Flu Clues

The avian influenza vaccine has been quite helpful in preventing the disease in poultry flocks. But while vaccination is one of the key tools employed to control an AI outbreak, it is not the sole approach towards its control, write Dr Shahan Azeem and Dr Muhammad Akram Muneer

Winter conjures up images and memories of warm cosy rooms, soups, peanuts, woollen clothing and misty mornings. But, like many things in life, along with numerous delights, winter also comes with its peculiar inconveniences.

Closed doors and windows, for example, cause the indoor environment, more appropriately the microclimate of a home, to become precipitated with germs (bacteria, viruses, fungi, etc.,) that can infect humans. That is why if one member of the family catches any type of flu, others soon become infected too. Another reason for the flu virus to survive and thrive in winters is the low environmental temperature. These factors also play a part in the high prevalence of avian influenza (AI) in poultry.

AI is an infectious orthomyxoviral infection caused by multiple serotypes of the virus that have the potential to infect humans, pigs, cats, horses, mink, marine mammals and poultry.

THE VIRUS
Avian influenza virions are typically spherical to pleomorphic and filamentous in shape, usually ranging between 80-120 nm. The virus possesses two surface glyco-proteins — rod-shaped trimers of hemagglutinin (HA) and mushroom-shaped tetramers of neuraminidase (NA).

A virus can be divided into subtypes on the basis of the possession of one of the 16 (1-16) antigenically distinct HA antigens and one of the 9 (1-9) neuraminidase antigens. The infectivity of an influenza virus depends on the cleavage of HA by specific host proteases (enzymes responsible for viral protein cleavage), while its NA is involved in the release of progeny virions from the infected cell surface. Another role of the NA protein of AI virus is to prevent clumping of the newly-formed viruses.

Virulent AI strains which cause a systemic disease have an HA that is cleaved by proteases present in all body cells of the host, on the other hand low pathogenic AI (LPAI) strains have an HA that is cleaved by the proteases restricted to respiratory and intestinal tract.

The influenza virus genome consists of eight segments of single-stranded, negative sense RNA. Fortunately, the flu virus is relatively unstable in the environment and is destroyed in 30 minutes at 60°C or in three hours at 56°C, hence it is easily destroyed by boiling or during cooking. It is inactivated by commonly employed disinfectants such as formalin, sodium hypochlorite, sodium hydroxide and iodine compounds.

VIRUS MUTATION
The re-assortment of the gene segments referred to as antigenic shift is a regular feature of influenza A viruses, resulting in the emergence of novel virus subtypes, leading to pandemics. The annual epidemics, however, are due to evolution of the surface antigens of influenza A and B viruses as a result of point mutation(s) in gene(s), a phenomenon known as antigenic drift.

AVIAN INFLUENZA IN POULTRY IN PAKISTAN
In poultry, AI due to H7N3 virus was first diagnosed in Pakistan in 1994. The disease outbreaks were associated with high mortality, morbidity and growth and production losses mainly in the laying broilers breeder chickens. Subsequently, in March 2001, AI viruses were again identified in chickens at farms 200km southwest of Islamabad. The affected population was layers, broilers and broilers breeder chickens.

Approximately 75 per cent of the population at those farms indicated mortality between 20 and 85 per cent. The isolates obtained through flock sampling were H9N2 and H7N3 AI type viruses occurring alone or in combination with Newcastle disease viruses. Both HPAI and LPAI forms of H7N3 virus are known to infect poultry.

During March 2003, another epidemic of H7N3 avian influenza was recorded, which caused heavy mortality in the commercial layers of various farms in the Karachi area. This AI outbreak was quite severe in the commercial layer flocks which were at the peak of egg production. The infection of avian influenza H9N2, however, continued in Karachi and its adjoining areas. The professionals working at various research laboratories purified the isolate from morbid tissues and developed a vaccine which provided satisfactory protection against the field virus in the inoculates. Till now, the major serotypes of the AI virus isolated from outbreaks in breeder and commercial laying and broiler flocks in Pakistan were characterised as H7N3, H7N2 and H9N2. But from 2006 onwards the H5N1 virus infection has also been reported at poultry farms in NWFP, Punjab and Sindh.

