Theileriosis in roan antelope (Hippotragus equinus) : identification of vectors and experimental transmission using a tick-derived stabilate

Abstract

Four hand-reared, naïve roan antelope 6 months of age were exposed to naturally infected pasture on a game farm in Mpumalanga where roan are known to die from theileriosis. The predominant ticks parasitising these animals at this time (during the months of January and February) were Rhipicephalus appendiculatus and R. evertsi evertsi adults. After a period of 5 weeks the animals developed signs of clinical theileriosis, characterized by anorectal lymphadenomegaly, shortly followed by pyrexia and generalised peripheral lymphadenomegaly. Around the time of pyrexia, peripheral blood smears showed severe mononuclear leukocytosis, with some leukocytes containing cytoplasmic theilerial schizonts (Koch’s bodies). This was followed by erythrocytic piroplasmaemia. Animals were treated successfully using buparvaquone. Primary hyperplasia of the local draining lymph nodes (Lnn. anorectales) of adult R. e. evertsi feeding sites indicated vector status of theileriosis for this tick species. After recovery from theileriosis, these animals were confirmed carriers of Theileria sp. (sable) by PCR and DNA probe analysis. Laboratory-bred larvae and nymphae of R. e. evertsi and R. appendiculatus respectively were fed on the ears of these roan antelope, now known to be carriers. Engorged nymphae were recovered from the roan. A cryopreserved stabilate was produced from each species, using an adapted protocol for Theileria parva tick stabilate preparation. Both stabilates were tested for infectivity in T. sp. (sable) negative (PCR analysis) roan antelope calves that were intensively hand reared under tick-free conditions. The stabilate derived from R. e. evertsi induced clinical theileriosis at doses between 5 and 60 tick equivalents per calf. The R. appendiculatus stabilate did not induce clinical disease or infection; the calves remained PCR negative throughout the trial period. The calves that survived the R. e. evertsi stabilate trial showed no clinical reaction to field exposure, in contrast to the controls and R. appendiculatus stabilate inoculated calves which all exhibited clinical theileriosis The stabilate has the potential to be used as the infection source in an infection and treatment method of immunising roan antelope against theileriosis. Copyright