Avian Influenza in Pakistan

7/25/2019 Avian Influenza in Pakistan

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Issues & Analysis Home Issues

The whole truth about bird fluBy Dr Shahan Azeem & Prof Dr M. A. Muneer

It's an early morning in Karachi. As a poultry farmer gets up a nd goes to hisflock, he sees some of the birds gasping. Their heads are swollen, legs thaveturned reddish and water is running from their eyes.

Some have died, andmany more are dying.He gets alarmedbecause he hasinvested a fortune in theflock. On postmortem, itis revealed that the birdshad respiratory tractinfection withhemorrhage in trachea.

Blood serum tests are done on some live birds.

Serum analysis reveals influenza virus infection. With no cure for the disease,the whole flock dies - a huge loss for the farmer. Soon the disease spreads tonearby farms.

Commercialization of animal-rearing enterprises has lead to increasedpopulation density of birds per farm. Overcrowding of farms in an area andincreased meansof communication and transportation have raised theincidence of infectious diseases to much higher level as compared to pastyears.

The recent outbreak of bird flu in south-east Asia and its potential to infecthuman beings has raised enormous concerns all over the globe.

Due to widespread publicity via mass media and a recent outbreak of highlypathogenic avian influenza (HPAI) in poultry farms of Karachi, which killed over3.5 million layer birds, most people are not consuming eggs and meat, the onlyeconomical sources of proteins in the country.

A report in Dawn (Jan. 31) says the c onsumption of chick en it ems has dropped

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by 25-30 per cent. According to the Pakistan Poultry Association, dailyconsumption of chicken in Karachi had gone down to 125,000-150,000 birdscurrently as compared to the normal consumption of 300,000-350,000 daily.

Before delving deep into the nature of the bird flu and its implications on publichealth, let us understand the nature of influenza virus first.

The causative agent belongs to the virus family Orthomyaxoviridae and genusinfluenza A. The virus infects human beings, pigs, equines and various avianspecies including poultry and wild aquatic birds. The virus is about 100 nm indiameter and spherical forms are commonly seen with a nucleocapsidcontaining its genetic material.

The genome is segmented with eight segments. It is a single-stranded RNA

virus, the genome is minus sense.

A peculiar characteristi c of t he vi rus is that it contains a rod shapedglycoprotein called haemagglutinin (H) and a mushroom-shaped glycoproteincalled neuraminidase (N). These are called spikes or peplomers.

These are very important in subtyping of virus and hence to identify the exactvirus type involved in a particular outbreak. Till today 15 subtypes of H (H1-H15) and 9 subtypes of N (N1-N9) have been reported and can be found in anycombination. So there could be 276 possible combinations of H and N.Common combinations reported inrecent outbreaks are as follows:

Species Virus Strain

Human Beings H2N8, H3N8, H1N1, H2N2, H3N2

Horses Usually H7N7 or H3N8

Pigs Predominantly H1N1 and H3N2

Birds/Chickens H5N1, H5N3, H7N3, H5N9, H7N7, H5N2, H5N8, H7N4, H7N1(In Pakistan H7 and H9 have been reported).

* H5 N1 (Bird flu in Hong Kong in 1997, 1999, 2003)

The virus is relatively unstable in the environment and is killed at 56C for threehours or 60C for 30 minutes hence it is easily destroyed by boiling. It is easily

inactivated by commonly used disinfectants like formalin, sodium hypochlorite,sodium hydroxide and iodine compounds.

Influenza viruses are protected by organic material such as nasal secretions orfaeces, which increase resistance to physical and chemical agents.

Cool and moist conditions favor long survival of influenza viruses in the


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environment. A I viruses have been viable in liquid manure for 105 days in thewinter and in faeces for 30-35 days at 4C and for 7 days at 20C.

A I Virus Subtype Number affected A/chic ken/Pennsylv ania/1370/83 H5 N217m birds mostly chickens. A/chicken/Pakistan/447/95

A/chic ken/Pakis tan/1369-CR2/95 H7 N3 3.2m broilers & broiler breederchickens.

A/chic ken/Hong Kong/220/97 H5 N1 1.4m chick ens & various ot her domesticbirds. A/turkey/Italy/4580/99 H7 N1 10.5m chickens & 2.7m turkeys.

A/chic ken/Hong Kong/2001 H5 N1 1 million birds.

Flu in birds

Influenza is often termed as "Fowl Plague" Due to significant morbidity andmortality across the globe. Some important outbreaks resulting in millions ofmortalities and economic classes are given in the chart above.

The disease presents a variable picture according to the type of virus involvedand its virulence. But in typical outbreak with H7 or H9 following symptoms maybe found: respiratory distress, labored breathing, diarrhoea, swollen head, eyedischarge, cyanosis and swelling of wattles and combs, subcutaneoushemorrhages on unfeathered skin/cyanosis of shank and toe. In layer flockmarked decline in egg production has also been reported.

Spread of disease

The first incidence of bird to human infection was reported in 1997 in HongKong where 18 people got infected and 6 of them died.

