Immunization of cattle with a Theileria parva bovis stock from Zimbabwe protects against challenge with virulent T.p. parva and T.p. lawrencei stocks from Kenya

Following inoculation of 34 Bos indicus (Boran) cattle with a Theileria parva bovis (Boleni) stock from Zimbabwe, 18 animals underwent mild theilerial reactions, 12 underwent moderate reactions, three suffered severe reactions and one died. When these animals were subsequently challenged with different virulent stocks of either T.p. parva (Muguga, Marikebuni or Mariakani) or T.p. lawrencei (Ngong 1 or Nanyuki) from Kenya, all except two animals resisted challenge. The two reactors were part of the group challenged with the T.p. parva (Mariakani) stock. All 12 susceptible control animals underwent severe reactions and 11 died. The results of these experiments suggest that T.p. bovis (Boleni) may be used in some situations to immunize cattle against East Coast fever without the need to provide concomitant chemotherapy as in the infection and treatment method of immunization.     

Immunization against East Coast fever: the use of selected stocks of Theileria parva for immunization of cattle exposed to field challenge

Two antigenically different stocks of Theileria parva parva (Kilifi and Marikebuni), previously characterized as belonging to groups A and C respectively on monoclonal antibody (MAb) profiles, were selected for immunization of different breeds of cattle against East Coast fever (ECF) by the infection and treatment method. A total of 52 immunized cattle and 33 susceptible controls of different group sizes were exposed to field challenge by ticks for periods of 42-90 days at three field sites where ECF is endemic on the Kenyan coast. All immunized cattle survived ECF challenge, but 87% of the controls died of the disease. The cattle exposed at one site had been immunized 1 year earlier and maintained tick-free in the intervening period. The level of immunity in these cattle was similar to that of cattle which had been immunized 1 or 2 months prior to exposure. Thus, immunity had not waned over the 1-year period. A study at another site showed that acaricidal treatment of immunized cattle could be safely extended from twice a week to once every three weeks, whereas in susceptible cattle even twice weekly spraying did not control ECF. The isolates made from infected controls during the trials indicated the presence of three T. p. parva stocks as defined by MAb profiles. Of the two stocks used for immunization, T. p. parva Marikebuni induced broader protection. In view of the apparent limited antigenic diversity of T. p. parva strains within the Coast Province it is suggested that the Marikebuni stock might represent a key stock for vaccination in this area.     

Age resistance to Theileria parva bovis infection in calves

Data collected in the Zimbabwean province of Mashonaland-West, in the period 1980-1988, showed that mortality in calves owing to Theileria parva bovis infection (January disease) was significantly lower in animals younger than 7 months than in older cattle. Groups of seven Holstein-Friesian calves from non-immune dams aged approximately 1, 4, 7, 10 and 13 months were infected with a Theileria parva bovis tick-derived stabilate. The dose chosen was lethal for 40% of the calves in the trial. Mortality was highest in the 4-month age group. The reactions in the 7-, 10- and 13-month age groups became progressively milder. The reactions in the 1-month old calves were the least marked, being very mild. The age-related resistance in the youngest calves, as can be concluded from our results, is only of short duration and cannot explain the lower incidence of January disease observed in calves in the field.     

Clinical features associated with seroconversion to Anaplasma marginale, Babesia bigemina and Theileria parva infections in African cattle under natural tick challenge

A longitudinal study was conducted in Southeast Uganda for 14 months on 640 Zebu cattle kept under natural tick challenge, with a view to identifying clinical features for prediction of seroconversion to Anaplasma marginale, Babesia bigemina and Theileria parva infections. Physical examination, condition scoring and tick counts were undertaken on all cattle every 4 weeks. In addition, 5300 sera were collected and analysed for antibodies against A. marginale, B. bigemina and T. parva infections using the enzyme-linked immunosorbent assay (ELISA). The major clinical features compiled included weight loss, fever (rectal temperature), anaemia (packed cell volume), pallor of mucous membranes, lymph node enlargement, staring coat, diarrhoea and lacrymation. The risk factors included tick challenge at village level, sex, age, Rhipicephalus spp. density and Boophilus spp. density on individual animals. Using a binary logistic regression model, the clinical features and risk factors were analysed. The results suggest that increasing rectal temperature was associated with increased probability for seroconversion to A. marginale, while high level of Rhipicephalus spp. density and increasing packed cell volume (PCV) were significantly associated with reduced probability of seroconversion. Although statistically significant, none of the factors had large effects, with odds ratios (OR) of 0.87, 1.15 and 0.98 for Rhipicephalus spp. density, rectal temperature and PCV, respectively. For B. bigemina infection, a high level of Boophilus spp. density, anaemia and staring coat were significantly associated with increased probability of seroconversion (OR 1.50, 1.78, 1.37, respectively). Presence of lacrymation and old age were associated with reduced probability of seroconversion (OR 0.52, 0.86 respectively). For T. parva infection, lymph node enlargement (OR 1.30) was associated with increased probability of seroconversion, while high Rhipicephalus spp. density and increasing packed cell volume (PCV) were associated with reduced probability of seroconversion (OR 0.68 and 0.98, respectively). In conclusion, presence and intensity of the respective tick vectors for tick-borne diseases, age and clinical features such as anaemia, fever, staring coat, lymph node enlargement and lacrymation are indicators for seroconversion to A. marginale, B. bigemina and T. parva infections in cattle. These indicators for seroconversion could be exploited in the development of decision support tools for clinical diagnosis of tick-borne diseases.     

