Swine Flu - Mode of Transmission

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Mode of Transmission

The human to human mode of transmission of the deadly swine flu virus is likely to occur when an infected person coughs or sneezes in the presence of uninfected people.

One infected person can transmit the virus to hundreds of people and it is this “viral” spread that is wiorrying the WHO officials. Ban Ki-moon, UN secretary- general, observed “We are concerned that this virus could cause a new influenza pandemic. It could be mild in its effect or potentially be severe. We don’t know which way it will go.” Another possible mode of transmission is when an uninfected person touches any item that that has the virus on it.

A single droplet of 0.5 to 5 µm in diameter or a single virus is enough to infect a person. A single sneeze releases over 40,000 droplets. The droplets can either remain as aerosol or settle on objects.

The avian influenza virus can survive indefinitely when  frozen. The virus can survive for one to two days on surfaces such as plastic or metal and for about fifteen minutes on dry paper tissues but only five minutes on skin.

In the mucus secretions  it can survive longer. The virus is inactivated by heating to 56 °C (133 °F) for a minimum of 60 minutes and also by  pouring acids (at pH <2) on the infected surfaces.

In an interesting study done on the survival of the human influenza viruses on banknotes that are dispensed in billions daily it was found that  Influenza A viruses can survive in high concentrations for  up to 3 days.. The same inoculum in the presence of respiratory mucus showed a striking increase in survival time (up to 17 days). They concluded that the unexpected stability of influenza virus should be considered in the setting of pandemic preparedness.

Level of humidity and UV radiation can influence the survival of the virus. Low humidity combined with  lack of sunlight (during winters) can be ooptimal for the virus to  survive longer and this accounts for  the higher prevalence of flu during winter months. 

Influenza is known to occur commonly in pigs and the major route of transmission is these animals is also through direct contact between the infected and the uninfected animals. Pigs are raised and transported in close proximity and this increases  the risk of transmission. Direct touching or transmission through air are also possible.Wild animals play a role in transmitting the disease between farms.

Farm hands who work with poultry and swine are at an increased risk of acquiring a zoonotic infection. The others at risk, albeit at a lower scale include veterinarians and those involved in meat processing.

Continuous public health surveillance and vaccination against swine flu is paramount to protect these people and to prevent the spread of the disease.

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This is an informative article on this subject and I really enjoyed the read. My regards and appreciation to the writer of this amazing material... To know more about Flu Symptoms

I am so worried about catching the swine flu. I have done everything in my power to protect myself and my family. Even to the point that if it were to become so out of control that we needed to be locked in our house for some time due to the pandemic.

An interesting Abstract from a recent paper on Swine Flu

Novel Swine-Origin Influenza A (H1N1) Virus Investigation Team

Background - On April 15 and April 17, 2009, novel swine-origin influenza A (H1N1) virus (S-OIV) was identified in specimens obtained from two epidemiologically unlinked patients in the United States. The same strain of the virus was identified in Mexico, Canada, and elsewhere. We describe 642 confirmed cases of human S-OIV infection identified from the rapidly evolving U.S. outbreak.

Methods - Enhanced surveillance was implemented in the United States for human infection with influenza A viruses that could not be subtyped. Specimens were sent to the Centers for Disease Control and Prevention for real-time reverse-transcriptase–polymerase-chain-reaction confirmatory testing for S-OIV.

Results- From April 15 through May 5, a total of 642 confirmed cases of S-OIV infection were identified in 41 states. The ages of patients ranged from 3 months to 81 years; 60% of patients were 18 years of age or younger. Of patients with available data, 18% had recently traveled to Mexico, and 16% were identified from school outbreaks of S-OIV infection.

The most common presenting symptoms were fever (94% of patients), cough (92%), and sore throat (66%); 25% of patients had diarrhea, and 25% had vomiting. Of the 399 patients for whom hospitalization status was known, 36 (9%) required hospitalization. Of 22 hospitalized patients with available data, 12 had characteristics that conferred an increased risk of severe seasonal influenza, 11 had pneumonia, 8 required admission to an intensive care unit, 4 had respiratory failure, and 2 died. The S-OIV was determined to have a unique genome composition that had not been identified previously.

Conclusions A novel swine-origin influenza A virus was identified as the cause of outbreaks of febrile respiratory infection ranging from self-limited to severe illness. It is likely that the number of confirmed cases underestimates the number of cases that have occurred.

Raja Ramachandran, Senior Resident Nephrology, PGIMER, Chandigarh,INDIA

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