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Swine Flu Epidemic in North America

Swine influenza is a respiratory disease of pigs caused by type

A influenza viruses. Sometimes it may spread to Humans and cause flu-like symptoms.

The virus is influenza A virus, carrying the designation H1N1. It is a hybrid reassorted virus and contains DNA typical to avian, swine and human viruses, including elements from European and Asian swine

viruses. It clasically causes outbreaks from Mid March to mid May and

commonly causes fever, headache, fatigue and cough. As yet, none of the Eight Swine flu cases diagnosed in US has proved fatal, though

sources report about 80 fatal cases in Mexico in the past few weeks.

Current situation- In the past, CDC received reports of approximately one human swine

influenza virus infection every one to two years in the U.S., but from December 2005 through February 2009, a total of 12 human infections

with swine influenza were reported from 10 states in the United States. Since March 2009, a number of confirmed human cases of a

new strain of swine influenza A (H1N1) virus infection in California, Texas, and Mexico have been identified.

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In the Federal District of Mexico, surveillance began picking up cases

of ILI starting 18 March. The number of cases has risen steadily through April and as of 23 April there are now more than 854 cases of

pneumonia from the Mexican capital. Of the Mexican cases, 18 have been laboratory confirmed in Canada as Swine Influenza A/H1N1,

while 12 of those are genetically identical to the Swine Influenza A/H1N1 viruses from California. The US has 8 confirmed cases within

America and has tested atleast 14 specimens from Mexico, of which seven tested positive.

The regions currently affected have always showed an infection rate higher than the national average.

WHO has now activated its Strategic Health Operations Center (SHOC)

-its command and control center for acute public health events.

Life Cycle of Swine Flu virus-

Birds like Ducks, geese and swans are common reservoirs of Influenza virus and can harbor the virus without showing symtoms of the

disrease.

New England — 1.5% Mid-Atlantic — 2.9% East North Central — 1.9% West North Central — 1.7% South Atlantic — 2.2% East South Central — 2.5% West South Central — 4.8% Mountain — 1.5% Pacific — 3.0% National average- 2.4%

Mean Prevalence of Influenza in U.S

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Pigs most commonly get infected with flu viruses from other pigs

(swine flu), but also can get infected with flu viruses from birds (avian flu), and from people (human flu). This cross-species spread of flu

viruses can lead to new types of flu viruses. Pigs may sometimes harbor the virus without exhibiting any overt symtoms.

Studies have shown that 30% to 50% of commercial U.S. swine have

been infected with swine flu. H1N1 and H3N2 swine flu viruses are endemic among pig populations in the United States.. Recent studies

have shown that 15% to 25% of swine farmers might have been infected with swine flu viruses, as well as about 10% of veterinarians

Why are Pigs important in this cycle?

Replication of avian influenza viruses in pigs may allow them to adapt to and be able to efficiently infect mammals, and ultimately be

Signs of swine flu in pigs include:

• coughing (“barking”) • discharge from the nose • sneezing • breathing difficulties • going off feed

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transmitted to people. In addition, pigs can serve as hosts in which

two (or more) influenza viruses can undergo "genetic reassortment."

At this time, there are four main influenza type A virus subtypes that have been isolated in pigs: H1N1, H1N2, H3N2, and H3N1. However,

most of the recently isolated influenza viruses from pigs have been H3N2 and H1N1 viruses.

The reassortant H3N2 and H1N1 viruses currently circulating widely

and causing disease throughout the swine population of the United States all contain human influenza virus genes.

From Pigs to Humans-

Most commonly, these cases occur in persons with direct exposure to pigs (e.g. children near pigs at a fair or workers in the swine industry).

Families of swine owners who visit the farm atleast four times a week are also susceptible.

Humans to other Humans-

This is thought to occur in the same way as seasonal flu occurs in people, which is mainly person-to-person transmission through

coughing or sneezing of people infected with the influenza virus. People may become infected by touching something with flu viruses on

it and then touching their mouth or nose. Influenza normally affects the very young and the very old, but these age groups have not been

heavily affected in Mexico.

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Smcgee (http://www.flickr.com/photos/smcgee)

Malingering (http://www.flickr.com/photos/malingering/)

Symtoms-

People infected with flu typically have fever (often high), cough, body aches, headaches, fatigue and runny or stuffy nose. Vomiting and diarrhea may also occur.

Treatment– CDC recommends the use of oseltamivir or zanamivir for the treatment and/or prevention of infection with swine influenza viruses. These medicines should be started in the first 2 days of being ill to be

most effective.

Diagnosis- Diagnosis of swine influenza A (H1N1) virus infection should be

considered in patients with febrile respiratory disease and who

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1) live in San Diego and Imperial Counties, California, or Guadalupe

County, Texas, or traveled to these counties or 2) who traveled recently to Mexico or were in contact with persons

who had febrile respiratory illness and were in the two U.S. counties or Mexico in the 7 days preceding their illness onset.

To diagnose swine influenza A infection, a respiratory specimen would

generally need to be collected within the first 4 to 5 days of illness (when an infected person is most likely to be shedding virus).

However, some persons, especially children, may shed virus for 10 days or longer. Identification as a swine flu influenza A virus requires

sending the specimen to CDC for laboratory testing.

History- Swine influenza viruses were first isolated in the United States in

1930. The most well known is an outbreak of swine flu among soldiers in Fort

Dix, New Jersey in 1976. The virus caused disease with x-ray evidenceof pneumonia in at least 4 soldiers and 1 death.The virus was transmit

ted to close contacts in a basic training environment, with limited transmission outside the basic training group.

The virus circulated for a month and then disappeared just as mysteriously. The swine influenza A virus collected from the Fort Dix s

oldier was named A/New Jersey/76 (Hsw1N1)

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The number of isolates testing positive for Flu has been steadily

increasing over the years. The H1N1 strain has been specialy noted for rapid increase since 2006-07. The Human H1N1 strain is genetically

different from H1N1 strain seen in Swines.

Infection Control of Ill Persons in a Healthcare Setting

• Place all suspected cases in a single-patient room with the door kept closed.

• The ill person should wear a surgical mask when outside of the patient room, and should be encouraged to wash hands

frequently and follow respiratory hygiene practices.

• Cups and other utensils used by the ill person should be washed with soap and water before use by other persons.

• Standard, Droplet and Contact precautions should be used for all patient care activities, and maintained for 7 days after illness

onset or until symptoms have resolved.

• Personnel providing care to or collecting clinical specimens from suspected or confirmed cases should wear disposable non-sterile

gloves, gowns, and eye protection (e.g., goggles) to prevent conjunctival exposure.

General Advice

• Cover your nose and mouth with a tissue when you cough or

sneeze. Throw the tissue in the trash after you use it.

• Wash your hands often with soap and water, especially after you cough or sneeze. Alcohol-based hands cleaners are also effective.

• Try to avoid close contact with sick people.

• If you get sick, CDC recommends that you stay home from work or school and limit contact with others to keep from infecting them.

• Avoid touching your eyes, nose or mouth. Germs spread that

way.

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Main References-

Center For Disease Control –

http://www.cdc.gov/swineflu/key_facts.htm http://www.cdc.gov/media/transcripts/2009/t090423.htm

World health organization –

http://www.who.int/csr/don/2009_04_24/en/index.html

National Pork board - http://www.pork.org/PorkScience/Documents/PUBLICHEALTH%20influ

enza.pdf

Medscape – http://www.medscape.com/viewarticle/408402_8

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Written by-

Dr. Neelesh Bhandari MD (Path), PGP Human Rights

Advisor (Medical Communications) Mark IV Medical Communications.