Flavivirus is a family of viruses responsible for a wide range of diseases in humans and animals. Some of these diseases are more easily recognized by their common names, such as West Nile and yellow fever. The diseases are typically spread by mosquitoes when they bite an uninfected creature after biting one that has been infected with the virus.
There are seven main types of virus in the family. Members of this family can be found all over the world, wherever there are mosquitoes or ticks to spread the virus. Some are confined to a specific area; for example, louping ill is typically found in Great Britain. Insect carriers can spread the disease to a number of different recipients, including humans, birds, sheep, pigs, and horses.
The disease that gives the group of viruses its name is yellow fever. Widespread in Africa and South America, it is transmitted through the bite of a mosquito. There are several different stages to the progression of the disease, with each getting worse. Mild headaches and gastrointestinal distress will eventually lead to organ failure, shock, and death if not treated.
Not all types of flavivirus diseases are as deadly as yellow fever. West Nile virus can be deadly, but this is rare. More often, cases are mild and result in only gastrointestinal distress, headaches, and body aches. It is also an excellent example of how the virus can spread from one area to another. Originally thought to be exclusive to Africa, cases have been since identified in the northeastern United States. Cases of West Nile are thought to be spread through birds.
Some types of flavivirus are for the most part contained to animals. The louping ill virus of Great Britain is for the most part limited to livestock, small rodents, and some birds, although coming in contact with infected internal tissues can rarely spread the disease to humans. Other types present a very real danger to humans; Japanese encephalitis is not only found in domestic and wild animals, but kills a number of people throughout Asia every year.
Not all individuals and animals that come into contact with a flavivirus will get sick. Each type of virus has a different infection ratio, which means they all occur with varying likelihoods of developing the illness if bitten by a carrier. Vaccinations are available to keep many of the virus types from developing in a human or animal host. Once a flavivirus has infected an individual, care helps manage the symptoms of that particular virus while the body's immune system fights it.