Ticks, and the diseases they transmit, are of great economic and medical importance worldwide, and especially in Africa, where they are considered to be the greatest animal disease problem. The four major genera of ticks are Amblyomma, Rhipicephalus, Hyalomma and Boophilus. Ticks harm their animal hosts by sucking their blood thus reducing growth rate and milk yield, cause mechanical damage to hides and skins causing tick worry, introduce toxins and predispose the animals to myasis. Theileriosis, cowdriosis and dermatophilosis are the major tick-borne and tick-associated diseases of grazing cattle in Africa. The conventional method of tick control is the application of chemical acaricides, but it is associated with a number of problems including environmental pollution, chemical residues in meat and milk products as well as in wool, development of tick resistance and high cost. Some of the alternatives to chemical control of ticks that are available in Africa are discussed in this paper.

Studies were conducted into the development of anti-tick vaccines against two tick species, namely Boophilus anniilatus Say, 1821 and Argas persicus (Oken) 1818, which, respectively, are responsible for high economic losses in the cattle and chicken industries in Egypt. Repeated infestation of spring chicken with Argas persicus females stimulated 35.9 % resistance to tick feeding compared to 20.4 % in controls. This resistance was associated with the presence of antibody activity to tick salivary gland antigens. There was increase of both the chicken serum total protein and the number of protein bands separated by SDS-PAGE, which suggested an increase in immunoglobulins. Chicken resistance to tick feeding was also induced by repeated injection (vaccination) with crude Argas persicus salivary gland antigens, with intramascular injection being more efficient at inducing immunity than subcutaneous injection.

Prolonged infestation with Boophilus annulatus ticks induced immunity in cattle. Salivary gland and gut crude extracts of cattle exposed to the ticks contained antigenic proteins, with dominant 66 and 150 KDa glycoproteins. Antibodies against the two extracts or PAGE-separated antigens were detected in cattle that resisted tick feeding. Cell-mediated immunity (CMI) was also detected. The immune response was strong in non-infested Bos indicus and Bos indicus × Bos taurus Linneaeus, 1766 crossbreeds with low infestation, and weak in heavily infested Bos taurus.

—The sodium dodecyl sulphate polyacrylamide gel electrophoresis (SDS-PAGE) of gut supernate antigen (GS Ag) derived from partly fed Hyalomma anatolicum anatolicum Koch, 1844 (Acari: Ixodidae) adult females revealed 26 discrete potypeptide bands of molecular weight ranging from 25–208 kDa. Out of these, seven bandswere of major polypeptides with molecular weights of between 25.2 and 185.8 kDa. On immunoblotting with antisera raised in rabbits against gut supernate (crude extract), eight immunogenic polypeptides with molecular weights of between 51.7 and 185.8 were identified. The implications of these findings for the potential development of anti-tick vaccine are discussed.

A preliminary survey was conducted in coastal Kenya to assess the hosts of economically important tick species (Acari: Ixodidae) of domestic animals, as part of a training course for tick scientists from African research institutions. Ticks were collected from domestic animals in Kilifi and Kwale districts.

Eight tick species, namely Amblyomma variegatum, Boophilus decoloratus, B. microplus, R. appendiculatiis, R. evertsi evertsi, R. pulchellus, R. simus and A. gemma were identified. Further, more comprehensive surveys on the hosts, distribution and ecology of ticks of economic importance are recommended.

Topical application of crude ethanol extracts (CEs) of the leaves of 43 of 51 Jamaican plants produced varying degrees of multiple acaricidal effects on engorged Boophilus microplus Canst., including mortality (M), inhibition of oviposition (IO) and inhibition of embryogenesis (IE). Acaricidal indices (AI) ranged from 50 to 100 for the CEs of 29 plants, 38 to 47 for 9 plants and from 0 to < 25 for 13 plants. The most active CEs, in decreasing order of activity (AI values in parentheses) were those of: Simarouba glauca (100), Symphytum officinale (99), Nicotiana tabacum (95), Hibiscus rosa-sinensis (93), Ervatamia divaricata = Ricinus communis (82), Salvia serotina (80), Stachytarpheta jamaicensis (79), Blighia sapida = Ocimum micranthum (76), Spigelia anthelmia (75), Cycloptis semicordata (74), Mormordica charantia (71), Bontia daphnoides (69), Azadirachta indica (68), Capsicum annum = Catharantus roseus = Petiveria alliacea (66), Gliricida sepium (64), Lippia alba (62), Cuscuta americana = Erythrina corallodendrum (61), Piper amalago (60), Cannabis sativa = Cecropia peltata (58), Dioscorea polygonoides (56), Artocarpus altilis (53), Crotalaria retusa (51), Citrus aurantium (50).

The biological activity against Boophilus microplus of extracts of the berries, bark, leaves and twigs of Pimenta dioica was examined and compared with that of eugenol, methyl eugenol and four commercial acaricides, namely dimethoate, farnesyl methyl ether, carbaryl and diazinon. The berry essential oil was more effective at inhibiting oviposition and causing mortality of the ticks than all the extracts, the commercial acaricides and methyl eugenol. At a dose of 1.0 mg/g it was 33, 12, 6, and 3 times as effective in inhibiting oviposition as the non-polar extracts of the leaves, bark, twigs and berries, respectively. The potency of the berry essential oil is attributable to eugenol, a phenyl propanoid derivative, which accounts for over 65% of the oil content.

