Theileriosis in Kenya

D.P. Kariuki

National Veterinary Research Centre
Kenya Agricultural Research Institute
P.O. Box 32
Kikuyu, Kenya

Kenya has a human population of over 21 million (estimated at the end of 1980) and an area of 582670 sq. km. Of the total area, 20% is of high or medium potential and is suitable for crops, intensive forestry and stock raising. The high-and medium-potential zones support 80% of the total human population. The cattle population was estimated in 1986 to be 9 million, 20% of which were exotic and grade cattle. The high-producing dairy and beef cattle are found in the high- and medium-potential zones; indigenous cattle are found mainly in the range areas, which form approximately 70% of the country.

Theileriosis caused by Theileria parva is one of the major constraints to the development of the livestock industry in Kenya. The importance of this disease is due to the high rate of mortality it causes in livestock, the productivity losses it causes in animals that recover from the disease and the exclusion of exotic and grade cattle from much of the country. The infection occurs in cattle and buffalo and is transmitted by the ixodid tick, Rhipicephalus appendiculatus. The distribution of R. appendiculatus correlates closely with areas with the highest concentrations of exotic or grade cattle (Figures 1 and 2, respectively).

CURRENT STATUS OF THEILERIOSIS

Five species of Theileria are recognized in Kenya (Table 1). Theileriosis manifests itself in the form of East Coast fever (ECF) (T. parva parva) and Corridor disease (T. p. lawrencei). Theileria mutans, T. velifera and T. taurotragi infections usually cause at most mild transient fever and anaemia and are not reported as theileriosis in the field. Corridor disease occurs in areas where buffalo are found.

In an extensive survey carried out from 1971 to 1974 in 36 districts, antibodies to T. parva were detected in all districts where R. appendiculatus was found (Food and Agriculture Organization of the United Nations, 1975). The percentage of cattle showing positive reactions is shown by district in Figure 3. Reported and suspected cases of ECF have been increasing since 1974, probably as a result of improved reporting and diagnosis by the field veterinary staff, the availability of chemotherapeutic drugs and greater awareness of the disease by farmers. Since 1977 there has been an increase in the number of field staff, including veterinarians. Even so, it is suspected that the reported cases represent only 10% of the cases occurring in the field.

Figure 1. The distribution of Rhipicephalus appendiculatus, the vector of Theileria parva, in Kenya.

Figure 2. The distribution of exotic beef and dairy cattle breeds in Kenya, showing the percentages by district.

Table 1. Species of Theileria recognized in Kenyan cattle

Theileria	Disease	Serotype	Vector
T. p. parva	East Coast fever	T. parva	R. appendiculatus
T. p. lawrencei	Corridor disease	T. parva	R. appendiculatus
T. taurotragi	Usually benign	T. taurotragi	R. appendiculatus and R. pulchellus
T. mutans	Usually benign	T. mutans	Amblyomma spp.
T. velifera	Benign	T. velifera	Amblyomma spp.

TICK CONTROL

The strategy of tick and tick-borne diseases control in Kenya has focussed mainly on controlling R. appendiculatus to prevent theileriosis transmission and to introduce improved exotic breeds of cattle and upgraded indigenous populations into ECF-affected areas. In these areas tick control measures are enforced by the Cattle Cleansing Ordinance Act, under which the Minister for Livestock Development is empowered to proclaim infected areas and enforce weekly cattle cleansing with government-approved acaricides (Table 2).

Table 2. Approved and registered acaricides in Kenya

Chemical name	Product name	Manufacturer	Recommended concentration
Dioxathion	Delnav DFF	Coopers/Wellcome	0.050% v/v
Quintiophos	Bacdip	Bayer	0.020% v/v
Coumaphos	Asuntol	Bayer	0.100% v/v
Chlorofenvinphos	Supona	Shell	0.050% w/v
Chlorofenvinphos	Steladone	Ciba-Geigy	0.050% v/v
Chlorofenvinphos	Superdip	Coopers/Wellcome	0.050% v/v
Carbaryl	Sevin	May and Baker	0.200% w/v
Diamide	Triatics	Coopers/Wellcome	0.025% w/v

Figure 3. The percentages of cattle with antibodies to Theileria parva in Kenya by district.

Figure 4. The districts in Kenya included in government tick-control projects.

