Experimental infection of tigerfish (Hydrocynus vittatus) and African sharp tooth catfish (Clarias gariepinus) with Trichinella zimbabwensis.

Trichinella zimbabwensis naturally infects a variety of reptilian and wild mammalian hosts in South Africa. Attempts have been made to experimentally infect piranha fish with T. zimbabwensis and T. papuae without success. Tigerfish (Hydrocynus vittatus) and African sharp tooth catfish (Clarias gariepinus) are accomplished predators cohabiting with Nile crocodiles (Crocodylus niloticus) and Nile monitor lizards (Varanus niloticus) in southern Africa and are natural hosts of T. zimbabwensis. To assess the infectivity of T. zimbabwensis to these two hosts, 24 African sharp tooth catfish (mean live weight 581.75 ± 249.71 g) randomly divided into 5 groups were experimentally infected with 1.0 ± 0.34 T. zimbabwensis larvae per gram (lpg) of fish. Forty-one tigerfish (mean live weight 298.6 ± 99.3 g) were randomly divided for three separate trials. An additional 7 tigerfish were assessed for the presence of natural infection as controls. Results showed no adult worms or larvae of T. zimbabwensis in the gastrointestinal tract and body cavities of catfish sacrificed at day 1, 2 and 7 post-infection (p.i.). Two tigerfish from one experimental group yielded 0.1 lpg and 0.02 lpg of muscle tissue at day 26 p.i. and 28 p.i., respectively. No adult worms or larvae were detected in the fish from the remaining groups sacrificed at day 7, 21, 28, 33 and 35 p.i. and from the control group. Results from this study suggest that tigerfish could sustain T. zimbabwensis under specific yet unknown circumstances.

Epidemiology and hypothetical transmission cycles of Trichinella infections in the Greater Kruger National Park of South Africa: an example of host-parasite interactions in an environment with minimal human interactions.

Knowledge on the epidemiology, host range and transmission of Trichinella spp. infections in different ecological zones in southern Africa including areas of wildlife-human interface is limited. The majority of reports on Trichinella infections in sub-Saharan Africa were from wildlife resident in protected areas. Elucidation of the epidemiology of the infections and the prediction of hosts involved in the sylvatic cycles within specific ecological niches is critical. Of recent, there have been reports of Trichinella infections in several wildlife species within the Greater Kruger National Park (GKNP) of South Africa, which has prompted the revision and update of published hypothetical transmission cycles including the hypothetical options based previously on the biology and feeding behaviour of wildlife hosts confined to the GKNP. Using data gathered from surveillance studies and reports spanning the period 1964-2019, confirmed transmission cycles and revised hypothesized transmission cycles of three known Trichinella species (T. zimbabwensis, Trichinella T8 and T. nelsoni) are presented. These were formulated based on the epidemiological factors, feeding habits of hosts and prevalence data gathered from the GKNP. We presume that the formulated sylvatic cycles may be extrapolated to similar national parks and wildlife protected areas in sub-Saharan Africa where the same host and parasite species are known to occur. The anecdotal nature of some of the presented data confirms the need for more intense epidemiological surveillance in national parks and wildlife protected areas in the rest of sub-Saharan Africa to unravel the epidemiology of Trichinella infections in these unique and diverse protected landscapes.

TITLE: Épidémiologie et cycles de transmission hypothétiques des infections à Trichinella dans le Grand Parc National Kruger en Afrique du Sud : un exemple d'interactions hôtes-parasites dans un environnement où les interactions humaines sont minimales. ABSTRACT: Les connaissances sur l'épidémiologie, la gamme d'hôtes et la transmission des infections à Trichinella spp. dans différentes zones écologiques d'Afrique australe, y compris les zones d'interface faune-homme, sont limitées. La majorité des signalements d'infections à Trichinella en Afrique subsaharienne proviennent animaux sauvages résidant dans des zones protégées. L'élucidation de l'épidémiologie des infections et la prévision des hôtes impliqués dans les cycles sylvatiques au sein de niches écologiques spécifiques sont essentielles. Récemment, des infections à Trichinella ont été signalées chez plusieurs espèces sauvages dans le Grand Parc National Kruger (GPNK) en Afrique du Sud, ce qui a incité à la révision et à la mise à jour des cycles de transmission hypothétiques publiés, y compris les options hypothétiques basées précédemment sur la biologie et le comportement alimentaire des hôtes de la faune sauvage confinés au GPNK. À partir des données des études de surveillance et de rapports couvrant la période 1964­2019, les cycles de transmission confirmés et les cycles de transmission hypothétiques révisés de trois espèces connues de Trichinella (T. zimbabwensis, Trichinella T8 et T. nelsoni) sont présentés. Ceux-ci ont été formulés sur la base des facteurs épidémiologiques, des habitudes alimentaires des hôtes et des données de prévalence recueillies au GPNK. Nous supposons que les cycles sylvatiques formulés peuvent être extrapolés aux parcs nationaux et zones protégées similaires en Afrique subsaharienne, où les mêmes hôtes et espèces de parasites sont connues. La nature anecdotique de certaines des données présentées confirme la nécessité d'une surveillance épidémiologique plus intense dans les parcs nationaux et zones protégées du reste de l'Afrique subsaharienne pour démêler l'épidémiologie des infections à Trichinella dans ces paysages protégés uniques et diversifiés.

