A janitor sprays disinfectant over empty chicken cages at a market in New Taipei City, Taiwan, on Monday, April 29. Asian countries have stepped up vigilance against the spread of H7N9 bird flu after a case of the deadly strain showed up in Taiwan, the first outside mainland China.
(CNN) -- The H7N9 strain responsible for the bird flu outbreak in China is unlike any that has previously been seen in this type of virus.
So far, 110 cases have been reported, including one in Taiwan, and 23 people have died. Here are some things to know about this virus:
No evidence of human-to-human transmission to date
So far, authorities said, there is no evidence that this virus can pass from person to person. That doesn't mean it can't happen later.
"If limited person-to-person transmission is demonstrated in the future, this really will not be surprising," Keiji Fukuda, the World Health Organization's assistant director-general for health, security and the environment, told a news conference Wednesday in Beijing.
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It's dangerous and deadly to humans
The virus appears to be transmitted more easily from poultry to humans than H5N1, Fukuda said, referring to the strain responsible for the outbreak between 2004 and 2007, which claimed 332 lives.
"This is definitely one of the most lethal influenza viruses that we have seen so far," he said.
The H7N9 strain was never known to infect people until March. Before then, it was only found in birds.
If the virus does start to spread easily between people, it could trigger a pandemic.
"This is a serious public health situation and it's possible that a pandemic could start if this virus were to change to spread easily between people," the U.S. Centers for Disease Control and Prevention said on its website. "CDC is preparing for that possibility."
New bird flu well-adapted to infect people
There's still a lot of unknowns
It's not clear why this virus strain is infecting humans now, and the source of the infection is unknown.
Scientists have analyzed the genes of the H7N9 viruses and found that they show signs indicating they can adapt to grow in mammals. It appears they can bind to mammalian cells and grow at temperatures near mammals' normal body temperatures, which is lower than that of birds, WHO said.
There is no vaccine available, but WHO said efforts are underway in other countries after Chinese officials said international help would be needed. The CDC said researchers there are working on a vaccine candidate virus.
Cooking poultry can kill the virus before you eat it
In normal cooking temperatures -- so all parts of the meat reach at least 158 degrees Fahrenheit (70 degrees Celsius) with no "pink" -- the virus would be inactivated, including in poultry and game birds.
Generally, eating raw meat is discouraged anyway, as doing so can lead to a variety of foodborne illnesses.
You should not, however, eat diseased animals or animals known to have died from diseases.
No travel restrictions; low U.S. risk
The CDC is not advising against traveling to China, but travelers who go there should refrain from touching birds and other animals and wash their hands often.
There is currently no incidence of the virus in the United States, but the most likely scenario for it to get there would be through a person traveling from China.
The risk to persons in the United States is low, the CDC said.
There are no tests available at pharmacies or doctors' offices to distinguish this flu quickly from any other flu virus, the CDC said. However, there is a sophisticated test to detect the H7N9 virus in particular, which takes at least four hours.
"Anyone with fever, coughing or shortness of breath within 10 days of traveling to China should see a doctor and tell the doctor about the recent travel to China," the CDC said on its website.
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A New Taipei City Department of Environmental Protection truck sprays a virus disinfectant in a park on April 29.
Doctors hold a consultation on the treatment for a patient surnamed Luo, the province's first human case of H7N9 avian influenza, at the No. 2 Hospital in Longyan City, in southeast China's Fujian Province, on April 27. Luo, 65, a local resident, showed symptoms of repeated coughing, low fever and a tight chest on April 18. Luo tested positive for the H7N9 virus on Friday by the Chinese Center for Disease Control and Prevention. Thirty-seven people who have been in close contact with Luo have not shown any abnormal symptoms so far.
A vendor stands by her chicken coop in Fuqing, southeast China's Fujian Province on April 26. At least 20 people have died from the virus which, while common in birds, hadn't been detected in humans before the first cases were reported in March.
A woman wearing a medical mask walks past vending machines that sell masks outside National Taiwan University Hospital in Taipei on April 26. A 53-year-old Taiwanese businessman has contracted the H7N9 strain of bird flu while traveling in China, Taiwan's Health Department said on April 24. It's the first reported case outside of mainland China. The man was hospitalized after becoming ill three days after returning from Suzhou on April 9.
