Avian nephritis viral infections are contagious infections of chickens characterized by renal damage and visceral urate deposits, growth retardation, runting-stunting syndrome, and limited mortality (0–10%). They are seen mainly in chickens <7 days old, but interstitial nephritis can be observed in chicks up to 4 wk old. These infections have been reported worldwide. Subclinical infections are common and have been detected by serologic surveys in some SPF flocks and in turkeys.
Etiology and Transmission
The causal viruses are avian nephritis virus (ANV, an astrovirus), 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.
Clinical signs vary from none to the so-called runting-stunting syndrome. Diarrhea and growth retardation are common in broilers. Outbreaks with mortality of 0–10% can occur in chicks newly hatched up to 7 days old; cardinal necropsy findings are renal damage and visceral urate deposits (baby chick nephropathy).
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. Histologic 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.
Nephropathogenic strains of infectious bronchitis virus (see Infectious Bronchitis) also cause interstitial nephritis. Therefore, when nephritis is diagnosed, it is necessary to isolate the causative agent.
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 microscopic examination of fecal preparations. Direct immunofluorescence performed on kidney sections is also a useful diagnostic procedure and allows quick differentiation from infectious bronchitis virus. ANV genes can be detected by reverse transciptase PCR.
Serologic diagnosis can be made using indirect immunofluorescence, seroneutralization, or ELISA tests.
Treatment and Prevention
There is no effective treatment. General hygienic precautions are the only applicable preventive measures.
Last full review/revision March 2012 by Tadao Imada, DVM, PhD