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| December 2002 |
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| Goats are gold
on four hooves in many poor parts of Africa, a major part of the
economy. For years, goat farmers have been told to dose their entire
herd even if just one goat falls ill with gastrointestinal parasites,
and then transfer them to a disease-free pasture - no easy task for
communal farmers. These cash-strapped farmers have been blamed for
creating drug resistance but now it seems veterinary practices may be causing the problem. |
These pathogenic agents exert negative influences on goats and other farm
animals in various ways. Animals may succumb as a result of
heavy parasitic infection, especially in circumstances where infection is
accompanied by malnutrition and general poor management. Increased mortality in
goat herds also occurs when parasitism is accompanied by other
diseases and serious stressful conditions.
Gastrointestinal worms (helminths) in goats cause economic and nutritional
hardship in poor farming communities. Intestinal parasites cause inefficient
feed utilization leading to lowered growth rates in young animals, reduced
weaning weights, low milk production, enhanced susceptibility to other
diseases, and poor quality products.
Strategic and/or tactical de-worming are practices often recommended by
veterinary practitioners. All animals in a flock must be given recommended
therapeutic doses of anthelmintic (agents that destroy or dispel intestinal
worms) remedies when parasitological diagnostic techniques reveal high parasite
burdens. Animals are transferred to rested worm-free pastures immediately
following the deworming exercise.
But most poor farmers are unable to carry out the prescribed deworming of
their flocks. Costs of anthelmintic remedies are prohibitive and the large
amount of drugs needed to treat all the animals is way beyond the means
available to the small farmer.
Poor farmers are also obliged to utilize the same communal grazing
facilities all year round and, consequently, they do not have the
opportunity to move dewormed animals to cleaner environments as recommended.
In most parts of Africa, a huge variety of ethno-botanic remedies are
utilized against human and animal diseases. Many of these are used in
the treatment of parasitic diseases in farm animals. Animals that do not
show clinical signs are never subjected to treatment with traditional
medicine.
In a recent study undertaken by me in a communal farming region
in the east of Namibia, it was found that many indigenous farmers are
replacing the use of traditional remedies with the more potent registered
parasiticidal preparations. It would seem that the use of registered
pharmaceutical products in traditional medicine is on the increase among
poor livestock farmers in Africa.
Registered anthelmintic drugs are used by poor farmers to treat only
individual animals showing clinical signs and, to cut down on costs,
treatment is discontinued once clinical signs subside. The immediate
objective of the poor farmer, for whom every individual animal in the small
flock is important, is to eliminate the symptoms and prevent death.
The traditional approach to disease control, as described above, has
always been condemned by veterinary practitioners and drug manufacturers who say
the practice causes anthelmintic resistance. Professionals insist on the strict
adherence to prescribed doses of anthelmintics or, better still, to the use of a
combination of anti-parasitic agents.
On the contrary, recent observations appear to indicate that strategic
and tactical protocols are in themselves the main cause of widespread
development of anthelmintic resistance experienced worldwide. In southern
Africa, the phenomenon is specially pronounced on commercial farms where strict
adherence to recommended strategic/tactical practices is the norm. To understand
the role of strategic/tactical deworming practices in the development of anthelmintic
resistance, it is necessary to briefly review levels of performance of
parasiticidal products.
Few anthelmintic medicines are 100% effective. According to Van Wyk et
al.(1998) and Van Wyk (2001), even the best anthelmintic remedies in
current use are less than 100% effective. This shows that when such drugs
are administered to infected animals, even at strict recommended dosages,
not all of the parasitic population inhabiting the gut of the animals is
eliminated. Depending on the drug's degree of efficacy, only a certain
percentage of the worms harboured are killed. The sub-population of
parasites remaining in animals at the end of treatment is consequently 100%
resistant to the drug that was used. The result is that, when treated
animals are relocated to parasite free pastures, as recommended for
strategic/tactical deworming treatment, new parasitic colonies spreading in
the new farm environment will be drug-resistant strains. Obviously multiple
drug resistance will develop in the new farm environment if the deworming
exercise involved the use of multiple drugs. Thereafter the drugs that were used
will be incapable of curing animals developing symptoms of parasitic disease on
that farm.
The word refugia is used to denote parasitic populations that have not
been exposed to a particular drug and hence still contains a large
proportion of susceptible organisms. It would be expected that a big source of
refugia is the environment inhabited by infected animals before treatment and
relocation since this is where the free-living forms of the worms are.
As previously mentioned, treatment will eliminate the susceptible population
of parasites harboured by the host animal showing clinical signs and,
although the resistant proportion of the parasitic population still persists
in the animal, clinical signs subside and the animal, if properly fed, may
regain normal levels of production.
