Molecular characterization of cosmopolitan and potentially co-invasive helminths of commensal, murid rodents in Gauteng Province, South Africa.

Concurrent studies of helminth parasites of introduced and native rodent species are few and miss the opportunity to identify potential co-invasive parasite species. This study employed molecular tools to infer the phylogeny and elucidate the origin of potentially co-invasive parasites of commensal, murid rodents by assessing introduced Rattus norvegicus, Rattus rattus, Rattus tanezumi, and native Mastomys coucha in Gauteng Province, South Africa. Genotypes of Nippostrongylus brasiliensis recovered from R. norvegicus are nearly identical to those recovered from elsewhere in the world. The pinworms, Aspiculurus tetraptera, recovered from introduced R. tanezumi and R. rattus, Syphacia muris recovered from R. tanezumi, and Syphacia obvelata recovered from indigenous M. coucha have affiliations to those recovered of laboratory rodents from the USA and China. Syphacia obvelata was previously only known as a commensal endoparasite of laboratory rodents, and the S. muris genotype recovered from R. tanezumi in this study shows an affiliation to a genotype recovered from the same host species in Indonesia which is part of the native range. The study emphasizes the need for surveillance of potential co-invasive species and contributes in documenting genetic diversity of endoparasites of well-known hosts.

Helminth composition and prevalence of indigenous and invasive synanthropic murid rodents in urban areas of Gauteng Province, South Africa.

Although synanthropic rodents such as the indigenous species, Mastomys coucha, and the invasive species, Rattus norvegicus, R. rattus and R. tanezumi, are well-known to be hosts to various micro- and macroparasites, their helminth parasite fauna is poorly studied in South Africa. In an attempt to remedy the situation, the aim of the present study was to investigate the helminth fauna of these sympatric rodent species, which were obtained from the informal settlements of Alexandra, Tembisa, Diepsloot and residential suburbs of Pretoria and Hammanskraal, Gauteng Province, South Africa. Helminths were recovered from the urinary bladder, liver and gastrointestinal tract and were identified morphologically and molecularly. The recovered nematodes were all rodent-specific and included Aspiculuris tetraptera, Eucoleus sp., Heterakis spumosa, Mastophorus muris, Nippostrongylus brasiliensis, Protospirura sp., Strongyloides ratti, Syphacia obvelata, Syphacia muris, Trichuris sp. and Trichosomoides crassicauda. Syphacia obvelata, a commensal nematode of laboratory rodents, was recovered from indigenous M. coucha. Strobilar stages of cestodes recovered included Hymenolepis diminuta, Hymenolepis nana and Inermicapsifer madagascariensis. Recovered metacestodes were strobilocerci of Hydatigera taeniaeformis from all three invasive Rattus species and coenurostrobilocerci of Hydatigera parva from M. coucha. An acanthocephalan, Moniliformis moniliformis, was recovered from R. rattus only. All rodent species examined showed high helminth infection prevalence (≥70%) with equal or higher nematode than cestode prevalence. Mastomys coucha, however, showed significantly lower cestode prevalence than Rattus species where they co-occur. Interspecific transmission of helminths likely occurs between invasive and indigenous rodents, and these rodents harbour several helminths that have zoonotic implications.

A mathematical epidemiological model of gram-negative Bartonella bacteria: does differential ectoparasite load fully explain the differences in infection prevalence of Rattus rattus and Rattus norvegicus?

We postulate that the large difference in infection prevalence, 24% versus 5%, in R. norvegicus and R. rattus, respectively, between these two co-occurring host species may be due to differences in ectoparasite and potential vector infestation rates. A compartmental model, representative of an infectious system containing these two Rattus species and two ectoparasite vectors, was constructed and the coefficients of the forces of infection determined mathematically. The maximum difference obtained by the model in the prevalence of Bartonella in the two Rattus species amounts to 4.6%, compared to the observed mean difference of 19%. Results suggest the observed higher Bartonella infection prevalence in Rattus norvegicus compared to Rattus rattus, cannot be explained solely by higher ectoparasite load. The model also highlights the need for more detailed biological research on Bartonella infections in Rattus and the importance of the flea vector in the spread of this disease.