Disease control workers examine a chicken in a poultry farm in Fuqing on April 26.
Three people wearing masks walk outside the National Taiwan University Hospital in Taipei on Thursday, April 25. China has reported 83 cases of H7N9 avian influenza.
An H7N9 bird flu patient walks in the corridor of a hospital after his recovery and approval for discharge in Bozhou, in central China's Anhui Province, on Friday, April 19.
Chickens line the walls at a poultry farm on Thursday, April 18, in Yuncheng, China.
A 7-year-old girl, who was the first confirmed bird flu case in Beijing, is discharged from Beijing Ditan Hospital on Wednesday, April 17.
Health workers collect blood samples from chickens at a poultry farm in Taizhou, China, on April 17.
Chickens roost at a poultry farm in Taizhou, China, on Wednesday, April 17.
Pedestrians in Shanghai wear face masks to protect themselves from the H7N9 bird flu virus on Tuesday, April 16.
A man throws ducklings into a stove at a duck farm in Zhangzhou in China's Fujian province on Sunday, April 14. The farm has had to kill more than 400,000 newborn ducks every week after the H7N9 bird flu affected the domestic poultry market.
A woman uses a lamp to illuminate a batch of eggs in the hatchery of a duck farm in Zhangzhou on April 14.
Cheng Jun, vice president of Beijing's Ditan hospital, shows a video of the first bird flu victim in intensive care during a press conference on Saturday, April 13.
Officials in Hong Kong test poultry at the border with mainland China on April 11 as authorities step up measures against the spread of the deadly H7N9 bird flu.
Empty cages are seen at a closed bird market on April 10 in Shanghai.
A technician conducts tests for the H7N9 bird flu virus at the Kunming Center for Disease Control on April 10 in Kunming, China.
Medical workers take part in a drill that simulates human infection of the H7N9 bird flu virus on April 9 in Hefei, China.
People wear masks to protect themselves from the H7N9 virus, or bird flu, while riding the underground in Shanghai on Tuesday, April 9.
Employees work on the production line of Shufeng Jiedu Capsule, an herbal medicine for treating avian influenza patients, at a workshop of Anhui Jiren Pharmaceutical Co., Ltd on Monday, April 8 in Bozhou, China.
A public park staff carries a cage to catch pigeons at a public area in People's Square, downtown Shanghai on Saturday, April 6. Shanghai municipal government has ordered workers to remove pigeons from public area to prevent the spread of H7N9 bird flu to humans, local media reported.
A boy looks at pigeons at a public park in People's Square in Shanghaion on April 6. Health authorities in China said on Saturday that the country's 16 confirmed H7N9 bird flu cases were isolated and showed no sign that it is transmitted from human to human, Xinhua News Agency reported.
A public park worker catches a dove in People's Square in downtown Shanghai on April 6.
A public park worker places a dove in a cage in Shanghai on April 6.
A masked security guard stands outside Taipei Hoping Hospital on April 6, where new isolation units have been set up to treat potential new avian influenza cases.
Taiwan's Health Minister Chiu Wen-ta checks the negative pressure system in a isolation room as he inspects preparations for the virus in Taipei City Hospital Heping Branch, on April 6.
A woman wears a face mask inside a subway station in Shanghai, China, on Friday, April 5. The Chinese minister of agriculture said Thursday it had discovered the H7N9 virus in samples taken from pigeons at Huhai agricultural market, China's state-run Xinhua news agency reported.
Health workers gather dead chickens at the Huhai poultry wholesale market, where the H7N9 bird flu virus was detected in pigeon samples, in Shanghai on April 5.
Cabin attendants are seen on a thermographic imaging device after their arrival from Shanghai at the quarantine station at Haneda International Airport in Tokyo on April 5.
Men wear face masks at a shopping mall in downtown Shanghai on April 5.
Chinese health workers collect bags of dead chickens at the Huhai wholesale market on April 5.
A policeman goes after a chicken that broke loose as Chinese health workers started culling chickens at Huhai wholesale market on April 5.
A woman cleans a birdcage at a store in Taipei, Taiwan, on Thursday, April 4.
Staff members from Taiwan's Center for Disease Control stand at the entrance of Sungshan Airport in Taipei.
A passenger has her temperature checked by a CDC staff member at the entrance of Sungshan Airport in Taipei.
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