Swine influenza

Swine influenza or swine flu is a highly contagious respiratory disease caused by one of the subtypes of swine influenza A viruses (H1N1, H1N2, H2N3, H3N1 and H3N2). The name influenza has its origin in early fifteenth century Italy and was adopted in Europe to explain the sudden appearance of an epidemic disease thought to be under the influence of the stars. The swine influenza virus (SIV) is seen mainly in pigs and spreads rapidly within a herd causing considerable economic loss to farmers. Though pigs form the main hosts, swine influenza virus can also be transmitted to humans, and vice versa. In humans, it usually results in antibody production and does not cause disease. When transmission to humans causes human influenza, it is called zoonotic swine flu.

Epidemiology

Swine influenza virus was first isolated from humans in 1974 and evidence for transmission of swine influenza virus to humans before 1974 is minimal and circumstantial. The 2009 H1N1 is a new influenza virus causing illness in people. Cases of influenza-like illness were first reported in Mexico on March 18, 2009; the outbreak was subsequently confirmed as H1N1 influenza A. On April 17, 2009, the Centers for Disease Control and Prevention (CDC) determined that two cases of febrile respiratory illness in children who resided in adjacent counties in southern California were caused by infection with H1N1 virus. In United States, the new virus was first detected in people in April, 2009. This virus spread from person-to-person worldwide, probably in much the same way that regular seasonal influenza viruses spread. On June 11, 2009, the World Health Organization External Web Site Icon (WHO)
signaled that a pandemic of 2009 H1N1 flu was underway.

Pathogenesis

H1N1 Influenza VirusThe H1N1 strain is implicated in the 2009 pandemic in humans. This virus was originally referred to as “swine flu” because laboratory testing showed that many of the genes in this new virus were very similar to influenza viruses that normally occur in North American pigs. But further study has shown that this new virus is very different from what usually circulate in pigs. The emegence of new virus has been attributed to reassortment of genes. Like all influenza viruses, swine flu viruses change constantly. Pigs can be infected by avian influenza and human influenza viruses as well as swine influenza viruses. When influenza viruses from different species infect pigs, the viruses can reassort (i.e. swap genes) and new viruses that are a mix of swine, human and avian influenza viruses emerge. Thus the H1N1 virus has two genes from flu viruses along with avian (bird) and human genes. Scientists call this a "quadruple reassortant" virus.

Transmission

The transmission of swine influenza viruses to humans is uncommon. However, the swine influenza virus can be transmitted to humans via contact with infected pigs or environments contaminated with swine influenza viruses. Once a human becomes infected, he or she can then spread the virus to other humans, presumably in the same way as seasonal influenza is spread (ie, via coughing or sneezing).

Exposures not thought to spread 2009 H1N1 Flu

  • Eating pork or pork products. It does not spread through food and eating well cooked (160°F) pork is safe.
  • Drinking water.
  • Spread through water in swimming pools, spas, water parks, interactive fountains, and other treated recreational water venues (never through exposure to water, but definitely from infected people who are using the facility at the same time).

Symptoms and signs

Swine flu symptoms
Manifestations of H1N1 influenza (swine flu) are similar to those of seasonal influenza. Patients present with symptoms of acute respiratory illness, including at least two of the following:

  • Fever above 100.4 F
  • Cough
  • Sore throat
  • Body aches
  • Headache
  • Chills and fatigue
  • Diarrhea and vomiting (possible)

People infected with seasonal and 2009 H1N1 flu shed virus and may be able to infect others from a day before getting sick to 5 to 7 days after. This can be longer in some people, especially children and people with weaker immune systems and in those infected with the new H1N1 virus.

Morbidity and Mortality

  • Illness with the new H1N1 virus has ranged from mild to severe. While most people who have been sick have recovered without needing medical treatment, hospitalizations and deaths from infection with this virus have occurred. About 70 percent of people who have been hospitalized with 2009 H1N1 virus have had one or more medical conditions previously recognized as placing people at high risk of serious seasonal flu-related complications. This includes pregnancy, diabetes, heart disease, asthma and kidney disease.
  • One thing that appears to be different from seasonal influenza is that adults older than 64 years do not yet appear to be at increased risk of 2009 H1N1-related complications thus far. CDC laboratory studies have shown that no children and very few adults younger than 60 years old have existing antibody to 2009 H1N1 flu virus; however, about one-third of adults older than 60 may have antibodies against this virus. It is unknown how much, if any, protection may be afforded against 2009 H1N1 flu by existing antibodies.