Exposure of cattle immunized with different stocks of Theileria parva to buffalo-associated Theileria challenge on two game parks in Zimbabwe.

Eight cattle immunized with cattle-derived Theileria parva Boleni stabilate together with six susceptible controls were released in Dombawera Game Park on the Highveld of Zimbabwe. This coincided with Rhipicephalus appendiculatus nymphal activity. The cattle grazed together with African buffaloes (Syncerus caffer) and were not treated against tick infestation. The nymphal tick infestation was high, and seven of the eight immunized cattle and three of the controls had severe and fatal reactions. Subsequently, two stocks of Theileria parva to be tested for their immunizing abilities were prepared-one from adult ticks which were fed as nymphs on one of the sick control animals (Dom 268) and the other from adult ticks collected from pastures grazed by buffaloes (Bv-1). Two groups of cattle were immunized with either the Dom 268-derived strain (eight animals) or the Bv-1-derived strain (four animals). These together with three non-immunized controls, were released in Bally Vaughaun Game Park in the Highveld, where buffaloes are present, during the season of nymphal tick activity. A third group of five cattle, immunized with stabilate Bv-1, and three non-immunized controls were released at the same site during the season of adult tick activity. The nymphal and adult tick infestations of the cattle were large and more than 2000 nymphs and 1000 adult ticks were counted per animal. Cattle were treated with a pyrethroid pour-on preparation to control the tick infestation and screw-worm strike. The immunized cattle in the three groups survived the theileriosis challenge for a period of 18 months, but the non-immunized control cattle suffered a severe and fatal theileriosis 19-23 days after being placed on the pasture.     

Immunization of cattle against East Coast fever using Theileria parva (Marikebuni) and relaxation of tick control in North Rift, Kenya.

A total of 90 animals was immunized against East Coast fever (ECF) using Theileria parva (Marikebuni) stock on three large-scale farms in Kiminini Division, Trans-Nzoia District, North Rift, Kenya. Another 90 cattle served as non-immunized controls. Following immunization the number of cattle with significant indirect fluorescent antibody (IFA) titres increased from 43.9% to 84.4% and 6.7% of the cattle developed clinical ECF reactions. Two months after immunization, the immunized and non-immunized cattle were divided into two groups one of which was dipped every 3 weeks and the other dipped when total full body tick counts reached 100. All the animals were monitored for 51 weeks for incidences of ECF and other tick-borne diseases. Twenty-four cases of ECF were diagnosed among the non-immunized cattle compared to four cases among the immunized cattle; a difference that was significant (P > 0.05). There was no significant difference in the incidences of babesiosis and anaplasmosis between the immunized and non-immunized cattle.     

Chemotherapy of Theileria parva lawrencei infections in cattle with halofuginone

Halofuginone lactate, given once orally at a dosage rate of 1,2 mg/kg body mass on the 1st, 3rd or 5th days of fever, resulted in the recovery of only 1 out of 5 splenectomized cattle. Three splenectomized animals, treated on the 1st as well as the 4th day of fever, recovered and were then carriers. Six untreated controls all died. The potential value of a chemotherapeutic agent for Theileria parva lawrencei infections in South Africa is discussed.     

Failure of a recombinant Babesia bovis antigen to protect cattle against heterologous strain challenge

Groups of cattle were inoculated subcutaneously with (i) a recombinant DNA-derived Babesia bovis protein (KaBbl-GZ) fused to beta-galactosidase and combined with adjuvants, or (ii) native beta-galactosidase (GZ) plus adjuvant, or (iii) adjuvant only or (iv) a live, attenuated B bovis vaccine. KaBbl-GZ was produced in the lambda gt11-amp3 system as a 5-10 kD babesial polypeptide linked to GZ. KaBbl has previously been shown to be an immunodominant antigen of B bovis, localised at the apex of the parasite, and present in a range of B bovis strains. High levels of GZ antibodies were observed in KaBbl-GZ and GZ inoculated cattle, but specific KaBbl antibodies could not be detected by ELISA. Five months after primary inoculation, all cattle were blood challenged with a virulent heterologous B bovis strain. Despite four inoculations with KaBbl-GZ, significant protection against the challenge was not observed.     

