Influenza Virus A (H10N7) in Chickens and Poultry Abattoir Workers, Australia

In March 2010, an outbreak of low pathogenicity avian influenza A (H10N7) occurred on a chicken farm in Australia. After processing clinically normal birds from the farm, 7 abattoir workers reported conjunctivitis and minor upper respiratory tract symptoms. Influenza virus A subtype H10 infection was detected in 2 workers.

In March 2010, an outbreak of low pathogenicity avian infl uenza A (H10N7) occurred on a chicken farm in Australia. After processing clinically normal birds from the farm, 7 abattoir workers reported conjunctivitis and minor upper respiratory tract symptoms. Infl uenza virus A subtype H10 infection was detected in 2 workers. R eported outbreaks of low pathogenicity avian infl uenza (LPAI) viruses of infl uenza A subtype H10 in poultry are uncommon but have occurred among turkeys and emus in the United States (1,2), farmed Pekin ducks in South Africa (3), and chickens in Canada (4). Isolation of infl uenza virus A (H10N7) was reported in Italy from smuggled poultry products from China (5). Transmission of LPAI viruses from birds to humans, resulting in symptomatic disease, has been reported for infl uenza virus A subtypes H9N2 in China and Hong Kong, H7N2 in North America and the United Kingdom, H7N3 in Canada, H7N7 in the United Kingdom (6), and H10N7 in Egypt (7).

The Study
In March 2010, an outbreak of LPAI A (H10N7) was identifi ed in a biosecure intensive commercial poultry enterprise in New South Wales, Australia. For 8-14 days, 10-25 birds died each day, compared with the normal number of 2-6 birds per day. An egg production decrease of up to 15% was documented in the affected fl ocks. In contrast to other reported poultry outbreaks (1)(2)(3)(4), respiratory signs were absent in the fl ock.
All cloacal and tracheal swabs from 10 dead and 10 live birds submitted for infl uenza virus exclusion were positive by an infl uenza A matrix gene quantitative real-time reverse transcription PCR (8), and virus was detected at various levels (cycle threshold [C t ] 15-37). The infl uenza A viruses were then subtyped from swabs by using a microarray assay (Clondiag, Jena, Germany) that enabled the rapid identifi cation of infl uenza virus A (H10N7). The virus was readily cultured from swabs in embryonated chicken eggs and in MDCK cell cultures. Several viral genome segments were sequenced, which enabled confi rmation of the virus as LPAI A (H10N7) and performance of phylogenetic analysis. A fl uorescence-based neuraminidase inhibition assay showed the isolate to be sensitive to the antiviral drugs oseltamivir and zanamivir (mean 50% inhibitory concentration ± SD 0.5 ± 0.1 nmol/L and 1.8 ± 0.3 nmol/L, respectively) (9).
Serologic testing was conducted by using an infl uenza A nucleoprotein-based blocking ELISA and a subtype H10-specifi c hemagglutination inhibition test; results showed widespread infection in the affected fl ock, with 18 of 20 samples seropositive. Sampling across a 4 additional fl ocks on site showed that an additional 9 of 40 birds were seropositive for infl uenza A subtype H10.
Ten days after the outbreak was confi rmed, 3 previously seronegative fl ocks from the site were sent to an abattoir; 1 day earlier, they had passed state government clinical inspection, including inspection and examination of production and mortality records. Within a week, 7 workers at the abattoir showed signs of conjunctivitis; 2 also reported rhinorrhea and 1 a sore throat.
Conjunctival swabs were collected from 6 of the workers and nose and throat swabs from all 7. Infl uenza A RNA was detected by PCR 4 days after abattoir exposure in conjunctival swabs from a worker who reported conjunctivitis, rhinorrhea, and sore throat (C t 31.8) and 7 days after abattoir exposure from the nose/throat swab of another worker who reported only conjunctivitis with onset 2 days earlier (C t 35). Partial sequence analysis of the hemagglutinin genes from both samples (GenBank accession nos. CY063325 and CY063326) confi rmed the presence of infl uenza A subtype H10; the partial sequences were identical to the subtype H10 chicken isolate, although no virus was cultured from the workers.
The conjunctivitis and other reported symptoms among the 7 workers were mild and of short duration, and there was no evidence of seroconversion by hemagglutination inhibition or virus neutralization tests in any of the workers from whom convalescent-phase blood was collected, including the 2 with confi rmed infl uenza A subtype H10 infection. These fi ndings are consistent with the mild symptoms and lack of serologic evidence reported in humans after experimental infection with infl uenza A (H10N7), which may indicate the limited ability of the virus to multiply and stimulate a detectable immune response in humans (10). Other studies have reported no evidence of elevated subtype H10-specifi c antibody titers among poultry abattoir workers, although serologic evidence of subtype H10 infection was detected among turkey farmers in the absence of clinical symptoms (11). Although 4 farm staff members from the site of the initial infections reported conjunctivitis and other symptoms to health care workers, infl uenza was not confi rmed. The abattoir workers with laboratory-confi rmed infl uenza A subtype H10 infection handled offal and giblets in a section of the abattoir where automated evisceration usually took place; however, because of the size of the birds, evisceration was manually assisted on the day that these fl ocks were slaughtered.
No obvious breach of biosecurity occurred on the farm. The water supply to the farm was chlorinated town water; no large dams were on site, only small paddock dams for cattle. The sheds were birdproof and protected by additional bird netting. A feed mill supplied the feed, which was delivered into silos through blow pipes from outside the perimeter fence. Litter (wood shavings) was delivered in enclosed bales. Workers showered on the way in and out of facilities; disinfectant foot baths were placed at the entrance of each shed, and staff were required to use the separate footwear provided inside the shed. Staff were not allowed to have birds or pigs at home.

