What are Nephritis Viral Infections?

Nephritis viral infections in birds are contagious and involve damage to the kidneys among other problems. These infections are caused by Avian Nephritis Virus (ANV). ANV, which was first found in 1976, is from the family Astroviridae and genus Astrovirus. 

Nephritis viral infections are usually seen in chickens that are younger than seven days old, however interstitial nephritis can occur in chicks through four weeks of age. Occurring throughout the world, the infections sometimes show no symptoms.

Causing kidney damage among other issues in birds, nephritis viral infections are caused by avian nephritis viruses, which are very contagious and impact birds under seven days old.

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Symptoms of Nephritis Viral Infections in Birds

Symptoms vary widely in viral nephritis among birds. There may be no symptoms, diarrhea, kidney damage, visceral urate deposits, slowed growth (degree of which varies) and in severe cases, death. Other symptoms may include an increased appetite, redness of the skin, poor feather development and the bird becoming emaciated.

Diarrhea and stunted growth are common in broilers. In baby chick nephropathy, the peak of disease is around five days of age. This condition is considered to occur in most flocks of broilers.

Types 

Avian Nephritis Virus 1 or ANV-1

This virus can cause mild stunted growth, interstitial nephritis and in some cases death, particularly when affecting day old chickens. While day old chickens are the most sensitive to the virus, it can be found in chicken of all ages. It is thought that ANV-1 occurs throughout the world, based on the detection of antibodies.

Avian Nephritis Virus 2 or ANV-2

This leads to growth stunting in chickens, as well as mild diarrhea and small intestine distension.

Infectious Bronchitis Virus or IBV

This condition is usually linked to respiratory disease and/or kidney damage, as well as increased rate of death at the end of the broiler fattening cycle. Age and state of the immune system of the bird, strain of the virus and whether secondary infections are experienced will determine the extent of illness.

Causes of Nephritis Viral Infections in Birds

Nephritis viral infections are caused by avian nephritis viruses or ANV’s. Previously, some of these were known as enterovirus-like viruses (ELVs). Some evidence exists that an astrovirus called chicken Astrovirus (CAstV) can also lead to kidney damage and stunted growth and Infectious Bronchitis Virus (IBV) can also cause kidney damage in chickens. There are a variety of ANV strains and they have different levels of virulence. The virus is transmitted through either direct or indirect contact and there is some suggestion that egg transmission occurs. Oral transmission can occur in newborn birds. When infected, the virus can be isolated from the kidneys or feces of the bird within the first ten days after initial infection.

Diagnosis of Nephritis Viral Infections in Birds

To definitively diagnose nephritis viral infection, the veterinarian will seek to demonstrate the virus. To do this, tissue from the kidneys can be smeared and put on slides and immunofluorescence or immunohistochemistry used to confirm the viral antigens. Feces and the liver can be tested to find the virus. Many ANV’s can be hard to isolate. The best way to detect the presence of one is through reverse transcriptase (RT)-PCR or real-time, quantitative RT-PCR of the samples. These tests can detect more than one strain and help to quickly differentiate them from other viruses.

When looking to diagnose the infection after the bird has died, it will usually be noted that the kidneys have a pale cortex and pale yellow discoloration. Gout-like nodules and tubular casts may be seen. The nuclei of tubular cells that have been impacted are, in many cases, inflamed as a result of viral propagation.

Treatment of Nephritis Viral Infections in Birds

No treatment exists that can resolve nephritis viral infections. Helping birds maintain a strong immune system is helpful and it is recommended that exposure to cold weather be reduced, as well as avoiding dehydration, transport and overcrowded conditions, which will cause stress for the birds. 

Recovery of Nephritis Viral Infections in Birds

Practicing good hygiene is the best method of preventing the spread of the virus. Antibodies passed from the mother are often able to provide protection to the chick, so immunizing breeding hens is an option, however there is not a vaccine available as of yet.