Human Swine Influenza: a pandemic threat

Human Swine Influenza: a pandemic threat


Influenza (Flu) pandemics are caused by new influenza viruses that have recently adapted to humans and resemble major natural disasters both in terms of recurrence and magnitude. The influenza virus, known to be circulating as a pathogen in the human population since at least the 16th century is notable for its unique ability to cause recurrent epidemics and global pandemics. Genetic re-assortments in the influenza virus cause fast and unpredictable antigenic changes in important immune targets leading to recurrent epidemics of febrile respiratory disease every 1 to 3 years consistently necessitated the development of new vaccines. Each century has seen some pandemics rapidly progressing to all parts of world due to emergence of novel virus to which the overall population holds no immunity.


Swine flu viruses do not normally infect humans. However, sporadic human infections with swine flue have occurred. Most commonly, these cases occur in persons having direct exposure to pigs. In addition, there have been sporadic cases of one person spreading swine flu to others. Occasional human swine influenza virus infection occurs every one to two years in the U.S, but from December 2005 through February 2009, 12 cases of human infection with swine influenza have been reported.


Recently, human cases of swine influenza A (H1N1) virus infection have been recently reported in several countries. This is a novel influenza A virus that has not been identified in people before, and human-to-human transmission of virus appears to be ongoing and thus represents a real pandemic threat.


Surveillance is the foundation of all efforts to understand and control influenza. The monitoring of influenza disease patterns is essential for identification of high risk groups, planning of prevention and response activities for complications and for estimating the burden of disease in terms of health and economic impact. It is important to use standardized case definitions that enable comparisons between different areas within a country and also between countries. There are two case definitions used by the influenza surveillance system:

  • Influenza-like illness (ILI) is defined (according to WHO criteria) as:
  • Sudden onset of a fever over 38°C, AND
  • Cough or sore throat, AND
  • An absence of other diagnoses.

Severe Acute Respiratory Infections (SARI):.For persons = 5 years the definition for SARI is adapted from the WHO protocol on rapid response:

  • Sudden onset of fever over 38°C, AND
  • Cough or sore throat, AND
  • Shortness of breath or difficulty in breathing, AND
  • Requiring hospital admission

For children <5 years old: definition is adapted from the program for Integrated Management of Childhood Illness (IMCI):
Any child <5 years old clinically suspected of having Pneumonia or Severe/very Severe Pneumonia and requiring hospital admission.

  • Confirmed case of influenza is defined as any case with laboratory test results positive for influenza virus.

Causes of Swine Influenza

Swine flu is caused by a virus. The most common subtype, or strain, is influenza type A H1N1, and this subtype has also caused infection in people. The letters H and N in the subtype name stand for proteins found on the surface of the virus, which are used to distinguish between different subtypes. Other virus subtypes found among pigs include H1N2, H3N1, and H3N2.

Influenza viruses are constantly changing their genes, a process called mutation. When a swine flu virus is found in humans, it is said to have “Jumped the species barrier.” This means that the virus has mutated in a way that allows it to cause the condition in humans. Because humans have no natural protection or immunity to the virus, they are likely to become ill.

Humans do not normally become infected with swine flu. However, there have been periodic human infections; most of these cases occur in people with direct exposure to pigs (e.g., people working on pig farms). People have also infected pigs with strains of human flu virus as well.

H1N1 flu virus (human swine flu) is contagious. Person–to–person transmission of H1N1 flu virus (human swine flu) has been documented, but it is not clear how easily the virus is spread among people. It is believed that it is spread the same way as regular seasonal influenza. A person infected with H1N1 flu virus can infect others starting 1 day before symptoms develop and up to 7 or more days after becoming ill.

Influenza is spread from person to person when the virus enters the body through the eyes, nose, and/or mouth. Coughing and sneezing release the germs into the air, where they can be breathed in by others. The virus can also rest on hard surfaces like doorknobs, ATM buttons, and counters. A person who touches these surfaces with their hands and then touches their eyes, mouth, or nose can become infected with the virus. You cannot get infected with the H1N1 flu virus (human swine flu) from eating pork products that have been properly cooked – heated through to 71°C (160°F).

Mode of Transmission

There are basically two modes of transmission of swine flu to humans:
From Pigs to Humans
It is the most common mode of swine flu transmission to humans. Those who work closely with the animals especially those who work with poultry or swine and the veterinarians are most exposed to the virus.

From humans to Humans
It is not the common mode of transmission of swine flu, although it is expected to be a reason of the extensive spread of this virus in humans, as the virus is also seen in people who had no direct interaction with the pigs.The virus gets into the air when an infected person sneezes or coughs and the droplets with the virus come in direct contact with another person’s eyes, nose or mouth.

