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Author: Prof Joop Boomker

Infections of the liver

Pletcher, Horak, De Vos & Boomker (1988) describe the lesions caused by Cooperioides hepaticae in impalas from the KNP (Fig. 17), and came to the conclusion that members of this genus are usually considered of minor pathological significance, unless present in large numbers and in combination with other trichostrongyles. Gallivan, Barker, Culverwell & Girdwood (1996) described lesions caused by hepatic parasites in general, in the same antelope from Swaziland. Despite the nematodes being present in the majority of impala that were examined during several surveys, clinical signs have never been observed.

Fig. 17: The greenish discoloration is due to an eosinophil accumulation in the bile duct of an impala as result of Cooperioides hepaticae infection. (Reproduced with permission of Prof. Wilmien Luus-Powell, University of Limpopo)

Monodontus giraffae is an extremely common parasite of the bile ducts of giraffe and causes mild to severe cholangitis, depending on the number of worms present (Basson et al., 1971).

Fasciolosis seems to be a rare occurrence in free-living antelope. Basson et al. (1970) did not find a single case in the 100 buffalo they examined in the southern part of the KNP. Boomker (1990) examined 386 browsing antelope from all overSouth Africa and the northern parts of Namibia and found a single grey rhebuck in the Bontebok National Park to harbour only two Fasciola specimens. Boomker & Horak (unpublished, 1980 – 1990) did not find Fasciola spp. in any of the 162 impalas examined from five localities in the KNP, and neither did Heinichen (1973) in the north-eastern region of KwaZulu-Natal. However, Horak (1978) found Fasciola gigantic in one of 36 impala at Nylsvley, Limpopo Province, where they shared pastures with cattle.

Even though antelope seem to be resilient to infections with Fasciola, cases of acute fasciolosis are known. These, however, were present on game farms, or where antelope were overcrowded. In the dry north-western part of Limpopo Province metacercariae of Fasciola were found in water troughs, together with the intermediate hosts, Lymnaea truncatula.

Contrary to Fasciola, the non-pathogenic liver tapeworm, Stilesia hepatica (Figs. 18 & 19) has a high prevalence in a variety of antelope. Buffalo from the KNP, however, did not harbour Stilesia (Basson et al., 1970).

Cysticercosis due to the metacestodes of Taenia hydatigena is a common finding at necropsy of a number of antelope (Fig. 20). After the egg has been eaten, the oncosphere or hexacanth larva hatches and burrows through the wall of the small intestine, crosses the abdominal cavity and enters the liver. It migrates through the liver parenchyma for a while and leaves the liver in the vicinity of the bile duct. It attaches to the mesenterium in the immediate vicinity of the liver. The infection is dependent on the presence of jackal, Cape hunting dogs or domestic dogs. Boomker (1990) found these cysticerci in blue and grey duikers, but associated pathology was not seen. Round (1968) lists 15 species of intermediate hosts for this tapeworm, including warthogs and bushpigs.

Fig. 18:  Stilesia hepatica in the common bile duct of a red duiker, Cephalophus natalensis

Fig. 19:  Stilesia hepatica. Note the thickened bile ducts to the right side of the liver

Fig. 20: The typical appearance and localization of the metacestodes of Taenia hydatigena, also known as Cysticercus tenuicollis

Fig. 21: This photograph of cysts in a sheep liver is presented as illustration of cystic hydatidosis

Hydatid cysts of Echinococcus granulosus (Fig. 21) were found in one kudu out of the 386 antelope examined by Boomker (1990) and Basson et al (1970) found a 5% prevalence in the buffaloes they processed. Hydatids were not found in the impalas examined by Heinichen (1973), Horak (1979) and Boomker & Horak (unpublished data). Hydatidosis, or cystic echinococcosis does not seem to be of importance in the larger nature reserves but could theoretically become problematic on game farms.

Infective nymphs of the pentastome genus Linguatula are often encountered in antelope (Fig. 22). They utilize antelope as intermediate hosts and the large carnivores, especially lions, as final hosts. The nymphs tunnel in the liver without causing haemorrhage and were found in 63.2% of kudus (Horak, Boomker, Spickett & De Vos, 1992), 21.8% of blue wildebeest (Horak, De Vos & Brown, 1983) and 35.5% of warthogs (Horak, Boomker, De Vos & Potgieter, 1988), all surveyed in the KNP. It is interesting that kudus, which are browsing antelope, have the highest prevalence of this parasite, whereas blue wildebeest, which graze short grass, have the least.

Fig. 22: Infective nymphs of Linguatula nuttalli on the liver of a kudu