Perspective

CDC confirms new cases of influenza A/H3N2 variant virus

Twelve new cases of influenza A/H3N2 variant virus were identified in Hawaii, Indiana and Ohio in the past week, making 29 total cases since the virus was first detected in humans in July 2011, CDC officials said during a press briefing today.

“Each of the 16 total cases identified in the past two weeks reported contact with swine,” Joseph Bresee, MD, medical epidemiologist in the influenza division at the CDC, said in a media briefing. “In 15 of these cases, contact with the swine occurred while attending or exhibiting swine at an agricultural fair. All cases have been laboratory-confirmed by the CDC.”

According to Bresee, no human-to-human spread of the influenza A/H3N2 variant virus has been identified in the most recent cases. However, limited transmission from person to person may have occurred in three cases in the fall of 2011.

Of the 16 recent cases, 13 of them were among children, which is consistent with data that indicate that children are more susceptible to the infection, Bresee said. No hospitalizations or deaths occurred with the most recent 16 cases, but there were three hospitalizations in the fall of 2011 related to the virus. All of the hospitalizations occurred in people with underlying diseases that put them at high risk for severe influenza.

To avoid the virus, Bresee said the following are important messages: wash your hands before and after contact with swine; avoid drinking and eating around the animals and do not take food or beverages in with the animals; and avoid contact with swine if you have a condition that puts you at high risk for serious complications from influenza, such as lung disease or diabetes.

“Because most cases occurred among people who had contact with swine in the setting of agricultural fairs, special attention should be paid to preventing transmission in these settings, especially since many of these fairs are ongoing now,” Bresee said.

Bresee said that medications that have been effective at preventing and treating seasonal influenza are likely to be effective at treating this variant virus infection. A vaccine for the variant virus has been prepared and clinical trials are planned.

“CDC, along with state and local health departments and our colleagues in animal health, will continue to monitor cases and provide information on how to prevent them,” Bresee said.

Twelve new cases of influenza A/H3N2 variant virus were identified in Hawaii, Indiana and Ohio in the past week, making 29 total cases since the virus was first detected in humans in July 2011, CDC officials said during a press briefing today.

“Each of the 16 total cases identified in the past two weeks reported contact with swine,” Joseph Bresee, MD, medical epidemiologist in the influenza division at the CDC, said in a media briefing. “In 15 of these cases, contact with the swine occurred while attending or exhibiting swine at an agricultural fair. All cases have been laboratory-confirmed by the CDC.”

According to Bresee, no human-to-human spread of the influenza A/H3N2 variant virus has been identified in the most recent cases. However, limited transmission from person to person may have occurred in three cases in the fall of 2011.

Of the 16 recent cases, 13 of them were among children, which is consistent with data that indicate that children are more susceptible to the infection, Bresee said. No hospitalizations or deaths occurred with the most recent 16 cases, but there were three hospitalizations in the fall of 2011 related to the virus. All of the hospitalizations occurred in people with underlying diseases that put them at high risk for severe influenza.

To avoid the virus, Bresee said the following are important messages: wash your hands before and after contact with swine; avoid drinking and eating around the animals and do not take food or beverages in with the animals; and avoid contact with swine if you have a condition that puts you at high risk for serious complications from influenza, such as lung disease or diabetes.

“Because most cases occurred among people who had contact with swine in the setting of agricultural fairs, special attention should be paid to preventing transmission in these settings, especially since many of these fairs are ongoing now,” Bresee said.

Bresee said that medications that have been effective at preventing and treating seasonal influenza are likely to be effective at treating this variant virus infection. A vaccine for the variant virus has been prepared and clinical trials are planned.

“CDC, along with state and local health departments and our colleagues in animal health, will continue to monitor cases and provide information on how to prevent them,” Bresee said.

    Perspective
    Arnon Shimshony

    Arnon Shimshony

    Influenza viruses that circulate in swine are called swine influenza viruses when isolated from swine, but are called variant viruses when isolated from humans. Since July 2011, sporadic human cases of infection with a variant influenza A(H3N2) virus have been detected in the United States. All cases, investigated so far, were found to be preceded by direct contacts with pigs.

    This virus has different virological characteristics from current circulating seasonal influenza viruses in humans, and has a new gene constellation: seven genes from the triple reassortant A(H3N2) viruses known to have been circulating in pigs in North America and the M gene from an A(H1N1)pdm09 virus, a seasonal virus currently circulating in humans.

    In one of the foci of human infection at the county fair, mild respiratory illness among swine was reportedly recorded. From both species, collected specimens were found positive for influenza A (H3N2) virus. Preliminary genetic analysis has shown a very high level of similarity between the gene sequences of H3N2v viruses from humans and the H3N2 viruses from swine.

    In order to improve communications and avoid confusion, in late 2011 FAO, OIE and WHO established a working group of experts to standardize the terminology for variant influenza viruses. The joint recommendation for the above mentioned A(H3N2) virus was: A (H3N2)v , where ‘v’ stands for ‘variant’.

    There are A influenza virus strains which cause a serious swine disease, Swine Influenza. Swine influenza is a highly contagious viral infection of pigs. Swine influenza virus (SIV) infections cause respiratory disease characterized by coughing, sneezing, nasal discharge, elevated rectal temperatures, lethargy, breathing difficulty and depressed appetite. In some instances, SIV infections are associated with reproductive disorders such as abortion. Clinical signs and nasal

    shedding of virus can occur within 24 hours of infection. Morbidity rates can reach 100% with SIV infections, while mortality rates are generally low. Secondary bacterial infections can exacerbate the clinical signs following infection with SIV. Transmission is through contact with SIV-containing secretions such as nasal discharges and aerosols created by coughing or sneezing. (H3N2)v, causing sub-clinical or mild disease in swine, seems not to be regarded as the notifiable SIV.

    During 2009/2010, when the A(H1N1)pdm09 virus (‘Pandemic influenza A/H1N1 (2009) virus) was reportedly spreading globally in humans becoming a cause for international concern, more than 20 countries notified the OIE about the identification of the virus in swine, as an emerging disease. This virus was regarded to spread through the human-to-swine route.

    According to CDC current recommendations, persons who raise swine or come into close contact with swine at fairs or other venues should be aware of the potential risk for influenza transmission between swine and humans. To reduce this risk, preventive measures such as practicing frequent hand hygiene and respiratory etiquette are recommended. Persons also should avoid close contact with animals that look or act ill, when possible, and if experiencing influenza-like illness themselves, should avoid contact with swine. Additional guidelines on prevention of influenza transmission between humans and swine are available at www.cdc.gov/flu/swineflu/industry_guidance.htm.

    • Arnon Shimshony, DVM
    • Infectious Disease News Editorial Board member