Conclusions
During 2010, the number of wild waterfowl observed on the affected site was unusually low. Surveillance of poultry fl ocks within a 2-km radius of the affected farm did not detect any serologic or virologic evidence of subtype H10 infection. Ongoing surveillance of wild waterfowl in New South Wales reported infl uenza virus A (H10N7) in other areas in the previous year (K.E. Arzey, unpub. data); however, during 2007-2008, onsite surveillance detected no evidence of infl uenza A infection among wild waterfowl (G.G. Arzey, unpub. data).
The phylogenetic analysis of the full hemagglutinin sequence from the infl uenza A (H10N7) infections reported here in chickens showed a high degree of homology with North American avian infl uenza A subtype H10 viruses (Figure). This is an unusual fi nding, given that most avian infl uenza viruses detected in Australia are related to Eurasian avian infl uenza strains (12).
The fi nding of LPAI in commercial poultry in Australia is rare, with only 2 reports published (13). To our knowledge, no transmission to humans has been reported previously, including during the 5 reported HPAI outbreaks in Australia during 1976-1997 (13). The United Kingdom Advisory Committee on Dangerous Pathogens (14) acknowledged the occupational risk from slaughter of LPAI-infected birds and recommended that appropriate personal protective equipment (PPE) be used during handling of infected birds. However, because of the recent testing of the fl ock, the birds in this instance were assumed to be free of infection, and workers did not wear goggles and face masks in the evisceration section on the day the fl ocks were processed. After this incident, use of full PPE, including the use of enclosed rim goggles and P2 (N95) face masks, was implemented in sections of the abattoir where exposure to birds and carcasses from the infected site was likely. Staff training, compliance with PPE use, and the decision to slaughter fl ocks from the site only after a suffi cient number of birds were sampled to enable detection of a low infection prevalence and at a 99% confi dence level resulted in no further reported infection of workers during the processing of all fl ocks from the site over 10 months. Analysis of preslaughter samples showed that the spread of infection stopped about 4 weeks after infl uenza virus A (H10N7) was fi rst confi rmed on the site.