Antibody-blocking of a tick transporter impairs Anaplasma phagocytophilum colonization in Haemaphysalis longicornis ticks

The invasive Asian longhorned tick Haemaphysalis longicornis that vectors and transmits several animal pathogens is significantly expanding in the United States. Recent studies report that these ticks also harbor human pathogens including Borrelia burgdorferi sensu lato, Babesia microti, and Anaplasma phagocytophilum. Therefore, studies that address the interactions of these ticks with human pathogens are important. In this study, we report the characterization of H. longicornis organic anion-transporting polypeptides (OATPs) in interactions of these ticks with A. phagocytophilum. Using OATP-signature sequence, we identified six OATPs in the H. longicornis genome. Bioinformatic analysis revealed that H. longicornis OATPs are closer to other tick orthologs rather than to mammalian counterparts. Quantitative real-time PCR analysis revealed that OATPs are highly expressed in immature stages when compared to mature stages of these ticks. In addition, we noted that the presence of A. phagocytophilum upregulates a specific OATP in these ticks. We also noted that exogenous treatment of H. longicornis with xanthurenic acid, a tryptophan metabolite, influenced OATP expression in these ticks. Immunoblotting analysis revealed that antibody generated against Ixodes scapularis OATP cross-reacted with H. longicornis OATP. Furthermore, treatment of H. longicornis with OATP antibody impaired colonization of A. phagocytophilum in these ticks. These results not only provide evidence that the OATP-tryptophan pathway is important for A. phagocytophilum survival in H. longicornis ticks but also indicate OATP as a promising candidate for the development of a universal anti-tick vaccine to target this bacterium and perhaps other rickettsial pathogens of medical importance.

Molecular detection and characterisation of protozoan and rickettsial pathogens in ticks from cattle in the pastoral area of Karamoja, Uganda

Ticks and tick-borne diseases (TBDs) significantly affect cattle production and the livelihoods of communities in pastoralist areas. Data on protozoan and rickettsial pathogens in ticks infesting cattle in Uganda is scanty; while it is an indicator of the likelihood of disease transmission and occurrence. A cross-sectional study was conducted amongst cattle in the Karamoja Region, northeastern Uganda, from July through September 2017, to determine the tick species diversity, identify protozoan and rickettsial pathogens in the ticks, and characterise pathogenic species by sequence and phylogenetic analyses. About 50 % of the ticks detected from each predilection site on each animal were collected from 100 purposively-selected cattle from 20 randomly-selected herds. Twelve tick species belonging to the genera Amblyomma, Rhipicephalus and Hyalomma were identified, the most abundant being Amblyomma lepidum (93.9 %), followed by Amblyomma variegatum (2.0 %) and Rhipicephalus evertsi evertsi (1.0 %). Tick species that have not been reported in recent studies amongst cattle in Uganda were found, namely Rhipicephalus pravus, Rhipicephalus praetextatus and Rhipicephalus turanicus. The ticks were grouped into 40 pools, by species and location, and the reverse line blot (RLB) hybridisation assay was used to detect pathogens from the ticks. The most frequently detected tick-borne parasites were Theileria mutans, Theileria velifera and Theileria parva, each observed in 25 % (10/40) of the tick pools. Tick-borne pathogens, namely Babesia rossi, Babesia microti and Theileria sp. (sable) that are not common to, or not known to infect, cattle were identified from ticks. The gene encoding Ehrlichia ruminantium pCS20 region, the Ehrlichia and Anaplasma 16S rRNA gene, and T. parva p67 sporozoite antigen gene were amplified, cloned and sequenced. Seven novel E. ruminantium pCS20 variants were identified, and these grouped into two separate clusters with sequences from other parts of Africa and Asia. The T. parva p67 sequences were of the allele type 1, and parasites possessing this allele type are commonly associated with East Coast fever in eastern Africa. Analysis of the Ehrlichia and Anaplasma 16S rRNA gene sequences showed that they were closely related to Rickettsia africae and to a new Ehrlichia species variant recently found in China. Our R. africae 16S rRNA sequences grouped with R. africae isolates from Nigeria, Egypt and Benin. The information on tick species diversity and pathogens in the various tick species provides an indicator of potential transmission amongst cattle populations, and to humans, and can be useful to estimate disease risk and in control strategies.

