Dr Kritima Kapoor
A very recent disease causing extremely high mortality in birds like chicken, ducks, turkeys, geese or quails is nowadays recognized as Bird flu. It was found to be caused by a severely pathogenic virus known as “Avian influenza virus” which is adapted to birds. The disease is informally known as avian flu, bird flu or fowl plague (‘plague’ is a Latin word for ‘blow’). Therefore, the disease causing high mortality was termed as ‘plague’.
Bird flu is a phrase similar to swine flu, dog flu, horse flu or human flu in that it refers to an illness caused by any of the many different strains of influenza viruses that have adapted to a specific host. All known viruses that cause influenza in birds belong to the species influenza A virus. Avian influenza virus is of two subtypes: (i) viruses of low virulence and (ii) viruses of high virulence capable of causing severe mortality (100%) in poultry and, therefore, termed as highly pathogenic avian influenza (HPAI). It is basically an enveloped RNA virus belonging to Family Orthomyxoviridae with two different surface projections or “spikes” i.e., haemagglutinin (HA) and neuraminidase (NA). Based on these HA and NA surface receptors, a particular virus is named, e.g., H1N1, H5N1 etc and this also determines its virulence (disease causing ability).
Avian influenza viruses are distributed throughout the world in many domestic birds including chicken, ducks, turkeys, geese, guinea fowls, pheasants and quails and also in wild birds. Although it’s most highly pathogenic strain i.e., H5N1 had been spreading throughout Asia since 2003. Avian influenza reached Europe and the Middle East, as well as Africa in 2005. In 2012, China reported its second human death due to bird flu in a month following other fatalities in Vietnam. Pigeons do not contract or spread the virus. Eighty four percent of the affected bird populations are composed of chicken and farm birds, while the rest 15 percent is made up of wild birds according to capture-and-release operations in the 2000s, during the SARs pandemic. Recently, in India, strain H5N1 was identified in Kerala in November, 2014 and mass culling operations were carried out slaughtering close to 3 lakh ducks. Moreover, ducks may get infected but they don’t suffer from clinical disease because of marked resistance these birds show even to strains that are highly virulent for chicken and turkeys. Ducks, therefore, act as reservoirs and carriers of avian influenza and spread the virus to chicken and turkeys, which suffer the disease clinically. Infected birds excrete virus from respiratory tract, conjunctiva and faeces (excreta). Therefore likely modes of transmission among birds include both direct and indirect contact between infected and susceptible birds. Indirect contact includes contact with contaminated aerosol (droplets), anything contaminated with faecal material like feed, water, equipment, cages and delivery vehicles etc. Therefore, the faecal/oral route appears to be the main route of spread among birds.
Human spread
According to Centers for Diseases Control and Prevention, the spread of avian influenza viruses from one ill person to another person has been reported very rarely, and has been limited, inefficient and unsustained. A growing body of evidence suggests that pandemic strains of influenza in humans often arise as a result of genetic recombination or re-assortment between human and avian viruses. Most human contractions of the highly pathogenic H5N1 virus are a result of either handling sick infected or dead birds, from contact with infected fluids, surfaces contaminated with secretion/excretions from infected birds or being in contact with the faeces of infected birds. That is because there is no natural immunity from bird flu in humans. Human body cannot develop antibodies and therefore hospitalization is required. Influenza A (H5N1) infection indicates an incubation period ranging from 2 to 8 days and possibly as long as 17 days.
Symptoms
The preliminary symptoms of flu are similar to any other flu, but unlike a common cold, the flu hits hard and fast with symptoms of fever with temperature higher than 38°C, headache, extreme fatigue, dry cough, sore throat, runny or stuffy nose, muscle aches and stomach symptoms with abdominal pain and diarrhea, which are more common in children than in adults. The symptoms worsen with time and a person may experience respiratory problems with intense cough and flu settling in the lungs. The condition may get severely chronic resulting in pneumonia, wherein a person may start coughing blood and may also fall prey to multiple organ failure (e.g. kidney failure) and death. Complications, such as bacterial pneumonia, are common in patients infected with H5N1 virus. Influenza occurs most commonly in school-age children. Still, the most severe cases of the flu typically occur in infants, older adults, and in those with weak or compromised immune systems.
Prevention of avian influenza
The spread of H5N1 virus infection is prevented by following certain dos and don’ts:
Don’ts
* The best way to prevent infection is to avoid any contact with sick or dead poultry.
* Avoid visiting live poultry markets that may be infected with H5N1 when travelling.
* Avoid contact with sick people who might have H5N1 virus infection in affected countries.
* When preparing foods, do not use the same utensils for cooked and raw meats.
* Do not eat raw, uncooked or partially cooked meat.
Dos
Centers for Diseases Control and Prevention further recommend some tips that you should keep in mind while cooking meat and eggs:
* Wash your hands with soap and warm water for at least 20 seconds before and after handling raw poultry or eggs.
* Clean cutting boards and other utensils with soap and hot water to prevent raw poultry from contaminating other foods.
* Use a food thermometer to make sure you cook poultry to a temperature of at least 165o F. Various health organizations including WHO (World Health Organization), FDA (Food and Drug Administration, United States) and AIIMS (All India Institute of Medical Science) support the fact that there is no evidence that the highly pathogenic H5N1 virus infection can be spread to people through properly cooked food. So, make sure that the meat is not raw, uncooked or partially cooked by using a thermometer.
* Cook eggs until whites and yolks are firm [as per US Food and Drug Administration (FDA)].
Treatment
Antiviral drugs, namely Oseltamivir (Tamiflu), can reduce the duration of viral replication and improve prospects of survival. In suspected cases, Oseltamivir should be prescribed as soon as possible (ideally, within 48 hours following symptom onset) to maximize its therapeutic benefits. Moreover, Zanamivir (Relenza) is also found to be effective in treating influenza caused by the H5N1 bird flu virus. However, more studies are needed to demonstrate their effectiveness. However, drug resistance is a growing problem with H5N1 human infections as scientists from the USA and China reported in the journal Antiviral Research that they detected drug resistance in an alarming number of human H5N1 viruses they tested. Along with these medications, patients diagnosed with avian flu should take adequate rest, drink lots of fluids and receive proper nutrition.
WHO is monitoring avian influenza very closely, developing and adjusting appropriate interventions in collaboration with its partners. Such partners include animal health agencies and national veterinary authorities responsible for the control and prevention of animal diseases, including influenza. Specifically, WHO, the World Organization for Animal Health (OIE) and the Food and Agriculture Organization (FAO) collaborate through a variety of mechanisms to track and assess the risk from animal influenza viruses of public health concern and to address these risks at the human animal interface wherever in the world they might occur. As Influenza A/H5N1 virus has evolved into a flu virus strain that infects more species than any previously known strain, it is deadlier than any previously known strain and continues to evolve, becoming more widespread and more deadly. Therefore, WHO is monitoring the situation constantly as it evolves and as more information becomes available, it will revise its guidance and actions accordingly. However, till then just stay safe and healthy by taking note of the above mentioned precautions and care measures.
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