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
