Our company recently participated in one of the national agricultural exhibitions. As a way of encouraging farmer participation, I always ask them what topics they would like to have covered in Smart Harvest. Disease management and control is top on the list – with Newcastle Disease being one of the commonest diseases that elicits interest.
Newcastle is an infectious and very contagious viral disease that affects different poultry species. It is present worldwide.
It can be categorised into three different groups of strains depending on harm caused to the bird (pathogenicity). Velogenic- highly pathogenic and easily transmitted; mesogenic- moderate: and lentogenic strain- low and mild clinical signs in chicken. Classification of the disease can also be done according to body systems affected- pneumotropic (respiratory system), viscerotropic (gastrointestinal and other internal organs) and neurotropic (nervous system).
Local and free-roaming chickens are believed to act as reservoir of the disease causing virus. Guinea fowls are also suspected to harbor the virus and have been linked to Newcastle outbreaks in different parts of Africa.
Newcastle disease is associated with rapid post-exposure onset of clinical signs with younger birds showing signs sooner than older birds. Clinical signs presented depend on the type of virus strain involved.
But common symptoms include watery discharge from nostrils, laboured breathing (gasping), sneezing/ coughing, watery-greenish diarrhoea among others.
Nervous signs include drooping wings, twisting of head and neck, circling, inappetence and complete paralysis. The mild pathogenic type of the disease is characterised by reduced egg production and mild respiratory signs.
Clinical signs such as drastic drop in egg production and production of soft-shelled eggs are characteristic of the moderately pathogenic type. Eggs from affected flock maybe abnormal in colour, shape and have watery albumen. The very virulent type has similar clinical signs to moderately pathogenic type with high mortality rates that could be as high as 100 per cent.
The virus is usually shed through body fluids, secretions and droplets from the breath of infected birds. Spread of the disease normally happens through contaminated air exhaled by the infected birds. Transmission also takes place via respiratory discharges and droppings. Birds infected by the virulent type lay eggs infected with the virus- this leads to infected embryos which normally die before hatching.
Transmission of the virus also occurs through contaminated fomites which include shoes, farm worker clothing, vehicles, contaminated feed, visitors and farm equipment as well as wild birds.
Treatment and prevention
Newcastle disease has no specific treatment. In mild cases, use of antibiotics may be helpful in prevention of secondary infection especially those caused by E.coli bacteria.
Well implemented bio-security program that ensures good sanitation standards are of utmost importance in prevention of the disease occurrence. This should be accompanied with a well-designed and executed vaccination regime.
Vaccination of birds against ND starts at day-old in the hatchery level in most breeds.
Some hatcheries recommend first dosage to be administered at day 7. The dose is repeated at day 18-21, at 8 weeks, 18 weeks then every 3 months thereafter. The regime may vary depending on the breed as well as location. Availability of vaccines such as “ITA-NEW” from Ultravetis guarantees year-long protection against the disease when administered – through subcutaneous or intramuscular injection. The ‘ITA-NEW” vaccine should be used when administering the week 18 dose. This means that the next dose will now be done after 1 year. It is more economical in the long run and there is also less stress to the birds since administration is once every 12 months as compared to the other regime where administration is every 3 months.
The writer is a veterinary surgeon and runs Nature Kuku, a farm in Naivasha that produces kuku kienyeji breed and trains small holder farmers on rearing them. You can reach him on [email protected]