Flu Scan for Sep 16, 2014

Novel H3N1 viruses in swine
;
H5N6 outbreak in Laos
;
Flu immunity

USDA says H3N1 viruses with human flu genes found in swine

The US Department of Agriculture (USDA) has found rare H3N1 influenza viruses in swine in two states in recent months, and two of the isolates carry genes from human seasonal flu viruses. The developments are grounds for serious concern about the potential spread of disease at fairs this fall, according to one animal health expert.

Christina M. Loiacono, DVM, PhD, of the USDA said "several" H3N1 isolates have been found in at least two states since last December. H3N1 viruses in swine are not unheard of but are rare, said Loiacono, who is associate coordinator of the National Animal Health Laboratory Network (NAHLM).

She said two of the isolates carry hemagglutinin (H) genes that come from contemporary human seasonal flu viruses "and are distinct from our current swine H3 viruses." Her report was posted today on ProMED-mail, the reporting service of the International Society for Infectious Diseases. It was originally sent to all NAHLN labs that work with swine flu viruses.

"Potential spread of H3N1 or H3N2 that carries the human-like H3 could have significant impact in swine herds due to poor herd immunity as well as potential public health ramifications," Loiacono wrote. "Preliminary findings by USDA-ARS [Agricultural Research Service] from testing of one of these H3N1 isolates with the human-like H3 gene in swine indicate the virus is fully virulent, causing typical influenza disease."

In the ProMED post, Tam Garland, DVM, PhD, of Texas A&M University's College of Veterinary Medicine, called Loiacono's notice "a serious alert." She is ProMED's moderator for animal diseases and zoonoses.

"It is especially concerning as we enter the autumn livestock show and fair season," Garland wrote. "Animals congregate at these gatherings, as do people. The opportunity for viral spread and viral assortment at these shows is quite large."

Noting that infected animals can spread disease before they look ill, she said swine owners who have sick animals or sick family members should keep them at home.
Sep 16 ProMED-mail post

 

First appearance of H5N6 in Laotian poultry

Low-pathogenic H5N6 avian flu, reported as a new strain in several outbreaks in Vietnam since August, has now appeared in Laos, says a report yesterday from the World Organization for Animal Health (OIE).

Two birds in a flock of 200 on a poultry farm in Viengsavang, Luangprabang, showed signs of clinical disease and died, for an apparent morbidity rate of 1% and an apparent case-mortality rate of 100%.

Testing by real-time polymerase chain reaction (PCR) at the National Animal Health Laboratory confirmed H5N6. The remaining birds in the flock were destroyed.

The report says active surveillance for avian flu was started in five Laotian provinces in July with support from the US Agency for International Development through the Food and Agriculture Organization of the United Nations.
Sep 15 OIE report
Most recent (Sep 4) CIDRAP News scan on Vietnamese outbreaks

 

Study: Preseason antibodies influence immunity to H3N2, flu B, not H1N1

Increased homologous hemagglutination-inhibiting (HI) antibody titers are significantly associated with protection against both H3N2 and type B but not H1N1 influenza in people whose influenza immunity has been shaped by prior natural infection rather than vaccination, according to a study today in the Journal of Infection. Resistance to H1N1 is influenced more by age, the authors found.

The researchers, from England, Australia, and Vietnam, carried out 3 consecutive years of surveillance for influenza-like illness (ILI) (ie, fever >38°C with cough or sore throat), in 940 individuals from 270 Vietnamese households (1,793 person-seasons) in which the residents had never received flu vaccine. The flu seasons covered, from 2007 to 2010, included recirculating flu strains, new antigenic variants, and H1N1 pandemic flu.

Nose and throat swabs and blood samples were collected at baseline and between each of the flu seasons in subjects with ILI. Paired blood samples spanning each season were available for at least 490 subjects.

Influenza was defined as either detection of flu RNA by reverse-transcriptase PCR in a swab sample or of seroconversion (ie, a four-fold or greater rise in HI titer, with a second titer of at least 40).

A significant linear effect of HI titer on the risk of H3N2 was apparent in season 2, as it was for influenza B Yamagata in seasons 1 and 2. No such effect was present for H1N1 in any of the three seasons. However, age was found to be independently associated with a decreasing risk of seasonal H1N1 infection in season 1 (P = 0.08) and season 2 (P < 0.0001), and with pandemic flu in season 3 (P < 0.0001).

As stated by the authors, "Our findings indicate that in this unvaccinated population, prior natural influenza H1N1 infections induced immunity against infection with new drifted and novel strains, which did not appear to be reliant on HI antibodies. . . . Non-HI antibodies could prevent HI antibody induction either by enhancing virus clearance or by competing for antigen. It will be important to confirm whether non-HI neutralizing antibodies account for the absence of a detectable protective effect of baseline H1N1 HI antibodies in our cohort."
Sep 16 J Infect abstract

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