Infection and treatment method (ITM) vaccine against East Coast fever: reducing the number of doses per straw for use in smallholder dairy herds by thawing, diluting and refreezing already packaged vaccine

A single exon-encoded Theileria parva strain Muguga cysteine protease (ThpCP): Molecular modelling and characterisation

The tick-transmitted apicomplexan Theileria parva causes East Coast fever, a bovine disease of great economic and veterinary importance in Africa. Papain-like cysteine proteases play important roles in protozoan parasite host cell entry and egress, nutrition and host immune evasion. This study reports the identification and characterisation of a T. parva strain Muguga cathepsin L-like (C1A subfamily) cysteine protease (ThpCP). Molecular modelling confirmed the papain-like fold of ThpCP, hydrophobic character of the S2 substrate binding pocket and non-covalent interaction between the pro- and catalytic domains preceding low pH autoactivation. ThpCP was recombinantly expressed in a protease deficient E. coli (Rosetta (DE3)pLysS strain) expression host as a 46 kDa proenzyme. Following Ni-chelate affinity chromatography and acidification, the 27 kDa mature ThpCP was purified by cation-exchange chromatography. Purified ThpCP hydrolysed typical cathepsin L substrates N-α-benzyloxycarbonyl (Z)-Phe-Arg-7-amino-4-methyl-coumarin (AMC) (k_cat/K_m = 4.49 × 10⁵ s^-1M^-1) and Z-Leu-Arg-AMC (k_cat/K_m = 4.20 × 10⁵ s^-1M^-1), but showed no activity against the cathepsin B-selective substrate Z-Arg-Arg-AMC. Recombinant ThpCP was active over a broad pH range from pH 4.5 to 7.5, thereby showing potential activity in the acidic parasite food vacuole and close to neutral pH of the host lymphocyte cytoplasm. Recombinant ThpCP was inhibited by the cysteine protease inhibitors E64, iodoacetate, leupeptin, chymostatin, Z-Phe-Ala-diazomethylketone (DMK) and Z-Phe-Phe-DMK and hydrolysed bovine proteins: haemoglobin, immunoglobulin G, serum albumin and fibrinogen as well as goat IgG at pH 6 and 7. Functional expression and characterisation of Theileria cysteine proteases should enable high throughput screening of cysteine protease inhibitor libraries against these proteases.

Safety and Efficacy of the East Coast Fever Muguga Cocktail Vaccine: A Systematic Review

Immunisation of livestock with high quality vaccines is considered an essential approach to controlling many animal diseases. The only currently available commercial vaccine to protect cattle from East Coast fever (ECF), a tick-borne disease caused by Theileria parva, is an unconventional “infection and treatment method” (ITM) involving administration of a combination of live T. parva isolates, referred to as the “Muguga cocktail”, and simultaneous treatment with long-acting oxytetracycline. Veterinary vaccine research and development typically involves studies designed to demonstrate vaccine quality, safety, and efficacy; however, as there were no such purpose-designed registration studies conducted for the Muguga cocktail, evidence for safety and efficacy is solely based on that which is available in the clinical literature. An extensive systematic review was conducted to analyse the evidence available in the literature in order to establish the safety and efficacy of the Muguga cocktail vaccine. A combination of meta-analyses and narrative summaries was conducted. A total of 61 studies met the criteria to be included in the systematic review. The majority of studies demonstrated or reported in favour of the vaccine with regards to safety and efficacy of the Muguga cocktail vaccine. Proximity to buffalo often resulted in reduced vaccine efficacy, and reports of shed and transmission of vaccine components affected the overall interpretation of safety. Better understanding of control options for this devastating livestock disease is important for policymakers and livestock keepers, enabling them to make informed decisions with regards to the health of their animals and their livelihoods.

A review of recent research on Theileria parva: Implications for the infection and treatment vaccination method for control of East Coast fever

The infection and treatment (ITM) live vaccination method for control of Theileria parva infection in cattle is increasingly being adopted, particularly in Maasai pastoralist systems. Several studies indicate positive impacts on human livelihoods. Importantly, the first detailed protocol for live vaccine production at scale has recently been published. However, quality control and delivery issues constrain vaccination sustainability and deployment. There is evidence that the distribution of T. parva is spreading from endemic areas in East Africa, North into Southern Sudan and West into Cameroon, probably as a result of anthropogenic movement of cattle. It has also recently been demonstrated that in Kenya, T. parva derived from cape buffalo can 'breakthrough' the immunity induced by ITM. However, in Tanzania, breakthrough has not been reported in areas where cattle co-graze with buffalo. It has been confirmed that buffalo in northern Uganda national parks are not infected with T. parva and R. appendiculatus appears to be absent, raising issues regarding vector distribution. Recently, there have been multiple field population genetic studies using variable number tandem repeat (VNTR) sequences and sequencing of antigen genes encoding targets of CD8+ T-cell responses. The VNTR markers generally reveal high levels of diversity. The antigen gene sequences present within the trivalent Muguga cocktail are relatively conserved among cattle transmissible T. parva populations. By contrast, greater genetic diversity is present in antigen genes from T. parva of buffalo origin. There is also evidence from several studies for transmission of components of stocks present within the Muguga cocktail, into field ticks and cattle following induction of a carrier state by immunization. In the short term, this may increase live vaccine effectiveness, through a more homogeneous challenge, but the long-term consequences are unknown.

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.