Newcastle disease: Signs, prevention and treatment

Every poultry farmer keeping a large number of birds for commercial purposes is mainly concerned with three or four issues, with the ability to raise flocks with minimum mortality losses (high survival rates) being paramount. For broiler farmers, a final mortality rate of 2-5 per cent is acceptable until birds are sold off at 35-37 days of age, while for layer farmers, a survival rate of 90 per cent over a period of 24-28 months is acceptable. Other factors that farmers must manage include nutrition and the cost of poultry feed, basic animal husbandry practices, and access to markets. Today, we will focus on a respiratory disease of poultry called Newcastle disease, which every farmer needs to know about.

What causes Newcastle?

Newcastle disease is caused by a virus called the Newcastle disease virus. The virus commonly inhabits a wide range of bird species, including parrots, doves, eagles, and partridges, where it does not typically cause high mortality. Found worldwide, the disease occasionally spreads from these wild birds to infect our domestic chickens, remaining a persistent challenge for poultry farmers now and into the future. This disease affects birds of all ages and can also impact ducks, turkeys, and ornamental birds. Farmers must remain vigilant as this disease has a direct cost implication on the financial performance of chicken flocks. As we will discuss here, biosecurity programs will be essential to manage and contain the spread of the virus to adjacent farms.

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What are the signs?

The disease can cause moderate to severe mortality in non-vaccinated flocks, reaching up to 90 per cent. This underscores the importance of regularly vaccinating birds. Sick birds will discharge greenish diarrhea due to extreme starvation. Some birds will exhibit nervous signs such as star gazing, twisted necks, unsteady gait, and falling over. These birds will rarely eat, resulting in greenish diarrhoea. Infected birds will experience difficulty in breathing, red 'crying' eyes, and blocked nares with mucoid discharge. For birds in production, egg numbers will drop, and eggshells become weak, leading to breakages and losses. Most of these signs will be observed in flocks that have not been properly vaccinated either in the hatchery or on the farms, or both.

Always ensure your birds are adequately immunised against Newcastle disease at the hatchery or immediately on arrival at the farm. The nervous type of Newcastle disease is spontaneous, and the spread is rapid, affecting up to 90 per cent of the population in non-vaccinated flocks with dire consequences.

Prevention and treatment

Unfortunately, there is no treatment for Newcastle, but support therapies such as vitamin and electrolyte supplements and antibiotics to treat any secondary bacterial infections may reduce the impact of the disease. Depopulation and rigorous disinfection of contaminated farms have achieved limited success in preventing disease spread. Prevention is through good biosecurity and vaccination, including passive protection via breeders and vaccination. Vaccination is a better strategy; one must ensure that the right type of vaccine is applied timely, correctly, and appropriately to achieve full protection.

Vaccination

The preferred route of administration is through spray application as this directs the vaccine virus into the upper respiratory tract. However, eye/nose drop vaccination is an alternative and, if administered effectively, will yield comparable results.

How to control the disease through Bio-security measures

Farmers can also practice good biosecurity measures to reduce field challenges and help eradicate this condition on our farms. Avoid direct contact of healthy birds with sick birds and their droppings and nasal discharge. Avoid contact with people, their clothes, and shoes who have been in contact with infected flocks. Wild birds are healthy carriers of the virus, so keep your flocks in bird-proof units or barns. Control the movement of your staff, no visits to poultry markets and neighbouring farms. Properly clean and disinfect your sites before the arrival of new flocks. Practice the all-in all-out flocks’ principle and avoid mixing flocks of different ages on one site.

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