Avian Influenza, known as bird flu – is a viral infection caused by the avian Influenza Type A virus. These viruses are naturally found in aquatic birds and can infect domestic poultry and animal species. While some bird species may not become ill from the virus, it is highly contagious and can be deadly to certain domesticated bird species, such as chickens, ducks, and turkeys. With the potential for widespread transmission among bird populations, avian Influenza poses a significant threat to animal health and the economy.
Avian Influenza Management in Chicken
Causes of Avian Influenza Disease
- Influenzavirus, A virus of the family Orthomyxoviridae, causes avian Influenza.
- The virus has several subtypes based on antigenic relationships in the virus glycoproteins haemagglutinin (H) and neuraminidase (N).
- There are 15 recognized H subtypes and nine neuraminidase subtypes. The pathogenicity of the virus also varies, with very virulent strains causing highly pathogenic avian Influenza (HPAI) with high mortality rates.
- In contrast, other strains cause a milder disease known as low pathogenic avian Influenza (LPAI). Certain avian influenza virus subtypes of low pathogenicity may mutate into highly pathogenic virus strains after circulating in a poultry population for some time.
- Although H5 and H7 subtypes have been shown to cause highly pathogenic avian Influenza in susceptible species, not all H5 and H7 viruses are.
Disease cycle of Avian Influenza
- Enters the host cell, entry of viral ribonucleoprotein (vRNP) into the nucleus.
- Transcription and replication of the viral genome.
- Export of vRNP from the nucleus and assembles budding at the host cell plasma membrane.
- Entry of the virus from the host cell by binding to sialic acid on the host cell membrane with the viral membrane’s hemagglutinin (HA).
- The virus is taken up into the host cell by receptor-mediated endocytosis.
- It enters an endosome with a low pH that triggers the fusion of the viral and endosomal membranes.
- The acidic environment also opens up the M2 ion channel, acidifying the viral core and releasing the vRNP from M1, allowing it to enter the host cell’s cytoplasm.
Symptoms of Avian Influenza Disease
- The symptoms of avian Influenza in birds vary depending on whether it is low or highly pathogenic.
- There may be few clinical signs in low pathogenic avian Influenza, but infected flocks may show respiratory distress, diarrhea, and a drop in egg production of more than 5%.
- In highly pathogenic avian Influenza, affected birds may develop swollen heads, blue coloration of the comb and wattles, respiratory distress, diarrhea, and a significant drop in egg production. Mortality can be very high, and the severity of the disease can vary.
- It is important to contact your local animal health office if you suspect your flock has any form of avian Influenza.
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Diagnosis of Avian Influenza in Chicken
Detecting the virus or specific antibodies against it is required to diagnose avian Influenza (AI) in chickens. However, the presence of clinical disease is not enough to confirm a diagnosis.
- In a laboratory, samples are collected from live or dead birds and analyzed. Internal organs and oropharyngeal and cloacal swabs can be used to isolate the virus. In addition, In addition, AI viruses can be detected using hemagglutination inhibition or other immunoassays because they grow well in the allantoic sac of embryonated chicken eggs. Reverse transcriptase PCR can detect viral RNA.
- Serologic tests for AI antibodies, such as AGID or ELISA, are used to confirm infection in birds that have recovered from clinical disease. Hemagglutination and neuraminidase inhibition tests can also be performed to classify the virus by its subtype.
- Differential diagnosis is necessary to distinguish LPAI from other diseases or causes of decreased egg production, such as viral or bacterial infections and fungal diseases. HPAI must be differentiated from other high-mortality conditions, such as virulent Newcastle disease, fowl cholera, heat exhaustion, and sever