Prevalence of Theileriosis in Red Hartebeest (Alcelaphus buselaphus caama) in Namibia

The Pathology of Pathogenic Theileriosis in African Wild Artiodactyls

The published literature on schizont-"transforming," or pathogenic theileriosis, in African wild artiodactyls is dated and based on limited information. Here the authors review the taxonomy, diagnosis, epidemiology, hematology, pathology, and aspects of control in various species. Molecular studies based on 18S and 16S rRNA gene sequences have shown that African wild artiodactyls are commonly infected with diverse Theileria spp., as well as nontheilerial hemoprotozoa and rickettsia-like bacteria, and coinfections with pathogenic and nonpathogenic Theileria species are often recorded. Although theileriosis is still confusingly referred to as cytauxzoonosis in many species, the validity of a separate Cytauxzoon genus in artiodactyls is debated. The epidemiology of theileriosis is complex; the likelihood of fatal disease depends on the interplay of parasite, vertebrate host, tick vector, and environmental factors. Roan calves (Hippotragus equinus) and stressed animals of all host species are more susceptible to fatal theileriosis. Even though regenerative anemia is common, peripheral blood piroplasm parasitemia does not correlate with disease severity. Other than anemia, common macroscopic lesions include icterus, hemorrhages (mucosal, serosal, and tissue), fluid effusions into body cavities, lung edema, and variably sized raised cream-colored foci of leukocyte infiltration in multiple organs. Histopathologic findings include vasocentric hyperproliferation and lysis of atypical leukocytes with associated intracellular schizonts, parenchymal necrosis, hemorrhage, thromboembolism, and edema. Immunophenotyping is required to establish the identity of the schizont-transformed leukocytes in wild ungulates. Throughout the review, we propose avenues for future research by comparing existing knowledge on selected aspects of theileriosis in domestic livestock with that in African wild artiodactyls.

The host-specificity of Theileria sp. (sable) and Theileria sp. (sable-like) in African Bovidae and detection of novel Theileria in antelope and giraffe

Tick-borne diseases caused by Theileria are of economic importance in domestic and wildlife ruminants. The majority of Theileria infects a limited number of host species, supporting the concept of host specificity. However, some Theileria seem to be generalists challenging the host specificity paradigm, such as Theileria sp. (sable) reported from various vertebrate hosts, including African buffalo, cattle, dogs and different antelope species. We tested the hypothesis that T. sp. (sable) uses Bovidae as hosts in general using a real-time polymerase chain reaction assay specific for T. sp. (sable) and a closely related genotype: T. sp. (sable-like). Various antelope species from the Tragelaphini (black wildebeest, blesbuck, blue wildebeest, gemsbuck, sable and waterbuck) tested positive for either T. sp. (sable) or T. sp. (sable-like). However, no African buffalo (n = 238) or cattle (n = 428) sampled in the current study tested positive, suggesting that these latter species are not carrier hosts. The results were confirmed using next-generation sequencing which also indicated at least 13 new genotypes or species found in various antelope and giraffes. Genotypes were found in single host species or in evolutionarily related hosts, suggesting that host specificity in Theileria may be a lineage specific phenomenon likely associated with tick-host-parasite co-evolution.

Adding injury to infection: The relationship between injury status and genetic diversity of Theileria infecting plains zebra, Equus quagga

Asymptomatic tick-borne infections are a common feature in wild herbivores. In human-dominated habitats, snare injuries to wild herbivores are common and are likely to co-occur with enzootic infections. The influence of injury on pattern, course and outcome of enzootic infection in wild herbivores is unknown. We identified Theileria species infecting zebra and assessed the relationship between host injury-status and parasitaemia, parasite diversity and selection regimes. We also determined host leucocyte differential as this can reveal mechanisms by which injuries influence infections. Theileria infecting zebra was identified using PCR and sequencing of the V4 region of the 18 s rRNA gene and confirmed with phylogenetic analyses. The influence of injury status on parasite infection patterns, genetic diversity and selection were assessed using population genetic tools. Parasitaemia estimated from prevalence and leucocyte differential were determined from microscopic examination of Giemsa stained thin blood smears. Phylogenetic and sequence analyses revealed that the zebra population studied was infected with three Theileria equi haplotypes. Parasitaemia was lower among injured compared to non-injured animals and lower during dry than wet season. Mean (±SD) genetic diversity was 0.386 (±0.128) in injured and 0.513 (±0.144) in non-injured zebra (P = .549). Neutrality tests indicated that T. equi is under strong purifying selection in injured females (Li & Fu's D* = -2.037) and demographic expansion in all zebra during the wet season (Tajima D = -1.904). Injured zebras had a higher median per cent of neutrophils (64% vs 37%) a lower median per cent of basophils (0% vs 1%) and eosinophils (2% vs 4.5%) than non-injured animals, suggesting a heightened immune response and a shift from a Th2 to Th1 T-Cell response favoring the elimination of intracellular parasites in injured animals. This study demonstrates the utility of population genetics in revealing factors influencing parasite diversity and infection patterns.

Tick-borne pathogens in the blood of wild and domestic ungulates in South Africa: interplay of game and livestock

We screened for tick-borne pathogens blood samples from 181 wild and domestic ungulates belonging to 18 host species in 4 South African Provinces. Polymerase chain reaction followed by reverse line blotting and sequencing allowed detecting 16 tick-borne pathogen species belonging to the genera Babesia, Theileria, Anaplasma, and Ehrlichia. Ten pathogen species were involved in 29 new host-pathogen combinations. Most infections (77.9%) involved more than one pathogen species. Principal component analysis (PCA) assigned the 163 infections, identified to species level, to 4 groups. Three groups were associated with sheep, cattle, and horse and their respective wild counterparts. Each group was characterised by high homogeneity in pathogen assemblage and host phylogenetic status. These groups characterised the most privileged transmission routes between and among wild and domestic ungulates. The 4th group showed high heterogeneity in pathogen assemblage and host phylogenetic status. This group seems to indicate frequent spill over events in impala of pathogens that usually circulate among cattle- or sheep-related species. Within 6 localities, we sampled an equal number of wild and domestic animals (n=128). On this dataset once having controlled for the significant variation among localities, the infection prevalence and intensity of infection did not differ significantly between wild and domestic hosts. This suggests that both animal types, domestic and wild hosts, could act as evenly efficient sources of infection for themselves and for each other. Overall, this study shed new light on the pathogen circulation naturally achieved at the interplay between wild and domestic ungulates.

Molecular characterization of Theileria species associated with mortality in four species of African antelopes

Pathogen DNA was isolated from roan antelope (Hippotragus equinus), sable antelope (Hippotragus niger), greater kudu (Tragelaphus strepsiceros), and common gray duiker (Sylvicapra grimmia) in South Africa whose deaths were attributed to either theileriosis or cytauxzoonosis. We developed Theileria species-specific probes used in combination with reverse line blot hybridization assays and identified three different species of Theileria in four African antelope species. The close phylogenetic relationship between members of the genera Theileria and Cytauxzoon, similarities in the morphologies of developmental stages, and confusion in the literature regarding theileriosis or cytauxzoonosis are discussed.