Usutu virus can infect animals and humans and in severe cases causes encephalitis. It belongs to the flavivirus group and is transmitted to humans by mosquitoes.
What is Usutu virus?
Usutu virus, which originates in Africa, can infect birds and mammals, as well as humans by means of transmission through mosquitoes. The name of the pathogen was derived from the longest river in Swaziland. Usutu belongs to the genus Flavivirus, which attacks the brain of animals and humans, and is related to the Japanese encephalitis virus and the West Nile virus. Infection has been fatal in several bird species. Usutu fever in humans was first identified in Italy in 2009. The disease has subsequently been most severe in immunocompromised and elderly patients. It manifests with violent fever, severe headache and skin rashes. In humans, the Usutu virus can lead to dangerous encephalitis (inflammation of the brain) in the most serious cases.
Occurrence, distribution, and characteristics
The first deaths among birds appeared in Austria in 2001. At that time, the first wild birds probably died due to Usutu infection. Deaths of blackbirds as well as some great horned owls, blue tits, house sparrows, great tits, song thrushes, and nuthatches were reliably detected in 2003. These bird deaths affected Vienna and some areas of Lower Austria. Comparable phenomena probably already occurred in Tuscany in 1996. However, they were only linked to the Usutu virus by retrospective investigations. In Italy, Switzerland, and Hungary, free-ranging wild birds died from the virus infestation starting in 2005 and 2006, respectively. In the summer of 2011, several hundred thousand blackbirds were estimated to have fallen victim to the Usutu virus in Germany. This largest bird mortality of its kind to date was attributed to infected exotic mosquitoes that had arrived in Germany with shipments of goods. Similarly, these incidents led specialists to realize that native mosquito species, as well as their eggs and larvae, can also harbor the Usutu virus. Transmission to birds occurs through bites from mosquitoes. Mass bird deaths in 2011 were concentrated in river valleys of the Rhine-Neckar region and other regions in Baden-Württemberg, Rhineland-Palatinate and Hesse. The infected birds initially appeared exceptionally apathetic and unsteady on their feet, increasingly lacked flight behavior, and developed disheveled plumage before dying. Bald patches on the head and neck were also conspicuous. The nervous system, liver, spleen and heart muscle of the diseased animals had undergone inflammatory changes. In the affected areas of Germany, massive population reductions in blackbirds were registered. Far less reduced were species such as owls and corvids. Some subpopulations of blackbirds were slow to recover from the major collapse, and only years later. The birds had never been in contact with the Usutu pathogen and thus had not been able to develop immunity to it. Increasingly, however, they became immune to this newly emerged virus. No further major losses of the bird population have been reported in the years following 2011.
Diseases and ailments
To date, Usutu viruses have been transmitted to humans through mosquito bites extremely rarely. That an acquired disease has taken a severe course has remained the absolute exception to date. Under normal conditions, it can be compared to a simple flu-like infection. Two people have so far been at greater risk from the infection. According to reports from doctors, these were two immunocompromised persons in Italy. They are said to have been infected in 2009 and subsequently fell ill with meningitis. Both remained alive. A person in Croatia also reportedly received clinical treatment related to Usutu infection. In Germany, viral infection was detected in one patient in 2012. However, no symptoms of disease subsequently emerged. The man was registered as a blood donor in Hesse, which is why the antibodies against the Usutu virus had been found in his blood. In order to be able to rule out any risk, no matter how small, medical experts recommend protecting oneself from mosquito bites to prevent an Usutu infection.This is most effectively done by wearing closed clothing, using suitable repellents and also using a mosquito net. If necessary, large accumulations of water at houses or in gardens should be avoided, since hundreds of house mosquitoes can be found in rainwater barrels, for example, or develop from larvae. It is also possible here to use special protein tablets, which are harmless to humans and animals but kill mosquito larvae in the water. Live or dead wild birds should always be handled with care, even if they cannot transmit the virus directly to humans. Direct contact with wild birds should always be avoided. Their contact is best done only with gloves. After such an incident, it is necessary to wash hands thoroughly and disinfect them. Dead birds should not be buried or added to household garbage, but should be turned in to official agencies. Special care should be taken when pets have or have had contact with infected birds. Evidence shows that the Usutu virus has acquired the ability to survive even in harsh winters. Thus, it is considered to be permanently established in Western Europe. It has a comparatively high potential for spread, as it is also easily transmissible from mosquito to mosquito. The enveloped, single-stranded virus belongs to the RNA group, i.e. its genetic material consists of ribonucleic acid. Relatives of the Usutu virus have been established in southern and southeastern Europe and on the Asian continent, respectively, for some time.
