Animal diseases cause heavy economic losses both for individual farmers and at national or regional levels. The prevention and control of diseases aims to permanently or temporarily reduce these losses and, as far as the major animal epidemics are concerned, to prevent the economic and social catastrophes which accompany them.
The control of animal health presents three categories of possible repercussions on the environment :
Disease can be defined as a disturbance of all or part of the biological functioning of the animal. Factors causing disease can be grouped into two large categories:
Eradication of disease normally uses one or more of the following methods.
To reduce the prevalence of animal diseases, two main types of action are implemented :
a) Preventive and therapeutic measures:
c) Chemical methods (e.g. insecticides, acaricides).
The same methods and sometimes the same products are used to control various species of flies e.g. tsetse flies, tabanids, stomoxes.
Ecological approaches (biotope modification of the vectors or of the intermediates hosts). Biological control measures (predators, parasites, growth regulators). Genetic measures (release of sterile males). Mechanical measures (trapping and repelling techniques. See Non-Chemical Methods for methods of trapping tsetse flies).
The Pan African Rinderpest Campaign is an example of a large scale vaccination campaign to control rinderpest in Africa. The campaign has succeeded in eradicating the disease from most countries and rinderpest remains present only in a few areas. The second step in diseases-free countries consists of sero-surveillance and more globally in an epidemic-surveillance activity.
Total eradication can be both very expensive and almost impossible. Therefore, in such cases, the aim is not eradication, but diminution of infection to a reasonable level at which economic and/or social consequences are minimal. Hence, the acaricid treatments now aim at maintaining a minimum load for ticks on cattle. In this case, a minimum load is necessary to keep a natural immunity, which is useful in cases where cessation of treatment occurs. For these control programs to be optimised, an acceptable maximum load must also be determined, above which the negative effects on animal production are considered too heavy.
Evaluating the costs of animal health control has to take into account the methods and the technologies applied, the strategy of prevention or treatment, as well as the country where the progrmmme is to be implemented (cost of services, of salary, cost of products etc).
The costs include equipment, products, transport, infrastructures and labour.
Targeted Livestock Systems
The control of animal health is relevant to all animal production systems.
Consequences for Livestock Production and Human Welfare
The control of zoonoses in animals has a positive impact on human health because animals can be a source of infection for human: for instance the control of rabies, of anthrax, of tuberculosis, of Rift Valley Fever, etc.
Diseases are a major constraint to livestock development. Alleviating disease impacts on livestock is an important condition for increasing animal population; productivity and animal production (milk, meat, energy..).
Monitoring: EIA, Indicators
References / Further Reading
FAO, 1984. Ticks and tick-borne disease control. A practical field manual. Rome, FAO, pp. 621.
Bussieras, J., Chermette, R. 1991. Abrégé de Parasitologie vétérinaire- Fascicule 4- Entomologie. Ecole Nationale Vétérinaire, Maisons Alfort, pp. 163.
Douthwaite, R.J. 1992. Non targets effects of insecticides used in tsetse control operations. FAO World Animal Review. 70-71: 8-14.
Koeman, J.H. 1979. Chemicals in the environment and their effects on ecosystems. In: GEISSBÜHLER H. Edit.; Advances in Pesticide Science. Part 1. World Food Production- Environment- Pesticides, Pergamon Press, Oxford, 25-38.
Müller P. 1988. Effects of pesticides on fauna and flora. In: IAEA ed.: Pesticides: Food and Environmental Implications. IAEA-SM-297-40, 11-27.
Nagel, P. 1995. Environmental monitoring handbook for tsetse control operations. CTA/RTTCP, Scientific Environmental Monitoring Group, pp. 323.
Nagel, P. 1994. The effects of tsetse control on natural resources. FAO Animal Production and Health paper , 121:104-119
OIE. 1994. Ectoparasites des animaux et méthodes de lutte. Revue scientifique et technique de l'OIE, 13(4), pp. 1430.
Reid R., Wilson C.J., Kruska R.L., Mulatu W. 1997. Impacts of tsetse control and land-use on vegetative structure and tree species composition in south-western Ethiopia. Journal of Applied Ecology, 34: 731-747.
Rodhain et Perez C. 1985. Précis d'entomologie médicale et vétérinaire,.Maloine S.A. pp. 458.
Uilenberg G., 1998. A field guidefor the diagnosis, treatment and prevention of African animal trypanosomosis. Rome, FAO, pp. 158.
Wilson C.J., Reid R., Stanton N.L., Perry B.D. 1997. Effects of land use and tsetse fly control on bird species richness in southwestern Ethiopia. Conservation Biology, 11(2): 435-447.
