Ticks and Dermatophilosis
biotec at goliat.ugr.es
biotec at goliat.ugr.es
Mon Mar 3 11:26:14 EST 1997
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 NDama 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.
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