Modelling relative abundance of Oligoryzomys flavescens,an Orthohantavirus reservoir,in an endemic hantavirus pulmonary syndrome zone

Hantavirus pulmonary syndrome (HPS) is a zoonotic emerging infectious disease caused by New World orthohantaviruses (family Hantaviridae) hosted by rodents of the family Cricetidae. In Argentina, one of its main hosts is the sigmodontine rodent Oligoryzomys flavescens, a widely distributed mouse of the Pampas, Delta and Espinal ecoregions of central-east Argentina. Because the abundance of the reservoir and its proportion in the rodent community affects both virus prevalence and human exposure risk, its estimation throughout its known geographical distribution is of key importance for the design of public health strategies to prevent HPS. The aim of this study was therefore to model the relative abundance of O. flavescens in most of the Pampas ecoregion within Buenos Aires Province, Argentina, where hantavirus pulmonary syndrome is endemic. To do this we used owl-pellet samples collected between 2006 and 2008 from 51 sites distributed throughout most of Buenos Aires province. Mammalian prey in each pellet was identified to the lowest possible taxonomic level by examination of the skulls, dentaries and molars. We modelled the frequency of O. flavescens found in each sample as a function of climatic, environmental, and topographic data of each site. The two best models were applied to a Geo referential Information System to build maps of estimated frequency (as a proxy of relative abundance) within Buenos Aires province. Estimated relative abundance of O. flavescens in Buenos Aires province was significantly associated with annual mean temperature, annual precipitation and presence of freshwater bodies, and varied among sub-regions, with the Inland and Rolling Pampas being the regions with highest frequencies. Knowing in which areas O. flavescens abundance is expected to be higher can be used to concentrate limited sanitary efforts in those areas that are most needed in order to reduce transmission and increase detection.     

New data about home range and movements of Oligoryzomys flavescens (Rodentia: Cricetidae) help to understand the spread and transmission of Andes virus that causes Hantavirus Pulmonary Syndrome

Hantavirus pulmonary syndrome is an emerging infectious disease caused by viruses of the genus Orthohantavirus. The rodent Oligoryzomys flavescens is distributed along four countries of South America. In Argentina, O. flavescens acts as a reservoir of three genotypes of ANDV orthohantavirus. The aims of this work were to estimate home range size and movements—with spool‐and‐line and radiotelemetry—of infected and non‐infected O. flavescens in order to understand the spread and transmission of the virus. O. flavescens use a wide area to satisfice its requirements, reaching a home range of 1.82 ha during spring. Orthohantavirus infection did not change the behaviour of individuals. We observed a great overlapping in the home range of infected and non‐infected individuals resulting in a high probability of virus dispersion on rodent population. These results show that human health risks could be high on island environments and knowledge about the movement ecology of O. flavescens provides useful information on prevention.     

Home range variability,spatial aggregation,and excursions of Akodon azarae and Oligoryzomys flavescens in Pampean agroecosystems

Rodents are reservoirs of various types of hantavirus, some of which are agents of hantavirus pulmonary syndrome in humans. Each hantavirus is associated with a single rodent host species but successive spill‐over events may eventually lead to host‐switching and new species’ becoming host of a given pathogen. This study aims to gain an understanding of the spatial ecology of two hantavirus‐host species, Akodon azarae, and Oligoryzomys flavescens, by identifying factors modulating their home range sizes and stability, and by evaluating intra‐ and interspecific spatial aggregation for these species and a third one—Oxymycterus rufus—living in sympatry. For this, eleven capture‐mark‐recapture surveys were carried out, spanning 22 months. We found that A. azarae males have larger and more mobile home ranges than females, independently of the season. Consequently, males could likely have a more relevant role in the transmission of hantavirus because of their greater exposure both to a higher number of contacts between individuals and viral contamination of the environment. Contrasting, O. flavescens individuals showed negligible displacements of their home range through time, which could limit the range of hantavirus spread in host populations. Since O. flavescens is host to Lechiguanas hantavirus (pathogenic to humans) this result encompasses epidemiological relevance, for it may imply the existence of local foci of infection. Additionally, individuals of both species performed excursions outside their home ranges. These events could enable hantavirus spread over distances beyond the normal range of movements and lead to new hantavirus outbreaks in formerly non‐infected rodent populations, favoring the persistence of the virus in nature.     