Trichinella zimbabwensis in wild Nile crocodiles (Crocodylus niloticus) of South Africa.

Recent discovery of Trichinella zimbabwensis in crocodiles from Zimbabwe, Lake Cahora Basa, Mozambique, and from lake Abaja, Ethiopia, prompted strict control measures to curb the possible spread of the infection to humans and also to prevent its introduction to other countries, which were considered free of this pathogen. In 2006, the Chief Directorate Veterinary Services of Mpumalanga Province of South Africa launched a survey to investigate the status of wild and commercial breeding crocodiles in the province. To evaluate if T. zimbabwensis was circulating in the environments where crocodiles are living in South Africa, 9 fish, 36 reptiles (including 27 Nile crocodiles) and 4 mammals have been investigated to detect Trichinella sp. larvae in their muscles. In January 2008, a Nile crocodile from Komatipoort, sampled by means of a tail biopsy, tested positive for Trichinella larvae. In June-July 2008, Trichinella sp. larvae were also detected in four other Nile crocodiles from the Olifants River Gorge. The prevalence of Trichinella infection in the investigated wild Nile crocodiles from South Africa is 38.5%. The larvae were identified as belonging to T. zimbabwensis by multiplex-PCR. These are the first reports of T. zimbabwensis in South Africa and suggest that the distribution area of this parasite species is wider than that believed in the past.

Adenoviral hepatitis in two Nile crocodile (Crocodylus niloticus) hatchlings from South Africa.

Adenoviral infections may cause mild to severe morbidity or fatality in a large array of animal species. In crocodilians, hatchlings under 5 months of age are usually affected. However, there is a paucity of information on actual incidences in hatchlings originating from South Africa. Two cases of adenoviral hepatitis in crocodile hatchlings about 2 weeks old, bred on a commercial farm in South Africa, are described. Both hatchlings showed typical clinical signs of hepatitis. The identification of intranuclear inclusion bodies in the liver was used to differentiate between adenoviral hepatitis and chlamydial hepatitis. Although vertical transmission has never been proven in crocodiles, the young age of the affected hatchlings raises the possibility of vertical transmission. The lack of epidemiological information on adenoviral hepatitis in crocodiles highlights the need for further characterisation of the virus and targeted surveillance.

Assessment of selected biochemical parameters and humoral immune response of Nile crocodiles (Crocodylus niloticus) experimentally infected with Trichinella zimbabwensis.

Fifteen crocodiles were randomly divided into three groups of five animals. They represented high-infection, medium-infection and low-infection groups of 642 larvae/kg, 414 larvae/kg and 134 larvae/kg bodyweight, respectively. The parameters assessed were blood glucose, creatine phosphokinase (CPK), lactate dehydrogenase (LDH), aspartate transaminase (AST) and alanine transaminase (ALT). The humoral immune response to Trichinella zimbabwensis infection was evaluated in all three groups by an indirect ELISA method. The results showed deviations from normal parameters of blood glucose, CPK, LDH, AST and ALT when compared with reported levels in uninfected reptiles. Contrary to studies involving mammals, hypoglycaemia was not observed in the infected groups in this study. Peak values of blood glucose were reached on post-infection (PI) Day 49, Day 42 and Day 35 in the high-infection, medium-infection and low-infection groups, respectively. Peak values of LDH and AST were observed on PI Day 56, Day 49 and Day 42 in the high-infection, medium-infection and low-infection groups, respectively. Peak values of CPK were observed on Day 35 PI in all three groups. Peak ALT values were reached on Day 56 in the high-infection group and on Day 28 PI in both the medium-infection and low-infection groups. No correlations between the biochemical parameters and infection intensity were observed. Peak antibody titres were reached on Day 49 PI in the medium-infection group, and on Day 42 PI in both the high-infection and low-infection groups. Infection intensity could not be correlated with the magnitude of the humoral immune response or time to sero-conversion. Results from this study were in agreement with results reported in mammals infected with other Trichinella species and showed that antibody titres could not be detected indefinitely.

Distribution patterns and predilection muscles of Trichinella zimbabwensis larvae in experimentally infected Nile crocodiles (Crocodylus niloticus Laurenti).

