Diagnosis of Avian Influenza

Clinical signs and post-mortal lesions may be indicative of avian influenza infection. Virus isolation is needed for a definitive diagnosis.

Read more about:

• Clinical signs
• Post-mortal lesions
  

Laboratory Diagnosis

Samples

1. Identification of the agent
   • Live birds – tracheal swabs and cloacal swabs or faeces
   • Dead birds – organs and faeces
     
2. Serology
   • Clotted blood samples or
   • serum 

Procedures

Identification of the Agent

Inoculation of 9-11-day-old embryonated chicken eggs followed by:

1. Haemagglutination immunodiffusion test to confirm the presence of influenza A virus
2. Subtype determination with monospecific antisera
3. Strain virulence evaluation: evaluation of the intravenous pathogenicity index (IVPI) in 4-8-week-old chickens
   

Serology

Tests available:

ELISA:

• Detects antibodies to all AI virus, does not distinguish subtypes
• Only suitable for testing chicken and turkey serum
• Within 1 week of infection, antibodies are detected in more than half the specimens. 

AGID (Agar Gel Immunodiffusion test)

• As for ELISA does not distinguish AI subtypes
• Within 1 week of infection, antibodies are detected in more than half the specimens. 

HI (Haemagglutination Inhibition test)

• Serotype specific test
• Test available for each H subtype
• HI titres are positive a few days later than ELISA or AGID, titres persist long after infection
• Standard test for all avian species 

IFT (Immunofluoresence test)

• Able to detect antibodies to specific N-subtype
• Can be used to detect infection in vaccinated birds if a heterologous vaccine is used. Read more in Monitoring. 

RT-PCR (Reverse-transcriptase polymerase chain reaction)

• Able to detect influenza virus at very low levels
• The presence of subtype H5 or H7 can be confirmed by using H5 or H7 specific primers.