AVIAN INFLUENZA
WHAT IS AVIAN INFLUENZA??
Avian influenza (AI), caused by the influenza virus Type‘A’, can affect several species of food producing birds (chickens, turkeys, quails, guinea fowl, etc.), as well as pet birds and wild birds with some strains resulting in high mortality rates. The virus has also been isolated from mammalian species including humans, rats and mice, weasels and ferrets, pigs, cats, tigers and dogs.
AI viruses are not new. There are many descriptions of historical outbreaks of AI in domestic poultry throughout available literature.
There are many strains of AI viruses and generally can be classifi ed into two categories: low pathogenic (LPAI) that typically causes little or no clinical signs in birds and highly pathogenic (HPAI) that can cause severe clinical signs and/or high mortality in birds.
The Asian origin highly pathogenic H5N1 strain of the AI virus has attracted much attention over the last few years because of signifi cant outbreaks globally in domestic and wild birds. Concern is raised because of the degree of virulence not only in poultry but also in wild birds as well as the ability to infect mammalian species. While AI viruses are generally highly species specifi c, the highly pathogenic H5N1 AI virus has also infected humans.
Low pathogenic strains of AI H5N1 virus exist but do not produce signifi cant clinical signs in birds
WHERE IS THE DISEASE FOUND???
AI occurs worldwide and different strains are more prevalent in certain areas of the world than others.Of particular interest are outbreaks of highly pathogenic H5N1 AI that began in south-east Asia in late 2003. Over the past years, several other Asian countries have reported outbreaks and in some, the disease is now considered to be endemic (always present). Outbreaks of HPAI H5N1 have also been reported in Africa and Europe.
In 2021 , currently this is outbreaks in India had so far been reported at 12 epicentres across four states — Kerala, Rajasthan, Madhya Pradesh and Himachal Pradesh — and issued advisories to contain further spread of the infection.
This disease first outbreaks in India in 2006.
HOW DISEASE TRANSMITTED AND SPREAD?
Several factors can contribute to the spread of AI viruses including globalization and international trade (legally and illegally), marketing practices (live bird markets), farming practices and the presence of the viruses in wild birds.
Wild birds normally can carry avian influenza viruses in their respiratory or intestinal tracts and usually do not get sick. Wild birds have historically been known as reservoirs for AI viruses, mostly of low pathogenicity. Around the world, surveillance measures have been put in place to monitor occurrence and characteristics of AI viruses in wild birds. In wild birds, it is common during routine testing to fi nd some infl uenza viruses. The vast majority of these viruses do not cause disease.
In studying current HPAI H5N1 outbreaks, the exact role of wild birds in spreading the virus over long distances is still not fully understood in all situations. Generally, there are many uncertainties about the wild species involved, the migratory routes used and, above all, the possibility that some species could become permanent reservoirs of the H5N1 virus, with carriers showing no clinical signs of the disease.
AI viruses can be spread through ddirect contact with secretions from infected birds, especially faeces or through contaminated feed, water, equipment and clothing.
Apart from being highly contagious among poultry, avian infl uenza viruses are readily transmitted from farm to farm by the movement of domestic live birds, people (especially when shoes and other clothing are contaminated), and contaminated vehicles, equipment, feed, and cages. Highly pathogenic viruses can survive for long periods in the environment, especially when temperatures are low. For example, the highly pathogenic H5N1 virus can survive in bird faeces for at least 35 days at low temperature (4ºC). At a much higher temperature (37ºC), H5N1 viruses have been shown to survive, in faecal samples, for six days.
Other species including cats and pigs can exceptionally become infected with the HPAI H5N1 virus. Infections of pigs are of concern because the species is susceptible to infections of both avian and human infl uenza viruses and this may provide the H5N1 AI virus the opportunity to reassort or mutate. While sporadic infection with HPAI H5N1 virus in both species have been reported over the past three years there is no Scientific evidence to suggest that either species plays a signifi cant role in the epidemiology of the disease or as a source of virus to other species.
WHAT ARE THE CLINICAL SIGNS OF DISEASE??
In the mild form, signs of illness may be expressed only as ruffl ed feathers, reduced egg production, or mild effects on the respiratory system.
In the severe form of the disease, the virus not only affects the respiratory tract, as in the mild form, but also invades multiple organs and tissues that can result in massive internal haemorrhaging.Some or all of the following clinical signs are evident in birds infected with a highly pathogenic strain of AI (including H5N1 strain):
– quietness and extreme depression;
– sudden drop in production of eggs, many of which are soft-shelled or shell-less;
– wattles and combs become swollen and congested;
– swelling of the skin under the eyes;
– coughing, sneezing and nervous signs;
– diarrhoea;
– haemorrhages on the hock;
– a few deaths may occur over several days, followed by rapid spread and a mortality rate that can then approach 100% within 48 hours
How is the disease diagnosed?
Avian infl uenza (AI) may be suspected on the basis of clinical signs and events leading to the disease. Laboratory tests are required to confirm the diagnosis
PREVENTION AND CONTROL
Prevention and control measures
It is extremely important to have early detection and warning systems and prevention measures in place as part of an effective strategy for AI. This needs to be coupled with similar efforts placed on preparing for a potential outbreak.
Around the world, surveillance measures have been put in place to detect the presence of infection in poultry according to OIE standards for the surveillance of avian influenza .Additionally, surveillance programmes monitor the occurrence, prevalence and characterisation of AI viruses found in wild birds. Wild bird surveillance considers different migratory flyways and particularly at mingling points for migrating birds from different continents.It is essential for poultry producers to maintain biosecurity practices to prevent introduction of the virus in their flock.
Measures that are recommended at the farm level include:
– keep poultry away from areas frequented by wild fowl;
– keep control over access to poultry houses by people and equipment;
– do not provide elements on property that may attract wild birds;
– maintain sanitation of property, poultry houses and equipment;
– avoid the introduction of birds of unknown disease status into fl ock;
– report illness and death of birds
– appropriate disposal of manure and dead poultry.
If the disease is detected, generally a‘stamping out’ (culling) policy is used in the efforts to eradicate the disease. Elements included in a response effort include:
– humane destruction of all infected and exposed animals ;
– appropriate disposal of carcasses and all products;
– surveillance and tracing of potentially infected or exposed poultry;
– strict quarantine and controls on movement of poultry and any at-risk vehicles;
– thorough decontamination of infected premises ;
– a period at least 21 days before restocking.
Culling may be complemented by a vaccination policy for poultry in a high-risk area. Vaccination aims to protect the susceptible population of birds from potential infection thereby reducing the incidence or the severity of disease. Vaccination strategies can effectively be used as an emergency effort in the face of an outbreak or as a routine measure in an endemic area
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