D.O. Chinombo; F. Mzoma and F.L. Musisi
Central Veterinary Laboratory
P.O. Box 527
Lilongwe, Malawi
There are just over one million cattle in Malawi, of which the indigenous short-horned Zebu, kept under traditional systems of management, are predominant. Within the national herd, there are about 13000 cross-bred (mainly Fresian crossed with Zebu) dairy cows and heifers kept on government farms, private estates and small holdings in the milk shed areas around Blantyre-Zomba in the south, Mzuzu in the north and Lilongwe-Dowa in the centre of the country.
Tick-borne diseases are endemic throughout Malawi. Of these, East Coast fever (ECF), a Theileria parva infection in cattle, is a major cause of cattle mortality. Exotic and cross-bred cattle are more susceptible to ECF than the indigenous cattle. A cattle survey carried out by a Malawian-Danish Project (Knudsen, 1971) showed that 66% of each year's calf crop from indigenous breeds died before two years of age and most of these deaths were attributed to ECF. While the overall national annual mortality among the traditionally managed herds was estimated at 10-15%, mortalities in the ECF-endemic areas of central and northern Malawi in calves and adults were 10% and 1% higher, respectively (Figure 1) (World Bank, 1988).
East Coast fever occurs where the vector tick, Rhipicephalus appendiculatus, is established. In the south, the River Shire seems to form a natural boundary for ECF; the only cases reported east of the river have been in cattle recently moved from infected areas. It appears that the disease has not become established in the southern region mainly because of the very low density of the vector in that region. However, if a breakdown occurs in the current efficient tick control practices and the disease is introduced in the area, ECF will likely become established in some parts of the region, particularly in the escarpment areas where the tick is known to occur.
The diagnosis of ECF in Malawi is based on the demonstration of schizonts in lymph node biopsy smears and of piroplasms in blood smears from clinically sick animals or schizonts from spleen smears of dead animals. Where applicable, this diagnosis is complemented by the indirect fluorescent antibody test (IFAT) using schizont antigen. Not all lymph node biopsy smears having schizonts are ECF cases (Malawi Government, 1975).
Figure 1. The distribution of Theileria parva in Malawi (dark shaded area), with numbers of cases diagnosed at different centres, 1983-87.
Figure 2. The number of confirmed cases of theileriosis in Malawi by district, 1983-87.
Figure 3. The number of confirmed cases of theileriosis in Malawi by month 1983-87
Figure 4. The number of cases of theileriosis confirmed at the Central Veterinary Laboratory, Malawi, 1983-87.
In the past five years, 1412 cases of ECF were confirmed at the Central Veterinary Laboratory (CVL). The cumulative number of cases are shown by districts in Figure 2. It appears that in a given district the number of diagnostic centres as well as the level of awareness in smallholder farmers that they should report dead or sick animals influence the frequency of cases reported. This is evident especially in Lilongwe, Dowa and Dedza districts, which are the districts closest to the CVL. Moreover, in these districts there are more cross-bred cattle, which are usually more susceptible than indigenous cattle to ECF, than in the other districts where indigenous breeds predominate. These confirmed cases represent 6% of the total smears examined at CVL from the districts indicated in Figure 2. Of the total smears examined, 22% were from spleens, of which 23% were positive for theilerial schizonts. There was an overall mortality rate of 5.0%, which was attributed to ECF among the specimens submitted.
The highest number of cases occurs between January and March (Figure 3) and the peak is markedly influenced by rainfall distribution over these months. Transmission at that time of the year is by the adult tick. A small peak occurring between May and July is due to nymphal transmission. This peak depends on the climatic conditions in this period, particularly moisture and temperature. From August to November there is a steady, slow decline in the number of ECF cases detected. In November and December adult tick activity increases with the onset of rains and the number of ECF cases increases as well.
The numbers of confirmed cases of tick-borne diseases at CVL have been steady during the past five years and records show that the distribution of ECF in the country and over the different seasons of the year has not changed. However, there was a slight increase in the number of laboratory confirmed ECF cases in the endemic areas in 1983 and 1986 (Figure 4), while the southern region remained free of the disease.
These observations indicate that ECF continues to be a major constraint to the improvement of the cattle industry in Malawi. Serious losses have been noted even among indigenous Zebu cattle when enzootic stability is disturbed. Controlling ticks and tick-borne diseases with acaricides is of paramount importance in Malawi, but smallholder dairy farmers would benefit more if their cross-bred cattle were immunized against ECF and other tick-borne diseases at the earliest possible opportunity. This and strategic tick control would reduce the costs of purchasing and administering acaricides.
REFERENCES
Knudsen, P.B. (1971). Final Report of Activities of the Malawian-Danish Cattle Survey in Malawi. DANIDA/Government of Malawi.
Malawi Government (1975). Veterinary Department Annual Report. Zomba, Malawi: Government Printer.
World Bank (1988). Livestock Development Studies in Malawi. Washington, D.C.: World Bank.
