Transmission of Theileria parva in the traditional farming sector in the Southern Province of Zambia during 1997-1998

p67 gene alleles sequence analysis reveals Theileria parva parasites associated with East Coast fever and Corridor disease in buffalo from Zambia

Theileriosis caused by Theileria parva infections is responsible for high cattle mortalities in Zambia. Although infected buffalo are a risk to cattle, the characterization of T. parva parasites occurring in this host in Zambia has not been reported. Furthermore, considering the advances in the development of a p67 subunit vaccine, the knowledge of p67 genetic and antigenic diversity in both cattle and buffalo associated T. parva is crucial. Therefore, blood samples from buffalo (n=43) from Central, Eastern and Southern provinces, and cattle (n=834) from Central, Copperbelt, Eastern, Lusaka, and Southern provinces, were tested for T. parva infection and the parasites characterized by sequencing the gene encoding the p67 antigen. About 76.7 % of buffalo and 19.3 % of cattle samples were PCR positive for T. parva. Three of the four known p67 allele types (1, 2 and 3) were identified in parasites from buffalo, of which two (allele types 2 and 3) are associated with T. parva parasites responsible for Corridor disease. Only allele type 1, associated with East Coast fever, was identified from cattle samples, consistent with previous reports from Zambia. Phylogenetic analysis revealed segregation between allele type 1 sequences from cattle and buffalo samples as they grouped separately within the same sub-clade. The high occurrence of T. parva infection in buffalo samples investigated demonstrates the risk of Corridor disease infection, or even outbreaks, should naïve cattle co-graze with infected buffalo in the presence of the tick vector. In view of a subunit vaccine, the antigenic diversity in buffalo associated T. parva should be considered to ensure broad protection. The current disease control measures in Zambia may require re-evaluation to ensure that cattle are protected against buffalo-derived T. parva infections. Parasite stocks used in 'infection and treatment' immunization in Zambia, have not been evaluated for protection against buffalo-derived T. parva parasites currently circulating in the buffalo population.

Seasonal occurrence of Theileria parva infection and management practices amongst Maasai pastoralist communities in Monduli District, Northern Tanzania

Theileria parva causes an economically devastating tick-borne disease called East Coast fever (ECF), which affects cattle in central, eastern and southern Africa. Determination of seasonal infection rates for T. parva is crucial for epidemiological understanding and for strengthening ECF management practices. However, this information is lacking for most pastoralist areas with high livestock density, such as the Monduli District in the Maasai steppe, northern Tanzania. A cross-sectional study was carried out to estimate the prevalence of T. parva in wet and dry seasons, and to assess understanding of management practices associated with T. parva amongst pastoralists' cattle. A total of 960 cattle owned by 130 pastoralists were randomly selected from ten study villages in each season and blood samples analysed for T. parva prevalence using a nested polymerase chain reaction (PCR). Seroprevalence for T. parva in the wet season was assessed using an enzyme-linked-immunosorbent assay (ELISA). Information on relevant management practices was gathered using a standardized questionnaire. Multivariable logistic regression was used to evaluate the association between T. parva parasitaemia and animal, farm and village-level factors. The prevalence of T. parva parasitaemia was 15.9% (95% CI=0.13-0.19) and 31.6% (95% CI=0.28-0.36) in wet and dry seasons, respectively. All cattle were sero-positive. T. parva parasitaemia was significantly associated with age of the animal, sampling season, and study village. All 130 cattle owners interviewed (100%) reported that they could easily recognise ECF and the vast majority (97.7%) identified swollen lymph nodes as the most prominent sign. At least 70% reported to understand the involvement of R. appendiculatus in ECF transmission. The use of both commercial drugs and herbal medicines for ECF treatment was reported by 54.6% of cattle owners. Among commercial drugs reported, the most commonly used was alamycin 300mg/ml (oxytetracycline dehydrates). Tick control by hand spraying was reported by the majority (90.8%) of cattle owners and less than half (45.4%) reported to vaccinate their cattle. This research provides evidence of widespread T. parva infection across Monduli District, and baseline information on seasonal occurrence. This information can assist the planning of more appropriate control strategies in pastoralist communities both now and into the future as predicted climatic changes progress in the region and potentially influence ECF occurrence and transmission.

