Showsilkies - Avian Nephritis Viral Infections

Avian Nephritis Viral Infections

Sunday, 29 June 2008

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Avian Nephritis Viral Infections

Avian nephritis viral infections are contagious infections of chickens and turkeys characterized by renal damage and visceral urate deposits, growth retardation, runting-stunting syndrome, and limited mortality (2-6%). They occur mainly in chickens <7 days old, but interstitial nephritis can be observed in chicks up to 4 wk old. These infections have been reported in Japan and Europe. Subclinical infections are common and have been detected by serological surveys in SPF flocks.

Etiology and Transmission:

The causal viruses are avian nephritis virus (ANV), ANV-like viruses, and related enterovirus-like viruses (ELV). Strains vary in virulence and in antigenicity. Transmission occurs by direct or indirect contact. Indirect evidence suggests that egg transmission may occur. Infection can be transmitted by oral administration of virus to day-old birds. Virus is consistently isolated from the kidneys or the feces during the first 10 days after infection.

Nephrotoxic strains of infectious bronchitis virus ( Infectious Bronchitis) also cause interstitial nephritis. Therefore, when nephritis is diagnosed, it is necessary to isolate the causative agent.

Clinical Findings:

Clinical signs vary from none to the so-called runting-stunting syndrome. Diarrhea and growth retardation are common in broilers. Outbreaks with mortality of 2-6% can occur in chicks newly hatched up to 7 days old; cardinal necropsy findings are renal damage and visceral urate deposits (baby chick nephropathy).

Lesions:

Nephritis is a common necropsy finding. Gross and microscopic lesions are often seen in the kidneys. Swelling, paleness, or yellowish discoloration with excessive urate deposition is frequent. Histological lesions consist of a degeneration of the epithelial cells with infiltration of granulocytes, interstitial lymphocyte infiltration, and moderate fibrosis. In the latter stages, lymphoid follicles develop.

Some ELV induce only intestinal lesions varying from decreased length of the microvillus border to total desquamation of the intestinal epithelium.

Diagnosis:

ANV and related viruses may be isolated by inoculation of suspected material (kidney or rectal contents) in the yolk sac of SPF chick embryos and in chick kidney cells. However, many ANV, ANV-like, and ELV viruses are difficult to isolate. The best method of detection is by electron microscopical examination of fecal preparations. Direct immunofluorescence performed on kidney sections is also a useful diagnostic procedure and allows quick differentiation from infectious bronchitis virus.