Bartonellae of the Namaqua rock mouse, Micaelamys namaquensis (Rodentia: Muridae) from South Africa.

The aim of this study was to determine Bartonella prevalence and diversity in Namaqua rock mice, Micaelamys namaquensis, a species endemic to South Africa, which can attain pest status. A total of 100 heart samples collected monthly from March to December were screened for Bartonella genome presence using three primer sets targeting the citrate synthase (gltA) gene, the NADH dehydrogenase gamma subunit (nuoG) gene and the RNA polymerase ß-subunit-encoding gene (rpoB). An overall prevalence of 44% was obtained, with no statistically significant differences or correlations between infection rates and rodent sex, month of capture or season of capture. Phylogenetic analysis of 34 unambiguous gltA sequences revealed the presence of three discrete Bartonella lineages in M. namaquensis, one of which corresponds to Bartonella elizabethae, a species with known zoonotic potential.

Untangling the roles of fire, grazing and rainfall on small mammal communities in grassland ecosystems.

In grassland systems across the globe, ecologists have been attempting to understand the complex role of fire, grazing and rainfall in creating habitat heterogeneity and the consequences of anthropogenic control of these factors on ecosystem integrity and functioning. Using a South African grassland ecosystem as a model, we investigated the impact of fire and grazing pressure on small mammal communities during three differing periods of a rainfall cycle. Over 2 years, 15,203 trap nights revealed 1598 captures of 11 species (nine rodents, one macroscelid and one insectivore). Results highlighted the importance of the interplay between factors and showed that the role of fire, grazing and rainfall in determining small mammal abundance was species-dependant. While no two species were affected by the same environmental variables, grass cover or height was important to 56% of species. Considered independently, high rainfall had a positive influence on small mammal abundance and diversity, although the lag period in population response was species-specific. High grazing negatively affected overall abundance, but specifically in Mastomys coucha; fire alone had little immediate impact on small mammal diversity. Six months after the fire, vegetation cover had recovered to similar levels as unburned areas, although small mammal diversity and richness were higher in burned areas than unburned areas. Grazing levels influenced the rate of vegetation recovery. In conclusion, low-level grazing and burning can help to maintain small mammal biodiversity, if conducted under appropriate rainfall levels. A too high grazing pressure, combined with fire, and/or fire conducted under drought conditions can have a negative impact on small mammal biodiversity. To maintain small mammal diversity in grassland ecosystems, the combined effects of the previous year's rainfall and existing population level as well as the inhibition of vegetation recovery via grazing pressure need to be taken into consideration before fire management is applied.

The chronobiology of the Natal mole-rat, Cryptomys hottentotus natalensis.

The Natal mole-rat, Cryptomys hottentotus natalensis, rarely, if ever, is exposed to external light cues because it occurs in completely sealed tunnel systems. As a result, their classical visual system is regressed, and therefore, their circadian system is expected proportionally to be expanded. Locomotor activity was investigated under a number of different photic regimes. Nine of the 12 mole-rats exhibited endogenous circadian rhythms of locomotor activity under constant darkness, with a mean free run period of 24.13 h (range 23.93-24.13 h), with these animals entrained to a light-dark cycle (12 L:12 D). Because C. hottentotus natalensis are able to entrain their locomotor activity to an external light source, light must reach the suprachiasmatic nucleus (SCN), suggesting a functional circadian clock. A clear day-night rhythm of melatonin secretion in animals housed under a neutral photoperiod (12 L:12 D) was observed, with higher melatonin concentrations in the dark compared with the light phase. The rhythm was maintained after the animals were transferred to either continuous light (LL) or dark (DD), suggesting that the endogenous rhythm was maintained under acute exposure to light and dark. However, under DD, the rhythm appeared to shift slightly, potentially as a result of the rhythm free running. These results show that C. hottentotus natalensis has endogenous rhythms of both locomotor activity and melatonin secretion, which are modulated by light.