Demonstration of differences in virulence between two Theileria parva isolates

In areas with a low incidence of infection due to unimodal presence of ticks, Theileria parva has been observed to induce a disease with relatively low pathology. This is followed by a carrier state, rather than death and therefore provides a better chance of transmission of the parasite back to the tick vector since in unimodal conditions, the different tick stages occur at different times. One isolate from such an area in Zambia, T. parva Chitongo, was compared for virulence with T. parva Muguga, isolated from an area exhibiting a continuous presence of all vector stages in East Africa. To reduce any variation due to infection dose, an in vitro standardized dose was used to initiate infection of groups of three local zebu cattle with each isolate. Parameters of virulence measured were prepatent period, fever, survival (based on ECF index), parasitosis, piroplasm parasitaemia and hematological parameters. Our results suggest that T. parva Chitongo developed a slightly later onset (1-2 days) and lower levels of parasitosis in the lymph node, causing less and later mortality. Comparison of the in vitro rate of transformation confirmed that the time needed to transform an infected lymphocyte took 4 days longer for T. parva Chitongo than T. parva Muguga. Elucidating the mechanism responsible for the lower virulence of T. parva Chitongo could be useful for designing an attenuated vaccine.

East Coast fever and multiple El Niño Southern oscillation ranks

East Coast fever (ECF), a tick-borne disease of cattle, is a major constraint to livestock development in Africa in general and southern Zambia in particular. Understanding the transmission patterns of this disease complex is very difficult as shown by previous studies in southern and eastern Zambia due to the interplay of risk factors. In this long-term study, we investigated whether global weather changes had any influence on disease transmission in traditionally kept cattle in southern Zambia. The results from this study show a strong association between increased Theileria parva contacts in cattle and the presence of El Niño, clearly linking a simple climatic index to disease outbreaks. We therefore propose that in southern Zambia, the simple and readily available multiple El Niño Southern oscillation index (MEI) ranks be used in planning ECF control programmes and early warning.

Survival of unfed Rhipicephalus appendiculatus and Rhipicephalus zambeziensis adults

Two ixodid tick species, Rhipicephalus appendiculatus (Neumann) and Rhipicephalus zambeziensis (Walker et al.) (Acari: Ixodidae), both originating from the southern province of Zambia, were used to study the survival time of adults at a range of different humidities and temperatures. In general, the experiment clearly demonstrates the different survival times of the two species in relation to the climatic conditions tested: survival of R. zambeziensis was better under more extreme conditions of temperature and humidity. These findings offer an explanation for the different distribution ranges of the two tick species. Rhipicephalus appendiculatus is more confined to cooler and wetter conditions, whereas R. zambeziensis is adapted to hotter and drier areas.

Theileria parva seroprevalence in traditionally kept cattle in southern Zambia and El Niño

Sero-epidemiological surveys involving 27,526 cattle over a period of 8 years show that Theileria parva, the parasite causing East Coast fever (ECF) is found throughout southern Zambia. Higher values of T. parva sero-prevalence were observed in the plateau districts of Monze, Choma and Mazabuka than in the valley districts of Siavonga and Sinazongwe. Our results reveal a strong association between high T. parva sero-prevalence and the presence of the periodic climatic phenomenon known as the El Nino Southern Oscillation. More T. parva sero-positive samples were recorded during El Nino years (1997/98) (P<0.001) than other years in the study period. From this association, we conclude that Multiple El Nino Southern Oscillation Indices can be used to predict years with high or low ECF infection prevalence thereby contributing to the improved control of ECF in the area.

Distribution and phenology of ixodid ticks in southern Zambia

Distribution data for epidemiologically important ticks (Acari: Ixodidae) in the Southern Province of Zambia, one of the main cattle areas of the country, are presented. Boophilus microplus (Canestrini) was not recorded in southern Zambia, whereas Boophilus decoloratus (Koch) is present throughout the area. New distribution patterns for less economically important ixodid ticks are also discussed. Southern Zambia is a transition zone because it is the most northern area in Africa where mixed Rhipicephalus appendiculatus Neumann and Rhipicephalus zambeziensis Walker, Norval & Corwin populations were reported. Although a second generation of adult R. appendiculatus/R. zamnbeziensis was encountered, simulations indicated that this phenomenon is very rare in southern Zambia, mainly because of the colder temperatures during the early dry season and lower rainfall. These simulations were supported by a development trial under experimental conditions. Tick body size measurements showed that southern Zambian ticks are larger than eastern Zambian R. appendiculatus. It is hypothesized that body size is related to diapausing intensity in this species. The epidemiological consequences are that a different approach to control Theileria parva (Theiler) (Piroplasmida: Theileriidae) and other tick-borne diseases is needed in southern Zambia, compared to the one adopted in eastern Zambia.