Evaluation of habitat requirements of small rodents and effectiveness of an ecologically‐based management in a hantavirus‐endemic natural protected area in Argentina

Hantavirus pulmonary syndrome is a severe cardio pulmonary disease transmitted to humans by sylvan rodents found in natural and rural environments. Disease transmission is closely linked to the ecology of animal reservoirs and abiotic factors such as habitat characteristics, season or climatic conditions. The main goals of this research were: to determine the biotic and abiotic factors affecting richness and abundance of rodent species at different spatial scales, to evaluate different methodologies for studying population of small rodents, and to describe and analyze an ecologically‐based rodent management experience in a highly touristic area. A 4‐year study of small rodent ecology was conducted between April 2007 and August 2011 in the most relevant habitats of El Palmar National Park, Argentina. Management involved a wide range of control and prevention measures, including poisoning, culling and habitat modification. A total of 172 individuals of 5 species were captured with a trapping effort of 13 860 traps‐nights (1.24 individuals/100 traps‐nights). Five rodent species were captured, including 2 hantavirus‐host species, Oligoryzomys nigripes and Akodon azarae. Oligoryzomys nigripes, host of a hantavirus that is pathogenic in humans, was the most abundant species and the only one found in all the studied habitats. Our results are inconsistent with the dilution effect hypothesis. The present study demonstrates that sylvan rodent species, including the hantavirus‐host species, have distinct local habitat selection and temporal variation patterns in abundance, which may influence the risk of human exposure to hantavirus and may have practical implications for disease transmission as well as for reservoir management.     

Bartonella spp. associated with rodents in an urban protected area,Buenos Aires (Argentina)

At least 15 of the 30 Bartonella species are involved in human pathologies, and several of them are associated with rodents and their fleas. The aims of this study were detect and molecularly characterize the Bartonella infections in rodents from an urban protected area of ​Buenos Aires City (Argentina). A total of 186 rodents were captured and identified. For PCR of the 16S rRNA fragment, 23.7 % of the samples tested positive, and two groups (GrA and GrB) were identified. Likewise, the comparison between the sequences obtained for the gltA gene determined the presence of three genotypes, closely related to Bartonella spp. detected in sigmodontine rodents and their fleas in the Americas, which form a well-separated clade. The high prevalence of Bartonella in rodents from an urban protected area of ​Buenos Aires city is relevant from a public health perspective.     

A long-term observation for ecology of pathogenic Yersinia in wild rodents living in Fukushima Prefecture,Japan

From 2012 to 2021, prevalence of pathogenic Yersinia in wild rodents captured in Fukushima Prefecture, Japan was investigated twice a year to clarify the ecology of this pathogen in wild rodent populations. Pathogenic Yersinia enterocolitica O8 was isolated from 13 (1.7%) of 755 wild rodents. The Y. enterocolitica O8 isolates harbored three virulent genes (ail, fyuA, and virF). This pathogen was isolated repeatedly from wild rodents in April 2015, 2016, and 2017, in June and November 2020, and in April 2021, which was 6 of 19 times of observations. All Y. enterocolitica O8 isolates showed the same PFGE patterns. These results indicated that the same clone of pathogenic Y. enterocolitica O8 has been maintained in wild rodent populations in Fukushima Prefecture. Therefore, wild rodent populations contribute substantially to the continuous transmission of Y. enterocolitica O8 and its persistence in the ecosystem. This is the first report on the isolation of pathogenic Y. enterocolitica O8 in wild rodents in Fukushima Prefecture, Japan.     