Extensive investigation revealed that close contact with live infected poultrywas the source of human infection.

Again in February, 2003, an outbreak of H5N1 avian i nfluenza in Hong Kongcaused 2 cases of human infection. Two other avian influenza viruses haverecently caused illness in humans. An outbreak of HPAI (H7N7) in TheNetherlands in February, 2003, caused the death of one veterinarian and mildillnesses in 83 other humans. Mild cases ofavian influenza strain H9N2 occurred in children in Hong Kong in 1999 and inmid December, 2003. H9N2 is not highly pathogenic in birds.

Avian flu in Pakistan

Avian influenza (serotypes H9 and H7) is endemic in Pakist an. I n t his

reference, a serious outbreak had been reported in 1994 whereby broiler breederflocks were affected in northern areas of the country, and about a million birdssuccumbed to death.The scientists isolated the pure virus and typed it as H7N3. An inactivatedvaccine by the isolate was prepared by various laboratories and has been quiteeffective in controlling the avian influenza problem since 1994.

H tb k f i i fl H9N2 ti t ti l l i


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However, an outbreak of avian influenza H9N2 continues to occur particularly inKarachi and adjoining areas till today. This virus isolate was also purifiedlikewise and a vaccine was prepared which provided satisfactory protection.

During March 2003, another epidemic of avian influenza occurred and heavymortality in commercial layers of Karachi was reported. This virus was isolatedand characterized as H7 at various public and private disease diagnosticlaboratories.

This outbreak occurred in commercial layer flock at their peak production.Despite all this, no human contract has yet been reported from any of the20,000 poultryfarms of the country.

Difficult to control

Influenza viruses depict some peculiar properties known as antigenic drift andshift. Antigenic drift is due to accumulation of point mutations in the genesresulting in amino acid changes in the protein. Virus does not have aproofreading mechanism and as a result erroneous versions of virus arereleased with different antigenic nature.

Since the mammalian/avian body has not been exposed to this new subtypeand hence not immune to it, it would result in occurrence of disease as theantigenic nature is changed.

On the other hand genetic reassortment results in development of newsubtypes and is called antigenic shift. Swine can serve as mixing vessel ofavian and human viruses.

Here genes are swapped resulting in emergence of completely new subtypestowards which there is no previous immunity. Avian and human influenzaviruses can exchangegenes when a person is simultaneously affected with viruses from bothspecies.

The added danger in case of birds to human transmission is that if the viruspersists in human population for some time and acquire sufficient human genesit would be very easily effecting human population via human to humaninfection (rather than bird to human infection) and could lead to seriousepidemic resulting in million of casualties around the world.

Sources of spread

Since the virus is shed in bird droppings, secretions from the respiratory trackand conjunctiva. Following factors could be attributed to the perpetuation ofinfection:

(1) Movement of contaminated vehicles, equipment, feed, cages, etc, from onefarm to another can carry the virus

(2) Technical personnel visiting various poultry farms in a day consecutively


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(2) Technical personnel visiting various poultry farms in a day consecutivelywithout changing cloths could be a source of spread

(3) Droppings from infected wild birds can introduce the virus to backyard aswell as commercial poultry flocks

(4) The places where live birds are sold are an important source of spread ofinfection. In these markets, birds caught or bought are placed in cages understress and in close proximity which serve as an ideal place of spread ofinfection

(5) Domestic/backyard poultry is at continuous risk as it frequently comes incontact with wild birds some times even to the level of sharing the watersources, etc

(6) Migratory waterfowl are the natural reservoir of bird flu viruses and thesebirds are also most resistant to it. They can carry the virus over greatdistances

(7) Scavenger animals or birds can play a part in the spread of infection

(8) Movement of live infected birds from one place to another can spread thevirus

(9) Mechanical vectors like rodents, flies and other insects can also carry thevirus from one place to another

(10) Non-effective poor quality vaccination

(11) Ability of virus to increase its pathogenicity if allowed to circulate in poultrypopulations

(12) Climatic conditions also play a part as highly pathogenic viruses cansurvive for long periods in the environment specially when temperatures arelow.

Following tests are commonly used for diagnosis of influenza virusinfection in various species of animals including human beings and birds:

(1) Isolation of the virus

(2) Identification of influenza isolate by hemagglutination inhibition

(3) Serologic diagnosis by hemagglutination inhibition

(4) Neuraminidase assay for antibody detection

(5) Direct detection of influenza viral proteins or nucleic acids

(6) Identification by Reverse Transcriptase Polymerase Chain Reaction (RT-PCR)


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(7) Intravenous Pathogenicity Test (IVPI)

(8) Agar gel precipitation test (AGPT) for the detection of antibodies to avianinfluenza using type specific Ribonucleoprotein (RNP) antigen.

Dr. Shahan Azeem is a microbiologist and assistant director researchat theUniversity of Veterinary and Animal Sciences, Lahore.

Prof. Dr M. A. Muneer is a renowned avian microbiologist and Dean, Faculty ofVeterinary Science, at the same university. .

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Avian Influenza in Pakistan