Trichinella infections in wildlife in the Greater Kruger National Park, South Africa: unravelling epidemiological gaps with special emphasis on infectivity of Trichinella zimbabwensis in selected tropical fishes.

Abstract

Trichinella species are widely distributed on all continents with the exception of Antarctica, although the full spectrum of Trichinella species found in sub-Saharan African countries and their hosts has not been fully documented. This study was conducted to review reports on Trichinella infections in wildlife in the Kruger National Park and also to identify species and/or genotypes of Trichinella larvae isolated from muscle tissues of wildlife from Kruger National Park and adjacent areas of the Limpopo and Mpumalanga provinces, South Africa referred to as the Greater Kruger National Park using molecular techniques. A review of Trichinella spp. isolates and their wildlife hosts from the Greater Kruger National Park covering the period 1964–2011 was conducted and the results were compared with recent findings where isolates collected between 2012 and 2016 were identified to genotype/species level using molecular techniques. In the first 15 years the prevalence of infection was only reported twice in scientific publications and the reports included only four carnivorous mammal species and one rodent species. However, since the last report of Trichinella in an African civet (Civettictis civetta) other wildlife species were tested in the KNP and one new host was identified. Advances in molecular techniques allowed scientists to identify two isolates, collected in 1966 and 1988 respectively as Trichinella T8. Another isolate collected in 1991 was described as T. nelsoni. All of the other isolates found before 1991 were erroneously identified as T. spiralis. Ninety samples collected during the 2012–2016 period representing 15 mammalian, two avian- and three reptilian species were screened for Trichinella infection using artificial digestion. Isolates detected were identified using a multiplex polymerase chain reaction amplification of the ITS1, ITS2 and ESV regions of ribosomal DNA followed by molecular analysis of the sequences. Twenty (20) samples from seven wildlife species were positive for Trichinella spp. larvae with an overall prevalence of 21.1% (20/90). The prevalence was higher in carnivores (18.9%, 18/90) than in omnivores (2.2%, 2/90). Analysis of sequences showed that eight of the isolates; two from spotted hyaena (Crocuta crocuta) (2/8), three from lion (Panthera leo) (3/13), one from leopard (Panthera pardus) (1/6), one from small spotted genet (Genetta genetta) (1/2) and one Nile monitor lizard (Varanus niloticus) (1/2) conformed to Trichinella zimbabwensis. One isolate from a hyaena was grouped under the encapsulated species clade comprising T. nelsoni and genotype Trichinella T8 reported to be present in South Africa. This is the first report confirming natural infection of T. zimbabwensis in hyaena, leopard, genet and Nile monitor lizard, adding to the body of knowledge on the epidemiology of Trichinella infections in the Greater Kruger National Park, South Africa. Ten Trichinella-like larvae recovered after digestion from four wildlife species in this study (2012–2016) revealed inconclusive results due to DNA degradation from poor storage or too few larvae for analysis in comparison to 20 isolates from five wildlife species not identified to species during the 1964–2011 period. Knowledge on factors influencing the infectivity, epidemiology and survival of Trichinella spp. in different climatological environments is scanty. Availability of this knowledge will allow for the elucidation of epidemiology of Trichinella infections and the prediction of probable host-parasite cycles within specific ecological niches. The recent identification of new host species infected with three Trichinella taxa within the Greater Kruger National Park prompted a revision of previously published hypothetical transmission cycles for these species. Using data gathered from surveillance studies spanning the period 1964– 2016, and the recently obtained data from molecular identification of isolates from the Greater Kruger National Park, the previously hypothesized transmission cycles were revised. The new hypothesized transmission cycles were established in consideration of epidemiological factors and prevalence data gathered from both the Greater Kruger National Park and similar wildlife protected areas in Africa where the same host- and parasite species are known to occur. The anecdotal nature of some of the presented data in the hypothesized transmission cycles confirms the need for more intense epidemiological surveillance in the rest of South Africa and continued efforts to unravel the epidemiology of Trichinella infections in this unique and diverse protected landscape. Furthermore, to determine the role of fish in the epidemiology of T. zimbabwensis in the Greater Kruger National Park, experimental infections were conducted to assess the infectivity of this species to catfish (Clarias gariepinus) and tigerfish (Hydrocynus vittatus). Twenty-four catfish (581.7 ± 249.7 g) were randomly divided into 5 groups and experimentally infected with 1.0 ± 0.34 T. zimbabwensis larvae per gram (lpg) of fish. Results showed no adult worms or larvae in the gastrointestinal tract and body cavities of catfish euthanized at day 1, 2 and 7 post-infection (p.i.). These results suggest that African sharp tooth catfish does not play a role in the epidemiology of the parasite irrespective of the fact that the fish cohabit with crocodiles and Nile monitor lizards in the Greater Kruger National Park. Forty-one tigerfish (298.6 ± 99.3 g) were randomly divided into three separate trials (T). Each trial (T) was divided into groups (G) as follows; Trial 1 (T1G1); Trial 2 (T2G1, T2G2) and Trial 3 (T3G1, T3G2, T3G3) infected with 2.12 ± 1.12 lpg of fish. An additional 7 tigerfish were assessed for the presence of natural infection. Two tigerfish from T1G1 yielded T. zimbabwensis larvae in muscle tissues on day 26 p.i. (0.1 lpg) and 28 p.i. (0.02 lpg), respectively. No adult worms or larvae were detected in the fish from trials 2 or 3 on days 7, 21, 28, 33 or 35 p.i. or from the control group. Results from this study suggest tigerfish to be generally unsuitable hosts for T. zimbabwensis. However, results from this study suggest that some individuals could, under very specific, and as yet to be elucidated circumstances, maintain the larvae of T. zimbabwensis but it could not be confirmed whether the parasite can fully develop and reproduce in this host. These results preclude any definitive conclusion in respect of the potential of African sharp tooth catfish and tiger fish to serve as potential hosts for T. zimbabwensis. The influence of temperature on T. zimbabwensis larval development and survival in fish remains inconclusive. It is possible that these fish could only become infected during warmer seasons and in warmer climates. It is also not clear whether potentially infected fish would retain the infection in subsequent colder seasons. Variability of temperatures between different geographic regions may additionally influence the susceptibility of these fish to T. zimbabwensis infection. However, the plethora of biological-, geographical- and climatic factors that could potentially influence the infectivity of T. zimbabwensis to certain fish host species precludes any definitive conclusion on the role of fish in the parasite’s natural ecosystem. Results from this study do suggest that tigerfish could, under very specific and as yet unknown circumstances, sustain the development and establishment of T. zimbabwensis.