Some Modes of Transmission are as below:

  • Influenza viruses can be directly transmitted from pigs to people and from people to pigs.
  • Human infection with flu viruses from pigs are most likely to occur when people are in close proximity to infected pigs, such as in pig barns and livestock exhibits housing pigs at fairs.
  • Human-to-human transmission of swine flu can also occur. This is thought to occur in the same way as seasonal flu which is mainly person-to-person transmission through coughing or sneezing by people infected with the influenza virus.
  • Disease spreads very quickly among the population especially in crowded places.
  • Cold and dry weather enables the virus to survive longer outside the body than in other conditions and, as a consequence, seasonal epidemics in temperate areas appear in winter.
  • People may become infected by touching/handling something contaminated with flu viruses on it and then touching their mouth or nose.
  • Swine influenza viruses are not transmitted by food.
  • Eating properly handled and cooked pork (at an internal temperature of =160°F) and pork products is safe.

Recommended Infection Control for a non-hospitalized patient (ER, clinic or home visit):

  1. Separation from others in single room if available until asymptomatic. If the ill person needs to move to another part of the house, they should wear a mask. The ill person should be encouraged to wash hand frequently and follow respiratory hygiene practices. Cups and other utensils used by the ill person should be thoroughly washed with soap and water before use by other persons.

Antiviral Treatment
Suspected Cases
Empiric antiviral treatment is recommended for any ill person suspected to have swine influenza A (H1N1) virus infection. Antiviral treatment with either zanamivir alone or with a combination of oseltamivir and either amantadine or rimantadine should be initiated as soon as possible after the onset of symptoms. Recommended duration of treatment is five days. Recommendations for use of antivirals may change as data on antiviral susceptibilities become available. Antiviral doses and schedules recommended for treatment of swine influenza A (H1N1) virus infection are the same as those recommended for seasonal influenza:

Confirmed Cases
For antiviral treatment of a confirmed case of swine influenza A (H1N1) virus infection, either oseltamivir (Tamiflu) or zanamivir (Relenza) may be administered. Recommended duration of treatment is five days. These same antivirals should be considered for treatment of cases that test positive for influenza A but test negative for seasonal influenza viruses H3 and H1 by PCR.

Pregnant Women
Oseltamivir, zanamivir, amantadine, and rimantadine are all "Pregnancy Category C" medications, indicating that no clinical studies have been conducted to assess the safety of these medications for pregnant women. Only two cases of amantadine use for severe influenza illness during the third trimester have been reported. However, both amantadine and rimantadine have been demonstrated in animal studies to be teratogenic and embryotoxic when administered at substantially high doses. Because of the unknown effects of influenza antiviral drugs on pregnant women and their fetuses, these four drugs should be used during pregnancy only if the potential benefit justifies the potential risk to the embryo or fetus; the manufacturers' package inserts should be consulted. However, no adverse effects have been reported among women who received oseltamivir or zanamivir during pregnancy or among infants born to such women.

Swine Influenza

Swine Influenza has been of great concern world–wide in the recent weeks. Human cases with acute respiratory syndrome, infected with a new strain of swine A (H1N1) have been reported initially by Mexico. This swine Influenza A virus is a novel reassortant with high pathogenicity at least in Mexico (US cases so far have been milder). A high proportion of cases with pneumonia required mechanical ventilation, and in fatal cases the progression of the disease was rapid. Health care workers (HCWs) and their family members with close contact are among those affected.

Genetic characterization of the influenza viruses from patients has identified them as swine influenza A (H1N1) viruses. The majority of their genes, including the hemagglutinin (HA) gene, are similar to those of swine influenza viruses that have circulated previously among pigs in the US. However, two genes coding for the neuraminidase (NA) and matrix (M) proteins are similar to corresponding genes of swine influenza viruses of the Eurasian lineage, a genetic combination that has not been recognized previously among swine or human isolates. The two viruses are resistant to amantadine and rimantadine, however, they are susceptible to neuraminidase inhibitors like Oseltamivir and Zanamivir.

WHO advises no restriction of regular travel or closure of borders, it is considered prudent for people who are ill to delay international travel and for people developing symptoms following international travel to seek medical attention, in line with guidance from national authorities.

There is also no risk of infection from this virus from consumption of well–cooked pork and pork products. Individuals are advised to wash hands thoroughly with soap and water on a regular basis and should seek medical attention if they develop any symptoms of influenza–like illness, and have travel history in affected areas(Mexico, USA, Canada, New Zealand, the United Kingdom, Israel and Spain).

Two laboratories, National Institute of Virology, Pune and National Institute of Communicable diseases, New Delhi have been identified for diagnostic testing. Case definition and criteria for diagnostic requirement will be laid down, circulated and updated from time to time by the Director General Health Services. Samples sent through public health system only be tested

Case Definition of Swine Flu in Humans

A suspected case of swine influenza A (H1N1) virus infection is defined as a person with acute febrile respiratory illness (fever = 380 C) with onset.

