Newcastle disease in Yemen [Archives:2005/898/Health]
Despite assurances and reassurances from the Yemeni government that there are no cases of bird flu in Yemen and that everything is under control, there is a confession of other viral disease called Newcastle disease (ND).
ND virus is infective for almost all avian species, both domestic and wild. Most susceptible are domestic chickens, turkeys, pigeons and parrots. Milder disease is seen in ducks, geese, pheasant, quails, guinea fowls and canaries.
The severity of the clinical signs are influenced by the strain of virus and the age, condition, pre-existing immunity , other intercurrent disease conditions and the species of the bird. Incubation period is usually 5-6 days but may vary from 2-15 days. ND virus produces four broad clinical syndromes.
Viscerotropic velogenic ND: Characterized by sudden appearance, rapid spread, marked depression, loss of appetite, a sharp drop in egg production, increased respiration, swollen heads, blue combs, and frequently a profuse green diarrhea that leads to dehydration and collapse. Birds may die within 2 days. Those that survive the initial phase will often develop nervous signs such as twisted necks and muscle twitching. Up to 90% of birds may die.
Neurotropic velogenic ND: Severe respiratory and nervous signs predominate, including coughing and gasping, head tremors, wing and leg paralysis and twisted necks. Depression, loss of appetite and a drop in egg production also occur. Ten to twenty percent of adults and a larger proportion of younger birds may die.
Mesogenic ND: This is a respiratory syndrome with coughing but not gasping. Birds are depressed and lose weight, and egg quality and production decrease for up to 3 weeks. Nervous signs may develop late in the course of the disease and death rates are about 10 percent.
Lentogenic ND: This is generally unnoticed as signs are mild or abscent. However, mild respiratory signs and impaired appetite and a drop in egg production may be noticed. No nervous signs occur and deaths are usually negligible.
contacting with infected or diseased birds, the disease usually spreads. The virus is excreted in manure and is expired into the air. Other sources of infection are contaminated equipment, carcasses, water, food and clothing.
The virus is destroyed by direct sunlight within 30 minutes, but in cool weather can continue to survive in manure and contaminated poultry sheds for many weeks. A minimum core temperature of 80 C for one minute destroys the virus in meat products.