From bird flu to yellow fever, we’re reading about zoonotic disease outbreaks

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Human cases of bird flu are surging, officials concerned of high pandemic potential – Genetic changes in the H7N9 virus are alarming public health officials globally and are causing officials to reexamine their pandemic preparedness. Over 460 people in China have been infected with the H7N9 bird flu virus this winter, representing one third of all reported cases since the virus was first discovered in humans in 2013. About one-third of people who have been diagnosed with H7N9 have died from their infections. The Centers for Disease Control and Prevention have placed the virus at the top of their list of pandemic threats from zoonotic viruses.

Most human infections of H7N9 have occurred after exposure to infected poultry – cases of human-to-human exposure have been rare so far. While most bird flus don’t kill poultry and may not even carry symptoms of illness in poultry, mutations in the genetic sequencing of several strains of the virus in southern China have made the virus more dangerous for chickens, and perhaps for people who become infected. Until now, the genetic sequencing of H7N9 have shown that the virus is of low pathogenicity, which means its potential to kill chickens is low. However, genetic sequencing of virus strains found in three patients and poultry samples in southern China show that virus has evolved into high pathogenicity there, which occurs when viruses are allowed to circulate in poultry for too long. While the evolution from low to high pathogenicity does not indicate that the virus has increased potential for infecting humans, infection with high pathogenicity strains can result in other organs besides the lungs being affected by the virus.

Rick Bright, the director of the Biomedical Advanced Research and Development Authority, or BARDA, said a new vaccine must be developed to protect against the latest strains, as the 12 million doses the U.S. currently has stockpiled – intended to be used by first responders in the case of a pandemic – are for protection against the older lineage of H7N9 virus and may be ineffective against the newer strains.

Chinese officials have reported that seven percent of human cases in the latest wave of infections have shown some signs of resistance to the two antivirals that are most commonly used to treat patients, however resistance was developed after treatment was initiated, indicating that antiviral resistant strains were not spread by poultry.

Yellow fever outbreak continues to spread in Brazil – Health officials in Brazil have identified over 1,500 people who have been infected with yellow fever since an outbreak began in that country in December. With a mortality rate of 34.2 percent, 241 people have died. While yellow fever is typically spread among humans by the same mosquito that spreads other arboviruses like Zika, dengue and chikungunya, all the cases in the current outbreak have been linked to an outbreak of yellow fever among monkeys in the Amazon basin and other tropical forests in Brazil. But the potential for human-to-human transmission involving the aedes aegypti mosquito is high, Dr. Anthony Fauci, head of the National Institute for Allergies and Infectious Diseases, wrote in a commentary. Fears of sustained human-to-human transmission in high population, urban areas have prompted the Brazilian Ministry of Health to distribute almost 15 million doses of the yellow fever vaccine. The last yellow fever outbreak that occurred in Angola and the Democratic Republic of Congo in December 2015 exhausted the World Health Organization’s emergency stockpile of yellow fever vaccine. That outbreak infected almost 1,000 people and killed 137.

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