Ehrlichia ruminantium seroprevalence in domestic ruminants in Ghana. II. Point prevalence survey.

Serum samples collected on a single occasion from cattle, sheep and goats at sites in all 10 regions of Ghana were tested for antibodies to Ehrlichia (previously Cowdria) ruminantium, the causative agent of heartwater, by polyclonal competitive ELISA (PC-ELISA). The survey revealed the presence of heartwater-exposed ruminants throughout the country, with local seroprevalence up to 100%. Seronegative, and therefore presumably susceptible, animals were also present in all regions, in some areas in numbers high enough to indicate local endemic instability. Overall seroprevalences in cattle, sheep and goats were 61, 51 and 28% respectively, and were generally higher in the northern part of the country and lower in the forest zone. Amongst animals over 1 year old, two thirds of cattle and sheep, and around one third of goats throughout the country had been exposed to E. ruminantium. In the north, seroprevalence in sheep sampled with and without cattle was similar, whereas in the south seroconversion rates in sheep were significantly higher in areas where cattle were present.

Incidence and prevalence of tick-borne haemoparasites in domestic ruminants in Ghana.

Giemsa-stained thin blood smears prepared monthly from cattle, sheep and goats in the Greater Accra region of Ghana between May 1994 and December 1996 were examined for presence of tick-borne haemoparasites. The majority of animals were less than 2 months old at the start of the survey. Monthly and cumulative incidences are presented of Anaplasma sp., Babesia bigemina, Borrelia sp., Eperythrozoon sp., Theileria mutans and Theileria velifera in cattle, Anaplasma sp., Borrelia sp., and Theileria sp. in sheep, and Anaplasma sp. in goats. T. mutans was the commonest parasite in cattle, with 100% incidence in calves by 10 months of age, and Anaplasma was commonest in small ruminants. The relative prevalence of these haemoparasites in blood smears from cattle, sheep and goats sampled on a single occasion at sites in all 10 regions of Ghana was found to be similar, though actual infection rates were lower. Packed cell volume (PCV) measurements from the sampled animals are also presented; no seasonal trends were evident in the PCV of the cattle, sheep and goats sampled monthly. In animals sampled on a single occasion, mean PCV was significantly higher in cattle and sheep without detectable haemoparasite infection, and in cattle was lowest in animals positive for both Babesia and Anaplasma, while there was no difference in mean PCV levels between parasitised and non-parasitised goats.

Ehrlichia ruminantium seroprevalence in domestic ruminants in Ghana; I. Longitudinal survey in the Greater Accra Region.

Serum samples collected monthly over a 34-month period from cattle, sheep and goats in the Greater Accra Region of Ghana were tested for antibodies to Ehrlichia (previously Cowdria) ruminantium, the causative agent of heartwater, by polyclonal competitive ELISA (PC-ELISA). Maternal antibodies, detected in about half of animals followed from under 1 month old, declined to negative levels within 2-4 months. Amblyomma variegatum tick vectors were present on livestock in rural areas throughout the year, and first seroconversion occurred at any age, although the majority of calves seroconverted between 1 and 10 months old, sheep by 11 months, and goats by 7 months. All the cattle in the study became seropositive by 20 months of age, except one animal which subsequently died of heartwater. Following seroconversion, 25% of bovine sera tested negative in the PC-ELISA. Just over half the sheep in the survey seroconverted before or during the study period; following seroconversion, less than 3% of ovine sera became PC-ELISA negative. About a quarter of the goats seroconverted, and 34% of their post-seroconversion sera tested negative in the PC-ELISA. Overall, the serology indicated that virtually all cattle on the survey farms were exposed to E. ruminantium without suffering disease, but that a substantial proportion of sheep and goats escaped exposure and thus formed a susceptible population. E. ruminantium was detected in brains of 14, 36 and 4% of cattle, sheep and goats submitted for post mortem at the Accra Veterinary Laboratory, indicating that sheep were most at risk from heartwater disease.

The association between Amblyomma variegatum and dermatophilosis: epidemiology and immunology.

A close association was found between infestation with Amblyomma variegatum and the occurrence of dermatophilosis on cattle on the coastal Plains of Ghana. Animals belonging to breeds traditionally regarded as more susceptible to the disease also tended to carry higher tick burdens. The basis of the association between infestation with this tick and the occurrence of dermatophilosis would appear to involve tick-induced immunosuppression.

Chemotherapy of dermatophilosis--a preliminary study.

In view of the unpredictability of results of antibiotic therapy of bovine dermatophilosis and following the report of successful use of 10% formalin administered intravenously at the dosage of 20 ml per 100 kg body weight, a trial was undertaken to evaluate the latter treatment in naturally-occurring dermatophilosis in a group of Friesian crossbred cattle. Group 1 animals were given only 10% formalin. Group 2 received 10% formalin and long-acting oxytetracycline (L/AO) at a dosage of 20 mg per kg body weight and Group 3 animals were given only L/AO. Treatments were repeated at intervals of four days. All animals recovered fully, the formalin only-treated ones after three treatments the L/AO-treated ones after a mean of 2.7 treatments and the combination-treated animals after a mean of 1.5 treatments. One LA/O-treated animal showed relapse after four months. This study is continuing.

Control of Amblyomma variegatum and dermatophilosis on local and exotic breeds of cattle in Ghana.

