Fasciolosis, caused by infection with the liver fluke Fasciola, can cause significant economic losses in African livestock [1, 2]. The complex nature of the lifecycle and epidemiology of this snail-borne disease presents challenges for predictive mapping at the herd-level, as well as disease management and animal husbandry at the individual-level . Fasciola gigantica and Fasciola hepatica can infect a wide variety of domesticated animals, wildlife and people [4–9]. Thus the disease-endemic zone can be difficult to define from parasitological data alone and so consideration of the distribution of associated snail intermediate hosts can be important . F. gigantica is the most common liver fluke in sub-Saharan Africa, being adapted to warmer conditions  likely due to the widespread distribution of its intermediate host Lymnaea (Radix) natalensis . On the other hand owing to a more limited distribution of its intermediate host Lymnaea (Galba) truncatula , F. hepatica can exist in zoonotic foci which are more restricted to cooler regions of Africa, including Kenya, Ethiopia and Tanzania [1, 10, 13]. Nonetheless, actual or potential overlap of both types of fasciolosis can occur especially where snail-habitats converge, for example, with increasing altitude as in the highlands of Ethiopia  or perhaps in upland zones of eastern Uganda, as yet to be fully explored. In the Mount Elgon area of Uganda, fasciolosis is poorly studied as there is no systematic veterinary or medical disease surveillance system.
Cattle are Uganda’s most economically important livestock species with an estimated population of 11 million . The majority are either indigenous Zebu or Sanga, with less than 5% being imported ‘exotic’ breeds, mainly Friesians . Livestock production is hampered by many disease constraints of which fasciolosis is considered the most important helminth infection . The Mount Elgon region consists of predominately rural subsistence farmers covering a zone between 1000-2300 m in altitude rising towards an important wildlife reserve, the Mount Elgon National Park (MENP). Encompassing a total area of some 1,145 km2, MENP commences at 2300 m and extends to 4321 m at Wagagi Peak. Within the park, a number of herds of wild ruminants are known including buffalo, antelope and elephant but illegal cattle trading routes, from Uganda to Kenya and vice versa, traverse throughout. However, with increasing Uganda Wildlife Authority (UWA) foot patrols servicing an increasing hiking and camping tourism, illegal cattle trafficking has declined in recent years.
Like elsewhere in Uganda, the lowland areas of Mount Elgon are known to be endemic zones for F. gigantica with reports documenting the prevalence of F. gigantica at 54.7% in cattle [16, 18, 19]. A contemporary situational analysis, however, is yet lacking. From a malacological perspective, there has been no update to the formal snail surveys conducted by Georg Mandahl-Barth and by Hubendick in their general treatise on Ugandan freshwater snails and Lymnaea, respectively over 50 years ago [12, 20]. Both Lymnaea natalensis and Lymnaea mweruensis have been reported from the area with the latter species now considered synonymous with Lymnaea truncatula, as collected by C.C. Cridland from Sasa River Camp at 2900 m (now within MENP). Such upland areas, like those in neighbouring Tanzania, are thought suitable zones for the transmission of F. hepatica, for example, L. truncatula being recently found at 2712 m & 2720 m with identifications confirmed by DNA analysis of the ribosomal 18S . Though F. hepatica has yet to be encountered in natural transmission cycles in Uganda, it has been known from earlier reports within UK-imported cattle .
Clearly defining such local zones of transmission in eastern Uganda is also important for further modelling of the suitability of habitats elsewhere in East Africa. Various authors have designed models based on climate and intermediate host presence to predict the prevalence of Fasciola spp. [14, 22]. However, areas that appear broadly similar in terms of climate can have very different snail populations due to variations in micro-climate and local aquatic factors, e.g. water pH and conductivity. This limits the accuracy of such climatic models, and localised parasitological and malacological data are still required for prediction of actual disease zones or outbreaks [22, 23]. In many countries, signalment of cattle condition  and subsequent meat inspection provides an opportunity to monitor the incidence of fasciolosis, also allowing access to adult worms enabling morphological identification [23, 25]. However, it is not able to detect past infections in those animals that have either been treated or developed immunity and self-cured. A suitable immunological test could fill this gap, and also detect pre-patent infections, but presently this is only available for assaying antibody titres in cattle to excretory/secretory (ES) antigens of F. hepatica . With this assay, heterologous reactions to F. gigantica are likely but as yet not known, however, serological testing should be an interesting adjunct in revealing putative transmission zones.
Using a combination of parasitological sampling, bolstered by experimental serology, our study aimed to investigate the occurrence of fasciolosis in bovids at low and high altitude areas on the slopes of Mount Elgon and also assessed animal condition (i.e. body signalment). The parasitological surveys were complemented with a conjoint malacological appraisal in an attempt to better define the actual or potential disease transmission zone of these parasites.