What you need to know about Newcastle disease
Dear Dr Messo
I keep layer chickens and I have noticed that some of them have twisted necks. What causes twisting of necks in chickens and can you shed more light on mad chick syndrome... [Caroline Koome]
It is common for avian veterinarians dealing with poultry farmers to hear complaints of twisted necks or circling motion or star gazing signs in a flock. It is important to collect more information about the history of condition, that include any previous vaccination, mortality pattern, level of biosecurity in the farm and any recent outbreak in the neighbourhood.
After thorough investigation which includes conducting postmortem examination and studying the blood picture (serology) of the live birds, the verdict should be a condition referred to as Newcastle disease. Here are six facts about Newcastle disease.
Newcastle disease is an old infection associated with poultry and wild birds as early as 1926. It is a respiratory disease and can cause high mortality in non-vaccinated flocks. Newcastle disease is notifiable, that means the government must be informed of its presence.
2. Etiology (Cause)
The disease is caused by a virus called avian paramyxovirus type 1. Over the years, scientists have isolated five different strains of the virus mostly associated with distinct signs of the disease commonly observed in the field.
3. Clinical signs
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Depending on the strain of the circulating virus, the disease can present five different and distinct clinical signs. The first form of the disease is mainly confined in the intestinal tracts of the birds where it causes massive hemorrhages, affecting the immune system and is very virulent resulting into huge mortality. The birds do not eat and pass out greenish diarrhoea. This form is called Viscerotropic velogenic type.
The second form causes high mortality following respiratory and nervous signs with birds appearing as if they are looking at the stars (star gazers), show twisted necks, walk in circles and have difficulty in breathing.
Layers will have drop in egg numbers. If the flock was vaccinated, there will be a rapid recovery in two to three weeks, this form is referred to as Neurotropic velogenic type.
In the third form, there will be involvement of respiratory signs and bit of the nervous signs, but mortality is very low. Farmers may not easily recognise the disease. It is referred to as Mesogenic form.
The fourth form of the disease -Lentogenic form- will affect the respiratory system with little or no infection. The last form is where there are absolutely no symptoms at all, and the infection is limited to intestinal tracts only. It is thus referred to as asymptomatic. It is important to state that not all cases of Newcastle can be picked up by just observing the signs in a flock of birds. This is why it is important for a qualified vet to do other tests to verify presence of infection.
4. Autopsy (lesions seen at postmortem)
There are no gross lesions specifically associated with this disease, if the respiratory form is present. One may observe at postmortem inflammation of the sinuses, trachea and air sacs. If the alimentary canal is affected, there will be pin point haemorrhages in the proventriculus, along intestines linings and cecal tonsils. A qualified vet should carry out postmortem and further laboratory analyses to confirm infection by use of serology and virus isolation.
5. Treatment and control
There is no treatment of this disease. The good news is there are vaccines that if used properly can reduce or minimise losses drastically. Consult your local veterinarian to give you a working vaccination programme with the right type of vaccines. Farmers can also practice good bio-security measures to reduce field challenge and help eradicate this condition in our farms. Avoid contact with infected flocks, keep your poultry units locked all the time and practice good hygiene.
[Dr Watson Messo Odwako, Company Veterinarian at Kenchic Limited [email protected]]