Cloned Theileria parva produces lesser infections in ticks compared to uncloned T. parva despite similar infections in cattle

Experimental transmissions of cloned Theileria parva in cattle with Rhipicephalus appendiculatus ticks were compared to transmissions with uncloned T. parva during studies on the potential for genetic recombination during syngamy of Theileria to produce antigenic diversity for evasion of bovine immunity. Prevalence and abundance of T. parva infection in adult ticks, which resulted from the feeding of nymphs on the calves, were significantly higher in the uncloned compared to the cloned T. parva. Development of sporoblasts of T. parva in the ticks to produce infective sporozoites was similar. There was no statistically significant difference in the clinical course of infection in cattle between cloned and uncloned T. parva. It was concluded that cloned T. parva has characteristics that reduce its viability during the tick stages of its life cycle.     

Cellular immunity against Theileria parva and its influence on parasite diversity

Theileria parva, a tick-borne parasite of African cattle, causes a fatal disease known as East Coast fever. Cattle that recover from the disease develop strong parasite-specific MHC-class I-restricted cytotoxic T-lymphocyte responses. Protection can be transferred between immune and na?ve calves in the CD8+ T cell fraction emanating from a responding lymph node. In vitro studies suggest that this response requires input from activated CD4+ T cells. The T parva life cycle involves developmental stages in mammalian and tick hosts and can lead to a number of different endemic scenarios for the disease. These range from a stable situation with high prevalence of herd infection, but low fatality rates, to a low prevalence/high fatality scenario. The impact on endemic stability is an important consideration for the design of vaccine implementation strategies. For subunit vaccines targeted at T parva schizonts, the principal issue in this regard is whether development of the piroplasm stage is blocked by immunity.     

Some preliminary observations on the susceptibility and resistance of different cattle breeds to Theileria parva infection

Theileria parva-na?ve Friesian (Bos taurus), Boran (Bos indicus) and Maasai Zebu steers (B. indicus) were infected with a T. parva sporozoite stabilate dose which had previously been shown to induce an estimated 50% mortality rate in Boran cattle. All the cattle developed patent infections with no significant differences in the length of the prepatent period to development of macroschizonts (P > 0.05) between the three groups. Clinical theileriosis occurred in all eight the Friesians (100%), five out of nine Borans (55.6%) and two out of five Zebus (40%). Three of the Friesians (37.5%), and two of the Borans (22.2%) died of theileriosis. The different cattle types were equally susceptible to the infective dose used as indicated by the length of the prepatent periods, but there was a marked difference in their development of clinical theileriosis. The gradation in resistance to disease confirms the findings of earlier less critical studies and identifies these cattle breeds as suitable for investigations into the mechanisms of resistance to theileriosis.     

Comparison of indirect fluorescent antibody test and enzyme linked immunosorbent assay in the detection of exposure of cattle to Theileria parva in Kenya.

Appraisal of the indirect fluorescent antibody test (IFAT) and antigen enzyme linked immunosorbent assay (ELISA) serological tests as carried out to detect cattle exposed to Theileria parva at the National Veterinary Research Centre, Muguga (NVRC), Kenya is reported. Using sera from T. parva naive cattle and cattle experimentally exposed to T. parva, the two tests were appraised in terms of their sensitivity and specificity. IFAT and ELISA had the same sensitivity of 90% while ELISA had a higher specificity (90%) than IFAT (80%). A comparison was also made of the capability of the two tests to detect exposure of dairy cattle to T. parva prior to immunization against East Coast fever (ECF). The positive outcome from the IFAT was significantly higher (chi 2 = 30.36; P < 0.001) than that from the ELISA. The agreement between the two tests was low (Kappa = 0.21). The two tests indicated a higher risk of ECF in the study area than was expected. Indications are that the ELISA has been effectively adopted at NVRC.     

