Koney, Enoch B. M.

2018-05-14T10:13:55Z

2018-05-14T10:13:55Z

1992

The professional and scientific literature on the epidemiology, treatment and economic importance of dermatophilosis has been reviewed. Particular attention being paid to the role of ticks, especially Amblyomma variegatum in causing overt disease and tick associated losses. In addition chemical and alternate methods of tick control including the use of resistant breeds of cattle, modification of vegetation and the microclimate, the introduction of tick-resistant grasses and host vaccination against ticks are discussed.

An experiment herd of 26 animals and five local herds containing 605 animals on the Coastal Plains of Ghana were studied.

The seasonal abundance of ticks, their association with dermatophilosis and the systemic effects of the ticks on their hosts were investigated. Four genera, Amblyomma, Boophilus, Rhipicephalus and Hyalomma were identified on cattle, A. variegatum being the predominant tick species occurring throughout the year with peak infestations in the two rainy seasons. A highly significant positive correlation was revealed between A. variegatum and dermatophilosis in four of five local herds. Unexpectedly, a significant correlation was found between Hyalomma rufipes and dermatophilosis twice and between Rhipicephalus senegalensis and dermatophilosis once in the local herds.

Clinical dermatophilosis developed two months after severe tick infestation. The immune responsiveness of tick-infested cattle was suppressed as assessed by the lymphocyte transformation test (LTT) and confirmed by [3H]-thymidine incorporation assays. Decreased lymphocyte responsiveness in the Friesian cattle coincided with peak tick levels and clinical dermatophilosis. In vitro lymphocyte responsiveness to Concanavalin A in culture medium containing foetal calf serum was suppressed by serum from cattle infested with ticks. Similarly, serum from cattle infested with ticks and infected with dermatophilosis suppressed lymphocytes derived from "clean" animals i.e. control animals treated with acaricides.

Repeated experimental infections in cattle healed spontaneously in spite of the fact that the immune responses of the animals were suppressed. Resolution occurred fast after the second and third infections but not after the fourth infection which healed at the same time as the first.

Cross-reaction was observed between D. congolensis and PPD. The practical significance of the observed association in relation to tuberculosis skin test is discussed.

It is suggested that indigenous breeds of cattle which are more resistant to ticks and dermatophilosis be kept on the Coastal Plains of Ghana. It is also recommended that acaricides with long residual activity backed-up with long-acting oxytetracycline injectables be used during periods of high tick activity to keep tick levels at low numbers. Selective hand-dressing may then be used to treat any individual animals with large tick burdens in the dry seasons.

http://hdl.handle.net/1842/29839

The University of Edinburgh

Annexe Thesis Digitisation Project 2018 Block 18

Already catalogued

Seasonal prevalence and distribution of ticks on the Accra Plains of Ghana and their association with dermatophilosis

Thesis or Dissertation

Doctoral

PhD Doctor of Philosophy