How does H5N1 bird flu spread to humans and what are the health risks?

How does H5N1 bird flu spread to humans and what are the health risks? The detection of a deadly strain of bird flu in seals in Australia may have you wondering about the risk to humans. Although H5N1 has previously spread to mammals elsewhere in the world, the chance of people catching it is considered low by Australia's Centre for Disease Control (CDC). Since a dominant new clade, H5N1 2.3.4.4b, emerged in Europe six years ago, there have been just 141 reported cases of H5N1 globally, including 24 deaths. CDC director-general Zoe Wainer said bird flu rarely transmitted from animals to people and spreading between people was also very rare. While the current risk of being infected is low, with no human cases in Australia, scientists are studying the potential of the virus to mutate and cause a human pandemic in the future. Raina MacIntyre, the head of the biosecurity program at the Kirby Institute, said flu viruses mutated rapidly and the H5N1 strain had already changed a lot since it emerged. That's because the virus has been hopping around a lot of different species beyond birds. "There's much greater opportunities for mixing between humans and infected birds or animals," Professor MacIntyre said. So how can you catch H5N1, what are the symptoms and how can you help protect yourself if it takes hold in Australia? How do humans get bird flu from animals? So far, most infections have come from close contact with farm animals. Seventy-one of the H5N1 cases in humans in the past six years have been in the US and mostly among poultry and dairy farm workers. Only a handful of people in the US have been infected from contact with wild animals or unknown sources. Professor MacIntyre said there were a couple of ways people could get bird flu from poultry. "The virus can be transmitted from infected poultry by direct contact or aerosolisation of any poultry components including faeces, respiratory secretions, and contaminated dust in coops, as well," she said. The US Centers for Disease Control and Prevention (US CDC) warns human infection may happen when someone touches the virus and then touches their eyes, nose or mouth. Raw milk from infected dairy cows is also thought to be a key transmission risk if workers come into contact with contaminated milk and touch their face or it splashes their eyes. Veterinary epidemiologist Jason Lombard, from Colorado State University, said how exactly the virus moved from cow-to-cow or people was still unknown. "Milk, which has the highest concentration of the virus, is believed to be a key component of disease transmission but studies evaluating transmission of disease during milking has not been able to replicate disease transmission," he said. "Other routes of exposure, including aerosol exposure has been documented but none of the possible modes of transmission has risen to the top as the most likely route." Human-to-human transmission of bird flu viruses is rare. But Professor MacIntyre said there was a report from Indonesia of this happening with a different clade of H5N1 in 2006. "This occurred in Sumatra in a remote area, where a family cluster of eight cases occurred," she said. "It was possibly because of the remote location that it died out." Can you get bird flu from eggs or milk? There have been no reported cases in the world of humans getting infected with H5N1 from consuming eggs or milk. Australian CDC advice said it was safe to eat properly handled and cooked meat or eggs. According to the US CDC, it could be possible to get infected by eating uncooked or undercooked poultry and eggs. But the watchdog also noted pasteurisation killed bacteria and viruses, including bird flu, in milk. Although there aren't any examples of people getting bird flu from consuming eggs or milk, there is some evidence animals can be infected. ViroEpiVet veterinary virologist and epidemiologist Robyn Hall said raw milk consumed by cats appeared to give them the virus. "What we've seen in the US, where a lot of cats on dairies were dying, is often the virus goes to the brain in cats and there's a very high mortality in that species," she said. What are the symptoms of bird flu in people? Professor MacIntyre said many people in the US infected with bird flu had conjunctivitis (eye inflammation). The Australian Centre for Disease Control highlighted several other symptoms, which usually start between one and 10 days of being infected, to watch out for: - fever - coughing - sore throat - runny nose - muscle aches and pains - headache - fatigue - nausea and vomiting Diarrhoea is also a less common but potential symptom. Some people who are infected with bird flu could also be asymptomatic and show no obvious signs of infection. How deadly is bird flu in humans? Professor MacIntyre said the fatality rate of the 2.3.4.4b clade was much lower than other H5N1 clades in the past. Out of the 71 cases of H5N1 in the US there has been one death. A second US bird flu death in November was from a different strain, H5N5. Most of the human cases in the US contracted from poultry and dairy herds have been from two different types of H5N1 2.3.4.4b known as D1.1 and B3.13. The type of bird flu detected in Australia is known as B3.2 and entered Australia via Antarctic islands. Are there treatments if you got bird flu? The US CDC recommends people are treated with an antiviral drug, like baloxavir and oseltamivir, as soon as possible if they show flu symptoms after being exposed to infected birds or animals. Antivirals are thought to work best within the first two days of symptoms and can reduce some complications from flu. A study published in Nature Communications earlier this year found mice infected with H5N1 clade 2.3.4.4b didn't die when given a dose of baloxavir. The researchers recommended baloxavir be considered in pandemic planning as a potential frontline therapeutic approach to treatment of humans. Professor Wainer said Australia had access to antivirals and pandemic influenza vaccines through the National Medical Stockpile as part of preparedness planning. What should you do about bird flu? There are a few ways you can keep yourself safe while authorities continue to investigate. The CDC recommends: - Washing your hands thoroughly before and immediately after handling any bird even if they are healthy - Staying away from sick or dead birds and their surroundings, droppings, body fluids, feathers and eggs - Not allowing pets to touch or eat sick and dead birds - Thoroughly cooking meat and eggs before eating There is currently no bird flu vaccine for the general public, but Professor MacIntyre urged people to stay up to date with their seasonal flu jab. That's because it could reduce the chance of someone getting human and bird flus at the same time. Could bird flu turn into a human pandemic? The virus would need to mutate further for this bird flu outbreak to turn into a pandemic. Professor MacIntyre said there were certain mutations in the different types of H5N1 that researchers were looking out for associated with adaptation to mammals. A particular mutation linked with mammal-to-mammal spread in the US is not present in the strain we know has arrived on Australian shores so far. Loading...The strain detected in Australia, the B3.2 genotype, is most closely related to an outbreak on Heard Island and McDonald Islands where thousands of birds and mammals, like southern elephant seals, were killed. But this genotype, according to a pre-print study on bioRxiv, has several mutations that increased disease severity or aided virus replication in mammals. Professor Wainer said the risk of a pandemic could increase if someone got both bird flu and seasonal human flu at the same time. "The viruses could exchange genetic material and this may create a new strain that more easily infects humans," she said. This is when you could get a pandemic, according to Professor MacIntyre. "A flu pandemic, if it starts, will start quite suddenly and could start anywhere in the world," she said. "It's not necessarily going to start in Australia." Professor Wainer said there were currently no human cases of bird flu in Australia. "Public health authorities are identifying and monitoring any individuals who may have had close contact with infected birds," she said. If you find a sick or dead bird take photos or video, if possible, and report it to the Emergency Animal Disease Hotline on 1800 675 888. Loading...