Environment and farm factors associated with exposure to Theileria parva infection in cattle under traditional mixed farming system in Mbeere District,Kenya

The objective of this study was to investigate the relationship between seroprevalence to Theileria parva infection in cattle and potential environmental and farm-level effects in 80 farms under traditional crop–livestock system in Mbeere District, Kenya. A standardized questionnaire was used to collect the effects characteristics as related to T. parva infection epidemiology. Serum samples were collected from 440 cattle of all ages for detection of T. parva antibodies by the enzyme-linked immunosorbent assay technique. The association between the variables was assessed using a generalized estimation equation logistic regression model. The overall T. parva seroprevalence, accounting for correlation of responses, was 19.3% (95% confidence interval (CI) 14%, 25%). Two variables, “administrative division” and “presence of the vector tick on the farm”, were significantly associated with the T. parva seroresponse. Respectively, cattle from farms in Gachoka, Evurore, and Mwea divisions were (and their 95% CI) 1.3 (0.36, 4.8), 4.4 (1.2, 15.9), and 15.2 (4.9, 47.1) times more likely to be seropositive relative to those from Siakago Division (P = 0.000). Cattle from farms in which the vector tick was present were 2.9 (1.2, 6.7) times more likely to be seropositive (P = 0.011). Results of this study suggested that both environmental and farm factors may be associated with T. parva infection epidemiology in Mbeere District. Under such circumstances, characterization of environmental suitability for the vector tick and corresponding environment-specific farm management practices in the district is required both for improved understanding of the disease and in planning disease control programs.     

Clinical and diagnostic features of East Coast fever (Theileria parva) infection of cattle

East Coast fever is a tick-borne protozoal disease affecting cattle in a large part of East and Central Africa. Since the vector occurs over an even wider range there is considerable potential for the disease to spread to countries which are currently disease free. This article, describing the clinical and diagnostic features of East Coast fever, may remind authorities in these countries of the potential hazards posed by the disease.     

In vivo comparison of susceptibility between Bos indicus and Bos taurus cattle types to Theileria parva infection

The objective of this study was to determine whether Bos taurus cattle differ form Bos indicus in their susceptibility to infection with the Muguga stabilate of Theileria parva and in their resistance to the resultant disease. Ten Friesians (B. taurus), ten improved Borans (B. indicus), ten unimproved Borans (B. indicus) and ten Zebus (B. indicus) born to dams from an East Coast fever (ECF) endemic area were inoculated with an infective dose50 dilution of T. parva Muguga stabilate 147. All the animals except one Friesian and one Zebu developed schizont parasitosis. All the improved Borans, nine of the Friesians, eight of the unimproved Borans and six of the Zebus developed a febrile response. Four of the improved Borans, four of the Friesians and three of the unimproved Borans died of theileriosis. No significant difference (P > 0.05) in the prepatent period occurred between the groups, but the Zebus had a significantly shorter duration of schizont parasitosis (P > 0.05) and took a significantly shorter time to recover (P > 0.05) than the other three groups. There was no significant difference in the two parameters between the other three groups. The study showed that three B. indicus breds and a B. taurus breed are equally susceptible to T. parva infection. However, Zebus born to dams from an ECF endemic area showed a better ability to control the course of disease than cattle from ECF free areas.     

Laboratory and field investigations into the Theileria parva carrier-state in cattle in Zimbabwe.

The Theileria parva carrier-state in cattle on commercial farms on Zimbabwe was investigated using parasitological and serological methods. The proportion of cattle showing Theileria piroplasms on two farms, which had recent histories of disease outbreaks, were 64% (n = 106, total of heifers and weaned calves examined) and 71.5% (n = 60) while the proportion of T. parva antibodies for the same animals were 59% and 98.5%, respectively. On four farms where no cases of the disease occurred for over 10 years, the average proportion of animals showing piroplasms and antibodies were 55.4% (range 32-82, n = 223) and 73% (range 47-91, n = 223), respectively. However, on another three farms which had no history of theileriosis outbreaks these proportions were very low, being 11.4% (0-24, n = 157) for piroplasms and 12.2% (5-23, n = 157) for antibodies. The mean infection rate in unfed Rhipicephalus appendiculatus adults collected from farms with a high prevalence of cattle which were carriers of Theileria piroplasms during the tick activity season was 29% (range 12-60%) with 9.3 (range 2-18.7) mean infected acini per infected tick. The infectivity of different tick batches to susceptible cattle produced a wide spectrum of theileriosis reactions. Laboratory controlled experiments were carried out to study the persistence of T. parva (Boleni) piroplasms in cattle immunized with this strain as well as its infectivity for ticks and its subsequent transmissibility to cattle. Examination of the salivary glands of 15 batches of ticks collected from six immunized cattle on three different occasions over 18 months showed that none were infected with Theileria parasites. However, the infectivity of other ticks in the same batches to susceptible animals was demonstrated 6, 10 and 18 months after cattle had been immunized with Boleni stabilate.