TICKS AND TICK-BORNE DISEASES (T & TBDs) IN AFRICA: Economic importance, control problems with acaricides and new hope based on use of Neem compounds.

Global losses: Global losses due to T & TBDs have been estimated at US$ 7 billion annually and approximately 80% of the world's cattle population of 1.2 billion are at risk from T & TBDs (McCosker, 1979). Unfortunately, over half of this occurs in Africa.

Importance of livestock in Africa: In Africa, livestock perform a wide variety of economic and social functions both in household and in national economics. They provide food (meat & milk), cash income, clothing, fuel, employment, draught power, sense of security, prestige, social status and cultural values (Mukhebi, 1992)

African losses: T & TBDs are the most serious constraints to increased production in the Africa's 186 million cattle. Unlike tsetse which infest only 40% of the African continent (Rogers & Randolf, 1985), ticks are found on livestock in the entire 30 million Km2 of the continent. The major TBDs of livestock are theileriosis, especially East Coast Fever (ECF) transmitted by Rhipicephalus appendiculatus, babesiosis and anaplasmosis transmitted by Boophilus decoloratus and Boophilus microplus and heartwater transmitted by Amblyomma ticks, A. variegatum and A. hebraeum. In case of theileriosis and heartwater for instance, morbidity and mortality in certain breeds of susceptible cattle can approach 100% (Hooke, 1981). Indigenous breeds are also at risk in situations where they are subjected to intensive tick control or when moved from disease free to endemic areas. While mortalities can vary from 0-50% under endemically stable condition (Otim, 1989), they can be as high as 80-100% under epidemic conditions (Julla, 1985). Calf growth in indigenous breeds is also severely impaired (Moll et. al., 1984), while calf mortality can be as high as 20% (Morgan, 1994). In indigenous cattle the outputs of milk and weaner calf are about 25% less in tick-infested than in tick-free herds (Pegram et. al., 1993). A single female R. appendiculatus ticks engorging on cattle can cause loss in body weight gain (bwg) of 4g and milk loss of 7g, A. hebraeum loss in bwg of 10g and milk loss of 7g, and A. variegatum loss in bwg of 45-60g (Pegram et. al., 1993)

Economic losses due to theileriosis alone have been estimated at US$ 168 million, including a mortality of 1.1 million cattle annually in eleven countries in East, Central and Southern Africa (Mukhebi, 1992). Apart from mortality, tick infestation causes serious economic losses in cattle, e.g. reduction in weight gains, reduction in milk yield, reduced fertiliy, reduced draught power, damage to hides and skins and predisposition to fungal, bacterial and parasitic diseases (Mukhebi & Perry, 1995).

Control of T & TBDs in Africa: The control of ticks in Africa has relied mainly on commercial acaricides since their introduction in South Africa in 1890 (Dipeolu and Ndungu, 1991). The intensive use of these imported chemicals has led to various problems, such as tick resistance, environmental pollution, including residues in meat and milk and escalating costs. Several acaricides have been withdrawn from the market due to toxicity and tick resistance and currently there is no acaricide in use to which ticks are not, at least partially, resistant. The annual cost of importing acaricides and curative drugs for TBDs have been estimated at US$ 10 million for Kenya (Young et. al., 1988), Zimbabwe US$ 9 million (Perry et. al., 1990) and Zambia US$ 10 million (Pegram et al., 1988).

Since acaricides are purchased with foreign currencies, some countries are finding it increasingly difficult to afford them. Even when purchased, other logistical, economic and social problems make their use in communal dips very inefficient. In some African countries, it is estimated that only 3% of cattle dips are functional at any time (Kagaruki). The cost of developing new drugs for treatment of TBDs is exorbitantly high and often the parasites develop resistance after only a few years. For instance, it cost about US$ 25 million in 1980's to develop Parvaquone and buparvaquone for the treatment of theileriosis and a single treatment costs about US$ 25 (McHardy, 1995) and may therefore not be affordable by the resource limited farmers. Currently, there is no company developing new conventional acaricides and ticks are developing resistance to the available acarcides, including the synthetic pyrethroids rapidly.