  • within 7 days of close contact with a person who is a confirmed case of swine influenza A (H1N1) virus infection or
  • within 7 days of travel to areas where there are one or more confirmed swine influenza A(H1N1) cases or
  • resides in a community where there are one
    or more confirmed swine influenza cases. A probable case of swine influenza A (H1N1) virus infection is defined as a person with an acute febrile respiratory illness who:
  • is positive for influenza A, but unsubtypable for H1 and H3 by influenza RT-PCR or reagents used to detect seasonal influenza virus infection, or
  • is positive for influenza A by an influenza rapid test or an influenza immunofluorescence assay (IFA) plus meets criteria for a suspected case, or
  • individual with a clinically compatible illness who died of an unexplained acute respiratory illness who is considered to be epidemiologically linked to a probable or confirmed case.

A confirmed case of swine influenza A (H1N1) virus infection is defined as a person with an acute febrile respiratory illness with laboratory confirmed swine influenza A (H1N1) virus infection at WHO approved laboratories by one or more of the following tests:

  • Real Time PCR
  • Viral culture
  • Four-fold rise in swine influenza A (H1N1) virus specific neutralizing antibodies.


Symptoms of Swine Flu are almost same as of the ordinary influenza.

  • Fever
  • Cough
  • Sore Throat
  • Runny Nose
  • Body Aches
  • Fatigue
  • Headaches
  • Chill
  • Diarrhea
  • Vomiting

You can well understand that there is not such symptom in the above mentioned ones that show that one has been inflicted with swine flu, thus a special lab test is necessary in order to be informed of one’s health status

Preventive Measures

There is currently no vaccine available against human swine influenza. One has to follow proper hand hygiene and respiratory etiquettes.

  • Avoid close contact with people who are having respiratory illness.
  • Sick persons should keep distance from others.
  • If possible, stay at home, away from work, school, and public places when you are sick.
  • Cover your mouth and nose with a tissue or handkerchief when coughing or sneezing.
  • If you have no tissue or handkerchief youshould not clean the nose with the hands but with the cuff of your shirt or clothes.
  • Washing your hands often with soap or alcohol based hand wash will help protect from germs.
  • Get plenty of sleep, be physically active, manage your stress, drink plenty of fluids, and eat nutritious food.
  • Persons who develop influenza-like-illness (ILI) (fever with either cough or sore throat) should be strongly encouraged to selfisolate in their home for 7 days after the onset of illness or at least 24 hours after symptoms have resolved, whichever is longer.
  • Persons who experience ILI and wish to seek medical care should contact their health care providers to report illness (by telephone or other remote means) before seeking care at a clinic, physician’s office, or hospital.
  • Persons who have difficulty breathing or shortness of breath should seek immediate medical attention and report to the nearby hospital.
  • If ill persons must go into the community (e.g., to seek medical care) they should wear a face mask to reduce the risk of spreading the virus in the community.
  • If a face mask is unavailable, ill persons needing to go into the community should use a handkerchief or tissues to cover any coughing and sneezing.
  • Persons in home isolation and their household members should be given infection control instructions like frequent hand washing with soap and water; use of alcohol-based hand gels (containing at least 60%alcohol).
  • When the ill person is within 6 feet of others at home, the ill person should wear a face mask, if available or handkerchief or tissues.
  • Household contacts who are well should:
  • remain home at the earliest sign of illness;
  • minimize contact in the community to the extent possible;
  • designate a single household family member as the ill person’s caregiver to minimize interactions with asymptomatic persons.

Precautions for School children:

  • Schools with a confirmed or a suspected case should be considered for closure.
  • All school or childcare related gatherings should be cancelled and encourage parents and students to avoid congregating outside of the school.
  • Schools and childcare facilities should bar students for a time period to be evaluated on an ongoing basis depending upon epidemiological findings.

Schools and childcare facilities should consult with their local or state health departments for guidance on reopening. If no additional confirmed or suspected cases are identified among students (or school-based personnel) for a period of 7 days, schools may consider reopening. For personnel who had unprotected exposure or a known breach in personal protective equipment to clinical material or live virus from a confirmed case of swine influenza A (H1N1), antiviral chemoprophylaxis with oseltamivir for 7 days after exposure can be considered.

Waste disposal
All waste disposal procedures should be followed as outlined in the respective facility standard laboratory operating procedures.

  • Schools and childcare facilities in unaffected areas should begin to prepare for the possibility of school or childcare facility closure.
  • Social Distancing Interventions:
  • Large gatherings linked to settings or institutions with laboratory-confirmed cases should be cancelled, for example a school event linked to a school with cases; other large gatherings in the community may not need to be cancelled at this time.
  • Persons with underlying medical conditions who are at high risk for complications of influenza may wish to consider avoiding large gatherings.

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