Swine Flu Outbreak Found Unrelated to Pigs

The 2009 so-called "swine influenza" outbreak in humans is due to a new strain of influenza A virus, an apparent reassortment of at least four strains of influenza A virus subtype H1N1, including one strain endemic in humans, one endemic in birds, and two endemic in swine.

First detected in Mexico City (Mexico) on March 18, 2009, the swine flu epidemic is currently classified by the World Health Organization (WHO; Geneva, Switzerland) as a phase 5 outbreak, one level below an official pandemic. Although initial reports identified the new strain as swine influenza, its origin is unknown. It is important to mention that the World Organization for Animal Health (OIE; Paris, France) has reported that this strain has not been isolated in pigs. On May 2, 2009, H1N1 was reported in pigs at a farm in Alberta (Canada), linked to the outbreak in Mexico; the pigs are suspected to have caught this new strain of virus from a farm worker who recently traveled to Mexico.

"Influenza is a virus that commonly infects pigs. There is no similar pandemic system for pigs," said Keiji Fukuda, M.D., WHO acting assistant director-general. "As far as I know--I don't know of any further outbreaks occurring in pigs at this time."

The new strain can be transmitted from human to human, an ability attributed to an as-yet unidentified mutation. Swine flu disease transmission is similar to seasonal influenza, through person-to-person spread via coughing or sneezing at close distance, or contact with droplet-contaminated surfaces. All respiratory secretions and bodily fluids of infected cases are considered potentially infectious. The infectious period is one day prior and up to seven days after symptom onset. Clinical findings include fever, headache, upper respiratory symptoms, myalgia, fatigue, chills, vomiting, and diarrhea. Disease severity and course are variable.

A suspected case is defined by acute febrile respiratory illness (38 ˚C and nasal congestion, rhinorrhea, sore throat, or cough) and onset within seven days of close contact with or travel to areas with a confirmed case. Suspected and confirmed cases warrant treatment with oseltamivir (Tamiflu) or zanamivir (Relenza) within two days of appearance of symptoms. Prophylaxis is appropriate for certain household contacts and some healthcare workers. The common seasonal influenza vaccine is unlikely to provide protection against swine H1N1 viruses. However, the majority of people infected with the virus make a full recovery without requiring medical attention or antiviral drugs. Personal hygiene measures, such as avoiding people who are coughing or sneezing and frequent hand washing, may prevent flu infection.

Influenza infection pathway studies have suggested that closing schools, theaters, and canceling gatherings in the early stages of a pandemic can limit its spread. Such measures would likely take place if health officials determine that the virus is spreading quickly enough and is deadly enough to cause a pandemic.

Related Links:
World Health Organization
World Organization for Animal Health