Beware of the Usutu virusThe alert was raised after the mayor of the municipality of Monte San Giusto, in the Macerata area (Marche), Andrea Gentili, reported in a notice to citizens in recent days about the presence of a positive case of the Usutu virus (Usuv) detected during surveillance of mosquitoes, the insects that carry the infection.
After an initial intervention on the larval outbreaks, in the next few hours, in the night between Tuesday 27 and Wednesday 28 August, a targeted disinfestation intervention will be carried out in the hamlet where traces of the presence of the virus were found and recommendations have also been issued on measures to be implemented to prevent the proliferation of potentially infected mosquitoes.
What is Usutu virus and how is it transmitted?
But what is the Usutu virus and how is it transmitted? It is a flavivirus transmitted mainly by infected mosquitoes, and has similar clinical manifestations to West Nile (WNV), as well as similar geographic distribution and species of vectors and hosts. And together with WNV, Usutu also belongs to the Japanese encephalitis virus complex. Its epidemiology has changed radically in the last two decades, scientists explained in a focus published a few years ago in ‘Frontiers in Veterinary Science’.
After its emergence in Italy in 1996 (as documented by retrospective studies in Tuscany), Usuv virus has spread to other countries causing mortality in several bird species. Co-circulation of both viruses (Usutu and West Nile) has been detected in humans, horses and birds. The main vector of both these viruses in Europe is the mosquito Culex pipiens, the common mosquito.
But these pathogens have also been found in the native mosquito species Culex modestus and perexiguus. Naturally infected Aedes albopictus and japonicus mosquitoes have also recently been reported. While West Nile neuroinvasive infections in humans are well documented, Usuv infections are only sporadically detected, experts say. However, there is growing evidence of a role for Usutu virus in human disease. Seroepidemiological studies have shown that circulation is more common than previously thought in some endemic regions.
The virus takes its name from a South African river, because it was first identified in South Africa in 1959. Today it is endemic in Africa and some parts of Europe with 8 genotypes (3 African and 5 European). There are more than 90 bird species that act as reservoirs for Usuv. Usutu and West Nile differ in the frequency with which cases of mortality are recorded in birds (high in the case of Usuv, low for Wnv) and in the impact on public health, given the rarity of cases of Usuv detected. The virus also infects other animals such as bats and mammals such as horses, dogs, squirrels, wild boars and deer, as stated in a document from the ISS (Istituto Superiore di Sanità).
Not much is known about the incubation period of Usutu virus even if it has many similarities with the symptoms of Wnv (whose incubation varies from 2 to 14 days, but can reach up to 21). Most infected people, experts point out, do not show symptoms. Among the cases that develop them, the symptoms vary from moderate (skin rash, fever and headache) to severe (neurological disorders). Neuro-invasive forms are sporadic. At the moment there is no vaccine or specific therapies for Usuv, only treatments for the symptoms. For this reason it is considered important to limit its presence. And a joint Wnv-Usuv surveillance is underway also in Italy. Prevention in fact consists in the identification of possible viral circulation in target species and vector insects. In the latest bulletin of the ISS, an update is also made on this virus, it appears that a case of Usutu was registered in the province of Modena.
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