The occurrence of dermatophilosis on cattle in the tropics is closely associated with infestation by Amblyomma variegatum ticks. Animals that are more susceptible to the disease also tend to carry higher tick burdens. Longitudinal studies carried out on the Accra Plains suggest that N'Dama cattle acquire an enhanced degree of resistance to these ticks following initial exposure. Lesions on zebu-type Ghana Sanga cattle tend to be confined to the predilection feeding sites of adult A. variegatum even when relatively large numbers of ticks are present suggesting that these cattle are able to contain the effects of the tick. Further studies are required to investigate the nature of the apparent resistance of indigenous cattle to the tick and/or its effects and the potential for controlling the disease by immunoprophylaxis using tick derived immunogens. Current methods of controlling the disease depend on the control of ticks using chemical acaricides. Susceptibility to A. variegatum associated dermatophilosis varies between breeds of cattle therefore the level of tick control required is breed dependant. Rigorous tick control is necessary for the prevention of dermatophilosis on highly susceptible exotic breeds of cattle. The limited use of acaricides applied either at the predilection feeding sites of A. variegatum and/or at selected times when the level of challenge increases is sufficient to control the occurrence of the disease on indigenous cattle.

Heartwater in Ghana: implications for control of ticks.

Heartwater, an often fatal rickettsial disease of domestic ruminants transmitted by Amblyomma variegatum ticks, ranks with the A. variegatum-associated skin disease dermatophilosis as a major constraint to the upgrading of livestock productivity in Ghana. An epidemiological survey, using new diagnostic tests, is being carried out to determine the incidence and distribution of heartwater and other tickborne diseases in Ghanaian cattle, sheep and goats. Preliminary results from a longitudinal survey being carried out at sites in the Greater Accra Region indicating that although the vector ticks and the disease agent are widespread outside urban areas, not all animals are being exposed to heartwater during the first few months of life when an inverse age related resistance allows development of immunity without clinical disease. Thus a susceptible sub-population, at risk from heartwater, can exist even in areas of high tick challenge. The significance of these results for present and future tick and disease control strategies is discussed.

Lymphocyte proliferative responses and the occurrence of dermatophilosis in cattle naturally infested with Amblyomma variegatum.

The proliferative response of lymphocytes from tick-infested Zebu type, N'Dama and Friesian cattle and acaricide-treated Zebu types and Friesians in concanavalin A (Con A) stimulated cultures was monitored regularly for periods ranging from 11 to 27 months. The numbers of ticks on the animals and the presence of dermatophilosis were also noted. The Friesian cattle carried most and the N'Dama fewest Amblyomma variegatum ticks. The tick-infested Friesians all developed severe clinical dermatophilosis within 5 months of becoming tick-infested. Dermatophilosis lesions on the tick-infested Zebu type and N'Dama cattle were less common and less severe especially in the N'Damas. The proliferative response of lymphocytes from tick-infested Friesians in Con A stimulated cultures fell to almost half that of the acaricide-treated Friesians soon after the former became tick-infested. The tick-infested Zebu types also developed a depressed response compared with the tick-free Zebu group over a 27 month study period. However, the responses of the N'Damas was similar to that of the tick-free Zebu types. The addition of autologous serum to Con A stimulated cultures of lymphocytes derived from the tick-infested Zebu types and N'Damas suppressed their proliferative response compared with that of similar cultures for the tick-free Zebu types.

Seasonal prevalence of ticks and their association with dermatophilosis in cattle on the Accra plains of Ghana.

The seasonal abundance of adult ticks on cattle and their association with dermatophilosis were investigated in five herds on the coastal plains of Ghana over a 26-month period. Four genera, Amblyomma, Boophilus, Rhipicephalus and Hyalomma were identified, A. variegatum being the predominant species occurring throughout the year with two peaks of infestation, one in April-May and the other in November. A significant positive correlation was revealed between A. variegatum and dermatophilosis in four of the five herds. Significant positive correlations were found between H. m. rufipes and dermatophilosis in two of the herds and between Rh. senegalensis and dermatophilosis in one herd. Negative correlations of statistical significance were observed between Boophilus species and dermatophilosis in three of the herds. Nevertheless, it was considered that A. variegatum was the most important tick factor involved in the pathogenesis of the disease.

The effect of tick control on the prevalence of dermatophilosis on indigenous cattle in Ghana.

The effectiveness of three tick control regimes on the occurrence of Amblyomma variegatum and dermatophilosis on cattle on the coastal plains of Ghana were compared. Animals at one kraal were sprayed with amitraz at predilection feeding sites of ticks every second week using a high concentration minimum volume technique. Animals at two other kraals were treated with a deltamethrin based pour-on acaricide; at one kraal it was applied once every month while at the other kraal it was used at strategic times based on the expected seasonal increases in the level of infestation with A. variegatum. Animals in a fourth kraal (control group) were treated, by the herdsmen, to control excessive tick build-up as practised under traditional management systems. Fortnightly treatment with amitraz reduced the level of infestation with A. variegatum and the prevalence of dermatophilosis dropped to a low level. The pour-on acaricide similarly depressed the prevalence of dermatophilosis.

Streptothricosis in cattle on the coastal plains of Ghana: a comparison of the disease in animals reared under two different management systems.

The prevalence of streptothricosis in selected cattle herds under two different management systems was investigated and related to the presence of various factors which the literature suggests may play a role in its development. The disease was more prevalent on farms with traditional management compared to that on farms with improved management.