Surveys of rodent‐borne disease in Thailand with a focus on scrub typhus assessment

The epidemiology of many rodent‐borne diseases in South‐East Asia remains ill‐defined. Scrub typhus and lep‐tospirosis are common and medically significant, while other zoonotic diseases, such as spotted fever group Rickettsiae have been identified, but their overall medical significance is unknown. Rodent surveillance was conducted from June 2002 to July 2004 in 18 provinces from Thailand. Traps were set up for one to three nights. Blood and serum samples and animal tissue samples (liver, spleen, kidney and urinary bladder) were collected. Chiggermites, ticks and fleas were removed from captured rodents. A total of 4536 wild‐caught rodents from 27 species were captured over two years of animal trapping. Rattus rattus was the dominant species, followed by Rattus exulans and Bandicota indica. Almost 43 000 ectoparasites were removed from the captured animals. Approximately 98% of the ectoparasites were chigger‐mites, of which 46% belonged to the genus Leptotrombidium (scrub typhus vector). Other genera included Schoengastia and Blankaartia. Tick and flea specimens together comprised less than 1% of the sample. Among the five species of ticks collected, Haemaphysalis bandicota was the predominant species caught, followed by Ixodes granulatus other Haemaphysalis spp., Rhipicephalus spp. and Dermacentor spp. Only two species of fleas were collected and Xenopsylla cheopis (rat flea) was the predominant species. Using both commercial diagnostic kits and in‐house molecular assays, animal tissue samples were examined and screened for zoonotic diseases. Seven zoonotic diseases were detected: scrub typhus, leptospirosis, murine typhus, tick typhus, bartonella, babesiosis and trypanosomiasis. Most samples were positive for scrub typhus. Other zoonotic diseases still under investigation include borrelosis, ehrlichiosis, the plague, and other rickettsial diseases. Using geographic information systems, global positioning systems and remote sensing technology, epidemiological and environmental data were combined to assess the relative risk in different biotopes within highly endemic areas of scrub typhus in Thailand.     

First insights into Puumala orthohantavirus circulation in a rodent population in Alsace,France

In‐depth knowledge on the mechanisms that maintain infection by a zoonotic pathogen in an animal reservoir is the key to predicting and preventing transmission to humans. The Puumala orthohantavirus (PUUV), the most prevalent orthohantavirus in Western Europe, causes a mild form of haemorrhagic fever with renal syndrome (HFRS) in humans. In France, this endemic illness affects the north‐eastern part of the country. We conducted a 4‐year capture–mark–recapture study in a bank vole population, combined with molecular analyses, to explore the epidemiological situation of PUUV in Alsace, a French region where human cases have occurred, but for which no studies have been conducted on this reservoir host. PUUV‐infected bank voles were detected in the 2 years that showed high bank vole density with a prevalence of 4%. The individual PUUV sequences identified in this study were similar from year to year and similar to other French sequences. On a very small spatial scale, the distribution of seropositive bank voles was very heterogeneous in time and space. The short distances travelled on average by bank voles resulted in spatial clusters of seropositive rodents, which spread only very gradually throughout the year.     

Associations between leptospiral infection and seropositivity in rodents and environmental characteristics in Argentina

Our objective was to look for associations between leptospiral infection in rodents and selected environmental and rodent characteristics in Santa Fe, Argentina. Rodents (n = 214) were trapped alive from January 1998 to December 1999 in three environmental settings. Kidneys from 118 rodents were cultured and serum samples from 201 were processed by enzyme-linked immunosorbent assay (ELISA). Logistic regression was performed with ELISA seropositivity as the dependent variable and rodent characteristics were offered as independent variables. Overall prevalence of positive ELISA reactions was 42% (84/201). In urban areas, leptospiral isolations belonged to the Ballum serogroup; in natural corridors, they belonged to the Icterohaemorragiae serogroup. M. musculus (house mouse) was the most-frequently captured species and the predominant one in urban areas. Most isolates and seropositivity results were obtained on this species. Adults and subadults had higher seroprevalences than juvenile rodents. Oligoryzomys flavescens had higher seroprevalence than Akodon azarae, Mus musculus, Rattus rattus and Rattus norvegicus.     

