Predictors of Trypanosoma lewisi in Rattus norvegicus from Durban, South Africa

Sewer-associated rodents in countries with lower human development, a time-bomb for zoonoses?

Sewer-associated rodents inhabiting urban and peri-urban areas constitute a potential infection source for many zoonotic pathogens at a global scale. However, there is a lack of scientific information about the implications of these micromammals in regions with fragile sanitary services, low economic resources and weak educational systems. Consequently, this study aimed to review the scientific knowledge about rodent-borne zoonoses in sewer-related environments from countries with lower Human Development Index (HDI). Our results revealed a low number of publications (n = 13) evaluating the epidemiology of sewer-associated rodents in countries with lower HDI, which were distributed across Central/South America (69.2 %; 9/13), Africa (23.1 %; 3/13) and Asia (7.7 %; 1/13). The most evaluated rodents were Rattus norvegicus -brown rat- (present in 10/13 articles), followed by Rattus rattus -black rat- (6/13) and Mus musculus -house mouse- (5/13). Fourteen zoonotic pathogens were assessed, specifically bacteria (n = 6 publications) and parasites (n = 7), with the highest prevalence described for Bartonella spp. (85.0 %), Calodium hepaticum (83.8 %), Rickettsia spp. (75.0 %), Leptospira spp. (68.0 %) and Hymenolepis nana (60.0 %). Most reviewed publications described the use of molecular methods and direct examination of samples to identify the pathogens studied (46.2 %; 6/13 each), followed by the MALDI-TOF technique (15.4 %; 2/13). The four clusters building the semantic network reinforced the pivotal role of sewer-associated rodents as reservoirs of both vector-borne pathogens and directly transmitted zoonoses. Our findings evidence a severe gap of knowledge in lower-resource areas about the role of sewer-associated rodents in the epidemiology of zoonotic diseases, which could impact on the sanitary system of not only the evaluated countries, but also in other developed and non-developed regions worldwide.

Toxoplasma gondii and Trypanosoma lewisi Infection in Urban Small Mammals From Cotonou, Benin, With Special Emphasis on Coinfection Patterns

A growing number of studies has highlighted the importance of coinfections in eco-evolutionary processes underlying host-parasite interactions and the resulting epidemiology of zoonotic agents. Small mammals, and particularly rodents, are known to be important reservoirs of many zoonotic pathogens, such as Toxoplasma gondii and Trypanosoma lewisi, that are responsible for toxoplasmosis and atypical trypanosomiasis in humans, respectively. Laboratory experiments on rodent models have shown that primary infection with T. lewisi increases the host sensitivity to other parasites, including T. gondii, following an alteration in the immune response. However, data on potential interactions between these parasites in wild small mammals remain scarce. In this study, we determined the T. lewisi prevalence in 553 small mammals from four localities of Cotonou city, Benin. The results were then combined with T. gondii data previously collected for the same individuals in order to investigate the influence of T. lewisi on T. gondii infection, and vice versa, using co-occurrence tests and generalized linear mixed models (GLMMs). Despite quite high overall prevalence (32.5% and 15.2% for T. lewisi and T. gondii, respectively), we observed a clear and significant segregation between the two parasites. This may be explained by (i) differences in the species-specific receptivity and/or sensitivity of small mammal host species to infection by these two parasites, with Rattus rattus (Rra), Rattus norvegicus (Rno), and Mastomys natalensis (Mna) being the main hosts of T. lewisi, while Crocidura olivieri (Cro) and Mus musculus domesticus (Mus) were the main hosts for T. gondii; and/or (ii) a possibly high mortality in coinfected animals in the wild. Although dedicated experimental studies are required to confirm this pattern, as they stand, our data fail to support that in nature, the infection of small mammals by one of these two parasites favors widespread infection by the second one.

