresses consistent individual differences, or personality types, in exploratory behavior (repeatability of 0.30, 95% CI: 0.21-0.36). In addition, we found a significant contrasting effect of age on exploration and activity where juveniles display higher exploration levels than adults, but lower field-activity. There was however no statistical evidence for a behavioral syndrome between these 2 traits. Contrary to our expectations, we found no correlation between MORV infection status and exploratory behavior or activity, which suggests that these behaviors may not increase exposure probability to MORV infection. This would further imply that variation in viral infection between individuals is not affected by between-individual variation in exploration and activity.

Effect of synthetic hormones on reproduction in Mastomys natalensis.

Rodent pest management traditionally relies on some form of lethal control. Developing effective fertility control for pest rodent species could be a major breakthrough particularly in the context of managing rodent population outbreaks. This laboratory-based study is the first to report on the effects of using fertility compounds on an outbreaking rodent pest species found throughout sub-Saharan Africa. Mastomys natalensis were fed bait containing the synthetic steroid hormones quinestrol and levonorgestrel, both singly and in combination, at three concentrations (10, 50, 100 ppm) for 7 days. Consumption of the bait and animal body mass was mostly the same between treatments when analysed by sex, day and treatment. However, a repeated measures ANOVA indicated that quinestrol and quinestrol + levonorgestrel treatments reduced consumption by up to 45%, particularly at the higher concentrations of 50 and 100 ppm. Although there was no clear concentration effect on animal body mass, quinestrol and quinestrol + levonorgestrel lowered body mass by up to 20% compared to the untreated and levonorgestrel treatments. Quinestrol and quinestrol + levonorgestrel reduced the weight of male rat testes, epididymis and seminal vesicles by 60-80%, and sperm concentration and motility were reduced by more than 95%. No weight changes were observed to uterine and ovarian tissue; however, high uterine oedema was observed among all female rats consuming treated bait at 8 and 40 days from trial start. Trials with mate pairing showed there were significant differences in the pregnancy rate with all treatments when compared to the untreated control group of rodents.

Arenavirus Dynamics in Experimentally and Naturally Infected Rodents.

Infectious diseases of wildlife are typically studied using data on antibody and pathogen levels. In order to interpret these data, it is necessary to know the course of antibodies and pathogen levels after infection. Such data are typically collected using experimental infection studies in which host individuals are inoculated in the laboratory and sampled over an extended period, but because laboratory conditions are controlled and much less variable than natural conditions, the immune response and pathogen dynamics may differ. Here, we compared Morogoro arenavirus infection patterns between naturally and experimentally infected multimammate mice (Mastomys natalensis). Longitudinal samples were collected during three months of bi-weekly trapping in Morogoro, Tanzania, and antibody titer and viral RNA presence were determined. The time of infection was estimated from these data using a recently developed Bayesian approach, which allowed us to assess whether the natural temporal patterns match the previously observed patterns in the laboratory. A good match was found for 52% of naturally infected individuals, while most of the mismatches can be explained by the presence of chronically infected individuals (35%), maternal antibodies (10%), and an antibody detection limit (25%). These results suggest that while laboratory data are useful for interpreting field samples, there can still be differences due to conditions that were not tested in the laboratory.

Correction: A systematic review of rodent pest research in Afro-Malagasy small-holder farming systems: Are we asking the right questions?

[This corrects the article DOI: 10.1371/journal.pone.0174554.].