What is bird Flu

WHAT IS BIRD FLU (H5)? Clinical Symptoms

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Bird flu is called an Avian influenza type A virus. The dreaded bird flu virus has claimed many lives and played havoc with the poultry industry in some countries of  Asia and Europe. It is also being detected every year around the world.

Definition of Bird Flu

Despite, all the precautionary measures, its entry into any country could not be stopped eventually. The exact definition of the Bird can be given in four-way-

  • By the poultry Book
  • Nomenclature Origin
  • Origin of Pathotype
  • European union definition

By the poultry Book

According to the Diseases of poultry book (5 th edition), it is defined as an appellation “bird flu” that is used as a simplified. Which alternative to avian influenza by the media to describe infections in poultry, humans, and other mammals with Type A influenza viruses derived from birds.

Avian Influenza (Bird flu) Since that outbreak in 2002, H5N1 HPAI also referred to as “bird flu. It is the primordial reservoir of all influenza A viral genes. In a similar way, all other Influenza  A  subtypes, the H5N1 subtype is an RNA virus.

From Nomenclature Origin

It is an infectious disease of birds caused by the Influenza  A (H5N1) virus. It is also called ‘H5N1 virus’– occurs mainly in birds. It is highly contagious among birds and can be deadly to them. It is defined, H5N1 is a subtype of the species  Influenza A  virus of the  Influenzavirus A genus of the  Orthomyxoviridae family.

According to Pathotype

High Pathogenic noticeable Avian Influenza (HPNAI) viruses must have an IVPI in six-week-old chickens greater than 1.2.  alternatively, cause at least 75% mortality in four- to eight-week-old chickens infected intravenously. In the case of the sub-type.

H5 or H7 viruses which do not have an IVPI of greater than 1.2. In another ward, H7 viruses which do not have an IVPI of greater than 1.2. if the amino acid motif is similar to that observed for other HPNAI isolates, the isolate being tested should be considered as HPNAI viruses.

But, make sure your bird should full free coccidiosis which also partially helps to prevent Newcastle disease.

See Also- The best drugs for coccidiosis in poultry

According to European union

Infection of poultry caused by an influenza A virus that has an intravenous pathogenicity index in 6-week-old chickens >1.2. or any infection with influenza A viruses of subtype H5 or H7  for which nucleotide sequencing has demonstrated the presence of multiple basic amino acids at the cleavage site of the haemagglutinin.

Types of Bird Flu

there are two types of infection found in poultry depends on clinical symptoms and mortality range.

1) High pathogenic Avian Influenza or Bird flu( HPAI) which is called H5N1

2) Low pathogenic Avian Influenza or Bird flu (LPAI).  which is called H9N2

H5N1 Type Bird Flu

It is also called High pathogenic Avian Influenza (HPAI) due to most all bird became died off in single infection just one infection. It is the most dangerous type of bird flu since its discovery.

Mortality range vary types of infection and bird age. It is spread all over the world. it is considered to be the number one threat to the poultry industry.

H5N1 Clinical Symptoms in layers bird

It affects the whole poultry systems such as the immune system respiratory system, nervous system, gastrointestinal system, reproductive system, in layer etc. The most clinical system of H5N1 in poultry are

  • Normal feeding and water but death suddenly
  • Egg production sable but sometimes increasing suddenly
  • all birds are death in same cage due to contagious in nature
  • Excessive drooling saliva
  • High fever
  • Cyanosis at com and wattle of bird before and after mortality
  • Milky color with slight greenish color feces is the characteristics signs
h5n1 bird flu
H5N1 bird flu stool

High Pathogenic Avian Influenza (H5N1)
H5N1 bird flu feces

  • Eyelid became swollen of bird
  • No changes of eggshell, shape, color, size and texture in maximum cases

Clinical symptoms of H5N1 in Pullet
  • Sometimes, it is starting with respiratory signs like coughing, sneezing, respiratory difficulty etc.
  • in some cases, mortality start with absence or repository signs.
  • birds became suddenly sitting down due to kidney became damage which is called gout.
  • Opisthotonus and torticulitis also pathognomic clinical symptoms at h5n1 infection.
  • Reduced feed intake first time but increase after few days.

Ramzan, DVM, Poultry Veterinarian


  1. Avian Influenza and Newcastle Disease by A Field and Laboratory Manual Foreword by Joseph Domenech and Bernard Vallat
  2. Diseases Of Poultry, 13 the edition
  3. Poultry Diseases, 6th edition
  4. OIE Manual Of Diagnostic Tests And vaccines For Terrestrial Animals

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