Trypanosoma lewisi in blood of Rattus rattus complex residing in human settlements, Nakhon Si Thammarat, Thailand: Microscopic and molecular investigations

Trypanosomes are blood parasites infected in various mammals, including rats. The presence of rats in human settlements can increase the chance of Trypanosoma transmission to humans. The molecular study of multispacer in Trypanosoma spp. in naturally infected rodents in Thailand is scanty. The objective of this study was to detect Trypanosoma in the blood of the captured rats in Nakhon Si Thammarat, Thailand, using microscopic and molecular techniques. This was a cross-sectional study conducted in human settlement areas. Ninety-nine blood samples were collected using cardiac puncture. A blood sample was smeared on a glass slide and examined using a compound light microscope and a scanning electron microscope. Moreover, polymerase chain reaction was applied to detect Trypanosoma evansi and T. lewisi in the blood. An additional primer set was used to confirm the species of the detected trypanosome. Approximately 18% of the rats had positive Trypanosoma infections. All Trypanosoma-positive blood samples were matched with sequences of T. lewisi. The stumpy form of trypanosome had higher nucleus related parameters than the slender form. Interestingly, the partial sequences of the alpha-tubulin gene of T. lewisi were first reported in the naturally infected RrC in this study. Based on the results obtained, T. lewisi biology, particularly the virulent components and route of transmission, pathogenesis, and in vitro experiments, are strongly recommended for further study.

Predicting the potential distribution of a previously undetected cryptic invasive synanthropic Asian house rat (Rattus tanezumi) in South Africa

Three species of Rattus, Norway rat (R. norvergicus), black rat (R. rattus) and Asian house rat (R. tanezumi) are currently known to occur in South Africa. The latter two species are cryptic and form part of the Rattus rattus species complex. Historically, R. norvegicus has been reported to occur along the coast and in urban centres, R. rattus is widespread in most urban areas, except in the drier areas, while R. tanezumi was only recorded to occur in the country (and Africa) ca. 15 years ago, and its distribution remains unknown. The aim of this study was to predict the potential distribution of R. tanezumi in South Africa and assess how it overlaps with that of R. norvegicus and R. rattus using species distribution modelling. Rattus tanezumi was predicted to mainly occur in most inland urban areas and along the coast. The distribution of R. rattus was as expected, in contrast, the predicted range of R. norvegicus was not restricted to the coast but also included inland urban areas. All three species showed broad potential distributional ranges that overlapped extensively indicating that their establishment and spread may be influenced by similar factors such as proximity to urban areas and a wet and moderate climate. These results allow insights into assessing their risk of establishment and for formulating appropriate intervention strategies for their management and control.

The pests of a pest: A systematic review of ectoparasitic fauna among synanthropic rodents in the 21st century with meta-analysis

Synanthropic rodents are important urban pests that frequently carry hematophagous ectoparasites. These blood-sucking pests are capable of transmitting epizootic and zoonotic pathogens by landing on one host after feeding on an infected animal. This study aimed to estimate the prevalence of ectoparasites carried by synanthropic rodents and discuss the pathogens that are associated with these external parasites. We searched relevant literatures using predefined criteria in the following databases: EMBASE, PUBMED, Web of Science and Scopus from January 2000 to June 2020. Quality of studies was evaluated using Newcastle-Ottawa scale (NOS). Of 35 included studies from 15 countries in Africa, America, Asia, Europe and Oceania, black rats (R. rattus), brown rats (R. norvegicus), pacific rats (R. exulans) and house mice (Mus musculus) were common synanthropic rodents. Mites (Mesostigmata, Sarcoptiformes and Trombidiformes) were the most prevalent (42.6%, 95% CI 26-59.2), followed by ticks (Ixodida) (21.5%, 95% CI 10.5-32.6), lice (Phthiraptera) (17.8%, 95% CI 7.7-27.9) and fleas (Siphonaptera) (14.1%, 95% CI 10.1-18.1). Heterogeneity (I2>96%) across studies was statistically significant. The ectoparasitic fauna was shared considerably by different urban rodent species and appeared to be more diverse in R. rattus and R. norvegicus. Nonetheless, pathogens carried by these ectoparasites were rarely investigated. In conclusion, ectoparasites are ubiquitous in urban-dwelling rodents but our understanding of the epidemiology and the associated pathogens of these parasites remains limited. Further studies are warranted to unravel the pathogen landscape found in rodent-associated ectoparasites.