Inactivated AI H7N3, H9N2 and H5N1 virus vaccination is currently being inoculated to immunise poultry. The use of vaccine has been quite helpful in preventing the clinical disease in poultry flocks. While vaccination is one of the key tools employed to control an AI outbreak, it is not the sole approach towards its control.

ZOONOTIC SIGNIFICANCE:
The first documented direct transmission of an AIV to humans was reported in Hong Kong in 1997. The H5N1 virus had caused a severe respiratory illness in 18 young adults, six of them died. In 1999, avian influenza H9N2 viruses were isolated for the first time from humans. Two children were hospitalised with uncomplicated upper respiratory tract infection in Hong Kong. However, both completely recovered from illness.

In 2003, two influenza cases in Hong Kong residents who had travelled to China were confirmed, one of the patients died. An outbreak of H7N7 avian influenza was also recorded in poultry farms in the Netherlands, the same year. A veterinarian who had visited an affected poultry farm died with signs of pneumonia. In the Netherlands in 2003, three family members of a farm worker were tested as infected with H7N7 virus, indicating its potential for human-to-human infection.

In February 2004, another outbreak of H7N7 avian influenza virus was recorded on a poultry farm in British Columbia, Canada, and resulted in at least 05 human infections, mainly conjunctivitis. Currently the H5N1 AI virus outbreaks have been observed in poultry in many Asian countries. In December 2003, a number of human H5N1 infection cases were reported from Vietnam and Thailand, and the mortality due to this infection was up to 70 per cent.

It is pertinent to mention here that World Health Organisation (WHO) has confirmed a total of 387 human cases due to H5N1 virus, of which 245 have died. Furthermore, in Pakistan, WHO (2008) reported three human cases of which one person died. Care should be exercised while handling live poultry or poultry meat.

Information available on avian influenza virus (AIV), its mutagenic and zoonotic nature implies implementation of proper precautionary measures (clothing and procedures) by poultry farm workers, live poultry handlers, raw chicken meat handlers, culling staff, veterinarians etc., while handling live suspected poultry, its meat or eggs.

Keeping in view the zoonotic nature of influenza virus following guidelines are issued to avoid public health hazard.

GUIDELINES FOR POULTRY/EGG CONSUMERS
1. Only healthy poultry meat be purchased, in case you prefer meat from freshly slaughtered birds.
2. If you chose to slaughter a chicken at home, dispose of the feathers, intestines and non-required organs properly. Preferably disinfect and bury such organs deep in the soil or burn them. Always wash the slaughtering knife, your overalls, hands and floor used for slaughtering with soap and clean water, followed by a disinfectant.
3. Clean the meat thoroughly and pack it properly in case you want to freeze it for future use.
4. Keep a separate knife to cut poultry meat. Clean the knife after use with a disinfectant or household detergent. Wash your hands thoroughly with a detergent/soap using clean water for at least 30-60 seconds.
5. Since the AIVs are killed well below boiling point, the fully cooked poultry meat is safe for consumption.
6. Similarly, the fully fried/boiled eggs can also be consumed without hesitation.
7. In case you see a dead bird (wild, domestic or fancy), report it to a government veterinarian.

AI CONTROL STRATEGIES

At poultry farms following measures, if properly employed, will help in the prevention of AI:

1. Awareness of poultry farmers, workers and market personnel about the infectious nature of the virus, influenza signs, reporting of cases, labs carrying out confirmatory tests, etc.
2. Implementation of proper bio-security measures at poultry farms.
3. Proper disposal of carcasses, disinfection of farm premises and water supplies, vermin control and protection of poultry sheds from wild birds and wild animals, etc.
4. Vaccination of poultry flocks against prevailing AI virus types can be helpful as a part of an overall control strategy.
5. Strict adherence to personnel hygiene practices.