Interactions between rodents and weeds in a lowland rice agro‐ecosystem: the need for an integrated approach to management

Rodents and weeds are important pests to rice crops in Southeast Asia. The interaction between these 2 major pests is poorly documented. In temperate cereal systems, seeds of grass weeds can be an important food source for rodents and weed cover along crop margins provides important refuge for rodents. In 2012 and 2013, a replicated study (n = 4) in Bago, Myanmar compared 4 treatments (rodents and weeds; no rodents and weeds; rodents and no weeds; no rodents and no weeds) each of 0.25 ha in transplanted rice. Weeds were managed with hand weeding in the wet season, and hand weeding and herbicides in the dry season. Plastic fences were installed to exclude rodents. We examined the weed cover and relative abundance of weed species, rodent damage, rodent population dynamics and rice yield loss caused by rodents and weeds. The dominant rodent species was Bandicota bengalensis. In the dry season, Cyperus difformis was dominant at the tillering stage and Echinochloa crus‐galli was the dominant weed species at the booting stage. In the wet season E. crus‐galli was a dominant weed throughout the season. Damage by rodents was higher in the dry season. There were larger economic benefits for best weed management and effective rodent control in the dry season (258 US$/ha) than in the wet season (30 US$/ha). Concurrent control of weeds in and around rice fields combined with coordinated community trapping of rodents during the early tillering stage and ripening stage of rice are recommended management options.     

Habitat use and demography of Mus musculus in a rural landscape of Argentina

The main goal of the paper was to determine the habitat distribution of the house mouse (Mus musculus) within a rural landscape of Buenos Aires province, Argentina. We also studied the seasonal variation in abundance and reproductive activity. The habitats studied were poultry farms, human houses in a small village, cropfields, pastures, cropfield and pasture edges, riparian habitats (streams), railway embankments and woodlots. We captured 817 M. musculus and 690 individuals of 5 native rodent species. M. musculus was captured in poultry farms, houses, riparian habitats, cropfield and borders, but it showed a significantly higher abundance in poultry farms compared to the other habitats. Its presence outside poultry farms was significantly related to the distance to streams and poultry farms. The mean trapping success index of M. musculus did not show significant variations between periods, but the proportion of active males was significantly higher in the spring–summer period than in the autumn–winter period. All captures of M. musculus in cropfields, borders and riparian habitats occurred in the spring–summer period. The capture of M. musculus in many types of habitats suggests that it can disperse outside poultry farms, and streams may be used as corridors.     

Differentiation in seed hoarding among three sympatric rodent species in a warm temperate forest

Although seed hoarding by rodents has been extensively studied, differentiation in seed‐hoarding behaviors among sympatric rodent species has not been well investigated. Using semi‐natural enclosures, we demonstrated that three sympatric rodent species showed clear differentiation in food selection, scatter versus larder hoarding behaviors and eating behaviors when offered seeds of four plant species from a warm temperate forest in northern China. The large field mouse Apodemus peninsulae preferred seeds of wild apricot (Prunus armeniaca) and Liaodong oak (Quercus liaotungensis), whereas the Chinese white‐bellied rat Niviventor confucianus preferred seeds of cultivated walnut and Liaodong oak, and the David's rock squirrel Sciurotamias davidianus preferred seeds of cultivated walnut, wild apricot and Liaodong oak. All three rodents showed larder hoarding of seeds from all four plant species, but the large field mouse showed scatter hoarding of wild apricot, and the David's rock squirrel showed scatter hoarding of Liaodong oak and wild walnut. Acorns of Liaodong oak, which have a soft seed hull, were more often eaten in situ, whereas wild walnuts, which have a hard seed hull and more tannin, were less hoarded by all rodent species. Differentiation in the scatter versus larder hoarding behaviors of sympatric rodent species suggests that sympatric rodents play different roles in the regeneration of different sympatric plant species.     