This short communication describes the morphological features of three specimens of Hyalomma truncatum which dropped off artificially infested rabbits in the laboratory.

A comprehensive review of the acquisition of resistance in bovine and laboratory hosts as a result of natural infestation with various species of ticks is undertaken. In this review I discuss the biological aspects of the expression of resistance, deal with acquisition of resistance to ticks by bovine and laboratory animals, give details on the environmental and physiological factors which affect the resistance and explain the mechanisms of resistance in both bovine and laboratory animals. I also deal with the relationships between ticks and their bovine hosts and emphasize the difference in the acquired resistance of individuals in the breed as well as the negative correlation between the decrease in mean weight of the ticks and the increase in the levels of globulins in the serum of the different hosts.

Aspects of cross resistance by hosts to different species of ticks are also discussed in this review.

Au Rwanda, on a identifié 45 espèces des tiques dont 5 d'entre-elles sont les plus répandues et les plus dangereuses. Ces tiques infestent le bétail qui lui paie un très lourd tribut suite aux effets du parasitisme et à la transmission des maladies graves telles que la théilériose, lababesiose, l'anaplasmose, les rickettsioses, etc. De nombreux efforts sont déployés depuis plus de 35 ans pour contrôler la population des tiques et pour prévenir et guérir les maladies transmises par ces vecteurs. L'insuffisance du budget et du personnel affecté à ce programme compromet les chances de succès des activités pourtant vitales pour l'économie de l'élevage. Il est impérieux de relancer le service national de lutte contre les tiques.

The various methods of controlling tick infestation on livestock are reviewed, highlighting their strengths and weaknesses. A framework for developing an IPM approach including socioeconomic considerations for ticks control is proposed. Efforts at practising IPM on ticks are highlighted.

Worldwide recognition of ticks and subsequent control experiences in USA, Australia and Africa is summarized. The symposium lecture includes three research challenges: (a) reduce the direct and indirect costs of ticks to African animal agriculture, (b) complete critical research required for an effective African tick control programme in spite of stable or reduced research funding, (c) learn to package and market new technology used in control schemes. Three questions are suggested for industry representatives and researchers to ask one another: (a) Is the new technology practical and affordable? (b) Is animal productivity really improved? (c) Are the schemes responsive to broader environmental and animal health concerns of society?

In many countries in eastern, central and southern Africa, twice-weekly to two-weekly acaricide applications are practised to prevent mortality of exotic cattle from tick-borne diseases. This practice has been extended to areas where only local cattle are present. These measures are very costly, inefficient in controlling diseases and ecologically undesirable.

In view of the many difficulties with the present method of tick control, exploitation of tick-resistant cattle breeds in enzootically stable situations would appear to be a pragmatic, alternative approach to the intensive use of acaricides. This paper reviews studies on host-tick relationships in Africa with a view to understand the role of naturally acquired resistance in limiting tick populations and hence its use in integrated pest management strategies. The levels of information required are outlined such as identification and quantification of resistance, effect of cattle breeds and productivity and economics in relation to host-resistance.

Tropical African ticks are found on their hosts throughout the year, but at varying infestation levels. These population changes, for most of the time, have been associated with climatic changes. Their development is inversely related to temperature. Several workers reported that development failed for a number of tick species at temperatures below 15°C, suggesting a possible lower temperature threshold for tick development. The upper development limit for most of the tropical rhipicephalids appear to be 37°C.

Ticks are particularly susceptible to attack during lethargic pre-moulting and the weak post-moulting period. Many biological features enable them, however, to survive especially well. They lay numerous eggs and withstand a comparatively wide temperature and humidity range with greater ease. They survive for months or years without food.

Their degree of host specificity varies from genus to genus or within subgroups of various genera. The requirement of two or more kinds of hosts often with divergent habits, limits their distribution to certain faunal areas.

This paper reviews our current knowledge on development and survival of ixodid ticks under tropical field conditions including some laboratory studies.

Populations of Rhipicephtdus sanguineus, Dermacentor variabilis and Amblyomma maculatum with high and low oviposition capacities were successfully bred in the laboratory. Mating of male and female ticks which possess high oviposition capacity produced female progenies with high oviposition capacity; male and female ticks which possess low oviposition capacity produced female progenies which possess low oviposition capacity. Crossmatings of males with females of opposite oviposition capacity produced female progenies which acquired the category of oviposition capacity of the males in predominant numbers after fourth and fifth generations. It is suggested that the genetic factor for high or low oviposition capacity is either possessed by male ticks alone or is stronger and dominant in the male over that of the female. This genetic factor is also potentiated by successive crossmatings of males and females possessing opposite oviposition capacities.

The possible application of these results to tick control through the suppression of natural population by field release of laboratory-bred populations of male ticks which possess low oviposition capacity is discussed.