Trypanosoma (Herpetosoma) diversity in rodents and lagomorphs of New Mexico with a focus on epizootological aspects of infection in Southern Plains woodrats (Neotoma micropus)

Protozoan parasites of the genus Trypanosoma infect a broad diversity of vertebrates and several species cause significant illness in humans. However, understanding of the phylogenetic diversity, host associations, and infection dynamics of Trypanosoma species in naturally infected animals is incomplete. This study investigated the presence of Trypanosoma spp. in wild rodents and lagomorphs in northern New Mexico, United States, as well as phylogenetic relationships among these parasites. A total of 458 samples from 13 rodent and one lagomorph species collected between November 2002 and July 2004 were tested by nested PCR targeting the 18S ribosomal RNA gene (18S rRNA). Trypanosoma DNA was detected in 25.1% of all samples, with the highest rates of 50% in Sylvilagus audubonii, 33.1% in Neotoma micropus, and 32% in Peromyscus leucopus. Phylogenetic analysis of Trypanosoma sequences revealed five haplotypes within the subgenus Herpetosoma (T. lewisi clade). Focused analysis on the large number of samples from N. micropus showed that Trypanosoma infection varied by age class and that the same Trypanosoma haplotype could be detected in recaptured individuals over multiple months. This is the first report of Trypanosoma infections in Dipodomys ordii and Otospermophilus variegatus, and the first detection of a haplotype phylogenetically related to T. nabiasi in North America in S. audubonii. This study lends important new insight into the diversity of Trypanosoma species, their geographic ranges and host associations, and the dynamics of infection in natural populations.

A Systematised Review of the Health Impact of Urban Informal Settlements and Implications for Upgrading Interventions in South Africa, a Rapidly Urbanising Middle-Income Country

Informal settlements are becoming more entrenched within African cities as the urban population continues to grow. Characterised by poor housing conditions and inadequate services, informal settlements are associated with an increased risk of disease and ill-health. However, little is known about how informal settlement upgrading impacts health over time. A systematised literature review was conducted to explore existing evidence and knowledge gaps on the association between informal settlement characteristics and health and the impact of informal settlement upgrading on health, within South Africa, an upper-middle income African country. Using two databases, Web of Science and PubMed, we identified 46 relevant peer-reviewed articles published since 1998. Findings highlight a growing body of research investigating the ways in which complete physical, mental and social health are influenced by the physical housing structure, the psychosocial home environment and the features of the neighbourhood and community in the context of informal settlements. However, there is a paucity of longitudinal research investigating the temporal impact of informal settlement upgrading or housing improvements on health outcomes of these urban residents. Informal settlements pose health risks particularly to vulnerable populations such as children, the elderly, and people with suppressed immune systems, and are likely to aggravate gender-related inequalities. Due to the complex interaction between health and factors of the built environment, there is a need for further research utilising a systems approach to generate evidence that investigates the interlinked factors that longitudinally influence health in the context of informal settlement upgrading in rapidly growing cities worldwide.

Zoonotic Trypanosomes in Rats and Fleas of Venezuelan Slums

Rattus spp. are reservoirs of many human zoonoses, but their role in domestic transmission cycles of human trypanosomiasis is underestimated. In this study, we report trypanosome-infected Rattus norvegicus and Rattus rattus in human dwellings in slums neighboring Maracay, a large city near Caracas, the capital of Venezuela. Blood samples of R. norvegicus and R. rattus examined by PCR and FFLB (fluorescent fragment length barcoding) revealed a prevalence of 6.3% / 31.1% for Trypanosoma lewisi (agent of rat- and flea-borne human emergent zoonosis), and 10.5% / 24.6% for Trypanosoma cruzi (agent of Chagas disease). Detection in flea guts of T. lewisi (76%) and, unexpectedly, T. cruzi (21.3%) highlighted the role of fleas as carriers and vectors of these trypanosomes. A high prevalence of rats infected with T. lewisi and T. cruzi and respective flea and triatomine vectors poses a serious risk of human trypanosomiasis in Venezuelan slums. Anthropogenic activities responsible for growing rat and triatomine populations within human dwellings drastically increased human exposure to trypanosomes. This scenario has allowed for the reemergence of Chagas disease as an urban zoonosis in Venezuela and can propitiate the emergence of atypical T. lewisi infection in humans.