Detection of Bartonella sp. and a novel spotted fever group Rickettsia sp. in Neotropical fleas of wild rodents (Cricetidae) from Southern Brazil

The Neotropical region shows a great diversity of fleas, comprising more than 50 genera. The importance of the study of fleas is linked to their potential role as disease vectors. The aim of this study is to investigate the presence of Rickettsia spp. and Bartonella spp. in Neotropical fleas collected from wild rodents in Southern Brazil. From 350 rodents captured, 30 were parasitized by fleas. A total of 61 fleas belonging to two genera and six different species were collected (Craneopsylla minerva minerva, Polygenis occidentalis occidentalis, Polygenis platensis, Polygenis pradoi, Polygenis rimatus, and Polygenis roberti roberti). In 13 % of fleas of three different species (C. minerva, P. platensis, and P. pradoi) Rickettsia sp. DNA was found. Phylogenetic analysis of concatenated sequences of gltA, htrA, and ompA genes showed that Rickettsia sp. found in rodent fleas (referred as strain Taim) grouped together with Spotted Fever Group Rickettsia. In reference to Bartonella spp., five genotypes were identified in seven fleas of two species (C. minerva and P. platensis) and in five rodent spleens. Also, 207 frozen samples of wild rodents were screened for these pathogens: while none was positive for Rickettsia spp.; five rodent spleens were PCR-positive for Bartonella spp.. Herein, we show the detection of potential novel variants of Bartonella sp. and Rickettsia sp. in fleas collected of wild rodents from Southern Brazil. Further studies are needed to fully characterize these microorganisms, as well as to improve the knowledge on the potential role of Neotropical flea species as diseases vectors.     

Deciphering the effects of disperser assemblages and seed mass on patterns of seed dispersal in a rodent community

The sizes of both seed dispersers and seeds are traits that are likely to interact to influence seed fate in many synzoochoric plant species. Here, we examined whether members of a granivorous rodent community consisting of species of different body size vary in their effectiveness as seed dispersers, and how this relationship may be altered by seed size. We marked northern red oak (Quercus rubra) acorns with plastic tags and placed them in size‐selective rodent exclosures. The exclosures allowed differential access of rodent groups based on different body size: (i) small (e.g. Peromyscus spp.); (ii) small and medium (e.g. Tamias striatus); and (iii) small, medium and large (e.g. Sciurus carolinensis) species of rodents. Acorn removal did not differ among exclosure types, but more seeds were missing when removed by small rodents, probably because of larderhoarding. The treatments did not influence the relative frequency of acorn consumption. However, small rodents cached considerably fewer and partially ate more acorns than the other 2 groups. The mean dispersal distance was the longest for cages with medium openings, intermediate for cages with large openings and the shortest for cages with small openings. Acorn mass positively affected the probability of caching and this relationship was unaffected by exclosure type. In conclusion, granivorous rodents of different body sizes strongly differed in their interactions with acorns, with small rodents acting primarily as acorn predators and medium and large species contributing significantly more to dispersal of red oaks.     

Field assessment of dog as sentinel animal for plague in endemic foci of Madagascar