Limited diversity in the CD8+ antigen-coding loci in Theileria parva parasites from cattle from southern and eastern Africa

Theileria parva infections in cattle causes huge economic losses in the affected African countries, directly impacting the livelihood of the poor small-holder farmers. The current immunization protocol using live sporozoites in eastern Africa, is among the control measures designed to limit T. parva infections in cattle. However, the ability of the immune protection induced by this immunization to protect against field parasites has been compromised by the diversity of the parasite involving the schizont antigen genes. Previous studies have reported on the antigenic diversity of T. parva parasites from southern and eastern Africa, however, similar reports on T. parva parasites particularly from cattle from southern Africa remains scanty, due to the self-limiting nature of Corridor disease. Thus, we evaluated the diversity of CD8+ T-cell regions of ten schizont antigen genes in T. parva parasites associated with Corridor disease and East Coast fever (ECF) from southern and eastern Africa respectively. Regions of schizont antigen (TpAg) genes containing the CD8+ T-cell epitopes (CTL determinants) were amplified from genomic DNA extracted from blood of T. parva positive samples, cloned and sequenced. The results revealed limited diversity between the two parasite groups from cattle from southern and eastern Africa, defying the widely accepted notion that antigen-encoding loci in cattle-derived parasites are conserved, while in buffalo-derived parasites, they are extensively variable. This suggests that only a sub-population of parasites is successfully transmitted from buffalo to cattle, resulting in the limited antigenic diversity in Corridor disease parasites. Tp4, Tp5, Tp7 and Tp8 showed limited to absence of diversity in both parasite groups, suggesting the need to further investigate their immunogenic properties for consideration as candidates for a subunit vaccine. Distinct and common variants of Tp2 were detected among the ECF parasites from eastern Africa indicating evidence of parasite mixing following immunization. This study provides additional information on the comparative diversity of TpAg genes in buffalo- and cattle-derived T. parva parasites from cattle from southern and eastern Africa.

Microsatellite and minisatellite genotyping of Theileria parva population from southern Africa reveals possible discriminatory allele profiles with parasites from eastern Africa

The control of Theileria parva, a protozoan parasite that threatens almost 50% of the cattle population in Africa, is still a challenge in many affected countries. Theileria parva field parasites from eastern Africa, and parasites comprising the current live T. parva vaccine widely deployed in the same region have been reported to be genotypically diverse. However, similar reports on T. parva parasites from southern Africa are limited, especially in Corridor disease designated areas. Establishing the extent of genetic exchange in T. parva populations is necessary for effective control of the parasite infection. Twelve polymorphic microsatellite and minisatellite loci were targeted for genotypic and population genetics analysis of T. parva parasites from South Africa, Mozambique, Kenya and Uganda using genomic DNA prepared from cattle and buffalo blood samples. The results revealed genotypic similarities among parasites from the two regions of Africa, with possible distinguishing allelic profiles on three loci (MS8, MS19 and MS33) for parasites associated with Corridor disease in South Africa, and East Coast fever in eastern Africa. Individual populations were in linkage equilibrium (V_D<L), but when considered as one combined population, linkage disequilibrium (V_D>L) was observed. Genetic divergence was observed to be more within (AMOVA = 74%) than between (AMOVA = 26%) populations. Principal coordinate analysis showed clustering that separated buffalo-derived from cattle-derived T. parva parasites, although parasites from cattle showed a close genetic relationship. The results also demonstrated geographic sub-structuring of T. parva parasites based on the disease syndromes caused in cattle in the two regions of Africa. These findings provide additional information on the genotypic diversity of T. parva parasites from South Africa, and reveal possible differences based on three loci (MS8, MS19 and MS33) and similarities between buffalo-derived T. parva parasites from southern and eastern Africa.

Molecular characterization of live Theileria parva sporozoite vaccine stabilates reveals extensive genotypic diversity

The current Infection and Treatment Method of vaccination against East Coast fever comprises an inoculation of live Theileria parva sporozoites and simultaneous administration of oxytetracycline. Immunization with a combination of parasite types has been shown to provide broader protection than inoculation of individual strains. In this study, we used a high-throughput capillary electrophoresis system to determine the genotypic composition of the Muguga Cocktail, a widely used vaccine stabilate derived from three seed stabilates-Muguga, Serengeti-transformed and Kiambu 5. Five satellite markers were used to genotype the vaccine and reference stabilates from two commercial-scale preparations of the vaccine. In addition, 224 cloned cell lines established by infection of bovine lymphocytes with T. parva parasites from the component stabilates were genotyped. The results indicate that, for the recently prepared batch, there are at least eight genotypes in each of the Muguga and the Serengeti-transformed stabilates, while parasites from the Kiambu 5 stabilate showed no diversity at the five loci. The Serengeti-transformed stabilate contained parasites of the Kiambu 5 genotype and of two genotypes present in the Muguga stabilate, whereas there were no genotypes common to the Muguga and Kiambu 5 stabilates. When stabilates from the two vaccine batches were compared, no allelic variations were identified between the Muguga and Kiambu 5 parasites, while lack of sufficient clones prevented a full comparison of the Serengeti-transformed stabilates. The findings will facilitate examination of the extent to which the vaccine strains become resident in areas under vaccination, the identification of 'breakthrough' strains and the establishment of the quality assurance protocols to detect variations in the production of the vaccine. The cloned cell lines will be useful for further understanding the antigenic diversity of parasites in the vaccine.