Avian nephritis virus infections are contagious and are characterized by renal damage, visceral urate deposits, growth delay, and death. They occur mainly in chickens < 7 days old, as well as in ducks and geese. Subclinical infections have been reported in turkeys. Diagnosis is based on PCR assay. No treatment or vaccines are available; prevention is by appropriate husbandry.
Avian nephritis virus (ANV) infections are contagious infections affecting primarily chickens but also various other avian species, including ducks, turkey, and geese. ANV infections cause gastroenteritis and other enteric diseases, as well as renal damage and visceral urate deposits, growth delay, and death. ANV infections are of concern as a cause of increased flock mortality rates and economic losses in the poultry industry.
Etiology of Avian Nephritis Virus Infections in Poultry
The etiological agent of ANV infections is avian nephritis virus, within the genus Avastrovirus in the family Astroviridae. Like other astroviruses, ANV has a positive-sense single-stranded RNA genome within a nonenveloped capsid.
There are three recognized viral serogroups (ANV-1, -2, and -3) and at least six more genogroups outside of the three serotypes (1). ANV strains vary in virulence and in antigenicity.
Some ANVs were previously termed "enterovirus-like viruses" (ELVs). Molecular and antigenic characterization has led to reclassification of these viruses.
In addition to ANV, other viral species within the genus Avastrovirus include chicken astrovirus (CAstV), turkey astrovirus (TAstV), and duck astrovirus (DAstV), distinguished by the hosts from which they were isolated, as well as by viral genome characteristics.
Epidemiology of Avian Nephritis Virus Infections in Poultry
Avian nephritis virus infections affect primarily chickens but also various other poultry species, including ducks, turkey, geese, and guinea fowl. ANV infections have been reported worldwide.
ANV infections occur mainly in chickens < 7 days old; however, interstitial nephritis can occur in chicks up to 4 weeks old. In a study assessing a method for quantifying ANV in chickens with runting and stunting syndrome, the highest numbers of viral copies were found in breeder hens > 44 weeks old (2).
Subclinical infections are common and have been detected by serological surveys in some specific-pathogen-free (SPF) chicken flocks and in turkeys (3). ANV has also been associated with increased mortality rates in 4-week-old ducklings and with late-stage (near hatching) embryo deaths in ducks and geese.
Transmission is via the fecal-oral route and occurs by direct or indirect contact with feces from infected birds. Vertical transmission can also occur, but it appears less common. As with all astroviruses, the young, including embryos, are the most susceptible to ANV infections.
ANV is consistently isolated from the kidneys or feces during the first 10 days after infection.
Outbreaks with death rates of up to 10% can occur in chicks during the first 7 days of life.
Clinical Findings of Avian Nephritis Virus Infections in Poultry
Clinical signs of avian nephritis virus infections in chickens vary from no signs to death resulting from kidney disease or severe growth delay. Diarrhea and growth delay are common in broilers.
ANV infections cause clinical signs primarily in young birds and are usually subclinical in adult poultry.
Lesions of Avian Nephritis Virus Infections
Cardinal necropsy findings for chicks with an ANV infection are nephritis and visceral urate deposits (baby chick nephropathy).
Gross and microscopic lesions occur often in the kidneys. Kidney swelling, paleness, or yellowish discoloration with excessive urate deposition is common (see pale kidneys image).
Courtesy of P. O'Kane, Slate Hall Veterinary Services, UK.
Histological avian nephritis lesions consist of epithelial cell degeneration with granulocyte infiltration, infiltration of the interstitium with lymphocytes, and moderate fibrosis. In the latter stages, lymphoid follicles develop.
Some ANVs induce only intestinal lesions varying from decreased length of the microvillus border to total desquamation of the intestinal epithelium.
Diagnosis of Avian Nephritis Virus Infections in Poultry
RT-PCR assay
Serological testing
Although avian nephritis viruses and related viruses can be isolated by inoculation of suspected material (kidney or rectal contents) in the yolk sac of SPF chick embryos and in chick kidney cells, many ANVs are difficult to isolate. The best way to detect an ANV is byreverse transcription PCR (RT-PCR) assay or reverse transcription quantitative real-time PCR (RT-qPCR) assay of kidney or gut content samples. These tests are designed to detect multiple strains and enable quick differentiation from other viruses.
Serological diagnosis can be based on direct or indirect immunofluorescence assay, seroneutralization tests, or ELISA. However, these tests might detect only a limited number of ANV strains because of their high antigenic diversity, and they are not widely available.
Besides ANVs, nephropathogenic strains of infectious bronchitis virus (IBV) and CAstV also cause interstitial nephritis. Therefore, when nephritis is diagnosed, it is necessary to identify the causative agent. However, identifying the causative agent can be complicated by coinfections of ANV and CAstV, which are common.
Treatment and Prevention of Avian Nephritis Virus Infections in Poultry
Prevention through appropriate husbandry
There is no effective treatment for or vaccine against avian nephritis virus infections.
Appropriate husbandry and biosecurity are important for prevention of ANV infections. Poultry house fogging, stringent cleaning and disinfection, and ample downtime between crops are recommended.
Key Points
Avian nephritis virus infections lead to intestinal and kidney damage of young birds, which can cause growth problems or death.
Enteric strains are contracted via the fecal-oral route.
Diagnosis is confirmed by PCR assay.
No treatments or vaccines are available.
For More Information
Behboudi S. Avian nephritis. CABI Compend. 2022;92910.
Shivaprasad HL, Brugère-Picoux J. Other viral infections. In: Brugère-Picoux J, Vaillancourt J-P, Shivaprasad HL, Venne D, Bouzouaia M, eds. Manual of Poultry Diseases. AFAS; 2015:chap 39.
Saif YM, Marlier D, Smyth VJ, et al. Other viral infections. In: Swayne DE, ed. Boulianne M, Logue CM, McDougald LR, Nair V, Suarez DL, associate eds. Diseases of Poultry. 14th ed. Wiley Blackwell; 2020:1236-1329.
References
Saif YM, Marlier D, Smyth VJ, et al. Other viral infections. In: Swayne DE, ed. Boulianne M, Logue CM, McDougald LR, Nair V, Suarez DL, associate eds. Diseases of Poultry. 14th ed. Wiley Blackwell; 2020:1236-1329. doi:10.1002/9781119371199.ch14
Loor-Giler A, Castillo-Reyes S, Santander-Parra S, et al. Development of a fast and sensitive RT-qPCR assay based on SYBR® green for diagnostic and quantification of Avian Nephritis Virus (ANV) in chickens affected with enteric disease. BMC Vet Res. 2024;20(1):33. doi:10.1186/s12917-024-03881-8
McNulty MS, Connor TJ, McNeilly F. A survey of specific pathogen-free chicken flocks for antibodies to chicken anaemia agent, avian nephritis virus and group a rotavirus. Avian Pathol. 1989;18(2):215-220. doi:10.1080/03079458908418596
