J.D. Woodford*
Small Holder Livestock Development Project
P.O. Box 368,
Pemba, Tanzania*Present address: Tana-Beles Project
P.O. Box 101463
Addis Ababa, Ethiopia
Clinical records maintained at the Ole District Livestock Extension Centre, Pemba, Tanzania, show that most cross-bred calves became infected with Theileria parva at a very early age, in spite of once weekly hand-spraying with coumaphos (Asuntol, Bayer). The mean age of detection of clinical infection with East Coast fever (ECF) in 50 cross-bred calves born in the Ole District between July 1985 and February 1986 was 63 days. The earliest infection was detected at 15 days. Approximately one-third of cross-bred calves treated with parvaquone (Clexon, Coopers Animal Health) at 10 mg/kg bodyweight suffered relapses or new patent infections, suggesting that although parvaquone is better than any previous chemotherapeutic agent, it is not entirely satisfactory. It is likely that artificially induced immunity using the infection-and-treatment method of immunization will produce a safer and more solid protective immunity.
It is not normally recommended to vaccinate calves under two months of age. Because of this and the evidence of early ECF infections in spite of once weekly hand-spraying with coumaphos, the efficacy of cypermethrin-impregnated ear-tags as an adjunct to tick control was investigated. It was thought that since the vector of ECF, Rhipicephalus appendiculatus, prefers to attach itself to the ears and head of livestock, this method of control might be particularly effective.
Cypermethrin-impregnated ear-tags (Decum, Fearing, USA) were placed in both ears of 20 East African shorthorn Zebu (Bos indicus) × Jersey (Bos taurus) calves at birth and removed at 8 weeks of age. The calves were hand-sprayed with coumaphos (Asuntol, Bayer) at weekly intervals. During the eight-week period of intensive tick control, no T. parva infections were recorded in this group of calves, either clinically or by blood and lymph gland biopsy smear examinations. Within three months of removal of the ear-tags, all 20 calves became infected with T. parva, which was confirmed microscopically.
The intensive tick control practiced in this trial protected the calves against T. parva infection. If vaccination cannot be given until the calves have reached immunological maturity, the use of acaricide-impregnated ear-tags may be a practical way of protecting calves until they can be immunized. However, if ticks are kept off calves completely for too long a period, the calves may not develop a natural immunity to Anaplasma marginale or Babesia species while still protected by natural age-related resistance.
ACKNOWLEDGEMENT
Cypermethrin-impregnated ear-tags were kindly supplied by Dr. A.S. Young, of the Kenya Agricultural Research Institute, Muguga, Kenya.
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Classification of the Protozoa Phylum III. APICOMPLEXA Levine, 1970 Class 2. SPOROZOEA Leuckart, 1879 Subclass 3. PIROPLASMIA Levine, 1961 Order 1. PIROPLASMIDA Wenyon, 1926 Babesia From Levine et al (1980). A newly revised classification of the protozoa. Journal of Protozoology 27 p. 37-58 |
