Frequently Asked Questions about Avian Influenza

What is avian influenza?

Avian Influenza is an infectious and contagious disease caused by viruses which mainly infects birds but can also cross species barrier and infect some other animals such as pigs, horse, large cats, dogs and occasionally humans. In domestic birds the disease mainly occurs in two forms; low pathogenic disease which results in mild symptoms and causes mortality in complicated situations only and can easily go undetected, while high pathogenic form can result in high mortality even up to 100% and spreads rapidly among bird.

Where is the disease found?

The disease in its low or high pathogenic form is prevalent in many areas across the globe. Italy, Vietnam, Pennsylvania, Mexico, Germany, Korea, Iran, Thailand, Indonesia, China, Myanmar, Bangladesh, Nepal, Bhutan, Pakistan and India have reported outbreaks of Avian Influenza. In India, the first isolation of the H9N2 was done in 2003 from the Haryana and Punjab States and since then the virus has been isolated from 10 more States. HPAIV H5N1 outbreaks have been recorded in Indian poultry in 2006 (Maharashtra, Gujarat and Madhya Pradesh), 2007 (Manipur) and 2008 (West Bengal and Tripura) and subsequently in Assam, Sikkim and West-Bengal.

How is the disease transmitted and spread?

Migratory birds especially waterfowls are thought of to be reservoirs of AI viruses. They carry the viruses along with their migration routes, usually in low pathogenic form however, in some cases also in high pathogenic form. They can transmit the virus to susceptible domestic birds on direct or indirect contact with them. Within domestic poultry low pathogenic virus circulates and can mutate to high pathogenic form. It seems highly likely that H1N1 viruses may pass readily between pigs, humans and turkeys and the introduction of viruses of this subtype to turkey flocks from infected pigs has been well documented. Illegal movement of live birds along with dressed carcasses of infected birds, eggs from infected hens, poultry waste and fomites contaminated feces can all be a source of infection among trans-boundary countries. When introduced in a flock the spread of virus within flock occurs readily in suitable climates of humidity and cold. Virus is excreted in large quantities in feces and respiratory secretions. Spread may be either through direct contact, via conjunctival sac, nares or through shared and contaminated drinking water. Airborne transmission occurs if birds are in close proximity and with appropriate air movement. Avian influenza viruses have been transmitted to different mammal species on several occasions. Pigs, in particular, have been frequently involved in such 'interclass transversions'. In addition to swine, marine mammals and horses have been shown to acquire influenza A viruses from avian sources. Natural infection with H5N1 was seen in tigers and other large cats after the animals were fed with virus-positive chicken carcasses.

What is the public health risk associated with the disease?

Human cases of infection with the H9N2 virus has been reported although with negligible mortality but crossing the species barrier to mammals highlighted the pandemic potential of H9N2 virus. Some avian H9 viruses have acquired receptor binding characteristics typical of human strains, increasing the potential for reassortment in both human and pig respiratory tracts which are potentially capable of infecting humans, suggesting that potential pandemic viruses may emerge directly from birds. Human infection with H5N1 virus has occurred in many countries with a variable but high mortality rate which depends on the condition of the host and critical care provided. But with the possibility of virus gaining the potentiality of human to human transmission, it poses a great risk to whole humanity.

What are the clinical signs?

The clinical presentation of avian influenza in birds is variable and symptoms are fairly non-specific which depends upon the characteristics of the isolate, the dose of inoculum, the species and age of the bird.

The symptoms following infection with low pathogenic AIV may be slight and discrete and even go undetected such as

• - Ruffled feathers
• - Transient reductions in egg production or weight loss
• - Slight respiratory disease.

In its highly pathogenic form, the illness in chickens and turkeys is characterized by a

• sudden onset of severe symptoms and a mortality that can approach 100 % within 48 hours. Laying flocks stops egg production and individual birds often reveal little or no mobility and produce soft shelled eggs.
• Edematous swelling visible at feather-free parts of the head, cyanosis of comb, wattles and legs, greenish diarrhoea and labored breathing may be inconsistently present. Nervous symptoms including tremor, unusual postures (torticollis), and problems with co-ordination (ataxia), compulsively swimming in narrow circles on a pond dominate the picture in less vulnerable species such as ducks and geese leading to a preliminary suspicion of HPAI. The disease in turkeys is similar to that of chickens, but is often complicated by secondary bacterial infections such as those due to fowl cholera, turkey coryza or colibacillosis.

How is the disease diagnosed?

How is the disease diagnosed?

Field diagnosis is based on clinical signs and gross lesions. However, for a confirmatory diagnosis laboratory tests are required. Specimens to be taken are nasal and cloacal swabs, brain, lungs, trachea, spleen, intestine and cloaca. Nasal and cloacal swabs must be taken separately. If person is not well trained for the purpose, whole bird should be sent bagged twice and maintained refrigerated all the time. Lab diagnosis includes antigen detection using rapid molecular diagnostic tests like real time PCR and RT PCR followed by virus isolation in eggs, identification of isolates as influenza A virus using HA and HI tests. Serological investigations include ELISA, AGID and HI tests. Pathogenicity testing of virus isolates by chicken inoculation is also essential to confirm the class of virus as HPAI or LPAI.

Measures required at farm level?

The primary aim of an early and rapid response to any occurrence of HPAI is to contain the disease before it spreads and eliminate it by stamping out affected premises and establishing proper disposal. There should be proper culling, strict quarantine and movement controls, and safe disposal of carcass with burial being the best method at farm level, decontamination of the affected premises, restocking of the bird after a safe period of destocking of 90 days. Vaccination, when applied must be in conjunction with other disease control measures including mass slaughter as due to continuous strain variation, vaccination is not absolutely effective.