The epidemiology of Yersinia pestis, the causative agent of plague, involves vectors and reservoirs in its transmission cycle. The passive plague surveillance in Madagascar targets mainly rodent and fleas. However, carnivores are routinely surveyed as sentinels of local plague activity in some countries. The aim of this study is to assess the use of domestic dog (Canis familiaris) as sentinel animal for field surveillance of plague in a highly endemic area in Madagascar. Cross-sectional surveys of plague antibody prevalence in C. familiaris were conducted in endemic areas with contrasting histories of plague cases in humans, as well as a plague free area. Rodent capture was done in parallel to evaluate evidence for Y. pestis circulation in the primary reservoirs. In 2 sites, dogs were later re-sampled to examine evidence of seroconversion and antibody persistence. Biological samplings were performed between March 2008 and February 2009. Plague antibody detection was assessed using anti-F1 ELISA. Our study showed a significant difference in dog prevalence rates between plague-endemic and plague-free areas, with no seropositive dogs detected in the plague free area. No correlation was found between rodents and dog prevalence rates, with an absence of seropositive rodents in some area where plague circulation was indicated by seropositive dogs. This is consistent with high mortality rates in rodents following infection. Re-sampling dogs identified individuals seropositive on both occasions, indicating high rates of re-exposure and/or persistence of plague antibodies for at least 9 months. Seroconversion or seropositive juvenile dogs indicated recent local plague circulation. In Madagascar, dog surveillance for plague antibody could be useful to identify plague circulation in new areas or quiescent areas within endemic zones. Within active endemic areas, monitoring of dog populations for seroconversion (negative to positive) or seropositive juvenile dogs could be useful for identifying areas at greatest risk of human outbreaks.     

Temperature Acclimation in Tilapia Sparrmanii: Some Effects of Thiourea

Mastomys natalensis, Aethomys chrysophilus and Saccostomus campestris are three common and widespread rodent species in the Kruger National Park. Chromosomal and protein electrophoretic investigations reveal that these species are in fact complexes of morphologically similar, though genetically distinct, species. Their respective distributions in the Kruger National Park are reported and species diagnostic characters (diploid chromosome number, genitalia, spermatozoa and electromorphs) are presented for the practical identification of the cryptic species. The value of a genetical approach to resolving cryptic species is emphasized with respect to ecological studies.     

Camera-trapping and seed-labelling reveals widespread granivory and scatter-hoarding of nuts by rodents in the Fynbos Biome

Many plant–animal interactions can be challenging to directly observe, due to species being small, cryptic and/or nocturnal. Previous research on seed predation and dispersal by rodents in the Fynbos Biome of South Africa has relied on indirect evidence, as methods for directly monitoring rodent–seed interactions were not available. The aims of the study were to determine which resident small mammals scatter-hoard nuts and the geographic, seasonal and taxonomic extent of scatter-hoarding in the Fynbos Biome. We used camera traps focused on seed stations at eight sites in the Fynbos Biome to determine the responses of small mammals to tagged nut-like fruits (nuts) of seven endemic plant species belonging to the Proteaceae (n = 3), Rosaceae (n = 2), Restionaceae (n = 1) and Cupressaceae (n = 1), as well as commercial sunflower seeds. We found Acomys subspinosus and Gerbilliscus paeba scatter-hoarded nuts, which they typically carried and buried individually. Rhabdomys pumilio and Micaelamys namaquensis only consumed nuts. Leucadendron pubescens and L. loranthifolium are added to the list of known plant species that are scatter-hoarded by rodents. Nuts of Cliffortia cuneata and C. phillipsii, and the critically endangered Widdringtonia cedarbergensis, were consumed but not dispersed by small mammals, whereas nuts of Ceratocaryum argenteum were neither consumed nor scatter-hoarded by rodents (within its native range). Gerbilliscus paeba and A. subspinosus scatter-hoarded nuts aseasonally, outside of seed-fall periods. Scatter-hoarding was widespread throughout the Fynbos Biome, although it was highly localised across and within sampled sites. The absence of scatter-hoarding rodents at sites with rodent-dispersed plants remains an important aspect for future investigation.     

Thermoregulation of the subterranean rodent genus Bathyergus (Bathyergidae)

The thermoregulation of the largest subterranean rodent, genus Bathyergus, comprising two species, B. suillus and B. janetta, occurring in mesic and semiarid habitats respectively, was investigated and compared with that of other subterranean rodents. Both species display low resting metabolic rates and low body temperatures characteristic of subterranean rodents. The lower metabolism and smaller body size of B. janetta, may be an ‘energy-saving’ adaptation to its semi-arid habitat.