Multilocus genotyping of Theileria parva isolates associated with a live vaccination trial in Kenya provides evidence for transmission of immunizing parasites into local tick and cattle populations

Abstract

The live infection and treatment (ITM) vaccination procedure using the trivalent Muguga cocktail is increasingly being used to control East Coast fever, with potential implications for Theileria parva population genetic structure in the field. Transmission of the Kiambu V T. parva component to unvaccinated cattle has previously been described in Uganda. We monitored the T. parva carrier state in vaccinated and control animals on a farm in West Kenya where an ITM stabilate derived from the Kenyan T. parva Marikebuni stock was evaluated for field efficacy. A nested PCR‐based Marikebuni‐specific marker identified a carrier state in nine of ten vaccinated animals, detectable for a period of two years. We used 22 variable number tandem repeat (VNTR) markers to determine multilocus genotypes (MLGs) of 19 T. parva schizont‐infected lymphocyte isolates derived from cattle and field ticks. Two isolates from unimmunized cattle were identical to the Marikebuni vaccination stock. Two cattle isolates were identical to a Muguga cocktail component Kiambu V. Seven isolates from ticks exhibited MLGs that were identical to the Serengeti/Muguga vaccine stocks. Six cattle and two tick‐derived stocks exhibited unique MLGs. The data strongly suggest transmission of immunizing genotypes, from Marikebuni vaccine‐induced carrier cattle to unimmunized cattle. It is possible that genotypes similar to those in the Muguga cocktail are present in the field in Western Kenya. An alternative hypothesis is that these parasites may have originated from vaccine trial sites in Eastern Uganda. If correct, this suggests that T. parva stocks used for immunization can potentially be disseminated 125 km beyond the immediate vaccination site. Regardless of their origin, the data provide evidence that genotypes similar to those in the Muguga cocktail are circulating in the field in East Africa, alleviating concerns about dissemination of ‘alien’ T. parva germplasm through live vaccination.

Genetic Diversity and Sequence Polymorphism of Two Genes Encoding Theileria parva Antigens Recognized by CD8+ T Cells among Vaccinated and Unvaccinated Cattle in Malawi

“…This demonstrates the transmission of the Kiambu 5 vaccine strain to unvaccinated cattle [12,13]. It has also been documented that the T. parva Marikebuni vaccine strain can also be transmitted to unvaccinated cattle [34]. Despite the MC being made up of three strains, we could not obtain sequences related to the Serengeti-transformed.…”

Sequence diversity of cytotoxic T cell antigens and satellite marker analysis of Theileria parva informs the immunization against East Coast fever in Rwanda

“…In order to implement an effective immunization programme against T. parva in regions that lack such programmes and to prevent occurrences such as the ECF outbreak in the Comoros Islands [ 47 ], it is imperative to conduct studies that provide information on the strains of T. parva present in that particular region [ 28 ] prior to introduction of ITM. This approach is favored because T. parva immunization only provides strain specific protection and transmission of vaccine components to unvaccinated animals has been shown to occur [ 29 , 48 – 50 ], consequently introducing new strains to a region and setting the platform on which recombination with local strains might occur, producing new parasite strains and thus causing disease. Furthermore, immunization against T. parva introduces carrier status in the immunized animals and these might also act as sources of future infection.…”

Characterization of a Novel Chimeric Theileria parva p67 Antigen Which Incorporates into Virus-like Particles and Is Highly Immunogenic in Mice

“…The current ITM vaccination regime against ECF is problematic and can cause the spread of the disease to previously unaffected regions [12]. A novel vaccine that does not involve the use of live parasites is therefore desperately needed.…”

“…This provides effective protection but has many disadvantages: these include the use of cattle, rabbits and ticks for the generation and extensive quality control of vaccine sporozoites; transport of live parasites in liquid nitrogen, which requires a cold chain, and the fact that the vaccine is lethal if the appropriate antibiotic dosage is not administered [2,11]. Furthermore, ITM-vaccinated cattle become T. parva carriers, which can spread the parasite to unvaccinated animals and introduce ECF into previously naïve regions [12,13].…”