Agriculture Reference
In-Depth Information
Figure
7.12.
Ducks searching for snails in a rice paddy.
7.4.6 Pests and Diseases
Animals are affected by numerous pests and diseases. Some are endemic to particular
regions of the world, while others are present in nearly all countries. All animal dis-
eases cause economic losses, and some are transmissible to humans, causing illness or
death. The OIE (World Organization for Animal Health) classifies animal diseases as
list A, list B, or list C. List A diseases have the potential for rapid spread, having
serious public health consequences and are of major importance in international
trade. List B diseases are of public health importance and are significant in inter-
national trade. List C diseases are all other diseases not included in List A or B.
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Several diseases affect all classes of poultry but only the ones in list A will be
mentioned here.
Avian Influenza.
Avian influenza is a Type A influenza virus. Within the
Type A virus there are 15 subtypes classified as H or N. Several of the H types can
infect humans and other animal species. Avian Influenza has been reported in
Eurasia, Africa, and North and South America. Symptoms include nasal discharge,
coughing and sneezing, diarrhea, and sudden death. The Type A virus can be low patho-
genic or high pathogenic. Low-pathogenic forms display few symptoms. Low-
pathogenic forms sometimes mutate to high-pathogenic forms, causing extensive
losses. An epidemic in Pennsylvania poultry in 1983 - 1984 caused by the H5N2
virus started as a low-pathogenic infection but within a few months mutated to a
high-pathogenic form causing up to 90 percent mortality in flocks. Control of the
outbreak resulted in the destruction of 17 million birds at a cost of around $65
million.
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The H5N1 strain is a high-pathogenic form causing up to 70 percent
mortality in humans.
Newcastle Disease.
The second most important viral disease affecting chickens
around the world is Newcastle disease, known as Ranikhet disease in Asia. It is an air-
borne virus that spreads quickly and has a high mortality among young birds. Wild,
