Hepatitis A is a viral liver disease that can cause mild to severe illness. Although we have not hear about any major outbreaks of it, World Health Organization warns us that epidemics of this disease can be explosive and cause significant economic loss.
For a very long time scientists thought that hepatitis A does not have any close relatives and only humans and other primates can be infected. However, now scientists in the Center for Infection and Immunity at Columbia University’s Mailman School of Public Health have discovered a new virus in seals, which is the closes relative to human hepatitis A virus ever known.
These findings are very significant for several reasons. This discovery provides new clues on the emergence of hepatitis A. For a long time scientists thought that hepatitis A is only common in primates. Now as they found similar virus in seals, it is possible that many more kinds of these so-called ‘hepatoviruses’ may also exist in other wildlife species.
Professor Simon Anthony, lead author of the study, said: “our data suggest that hepatitis A and this new virus share a common ancestor, which means that a spill over event must have occurred at some point in the past. It raises the question of whether hepatitis A originated in animals, like many other viruses that are now adapted to humans.”
Although hepatitis A is rarely fatal, it can cause debilitating symptoms and fulminant hepatitis (acute liver failure), which is associated with high mortality. Around 1.4 million people are infected worldwide every year, because it is a highly contagious disease. It can occur in individual cases, but there were quite a few epidemics too, for example, the epidemic in Shanghai in 1988 affected about 300 000 people.
Because prevention from hepatitis A mostly relies on good hygiene, it is quite common in developing world. In fact, according to WHO, 90% of children in developing countries have been infected with the hepatitis A virus before turning 10 years old. It is usually transmitted by the faecal-oral route – people can get infected from food and water (hepatitis A can withstand food-production processes routinely used to inactivate and/or control bacterial pathogens) or through contact with other people.
Scientists were analysing a deadly strain of avian influenza that killed over 150 harbour seals off the coast of New England in 2011, when they discovered this new relative of hepatitis A. Researchers wanted to find out what viruses might co-occur with influenza. Therefore, they performed deep sequencing of all the viruses present in three of the seals. They found a similar virus to hepatitis A and named it a phopivirus.
They continued research with analysis of 29 harbour seals, 6 harp seals and 2 grey seals living off the coast of New England and found 7 animals with this virus. However, it looks like phopivirus does not cause any harm to these seals and is quite common in their population. But scientists say that further research is needed in order to confirm how dangerous this virus may be. They think that it may act like hepatitis A in a way that it might only cause disease in adults.
Scientists also do not know how this virus got to both seals and humans. It may be that hepatitis A spilled over from humans to seals or vice versa. But it is also possible that both species got it from a third currently unidentified source. Researchers say that some reasons, like the fact that the virus was found in different species of seals, allow them to think that phopivirus has been present in seals for a fairly long time.
Now scientists will attempt to find similar virus in species that closely interact with seals. For example, coyotes regularly scavenge dead seals along the coast. In fact, scientists are also interested to investigate people who consume meat of seals in order to find out if the seal virus has ever spilled over to humans.
It would not be a unique case at all if it turned out that hepatitis A originated in wildlife and spread to human population through consumption of meat. Actually, the absolute majority of emerging infectious diseases in humans have origins in wildlife. This is why such researches are important. We have to understand how diseases spread between species in order to be prepared for next similar spill-over. This is why scientists say that the ultimate goal is to figure out the drivers behind the emergence of infectious diseases, so that pandemic preparedness could be enhanced.