When the dewormed animal is maintained within the contaminated farm
environment, as the case in poor regions, new parasite populations
in refugia, rapidly gaining access into the host animal, will continue to
dilute the resistant sub-population that was selected by treatment in
the animal body. More over, drug susceptible populations coming from
refugia will have time to establish themselves in the treated host animal
before the selected resistant groups harboured have recovered from the
effects of the medicine on their reproductive activity. This ensures that the
spread of a purely resistant progeny of parasites in the environment does not
occur. The absence of refugia in the clean pasture does not permit the above
occurrence. Hence with the level of protection achievable by use of anthelmintic
remedies of limited efficacy, continuous utilization of a given grazing
environment can proceed for many years ensuring that time is given for new drugs
to be developed before existing ones have become ineffective as a result of
overwhelming anthelmintic resistance.
One might wonder why certain ethno-botanic remedies in use since time
immemorial still confer good levels of protection while recently
developed potent medicines, utilized mainly on large commercial farms, lost
efficacy in relatively short durations. The answer seems to lie in the
important role of refugia in diluting resistant sub-populations of parasites
that remain in the gut of treated animals. The use of potent registered
drugs according to traditional approaches to worm control in poor regions,
whereby only clinically affected animals are treated and left in the same
environment with the rest of the herd, appears an affordable and more useful
innovative practice by the small farmer than is the strict treat-and-move
approach.
This not only enables the communal farmer to suppress clinical disease
in severely affected individual animals and prolong their lives and, hence,
their usefulness to the household, but it also permits the role of refugia
in preventing rapid anthelmintic resistance on communal farms.
How do farmers identify heavily infected animals before the disease gets out
of hand? In most instances, clinical signs caused by gastrointestinal
parasites are non-specific and not easily distinguishable by unsuspecting
farmers.
Current diagnostic protocols undertaken by veterinarians for parasites
are highly specialized and demand special skills and laboratory equipment.
The FAMACHA © system, initially developed in South Africa for sheep, has now
been shown to work for goats as well and promises an easy method for diagnosis
of heavy parasitic infection by local farmers. FAMACHA © involves a comparison
of the colour of the ocular mucous membrane of the animal to a colour chart that
categorizes animals into one of five colour categories ranging from 1 (healthy)
to 5 (severely anaemic). The degree of anaemia in the animal reflects the degree
of infection by dangerous blood sucking worms, hence the need for drenching.
Using the FAMACHA © eye colour chart, any farmer, even illiterate
individuals, can assess the eye colour of individual goats and decide on
which animals to treat. The use of FAMACHA © techniques and employment
of available potent anthelmintic remedies by poor farmers to treated animal
identified with heavy infection appear sustainable and effective approaches to
combat worm infection and maintain acceptable levels of goat production in poor
farming regions.
More Information:
Dr Kumba is with the Department of Animal Science, Faculty of Agriculture and Natural Resources, University of Namibia. Private Bag 13301, Windhoek, Namibia. Tel. 264 61 206 4128/3890; Fax. 264 61 206 3013. E-mail: fkumba@unam.na
References Used:
Barton, N.J. 1983. Development of anthelmintic resistance in nematodes
from sheep in Australia subjected to different treatment frequencies.
International Journal of Parasitology, 13:125-130.
Radostits, O.M., Blood, D.C. & Gay, C.C. 1994. Diseases caused by
helminth parasites. In: O.M. Radostits, D.C. Blood & C.C. Gay (Eds.),
Veterinary Medicine: a textbook of diseases of cattle, sheep, pigs, goats and
horses, 8th ed., Balliere Tindall, London, 1223-1230.
Van Wyk, J.A. 2001. Refugia - overlooked as perhaps the most potent
factor concerning the development of anthelmintic resistance. Onderstepoort
Journal of Veterinary Research, 68:55-67.
Van Wyk, J.A., Bath, G.F. & Malan, F.S. 1998. The need for alternative
methods to control nematode parasites of ruminant livestock in South
Africa. World Animal Review: the FAO Journal on Animal Health, Production and
Products, 30-33.
Van Wyk, J.A., Stenson, M.O.S., Van der Merwe, J.S., Vorster, R.J. &
Viljoen, P.G. 1999. Anthelmintic resistance in South Africa: surveys
indicate an extremely serious situation in sheep and goat farming.
Onderstepoort Journal of Veterinary Research, 66:273-284.
Vatta, A.F., Letty, B.A., Van der Linde, M.J., Van Wijk, E.F., Hansen,
J.W. & Krecek, R.C. 2001. Testing for clinical anaemia caused by Haemonchus
spp. in goats farmed under resource-poor conditions in South Africa using an eye
colour chart developed for sheep. Veterinary Parasitology, 99:1-14.
Vatta, A.F., Krecek, R.C., Letty, B.A., Van der Linde, M.J., Grimbeek,
R.J., De Villiers, J.F., Motswatswe, P.W., Molebiemang, G.S., Boshoff, H.M.
& Hansen, J.W. 2002. Incidence of Haemonchus spp. and effect on
haematocrit and eye colour in goats farmed under resource-poor conditions in
South Africa. Veterinary Parasitology, 103:119 -131.
Copyright 2002, Science in Africa, Science magazine for Africa CC. All Rights Reserved
