Ticks and Dermatophilosis

[biotec at goliat.ugr.es]

Ticks and Dermatophilosis

Dermatophilosis, a bacterial skin disease, is one of the most 
important constraints to increased livestock production in parts of 
the tropics, especially West and Central Africa and on some of the 
Caribbean islands.  Although the disease occurs in a variety of 
different species world-wide a particularly severe form affects 
cattle in these areas. It results in damage to hides, decreased 
productivity, considerable suffering and death.  High producing 
exotic breeds tend to be much more susceptible to the disease.  All 
attempts at upgrading the local cattle population of West Africa, 
by crossbreeding with more productive imported breeds, have 
collapsed because of dermatophilosis.  This has had a devastating 
effect on efforts to develop peri urban dairy production in the 
West African region.  Milder lesions are an important reason for 
the downgrading of hides and skins from local cattle causing 
concern to the leather industries of Nigeria and Ethiopia.  Its 
effects on the utilisation of draught animals, and thus on crop 
production, are particularly important as the occurrence of the 
disease often coincides with the onset of the rainy season.  The 
severe chronic form of the disease found on cattle in the tropics 
is often associated with infestation by the African tick Amblyomma 
variegatum.

Proposals were formulated for a project to characterise the nature 
of the association between infestation with A. variegatum and the 
occurrence of dermatophilosis and to evaluate possible control 
mechanisms.  Implementation of these proposals were made possible 
through the acquisition of funding from the European Commission 
(STD2 programme, project TS2-A-106) and the Overseas Development 
Administration of the Foreign and Commonwealth Office, London for a 
three year project which was later extended to four years.  The 
project, which began in 1989, involved collaboration between the 
Veterinary Services Department, Ghana and the Centre for Tropical 
Veterinary Medicine, University of Edinburgh. 

The findings of the project confirmed the suggested close 
association between infestation with adult A. variegatum and the 
occurrence of a particularly severe form of dermatophilosis on 
cattle.  Breeds of animals traditionally regarded as more 
susceptible to the disease also tend to carry higher tick burdens. 
 The comparative resistance of the small West African N’Dama cattle 
would appear to be related to their resistance to ticks and the 
data suggests that when they are infested with similar numbers of 
A. variegatum ticks to the Zebu-type Ghana Sanga they are equally 
if not more susceptible to the skin infection.  The basis of the 
association between infestation with A. variegatum and 
dermatophilosis would appear to involve immunosuppression.  Tick 
infested animals were found to be immunosuppressed compared to 
tick-free animals.  This was particularly marked in exotic Friesian 
cattle which carried very much higher numbers of ticks compared to 
local types of cattle.

Cattle in much of West Africa are at present largely reared under 
an extensive system involving low inputs and resulting in low 
returns.  This is probably the most suitable system for the breeds 
currently used.  These animals receive little if any acaricide and 
would not justify its greater use.  As more livestock owners move, 
because of pressure for land, towards settled livestock farming 
there is an increased need for improved types of animals. Provision 
has been made under the National Livestock Services Project in 
Ghana to develop the dairy industry in order to supplement the 
animal protein supply.  Dairy development would provide much needed 
milk as well as promoting import substitution and act as a tool for 
rural development by bringing more farmers into a cash economy, 
increasing the income of farmers and providing employment.  
However, any programme to increase the production of beef and dairy 
products must involve the utilisation of more productive exotic 
breeds unless the area currently under grazing is to be increased. 
 Keeping high producing exotic-type animals will require improved 
levels of tick control as practised in parts of East Africa for the 
control of East Coast Fever.

Rigorous tick control was shown to prevent the occurrence of 
dermatophilosis on highly susceptible breeds of cattle.  The 
limited use of acaricides, applied either at the preferred feeding 
sites of the tick or at selected times when the level of challenge 
increases, is sufficient to control the occurrence of the disease 
in indigenous cattle.