Human Swine Influenza: a pandemic threat

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Influenza (Flu) pandemics are caused by new influenza viruses that have recently adapted to humans. 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.

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Human Swine Influenza: a pandemic threat : 

Human Swine Influenza: a pandemic threat Dr.Kedar Karki Central Veterinary Laboratory Kathmandu

Swine Influenza : 

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).

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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.

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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.

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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.

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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.

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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).

Background : 

Background Influenza (Flu) pandemics are caused by new influenza viruses that have recently adapted to humans. 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.

Background : 

Background 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.

Background : 

Background The current Influenza vaccine available is unlikely to provide protection against Influenza A H1N1 virus. There is no specific vaccine available for H1N1 strain. Each century has seen some pandemics rapidly progressing to all parts of the world due to emergence of a novel virus to which the overall population holds no immunity.

What is Swine Influenza and Influenza A (H1N1)? : 

What is Swine Influenza and Influenza A (H1N1)? Swine influenza is a contagious respiratory disease that normally only affects pigs. It is commonly caused by H1N1 strains of swine influenza A virus. However, other strains, such as H1N2, H3N1 and H3N2 also circulate in pigs. While it is not usual for people to get swine flu, human infections do occasionally happen, mainly after close contact with infected pigs.

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Caused by influenza type A virus, there are regular outbreaks among herds of pigs, where the disease causes high levels of illness but is rarely fatal. It tends to spread in autumn and winter but can circulate all year round.

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There are many different types of swine flu and like human flu, the infection is constantly changing. Swine flu does not normally infect humans, although sporadic cases do occur usually in people who have had close contact with pigs.

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During March/April 2009, a new strain of swine influenza virus emerged in Mexico, and started to cause illness in humans. The World Health Organization says that this new strain of influenza, called influenza A (H1N1), can spread from person to person. Experts around the world are working closely with the World Health Organization to help determine what risk this virus poses to the public.

Swine Flu in Pigs : 

Swine Flu in Pigs Swine Influenza (swine flu) is a respiratory disease of pigs caused by type A influenza virus that regularly causes outbreaks of influenza in pigs. Swine flu viruses cause high levels of illness and low death rates in pigs. Swine influenza viruses usually circulate among swine throughout the year, but most outbreaks occur during the late fall and winter months similar to outbreaks in humans.

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The classical swine flu virus (an influenza type A H1N1 virus) was first isolated from a pig in 1930. H3N2 influenza viruses began circulating among pigs from 1998. The H3N2 viruses initially were introduced into the pig population from humans.

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Like all influenza viruses, swine flu viruses change constantly. Pigs can be infected by avian influenza, human influenza viruses as well as swine influenza viruses and hence the pigs are known to be a mixing vessel.

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There are four main influenza type A virus subtypes that have been isolated in pigs: H1N1, H1N2, H3N1 and H3N2. However, most of the recently isolated influenza viruses from pigs have been H1N1 viruses.

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When influenza viruses from different species infect pigs, the viruses can re–assort (i.e. swap genes) and new viruses, a mix of swine, human and/or avian influenza viruses – can emerge leading to development of new novel strain for which human beings do not have no immunity.

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Swine flu virus spreads mostly through close contact among pigs and possibly from contaminated objects moving between infected and uninfected pigs. Symptoms of swine flu in pigs can include sudden onset of fever, depression, coughing (barking), discharge from the nose or eyes, sneezing, breathing difficulties, eye redness or inflammation, and going off feed.

Swine Flu in Humans : 

Swine Flu in Humans Swine flu viruses do not normally infect humans. However, sporadic human infections with swine flu 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.

Swine Flu Outbreak : 

Swine Flu Outbreak 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 the virus appears to be ongoing and thus represents a real pandemic threat. WHO has upgraded the phasing of pandemic influenza from Phase – 5 to Phase – 6

Causes of Swine Influenza : 

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.

Causes of Swine Influenza : 

Causes of Swine Influenza 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.

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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.

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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.

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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 : 

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.

Mode of Transmission : 

Mode of Transmission 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: : 

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.

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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.

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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.

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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.

Infection Control : 

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

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 : 

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 : 

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.

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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.

WHO Phases of Pandemic Alert : 

WHO Phases of Pandemic Alert

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Phase 1No animal influenza virus circulating among animals has been reported to cause infections in humans. Phase 2An animal influenza virus circulating among domesticated or wild animals is known to have caused infection in humans, and is therefore considered a specific potential pandemic threat. Phase 3An animal or human–animal influenza reassortant virus has caused sporadic cases or small clusters of disease in people, but has not resulted in humanto – human transmission sufficient to sustain community–level outbreaks.

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Phase 4Human-to-human transmission(H2H) of an animal or human–animal influenza reassortant virus able to sustain community–level outbreaks has been verified. Phase 5The same identified virus has caused sustained community level outbreaks in two or more countries in one WHO region. Phase 6The pandemic phase, is characterized by community level outbreaks in at least one other country in a different WHO region in addition to the criteria defined in Phase 5.

Diagnosis of Swine Flu : 

Diagnosis of Swine Flu Patients with flu-like-symptoms should seek medical help immediately on onset of symptoms. This helps in early diagnosis, proper treatment and prevention of complications. For diagnosis of swine influenza A infection, respiratory specimen (NP (nasopharyngeal swab), throat swab , nasal aspirate, nasal washing) 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.

Sample Collection & Laboratory Diagnosis : 

Sample Collection & Laboratory Diagnosis Sample Collection and handling is same as for human avian flu or seasonal influenza like illness . Sample Collection: should be labeled clearly and include patient’s complete information and should be sent to laboratory within 24 hours for further investigations. Laboratory biosafety measures should be followed for collection, storage, packaging and shipping of influenza samples.

Available Laboratory tests: : 

Available Laboratory tests: Rapid Antigen Tests: not as sensitive as other available tests. RT–PCR Virus isolation Virus Genome Sequencing Four–fold rise in swine influenza A (H1N1) virus specific neutralizing antibodies. It is important to note that samples from all cases, once the Pandemic starts, are not required to be tested.

Preventive Measures : 

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

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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.

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If you have no tissue or handkerchief you should 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.

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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.

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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.

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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).

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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.

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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.

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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 : 

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: : 

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

Do's and Don'ts : 

Do's and Don'ts 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 hand cleaners are also effective. Wash your hands at regular intervals with disinfectants. Keep surfaces like doorknobs, tables, etc. clean with disinfectants.

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Don’t touch your mouth, nose, eyes after touching strangers and unknown surfaces. Don’t touch yourself or others after sneezing or coughing. First, wash your hands. Avoid public contact or use mask when in crowded areas. The swine fly attacks the respiratory tract. Avoid travelling, if you have any of the mentioned symptoms.

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Avoid close contact with people having respiratory illnesses. If you have no tissue or handkerchief, do not clean nose with hands. Instead, use the cuff of your shirt or clothes. Get plenty of sleep, be physically active, manage your stress, drink plenty of fluids, and eat nutritious food.

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If you develop influenza-like-illness (ILI) (fever with either cough or sore throat), self-isolate yourself at home for 7 days after the onset of the illnessor at least for 24 hours after symptoms have resolved, whichever is longer.

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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.

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CREAT AWARENESS ABOUT SWINE FLU

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