WHO. 1984. Chemical methods for the control of arthropod vectors and pests of public health importance. WHO, Geneva, pp. 108.
WHO. Safe use of pesticides. Ninth report of the WHO expert Committee on vector biology and control. WHO Technical Report Series 720, 60 pages.
WHO. 1989. DDT and its derivatives. Environmental aspects. International Programme on Chemical Safety (IPCS), Environmental Health criteria, N° 83, pp. 98.
WHO. 1989. Deltamethrin health and safety guide. International Programme on Chemical Safety (IPCS), N° 30, 31 pages.
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Using Chemicals and Medicines in Animal Health Control
Medical and chemical treatments should strictly follow the instructions for use: quantity of product, frequency of application, duration of treatment, as well as delay before eating meat or milk. People who apply the treatment should be specially trained in those aspects and in the correct use of the medicines.Incorrect usage may lead to ticks resistant to acaricides, and diseases resistant to treatment.
To control ticks, acaricides are regularly applied also, weekly, fortnightly or monthly, according to tick species and tick infestation rate. The use of organophosphates as acaricides requires a delay before consuming the meat. Other acaricides, e.g. pyrethroids need a shorter delay but are more toxic for fish.
Positive Environmental Impact
Insecticide treatments have been used for a long time against biting diptera, on the ground or by air (Spraying of the resting or reproduction places). The ground spraying of pen is quite easy, while the vast eradication campaigns with ground treatment of the big carriers' biotopes (glossines, mosquitoes ...) require significant labour as well as financial means and a great capacity for organisation. They are only applicable during the dry seasons. Helicopters and planes are used according to the situations.
The helicopter is very efficient in uneven areas with dense vegetation for it can act swiftly on large surfaces, but it is expensive and has an impact on the non-targeted fauna. (Sprays applied in areas with rich biodiversity, especially on the banks of surface waters; large doses used in ultra-low-volume-sprays). The plane is very efficient and quick against diptera from scarcely wooded Savannah in flat regions with light and regular winds.
Persistent treatments on the ground or by helicopter with DDT or dieldrin have short term sharp effects on the terrestrial (Hymenoptera) and aquatic entomofauna and maybe on vertebrates (carnivorous and insectivorous birds ; some small mammals), fish, with accumulation in the food chains (animal fat, maternal milk) ; the endosulfan reveals a strong and immediate effect on fish and terrestrial as well as aquatic arthropoda with a risk of intoxication for consumers of the fish affected. In persistent doses, the action of pyrethroids is strong on crustaceans (shrimps ...) and terrestrial as well as aquatic arthropoda (ephemera, ants, wasps, spiders).
Treatments with non persistent doses with endosulfan (14-24 g/ha) by plane still have a strong but very transient effect on fish and insect. Organochlorines are scarcely used nowadays because they are prohibited in many countries. They are replaced by pyrethroids. Deltamethrine in non-persistent doses (0.25 g/ha) has a passing knock-down effect on insects (Ephemera, Coleoptera, Hermiptera) and transient lethal effect on fish from waters that are not very deep. In the mid and long term, the effects of most of these products die down because tropical ecosystems have a strong capacity for regeneration (Generally after a year) and anti-vector treatments are in general unique compared to agricultural treaments that are repeated, multiproduced and used in high doses.
One must note that in environmental follow-ups,
the tendency is to entrust rural populations with the monitoring of some
biotic parameters well perceived by themselves (dynamics of some vegetal
and animal species) or abiotic parameters (quality of soils, water, etc)
in their living surroundings.
|Main Techniques Used
|Biconical trap Chalier-Laveissière for tsetse fly:
|Pyramidal trap for tsetse fly of Gouteux and Le Gall, (adapted from
Gouteux et al.).
|Mobile screen of Mérot-Filledier
(adapted from Mérot et al.).
|Monoconical trap "Vavoua" of Laveissière for tsetse fly.
(Laveissière - Les glossines, guide de formation et d'information.
Série Lutte antivectorielle, 1988).
|Endectocides (e.g. avermectines, milbémycines), easily
applied by injection or pour-on
are efficient against endoparasites (gastro-intestinal and pulmonar worms,
hypodermes, microfilaria) and certain ectoparasites (biting flies, lice,
Their relatively high cost limits their use to the richer farmers.
"Pour on" application on the back of an animal with a measuring bottle (adapted from Cuisance).
Health care and disease prevention for livestock has a positive effect on the animal populations. Basically they allow other livestock improvement technologies as :