Will the next pandemic be caused by the S-OtrH3N2 virus?

[Laidback Al]

Will the next pandemic be caused by the S-OtrH3N2 virus?

Currently, the CDC is watching the development of a novel strain of influenza A H3N2 identified as S-OtrH3N2 [Swine-Origin, triple reassortant (H3N2)]. Triple reassortant H3N2 was first identified in pigs in 1998 (link) and a few years later found to be endemic in pigs and turkey populations in the USA with evidence of interspecies transmission (link). The first reported possible human case of trH3N2 was a farm worker from Ontario Canada in 2005 (link).

Since 2009 there have been sporadic scattered human cases in the USA, most from apparent interspecies transmission.

2009-2010 Influenza Season

U.S. Novel Influenza Cases
. . . in addition to the pandemic strain virus infections, three cases of human infection with novel influenza A viruses were identified and then characterized at CDC. These three cases, identified in Kansas, Iowa, and Minnesota, were isolated cases of human infections with contemporary North American swine-lineage influenza A (H3N2) viruses currently circulating in swine herds. No additional human cases were linked to these three patients. Although the Minnesota patient reported visiting a live animal market in the days preceding illness onset (May 8, 2010), only the Kansas patient specifically reported contact with pigs in the week preceding symptom onset (July 28, 2009). The Iowa patient had onset of symptoms in September 2009. The Kansas and Iowa patients did not require hospitalization; the Minnesota patient was hospitalized, and recovered fully.

http://www.cdc.gov/mmwr/preview/mmwr...cid=mm5929a2_w

2010-2011 Influenza Season

Novel Influenza A Viruses
Five cases of human infection with a novel influenza A virus were reported during the 2010--11 influenza season from three states. All five cases were infected with swine-origin influenza A (H3N2) viruses. Two cases occurred in September (Pennsylvania and Wisconsin), one case in October (Pennsylvania), and two cases in November (Minnesota). Two of the five cases occurred in adults, and three occurred in children. Two of the five cases were hospitalized; all five have recovered fully from their illness. The two cases in Pennsylvania were not related. The cases in Wisconsin and Pennsylvania had direct contact with swine or lived in areas close to swine farms. The two cases from Minnesota occurred in a father (index case) and child. The father had a nasopharyngeal swab positive for swine-origin influenza A (H3N2) virus and had direct swine exposure 6 days before illness onset. The child, whose infection with influenza A (H3N2) virus was confirmed several weeks later by serologic testing, did not have direct swine exposure, and most likely acquired infection from close contact with her father. Other persons in the same household also had ILI during the same period, but serologic results were either negative or inconclusive.

http://www.cdc.gov/mmwr/preview/mmwr...cid=mm6021a5_w

2011-2012 Influenza Season

Since July 2011, 10 additional human trH3N2 cases have been reported in the USA, all carrying the M gene from the pH1N1 virus. The virus is now officially referred to as S-OtrH3N2. The first seven of these 10 cases appear to have resulted from interspecies jump from swine to humans on different occasions.

Seven of these 10 cases resulted in mild illness, but three of the infected persons were hospitalized for influenza; all patients have recovered. In all seven earlier cases, exposure to swine was identified in the patient or in a close contact of the patient.

http://www.cdc.gov/mmwr/preview/mmwr...m60d1123a1.htm

Of these seven cases 2 are from Indiana, 2 from Maine, and 3 from Pennsylvania.

Indiana (2):
1. http://www.cdc.gov/mmwr/preview/mmwr...cid=mm6035a6_w
2. http://www.in.gov/isdh/files/Week43-2011.pdf

Maine (2) : http://www.maine.gov/tools/whatsnew/...id=318365&an=2

Pennsylvania (3)
1. http://www.cdc.gov/mmwr/preview/mmwr...cid=mm6035a6_w
2. http://www.cdc.gov/media/haveyouhear...b_testing.html
3. http://www.cdc.gov/media/haveyouhear...b_testing.html

Human to Human Transmission ? Iowa

Yesterday, The CDC published an MMWR report on three new S-OtrH3N2 human infections from Iowa (link). These three reported cases are all children who attended the same day care center. The staggered onset dates suggests that one of the children infected the others. And none of the children were reported to have contact with swine. In addition, another sibling and parent of the children also exhibited ILI symptoms but were not tested. These 5 individuals perhaps represent the first reported human cluster of S-OtrH3N2 infection resulting from human-to-human (H2H) transmission. These cases represent intraspecies transmission of S-OtrH3N2; the threat of this novel virus as a pandemic virus has increased.

Discussion and Implications

So far, human infections with S-OtrH3N2 have not resulted in any deaths, but several of the cases have been hospitalized. Children under 10 years are the most commonly infected individuals, suggesting that previous exposure to earlier strains of H3N2 may provide some cross-protective immunity. The ultimate virulence of this novel strain as it continues to infect human is unknown. The CDC has already developed and submitted a sample strain of this virus for potential inclusion into future influenza vaccines (link).

[Giuseppe]

Re: Will the next pandemic be caused by the S-OtrH3N2 virus?

The above post is a nice representation of the public health concern event that is unfolding in the US after the continous circulation of the new influenza A subtype of swine origin H3N2.

I would like to express to the Author my gratitude for this useful picture of the situation.

Among the various unanswered questions about this new subtype there are - for example - the actual presence in the general population of cross-reactive antibodies against surface glycoproteins (from the human seasonal influenza virus donor strain A(H3N2) circulating in the early '90 of XX century) and the subsequent impact of this immunity in the transmission and circulation dynamics of the new strain.

Further, we need to know whether the clinical pattern of illness is really a mild, self limiting condition as happened so far for the children affected.

In addition, we have to know if the presence of a possible large proportion of population with cross-reactive antibodies is masking an already not containable outbreak in the US and perhaps elsewhere.

An international panel of experts should be created to evaluate and corroborate the information available on this virus and its epidemiology and pathology, as happened when the novel pandemic strain A(H1N1)pdm09 emerged in the 2009 spring.

Finally we must know if:

-- the antigenic properties of this new virus are really similar to the previously circulating seasonal donor strain and to measure the effective ability to the old seasonal virus directed immunity to reduce or abrograte the infection in adults or in a portion of population (age groups);

-- the effectiveness of a vaccine prepared upon old seasonal H3N2 vaccine seeds (1990 strain);

-- the complete characterization of the illness patterns and pathology;

-- the susceptibility of the new virus toward available antivirals (oseltamivir, zanamivir and peramivir, laninamivir) and the clinical effectiveness of antiviral therapy.

A rapid characterization of antigenic and etiopathological properties is urgently needed as well as the readiness to produce a vaccine based on an archived human seasonal seed strain.

Whether this virus may or not cause a pandemic or just a false, children pandemic remains to be established and we expect eagerly a quick response from National and Supranational Health Agencies. (IOH)