East Coast Fever

East coast fever, a disease of cattle caused by the protozoan parasite Theileria parva and transmitted by the three-host tick Rhipicephalus appendiculatus (the brown ear tick), is a major constraint to cattle production in Eastern, Central, and Southern Africa. In Kenya it is the most important tick-borne disease and a major constraint in cattle productivity. This is due to the high morbidity and mortality it causes in susceptible herds, the cost of control of the vector ticks, and the cost of treatment of clinical cases. Animals that recover from the disease also suffer from reduced productivity which can be long term. The limited distribution of the tick and the disease to only East, Central and Southern Africa also means that the market for therapeutic drugs and acaricides is small. Therefore, drug companies are not keen on funding research and development of new drug and acaricide molecules when resistance occurs.

STRUCTURE-ACTIVITY STUDIES ON ANALOGUES OF 4-METHYLGUAIACOL, A CATTLE ANAL ODOUR CONSTITUENT REPELLENT TO THE BROWN EAR TICK (Rhipicephalus appendiculatus)

Previously, 4-methylguaiacol, a major constituent of cattle anal odour, was found to have a high repellence on Rhipicephalus appendiculatus. In the present study, 10 structural analogues of the phenol were tested for repellence against R. appendiculatus in order to assess the effects of (i) absence or presence of the 4-alkyl group of varying length, (ii) inclusion of a double bond in the 4-alkyl chain, (iii) linking the two phenolic oxygen in a methylenedioxy bridge, (iv) replacement of the OCH3 with CH3 and inclusion of another CH3 at position 6, and (v) presence of an additional OCH3 group at position 6. The analogues comprised of 2-methoxyphenol (guaiacol), 4-ethyl-2- methoxyphenol, 4-propyl-2-methoxyphenol, 4-allyl-2-methoxyphenol (eugenol), 3,4-methylenedioxytoluene, 2,4- dimethylphenol, 4-ethyl-2-methylphenol, 2,4,6-trimethylphenol, 4-propyl-2,6-dimethoxy-phenol and 4-allyl-2,6- dimethoxyphenol, which were compared at different doses in a two-choice climbing assay set up. Each analogue showed either increased or reduced repellence compared with 4-methylguaiacol. The structural feature that was associated with the highest repellence was 4-propyl moiety in the guaiacol unit (RD75 = 0.031 for 4-propyl-2- methoxyphenol; that of 4-methylguaiacol = 0.564). Effects of blending selected analogues with high repellence were also compared. However, none of the blends showed incremental increase in repellence compared with that of 4- propyl-2-methoxyphenol. We are currently evaluating the effects of controlled release of the compound at different sites on cattle on the behavior and success of R. appendiculatus to locate their predilection feeding site.

Ants as predators of the Spinose Ear Tick, Otobius megnini (Dugès) in Sri Lanka

Many pathogens, parasitoids and predators have been documented as natural enemies of ticks, but their impact on tick populations are rarely evaluated. Here, we report the predatory behaviour of ants on the spinose ear tick, Otobius megnini. Ticks were collected from the ear canal of stabled horses in Nuwara Eliya and were brought to the laboratory. Eggs, unfed and engorged larvae, engorged nymphs and adults were naturally exposed to ants under laboratory conditions and the predatory behaviour of the different species and their feeding preferences were observed. Five ant species were found feeding on different life stages of O. megnini including eggs, larvae (fed/unfed) and adults; ants did not feed on the nymphal stages. Ant species were identified as Tapinoma melanocephalum, two species of Monomorium, one species of Pheidole and one species of Crematogaster. The predatory preference differed among the five ant species, with T. melanocephalum being identified as the best predator as it fed on eggs and adults, the non-parasitic stages of O. megnini. Different strategies have been used to control the infestations of O. megnini in the stabled horses but none of them were successful. Although we cannot extrapolate our empirical findings to a natural context, observations suggest that these ant species may be potential bio-suppressors of this tick species.