May 1, 2013 (CIDRAP News) – As labs in the United States study how the H7N9 virus behaves in humans and animals, state and local health officials should dust off their pandemic preparedness plans in case the virus becomes a bigger threat, the US Centers for Disease Control and Prevention (CDC) said today.
The CDC made the recommendation in a review of China's H7N9 outbreak and US efforts to learn more about the disease that appears in an early release of Morbidity and Mortality Weekly Report (MMWR). The CDC has a close collaboration with China's Center for Disease Control and Prevention (China CDC), and a team from the CDC was invited by China to help assess the situation and assist with investigations.
In its epidemiologic review, current as of Apr 29, the CDC said, of 82 confirmed case-patients with available information, 63 (77%) were exposed to live animals, mainly chickens (76%) and ducks (20%).
The agency also said at least three family clusters of two or three cases have been confirmed, which could have involved limited human-to-human transmission. However, no transmission in the follow-up of 1,689 close contacts, including healthcare workers, has been detected, and serologic investigations are ongoing.
A few days after the first human H7N9 cases were announced in China, the CDC urged state and local health officials to boost their surveillance for people who got sick 10 days after returning from China. So far 18 states have identified 37 travelers who fit the description, but none were infected with H7N9. Seven had seasonal flu, 1 had rhinovirus, 1 had respiratory syncytial virus, and 28 were negative for influenza A and B.
During that period, the US flu season was retreating to levels below seasonal baselines, with mainly influenza B detected in low numbers.
To learn more about the virus, CDC researchers are studying H7N9 gene sequences uploaded by China to the GISAID database and doing experiments based on two human H7N9 isolates from China. As of yesterday China had uploaded 19 partial or complete H7N9 sequences: 12 from humans, 5 from birds, and 2 from the environment.
Experiments on the human isolates so far show robust replication in eggs, cell culture, and the respiratory tracts of ferrets and mice. The H7N9 virus was deadly to mice infected with higher doses of the virus, according to the CDC.
Antiviral resistance testing shows that one of the human isolates is susceptible to oseltamivir (Tamiflu), while the other has a marker that suggests that it is not. The CDC said it is still assessing the clinical relevance of the change, but its identification is a good reminder that resistance can emerge spontaneously or during antiviral treatment.
Animal testing in China has detected the virus in a small number of poultry and environmental samples, primarily from poultry markets. The CDC said that, as of Apr 17, 4,150 samples had been collected from swine and environments from farms and slaughterhouses, and all swine samples tested negative.
Chinese officials have intensified their animal surveillance to answer questions about the animal reservoirs of the virus, and their efforts will focus on areas where human cases have been detected, the CDC said.
The US Department of Agriculture (USDA) has set up a situational awareness unit to study, along with the CDC, the epidemiology of the virus in humans and animals. So far the H7N9 outbreak strain has not been found in US animals, and federal officials don't allow the import of live poultry, other birds, or hatching eggs from countries affected by highly pathogenic avian influenza.
Surveillance programs are already in place to detect avian influenza in commercial poultry, and animal health labs have screening tests for avian flu that can be used with confirmation tests at the National Veterinary Services Laboratories to detect the H7N9 strain in poultry and wild birds, the CDC said.
The USDA's Animal and Plant Health Inspection Service is working with the US Department of the Interior to assess potential movement of Eurasian avian flu viruses into North America by wild birds.
Researchers in USDA labs are also conducting animal studies to learn more about the pathogenicity and transmission of the virus, the CDC said. Early results show that chickens and quail show no signs of illness but shed the virus. USDA Agricultural Research Service scientists have also completed an antigenic mapping study to help find isolates that could be used to develop a poultry vaccine, if needed.
The CDC's report also aired its public health concerns about the new virus. Compared with other influenza A virus, H7N9 has differences associated with respiratory-droplet transmission, increased binding to receptors in mammals' respiratory tracts, increased virulence, and increased replication.
Though investigations haven't shown evidence of sustained human-to-human transmission, further adaptation might lead to more efficient and sustained transmission, according to the report. CDC experts also noted that the H7N9 virus is much more severe in humans than other previous H7 viruses have been.
Federal officials have not decided to launch an H7N9 vaccine program in the United States, but if one is needed, the CDC and its partners are already working on a candidate vaccine virus and are planning for vaccine clinical trials.
In the meanwhile, the CDC recommends that state and local officials review and update their pandemic preparedness plans, because it would take several months to prepare a vaccination program, if necessary.
"CDC also recommends that public health agencies review their overall pandemic influenza plans to identify operational gaps and to ensure administrative readiness for an influenza pandemic," the agency added.
May 1 MMWR report