Lymphoid Leukosis is a leukaemia-like neoplastic disease. It affects chickens and is found in flocks worldwide. It can be transmitted from chicken to egg and there is no treatment or cure, and whilst the frequency of infection has been significantly reduced in flocks, knowledge of the disease is still important.
The infection has a long incubation period of between four to six months, and is usually seen in flocks of broiler chickens.
Chickens about five to eight months of age are most susceptible to the disease, with females being more susceptible than males. If infected, birds can become progressively weaker and emaciated, eventually leading to their death. It is characterised by tumour formation in the bursa of Fabricius, and if left unchecked, this could have a negative impact on your flock and your finances.
Cause
Lymphoid Leukosis is caused by a virus of the Leukosis/Sarcoma group. It’s a neoplastic disease which can take the form of a tumour and may metastasize to other tissues causing swelling of the abdomen.
Transmission
It’s transferred vertically from chicken to egg and susceptibility begins in the ovo but decreases as the bird ages. Horizontal transmission of the disease can also occur through the faecal-oral route, but is a secondary way in which this can occur. Continuing to breed using infected chickens will keep the disease in a flock.
Clinical signs
Chickens with this disease have few typical clinical signs. The virus has a long incubation period and signs are usually notable after 16 weeks. Visceral tumours are the main sign of Lymphoid Leukosis, although infected birds may not always develop tumours. The symptoms can include a reduction in egg production, enlargement of the abdomen, weight loss, weakness, emaciation and depression. At the terminal stage chickens develop greenish diarrhoea.
Diagnosis
There are distinct nodular tumours and tumours in the bursa of Fabricius, a lymphoid organ found only in birds. Infected breeders can be detected by testing blood samples and cloacal swabs for the presence of the virus. Lymphoid Leukosis may be confused with Marek’s disease but in Lymphoid Leukosis the nervous system is not involved so there is no paralysis.
Treatment and control
There is no treatment for Lymphoid Leukosis. The best control is to detect infected breeders and remove them from the breeding stock. Other diseases can increase the severity of this disease, so the need for the strictest, preventative biosecurity measures is vital.
Robust hygiene like cleaning and disinfection procedures to control diseases are also critical and form part of a preventative biosecurity strategy.
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