Biology of ticks

Ticks are an ancient group of obligate bloodsucking ectoparasites that has evolved over millions of years. Two general types of ticks are evident today: argasid or soft ticks, and ixodid or hard ticks. Each lineage exhibits distinct patterns of host coevolution and preference. However, about 10% of the approximately 850 species are of medical importance because of their indiscriminate host selection and catholic feeding behavior. As a result, a number of diseases have begun to emerge in the temperate zones, including Lyme borreliosis and several others putatively associated with ticks. Ticks may serve as both pathogens and disease vectors. Because of the unique physiology of the salivary glands and the contents in tick saliva of toxins, feeding alone may cause disease. Ticks also transmit a number of different types of pathogens (viruses, rickettsiae, spirochetes and bacteria, fungi, protozoa, filarial nematodes) and even exceed mosquitoes in this regard. Abatement and control of ticks emphasizes a broad approach because of the differing types of habitats in which pest species may be found. The use of repellents and acaricides as well as cultural and management practices are of primary importance. Other approaches (ivermectin) may be beneficial; with the advent of molecular genetics and its usefulness in immunology, the development of tick vaccines for common pest species appears promising.     

Control of ticks and tick borne diseases in exotic/cross-bred dairy cattle in India

Tropical Animal Health and Production -     

Cattle ticks in Malawi

Four genera of cattle ticks were found and identified during two tick surveys: Amblyomma, Boophilus, Hyalomma and Rhipicephalus. Amblyomma variegatum was the only species found of genus Amblyomma. The genus Boophilus was represented by two species: B. microplus and B. decoloratus, and the genus Hyalomma by two species: H. truncatum and H. marginatum rufipes. Ten different species of Rhipicephalus were identified: R. appendiculatus, R. sanguineus, R. compositus, R. pravus, R. simus, R. kochi, R. reichenowi, R. tricuspis, R. masseyi and R. punctatus.The results are compared with those from previous investigations conducted by the late Dr S.G. Wilson.All sites at which the different species of cattle ticks were found, and the distribution of each tick are illustrated by a series of maps. The territorial distribution of the ticks is discussed. R. appendiculatus was collected at five sites in the Shire Highlands, an area in which their presence has not been previously demonstrated.     

Goats as alternative hosts of cattle ticks

The objective of this study was to compare the presence on goats and cattle of adult ticks that usually infest cattle. To this end ticks collected from sets of five goats were compared with those collected from sets of five cattle at 72 communal dip-tanks in the eastern region of the Eastern Cape Province. Amblyomma hebraeum was present on goats at 25 and on cattle at 39 dip-tanks, and a total of 61 goats and 138 cattle were infested. Adult Rhipicephalus (Boophilus) microplus was present on goats at 48 and on cattle at 69 dip-tanks, and a total of 113 goats and 242 cattle were infested. The lengths of 84 of 148 female R. (Boophilus) microplus collected from the goats exceeded 5 mm or more, indicating that they could successfully engorge on these animals. The differences between the proportions of dip-tanks at which A. hebraeum or R. (Boophilus) microplus was present on goats and cattle and also between the proportions of goats and cattle that were infested were significant (Chi-square test, P < 0.01). Adult Rhipicephalus appendiculatus was present on goats at 70 and on cattle at 67 dip-tanks, and a total of 296 goats and 271 cattle were infested. The proportion of dip-tanks at which cattle were infested did not differ significantly from the proportion of tanks at which goats were infested (Fischer's exact probability test, P = 0.44), but the proportion of infested cattle was significantly lower than the proportion of infested goats (Chi-square test, P < 0.05). Adult Rhipicephalus evertsi evertsi was present on goats and cattle at all 72 sampling localities, and a total of 334 goats and 316 cattle were infested. The proportion of infested cattle was significantly lower than the proportion of infested goats (Chi-square test, P < 0.05). These results underscore the necessity of including goats in any tick control programme designed for cattle at the same locality.     

Control of Boophilus microplus ticks in cattle calves by immunization with a recombinant Bm86 glucoprotein antigen preparation.

Forty Egyptian native cattle calves of 4-6 months old randomly allocated into two groups of twenty animals each were used to assess the effect of immunization of animals with a recombinant Bm86 antigen derived from Boophilus microplus ticks on induction of immunity that could protect calves during tick season. The immunization protocol involved two injections administered intramuscularly, the first was applied with complete Freund's adjuvant and the second was given with incomplete Freund's adjuvant two months later. Control calves were given saline plus adjuvant. Immunization reduced the number of adult ticks developing from a subsequent challenge infestation by 78% in immunized calves. Vaccination also, significantly reduced the weight of adult ticks in immunized calves (30.51%). The results of skin delayed hypersensitivity reaction revealed that the diameter of sites injected with the recombinant Bm86 antigen was significantly larger in immunized calves than those in controls. Analysis of the immune response indicated that there was a significant increase in the level of IgG and IgA antibodies in serum of immunized calves and protection from reinfestation was correlated with the levels of circulating antibodies.     

Distribution ofBoophilus species ticks in Swaziland

Recent outbreaks of bovine babesiosis caused by Babesia bovis in Swaziland had indicated the presence of the vector tick Boophilus microplus in the country although it had never before been directly identified. Engorged female Boophilus ticks were collected from cattle at diptanks in the course of a tick resistance survey and used to map the distribution of the two different species of Boophilus. B. decoloratus was found to be widespread throughout the country. B. microplus was identified for the first time in Swaziland and was found to have a patchy distribution. The implications of these findings are discussed.