Avipoxvirus infections in brown kiwi (Apteryx mantelli)

CASE HISTORY: Nodular lesions were found on the skin of two immature brown kiwi (Apteryx mantelli) less than 6 months of age living freely on Ponui Island off the North Island of New Zealand. The lesions were observed during routine external examination undertaken as a part of the management of other research projects, one in 2006 and the other in 2011. Apart from the skin lesions, both birds showed no signs of illness and the lesions resolved spontaneously over a 2-month period.

PATHOLOGICAL FINDINGS: The first case showed several 3-mm diameter firm, brown nodules located on the skin below the hock of both legs. The second case had a single multinodular mass that measured 7×20 mm, on the base of the bill. A portion of the mass and scab samples were collected for diagnosis. Histological examination of the nodules revealed severe ballooning degeneration of keratinocytes and epithelial hyperplasia. Round eosinophilic structures resembling avipoxvirus (APV) intracytoplasmic inclusion bodies (Bollinger bodies) were observed in the layers of keratinocytes. In deeper layers of the epidermis, there was evidence of secondary bacterial growth and inflammation.

DIAGNOSIS: DNA was extracted from tissue samples and subjected to PCR analysis. Avipoxvirus 4b core protein gene was detected in both samples by PCR. Bootstrap analysis of APV 4b core protein gene revealed that APV isolates from two kiwi comprised two different subclades. One isolate displayed 100% sequence homology to subclade B1, and the other presented 100% sequence homology to subclade A3.

CLINICAL RELEVANCE: This study confirmed that kiwi are susceptible to APV infection and that at least two different strains of APV are present in the population examined. Since there is no information on the origin, virulence, or prevalence of APV in kiwi, a seroprevalence study would be useful to elucidate the degree of exposure and immune response to the disease. This would allow a more informed approach to risk management of the disease in wild and captive populations.