No controlled studies have been conducted to determine the predilection muscles of Trichinella zimbabwensis larvae in Nile crocodiles (Crocodylus niloticus) or the influence of infection intensity on the distribution of the larvae in crocodiles. The distribution of larvae in muscles of naturally infected Nile crocodiles and experimentally infected caimans (Caiman crocodilus) and varans (Varanus exanthematicus) have been reported in literature. To determine the distribution patterns of T. zimbabwensis larvae and predilection muscles, 15 crocodiles were randomly divided into three cohorts of five animals each, representing high infection (642 larvae/kg of bodyweight average), medium infection (414 larvae/kg of bodyweight average) and low infection (134 larvae/kg of bodyweight average) cohorts. In the high infection cohort, high percentages of larvae were observed in the triceps muscles (26%) and hind limb muscles (13%). In the medium infection cohort, high percentages of larvae were found in the triceps muscles (50%), sternomastoid (18%) and hind limb muscles (13%). In the low infection cohort, larvae were mainly found in the intercostal muscles (36%), longissimus complex (27%), forelimb muscles (20%) and hind limb muscles (10%). Predilection muscles in the high and medium infection cohorts were similar to those reported in naturally infected crocodiles despite changes in infection intensity. The high infection cohort had significantly higher numbers of larvae in the sternomastoid, triceps, intercostal, longissimus complex, external tibial flexor, longissimus caudalis and caudal femoral muscles (p < 0.05) compared with the medium infection cohort. In comparison with the low infection cohort, the high infection cohort harboured significantly higher numbers of larvae in all muscles (p < 0.05) except for the tongue. The high infection cohort harboured significantly higher numbers of larvae (p < 0.05) in the sternomastoid, triceps, intercostal, longissimus complex, external tibial flexor, longissimus caudalis and caudal femoral muscles compared with naturally infected crocodiles. Results from this study show that, in Nile crocodiles, larvae of T. zimbabwensis appear first to invade predilection muscles closest to their release site in the small intestine before occupying those muscles situated further away. The recommendation for the use of masseter, pterygoid and intercostal muscles as sampling sites for the detection of T. zimbabwensis in crocodiles is in contrast to the results from this study, where the fore- and hind limb muscles had the highest number of larvae. This study also supports the use of biopsy sampling from the dorso-lateral regions of the tail for surveillance purposes in both wild and commercial crocodile populations.

First report of a mixed infection of Trichinella nelsoni and Trichinella T8 in a leopard (Panthera pardus) from the Greater Kruger National Park, South Africa.

At least three Trichinella species, namely Trichinella nelsoni, Trichinella britovi and Trichinella zimbabwensis, and one genotype (Trichinella T8), have been isolated from sylvatic carnivores on the African continent. With the exception of T. britovi, the other species are known to circulate in wildlife of the Kruger National Park (KNP), South Africa, and KNP neighbouring game reserves (collectively known as the greater KNP area). Lions (Panthera leo) and spotted hyenas (Crocuta crocuta) appear to be the most important reservoirs of T. nelsoni and Trichinella T8 in the KNP and surrounding areas. Interspecies predation between lions and hyenas has been implicated as a primary mode of maintaining the life cycles of these two Trichinella species. This is the first report of a mixed natural infection of T. nelsoni and Trichinella T8 in a leopard (Panthera pardus) from South Africa. Trichinella muscle larvae were identified to species level by multiplex polymerase chain reaction (PCR). Probable sources of infection, based on the known dietary preference and prey species' range of leopards, are also discussed. The described occurrence of Trichinella species in a leopard from the greater KNP area raises the question of possible sources of infection for this predator species.

Trichinella nelsoni and Trichinella T8 mixed infection in a lion (Panthera leo) of the Kruger National Park (South Africa).

In South Africa, Trichinella sp. was first discovered in 1966 in the wildlife of the Kruger National Park (KNP). Since then, both Trichinella T8 and Trichinella nelsoni have been detected in the KNP, leading to a debate on the existence of a gene flow between the two taxa. In 2006-2008, four lions were killed in the Manyeleti Game Reserve, the Mthethomusha Nature Reserve, Numbi Gate, and Skukuza, which border the KNP. Larvae were isolated from muscles by artificial digestion. The molecular identification of single larva by multiplex PCR, followed by a specific PCR to distinguish between Trichinella T8 and Trichinella britovi, revealed Trichinella T8 in the lions from Manyeleti and Skukuza, a mixed infection with T. nelsoni and Trichinella T8 in the lion from Mthethomusha, and T. nelsoni in the lion from Numbi. No larva with a hybrid pattern between the two taxa was observed. No hybrid offspring resulted when crossing single males and females of T. nelsoni and Trichinella T8 in both directions, whereas hybrid offspring were obtained when crossing T. britovi and Trichinella T8 in both directions. This is the first report of a mixed infection with two Trichinella taxa in a host from the KNP, where both Trichinella T8 and T. nelsoni circulate among wildlife. Despite the sympatry status of these two taxa, field and laboratory data seem to exclude the possibility of gene flow, confirming their evolutive separation.