Complications

  • Worsening of chronic conditions, such as heart disease, diabetes and asthma
  • Pneumonia
  • Respiratory failure

Severe complications of human swine flu H1N1 seem to develop and progress rapidly.
A vaccination used to treat swine flu in 1976 was associated with some cases of Guillain-Barre syndrome, a disorder that leads to nerve inflammation that causes muscle weakness.

Diagnosis

Clinical diagnosis

The CDC criteria for suspected H1N1 influenza are as follows

  • Onset of acute febrile respiratory illness within 7 days of close contact with a person who has a confirmed case of H1N1 influenza A virus infection, or
  • Onset of acute febrile respiratory illness within 7 days of travel to a community (within the United States or internationally) where one or more H1N1 influenza A cases have been confirmed, or
  • Acute febrile respiratory illness in a person who resides in a community where at least one

Laboratory diagnosis

Specimen collection

The following should be collected as soon as possible after illness onset: nasopharyngeal swab, nasal aspirate or a combined nasopharyngeal swab with oropharyngeal swab. If these specimens cannot be collected, a nasal swab or oropharyngeal swab is acceptable. For patients who are intubated, an endotracheal aspirate should also be collected. Bronchoalveolar lavage (BAL) and sputum specimens are also acceptable.Ideally, swab specimens should be collected using swabs with a synthetic tip (e.g. polyester or Dacron®) and an aluminum or plastic shaft. Swabs with cotton tips and wooden shafts are not recommended. Specimens collected with swabs made of calcium alginate are not acceptable.

Transportation of Specimen

The swab specimen collection vials should contain 1-3ml of viral transport medium (e.g. containing, protein stabilizer, antibiotics to discourage bacterial and fungal growth, and buffer solution).All respiratory specimens should be stored at 4°C for no longer than 4 days. Clinical specimens should be shipped on wet ice or cold packs in appropriate packaging. All specimens should be labeled clearly and include information requested by your laboratory

Laboratory tests

  • Real-time RT-PCR

Real-time RT-PCR is the recommended test for confirmation of novel influenza A (H1N)1 cases. Currently, novel influenza A (H1N1) virus will test positive for influenza A and negative for H1 and H3 by real-time RT-PCR. If reactivity of real-time RT-PCR for influenza A is strong (e.g. Ct less than 30) it is more suggestive of a novel influenza A (H1N1) virus.

  • Rapid influenza antigen test

Some commercially available rapid tests can distinguish between influenza A and B viruses. A patient with a positive rapid test for influenza A may meet criteria for a suspected case of novel influenza A (H1N1) virus infection. However, it is not possible to differentiate from seasonal influenza A viruses. Also, these tests have unknown sensitivity and specificity to detect human infection with novel influenza A (H1N1) virus in clinical specimens, and have suboptimal sensitivity to detect seasonal influenza viruses. Therefore, a negative rapid test could be a false negative and should not be assumed a final diagnostic test for novel influenza A (H1N1) virus infection.

  • Immunofluorescence (DFA or IFA)

These tests can distinguish between influenza A and B viruses. A patient with a positive for influenza A by immunofluorescence may meet criteria for a suspected case. However, it is not possible to differentiate from seasonal influenza A viruses. Immunofluorescence depends upon the quality of a clinical specimen, operator skills, and has unknown sensitivity and specificity to detect human infection with novel influenza A (H1N1) virus in clinical specimens. Therefore, a negative immunofluorescence could be a false negative and should not be assumed a final diagnostic test for novel influenza A (H1N1) virus infection.

  • Viral culture

Isolation of novel influenza A (H1N1) virus is diagnostic of infection, but may not yield timely results for clinical management. A negative viral culture does not exclude infection with novel influenza A (H1N1) virus.

A confirmed case of novel influenza A (H1N1) virus infection is defined as a person with an influenza-like illness with laboratory confirmed novel influenza A (H1N1) virus infection by one or more of the following tests:
  • Real-time RT-PCR
  • Viral culture

Treatment

Most cases of flu, including human swine flu, need no treatment other than symptom relief. In a chronic respiratory disease, one might need to prescribe additional medication to decrease inflammation, open the airways and help clear lung secretions. The antiviral drugs oseltamivir (Tamiflu) and zanamivir (Relenza) can reduce the severity of symptoms, but flu viruses can develop resistance to them. To make development of resistance less likely and maintain supplies of these drugs for those who need them most, antivirals are reserved for people at high risk of complications. Tamiflu

High-risk groups are those who need treatment as follows

  • Are hospitalized
  • Have shortness of breath along with other flu symptoms
  • Are younger than 5 years of age
  • Are 65 years and older
  • Are pregnant
  • Are younger than 19 years of age and are receiving long-term aspirin therapy, because of an increased risk for Reye's syndrome
  • Have certain chronic medical conditions, including asthma, emphysema, heart disease, diabetes, neuromuscular disease, and kidney, liver or blood disease
  • Are immunosuppressed due to medications or HIV

What can you do if you come down with any Flu ?

