THE REALITIES ABOUT POULTRY The Modern Farm - The Realities About Poultry_Seco | Page 94

Infectious diseases are caused by pathogenic microorganisms, such as bacteria, viruses, parasites or
fungi; the diseases can be spread, directly or indirectly, from one person to another. Zoonotic
diseases are infectious diseases of animals that can cause disease when transmitted to humans.
Viral Diseases
Viral diseases are the most common cause of losses, not only in large commercial flocks, but also in
backyard chickens. Mostly, they do not respond to drug therapy. Treatment relies on supportive
measures. Prevention and control relies on vaccination where this is effective, or by limiting
exposure to infected birds. If a secondary bacterial infection is also present, ant ibiotics may reduce
the severity of an outbreak.
(1) Newcastle Disease (ND)
This disease spreads rapidly via airborne droplets spread by the coughing or sneezing of infected
birds. The virus can be carried by wild birds, through contaminated eggs, and on clothing. As
mortality is often 100 percent in young chickens, New castle disease is probably the most important
constraint to family poultry development. Birds of any age can be affected, although young ones are
more susceptible. Mortality in older chickens is usually lower, but egg production is usually severely
reduced.
The incubation period of three to five days is followed by dullness, coughing, sneezing and gasping.
Rapid breathing is accompanied by a gurgling noise in the throat. The respiratory signs usually
develop first and are sometimes followed by nervous signs, characterized by twisting of the neck,
sometimes combined with dragging of wings and legs.
Depending on the environment and the degree of resistance of the birds, not all symptoms may be
shown, or they may be in a mild or subclinical form. Some farmers have observed that the twisting
of the neck occurs only in birds that survive. Early loss of appetite results in a greenish diarrhea. The
most obvious diagnostic sign of New Castle Disease is very sudden, very high mortality, often with
few symptoms having had time to develop. Diagnosis of New Castle Disease can be difficult from
just the symptoms, as they are so varied, and as many other diseases share the same symptoms. For a
discussion on the control of New Castle Disease, see the “New Castle Disease Control” section
below. The high incidence of New Castle Disease among family free-range flocks is due to the
following factors:
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