"Proclaimed areas" are those in which ECF is present and cattle cleansing is compulsory. Before 1977 the Department of Veterinary Services, in the Ministry of Livestock Development, was responsible for supervising the Cattle Cleansing Act but not for managing dip tanks or spray races. Concern over escalating losses due to tick-borne diseases, in particular ECF, and the emergence of acaricide resistance, mainly in the Boophilus decoloratus population, accentuated by inefficient acaricide application, caused the Department of Veterinary Services to assume, through a Tick Control Programme, the management of communally operated dip tanks serving small-scale farmers in the proclaimed areas. Under this arrangement, the government provides acaricides for the dip tanks and levies a fee for each animal immersed. Each communal dip tank has a committee, composed of elected representatives from local livestock owners, which is responsible for liaising with the Department of Veterinary Services in running the dip and for providing labour when required. The districts included in the government tick-control projects are shown in Figure 4.

In other areas tick control is voluntary and at the discretion of livestock owners. Under the government tick-control programme there are 3330 dip tanks. The Department of Veterinary Services estimates that a further 1100 tanks are required in the proclaimed areas to ensure complete dipping. In 1985 the total cattle population in the government tick-control programme was just over 6 million, one-third of which were exotic or improved dairy and beef stock.

DISCUSSION

Tick and tick-borne diseases are a major constraint to the development of Kenya's livestock industry. A micro-economic analysis completed recently on eight large and medium-sized farms, with a total of 37779 head of cattle, in Nakuru District, Central Rift Valley, showed that the cost of acaricides, production losses and losses due to clinical theileriosis and other tick-borne diseases amounted to approximately US$ 515305 or $13.64 per animal per year (Young et al., in press and this meeting). The current strategy for controlling tick and tick-borne diseases is to attempt to reduce the tick population by applying acaricides, thereby reducing the direct losses due to tick-borne diseases, particularly ECF. Introducing immunization control methods against theileriosis would not only further reduce losses associated with ECF, but also reduce acaricide costs, since acaricides would then be applied strategically rather than universally.

Although the immunization method of infection and treatment, developed at the East African Veterinary Research Organization (EAVRO), Muguga, Kenya, has been approved by the Food and Agriculture Organization of the United Nations and is in use in a number of countries, this method has not been introduced in Kenya because the Veterinary Department wants some basic assurances and information, which include the following:

a) information on the Theileria strains from various ecological zones

b) the possibility of identifying a master strain(s) for the whole country

c) the availability of Theileria strain(s) to use in areas with both ECF and Corridor disease

d) the determination of a safe antigenic dose

e) the effects of immunization on the productivity of cattle

f) information on the T. parva carrier state

The National Veterinary Research Centre, at Muguga (formerly EAVRO), which is implementing an ECF project conducted jointly by the governments of Kenya and Britain, has been studying infection-and-treatment immunization against theileriosis in the laboratory and in the field, in collaboration with the Department of Veterinary Services, at Kabete, Kenya, and the International Laboratory for Research on Animal Diseases, Nairobi, so as to provide some of the above information and assurances.

Observations on the epidemiology of the disease and on immunization allow us to state the following confidently. Indigenous cattle in theileriosis-endemic areas of Kenya survive in the absence of artificial control measures because endemic stability is established. The carrier state is maintained by cattle that are resistant to the disease but carry a low number of the parasites, thereby providing a constant low source of infection for the tick and parasite challenge for newly born cattle. The introduction of susceptible cattle or tick control programmes in these areas disturbs this stability. Once the stability is disturbed or the tick control measures fail, mortality may be very high.

In areas where exotic and grade cattle are kept, artificial endemic stability of theileriosis can be established by immunization using the infection-and-treatment method. The cattle are immunized by infecting them with a known challenge and then controlling the infection with drugs; any subsequent challenge with a related stock boosts the immunity of the cattle. Livestock that will be moved from one region to another should be vaccinated before the move with a theilerial strain appropriate for the area to which they will be moved. Immunization would not be a problem if there was a master strain that would immunize livestock against all strains in the country. After immunization is implemented, acaricides may be applied strategically, non-conventionally or with reduced frequency.

REFERENCES

Food and Agriculture Organization of the United Nations (1975). Research on Tick-Borne Cattle Diseases and Tick Control, Kenya Epizootiological survey on tick-borne cattle diseases, Technical Report AG: DP/KEN/70/522 No. 1. Rome: Food and Agriculture Organization of the United Nations.

Young, A.S., Kariuki, D.P., Mutugi, J.J., Heath, D.L. and Long, R.C. (in press). Economic losses in cattle due to tick control and effects of tick-borne diseases on selected farms in Nakuru District, Kenya. Preventive Veterinary Medicine.