This is an example of Marek’s disease, caused by a highly contagious and cell-associated herpesvirus. It is very common and most birds are presumed infected; subclinical disease can lower both growth and egg production rates.
Fully infective viruses are released from feather follicles and the enveloped virus can be found in dander and dust. Clinical presentation is often as described in this case.
Clinical disease is highly variable, and depends on virus and vaccine strain and dose, host sex and genetics, maternal antibody, age at exposure, and underlying stress.
The most common finding at necropsy is enlarged nerves that lose their striations, especially the sciatic (as seen here), vagus, and brachial. Tumors (diffuse or nodular) may be seen in various organs.
Dx: Classically, look for tumors AND enlarged nerves at necropsy. Use histology and viral PCR to confirm. Prevent with vaccination and strict sanitation control.
Viral inclusion body hepatitis is an example of a condition caused by an adenovirus.
Swollen head syndrome is an example of a condition caused by a pneumovirus.
Infectious bursal syndrome is an example of an infection caused by a birnavirus.
Newcastle disease is an example of an infection caused by a paramyxovirus.
Image courtesy of Lucyin.