  • Drink plenty of liquids. Choose water, juice and clear broth to prevent dehydration. Drink enough to have clear or pale yellow urine.
  • Rest. Get more sleep to help your immune system fight the infection.
  • Take over-the-counter medication to reduce symptoms. Follow directions for taking acetaminophen to reduce fever and aches. Read package labels to be sure any product you give to a child or adolescent does not contain aspirin. Children and teens should not take aspirin because of the risk of Reye's syndrome, a rare but potentially fatal disease.

Prevention

  • 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. If soap and water are not available, use an alcohol-based hand rub.
  • Avoid touching your eyes, nose or mouth. Germs spread this way.
  • Try to avoid close contact with sick people.
  • If you are sick with flu-like illness, CDC recommends that you stay home for at least 24 hours after your fever is gone except to get medical care or for other necessities. (Your fever should be gone without the use of a fever-reducing medicine.) Keep away from others as much as possible to keep from making others sick.
  • Follow public health advice regarding school closures, avoiding crowds and other social distancing measures.
  • Be prepared in case you get sick and need to stay home for a week or so; a supply of over-the-counter medicines, alcohol-based hand rubs (for when soap and water are not available), tissues and other related items could help you to avoid the need to make trips out in public while you are sick and contagious.

Vaccination

The Food and Drug Administration approved the new swine flu vaccine on 15 th of September 2009. Current studies indicate that the risk for infection among persons 65 years or older is less vs persons in younger age groups(in contrast to seasonal flu). Therefore, the current recommendations do not include vaccinating persons 65 years or older until after an assessment is made of the vaccine availability and demand at the local level. National Institutes of Health, announced studies showing that one dose appears to protect adults and that protection kicks in just eight to 10 days after the shot, faster than scientists had predicted.

Inactivated vaccine

Inactivated vaccine which could be injected (intramuscular) as the seasonal flu vaccine will be available for use .

Some inactivated 2009 H1N1 vaccine contains a preservative called thimerosal . Some people have suggested that thimerosal might be related to autism. In 2004 a group of experts at the Institute of Medicine reviewed many studies looking into this theory, and found no association between thimerosal and autism. Additional studies since then reached the same conclusion.

Groups recommended to receive 2009 H1N1 vaccine first

  • Pregnant women
  • People who live with or care for infants younger than 6 months of age
  • Healthcare and emergency medical personnel
  • Anyone between the ages of 6 months and 24 years old
  • People between 25 and 64 years of age who are at higher risk for 2009 H1N1 because of chronic health disorders or compromised immune systems

Groups that can be vaccinated as more vaccine becomes available

  • Healthy 25 through 64 year old
  • Adults 65 years and older

Contraindications

  • Absolute-any severe (life threatening) allergy to eggs or to any other substance in the vaccine.
  • Relative -a life threatening allergic reaction after a dose of seasonal flu vaccine, Guillain Barre syndrome.

Dosage

Children through 9 years of age should get two doses of vaccine, about a month apart. Older children and adults need only one dose.

Live Attenuated intranasal vaccine (LAIV)

Live, attenuated intranasal vaccine (or LAIV) is sprayed into the nose .The 2009 H1N1 LAIV does not contain thimerosal or other preservatives. It is licensed for people from 2 through 49 years of age.The vaccine virus is attenuated (weakened) so it will not cause illness. This is now available for use .

Contraindications

Any severe (life-threatening) allergy to eggs, or to any other substance in the vaccine.

Groups to which 2009 H1N1 LAIV should not be given

  • Children younger than 2 and adults 50 years and older
  • Pregnant women
  • Anyone with a weakened immune system
  • Anyone with a long-term health problem such as - heart, kidney, liver or lung disease - metabolic disease such as diabetes, asthma, anemia and other blood disorders
  • Children younger than 5 years with asthma or one or more episodes of wheezing during the past year
  • Anyone with certain muscle or nerve disorders (such as cerebral palsy) that can lead to breathing or swallowing problems
  • Anyone in close contact with a person with a severely weakened immune system (requiring care in a protected environment, such as a bone marrow transplant unit)
  • Children or adolescents on long-term aspirin treatment.

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