Avian H10 viruses haven’t garnered a lot of attention until relatively recently, as they rarely produce symptoms in poultry, and human infections have been both rare, and mild. All of that changed last winter when China reported three fatal H10N8 infections (see Jiangxi Province Reports 3rd H10N8 Case) in quick succession.
LPAI (Low Path Avian Influenza) H10N8 had been previously reported in a duck sampled back in 2012 from Guangdong province, but was otherwise not well described.
Human infections with a close cousin – H10N7 – had previously been reported in two children in Egypt in 2004 (see Avian Influenza Virus A (H10N7) Circulating among Humans in Egypt) and among abattoir workers in Australia in 2012 (see EID Journal: Human Infection With H10N7 Avian Influenza).
In both cases illness was described as mild, and of short duration.
A side note, we also looked at a recent outbreak of H10N7 in European seals (see Avian H10N7 Linked To Dead European Seals), with warnings to the public to avoid contact.
Since testing for novel flu viruses among humans is only very rarely done, we don’t have a good handle on how often these `oddball’ avian flu viruses actually jump to humans.
While probably fairly rare – and largely restricted to those who have a lot of contact with wild or domesticated birds – it is is likely more common than we might otherwise think. For more on prior research on seroprevalence of other rare avian influenzas see A Little Background On H11 Avian Influenzas.
In any event, the 2012 detection of H10N8 in a Guangdong duck, followed last year by the infection and deaths of three people from this emerging virus, inspired a group of Chinese scientists go to back and test hundreds of archived blood samples taken prior to the first known human case, to look for signs of previous H10N8 infection.
Although the seroprevalence for this virus appears very low, out of 827 sera tested they found 21 mildly reactive , with three showing titers of at least 1:40. One, with an MN antibody titer of 1:80, was strongly suggestive of prior infection. With this baseline, future seroprevalence studies of animal workers might provide an indirect early warning system, should this virus continue to spread stealthily in the poultry population.
The study appears in BMC Medicine. (Note there appears to be a temporary problem with the link)
BMC Medicine 2014, 12:205 doi:10.1186/s12916-014-0205-3
Wenbao Qi, Shuo Su , Chencheng Xiao, Pei Zhou, Huanan Li, Changwen Ke , Gregory C Gray, Guihong Zhang , Ming Liao
Considered an epicenter of pandemic influenza virus generation, southern China has recently seen an increasing number of human H7N9 infections. However, it is not the only threat. On 30 November 2013, a human H10N8 infection case was first described in China. The origin and genetic diversity of this novel virus is similar to that of H7N9 virus. As H10N8 avian influenza virus (AIV) was first identified from a duck in Guangdong Province during 2012 and there is also evidence of H10N8 infected dogs in this region, we sought to examine archived sera from animal workers to see if there was evidence of subclinical human infections before the first human H10N8 cases.
We studied archived serum samples (cross-sectional study, convenience sample) collected between May and September 2013 from 710 animal workers and 107 non-animal exposed volunteers living in five cities of Guangdong Province. Study participants’ sera were tested by horse red blood cells (RBCs) hemagglutination inhibition (HI) and microneutralization (MN) assays according to World Health Organization guidelines. The A/Jiangxi-Donghu/346-1/2013(H10N8) virus was used. Sera which have an HI assay ≥1:20 were further tested with the MN assay. Questionnaire data were examined for risk factor associations with positive serological assays. Risk factor analyses failed to identify specific factors associated with probable H10N8 infections.
Among the 827 sera, only 21 animal workers had an HI titer ≥1:20 (18 had an HI titer of 1:20 and 3 had an HI titer of 1:40). None of these 21 subjects reported experiencing any influenza symptoms during the three months before enrollment. Among the three subjects with HI titers of 1:40, two had MN antibody titers of 1:40, and one had a MN antibody titer of 1:80 (probable H10N8 infections).
Study data suggest that animal workers may have been infected with the H10N8 virus before the first recognized H10N8 human infection cases. It seems prudent to continue surveillance or H10N8 viruses among animal workers.