ICIPE's Approach to the problems of T & TBDs: In view of the above mentioned problems relating to T & TBDs and their control, the Livestock ticks sub-programme at ICIPE is developing Integrated Tick Control (ITC) strategies which are environmentally - friendly and affordable by resource poor farmers. The ITM components are anti-tick vaccine, tick parasitoids, anti-tick grasses, tick pathogens (fungi) and botanical extracts such as neem.

Development of neem-based control strategies for African ticks: Since 1991, extracts of neem bark, seeds and leaves have been tested on various stages of ticks (larvae, nymphs and adults) at ICIPE. These extracts induced low to moderate mortalities, especially in the larvae and nymphs. In the adult ticks, mortalities were low but most of the eggs produced with the treated females were sterile. Eggs treated directly with these extracts also became sterile.

Recent pilot research at ICIPE done in collaboration between the livestock ticks sub-programme and the neem awareness project has revealed that all the three major species of African ticks; R. appendiculatus, A. variegatum and B. decoloratus are affected by neem oil. It inhibited larval and nymphal attachment and feeding (90-100%), reduced fecundity (30-45%), and hatchability of eggs (47-55%). It also reduced molting in larval (22-93%) and nymphal (98%) stages and sterilised most (80-90%) of the eggs exposed directly to the neem oil (Kaaya and Saxena; unpublished).

Ongoing experiments include testing of low concentrations of neem oil on all developmental stages of R. appendiculatus and A. variegatum and studying the effects of feeding neem cake to host animals on tick attachment and feeding. Future field study will involve spraying of neem oil and seed kernel extract on ticks feeding on cattle and on cattle prior to tick infestation. Possibilities of applying neem oil as a "pour on" will also be investigated.

References:
Dipeolu, O.O. and Ndungu, J. N. (1991). Acaricidal activity of Kupetaba, a ground mixture of natural products against Rhipicephalus appendiculatus. Vet. Parasitol. 38, 327-338.

Hooke, F.G. (1981) Commercial considerations for development of an anti-theilerial product. In: Advances in control of Theileriosis: Proc. Int. Conf., ILRAD, Nairobi, 9-13 Feb. 1981 (Eds. Irvin A.D., Cunningham, M.P. and Young, A.S.), pp177-185, Martinus Nijhoff Publishers,The hague.

Julla, I. I. (1985). Theileriosis in Southern Sudan. In: Immunization against theileriosis in Africa; Proc. Wksh., Nairobi, 1-5 October, 1984 (Ed. Irvin, A.D.), pp 27-30, ILRAD, Nairobi, Kenya

McHardy, N. (1995). Chemotherapy and Prophylactic Drug Treatment of Tick-borne diseaases. In: Ticks and Tick-borne diseases post-conference workshop, Pretoria, South Africa, August 5-8, 1995

McCosker, P. J. (1979). Global aspects of the management and control of ticks of veterinary importance. Rec. Adv. Acarol. 2; 45-53.

Moll, G., Lohding, A. and Young, A. S. (1984). Epidemiology of theileriosis in the Trans-Mara division of Kenya: Husbandry and disease background and preliminary observations on theileriosis in calves. Prev. Vet. Med. 2, 801-831

Morgan, D. (1994). Tackling ticks. African Farming July / August 1994 pp. 15-18. 2, 801-831.

Mukhebi, A. W. (1992). economic impact of theilerosis and its control in Africa. In: The Epidemiology of Theileroisis in Africa; pp 379-403 (Eds. Norval, R. A. I.; Perry, B. D. and Young, A. S.), Academic Press, London.

Dr. Godwin P. Kaaya,
The International Centre of
Insect Physiology & Ecology,
P.O. Box 30772,
Nairobi,
Kenya