Lack of evidence for Schmallenberg virus infection in highly exposed persons, Germany

Schmallenberg virus, a novel orthobunyavirus, is spreading among ruminants, especially sheep, throughout Europe. To determine the risk for human infection, we conducted a survey among shepherds to assess possible exposure and symptoms. We also performed serologic and molecular assays. No evidence of transmission to humans was detected.

In November 2011, a new virus of the genus Orthobunyavirus was isolated from diseased cattle in Germany and was provisionally called Schmallenberg virus (SBV). It has caused disease in ruminants, i.e., sheep, cattle, and goats. Acute clinical signs such as fever and diarrhea; severe congenital malformation, such as arthrogryposis and hydroencephaly; and a high proportion of stillbirths have been reported among infected animals. Transplacental transmission leads to fetal infection. The virus is vector borne and has been isolated from biting midges (Culicoides spp.). Genomic analyses showed a close phylogenetic relationship to epizootic viruses of the Simbu serogroup, for which zoonotic transmission has not been shown. However, SBV also bears new genetic and animal-related clinical and epidemiologic properties. Iquitos and Oropouche viruses of this serogroup are also transmitted by culicoids and cause outbreaks in humans. La Crosse virus and California encephalitis virus can cause disease in humans and belong to the genus Orthobunyavirus. A few vector-borne zoonoses from the same family Bunyaviridae, i.e., Rift Valley fever virus and Crimean-Congo hemorrhagic fever virus, also are highly transmissible to humans through handling of infectious animal tissue. However, this mode of transmission has not been described for orthobunyaviruses. Shortly after its recognition, SBV and associated disease were reported from an increasing number of European countries, and further spread is conceivable. The virus currently is isolated mainly from sheep farms. In Germany, North Rhine-Westphalia is the area most affected. Viral loads are high in infected animals and their birth products. Thus, shepherds can be considered as strongly exposed, especially during animal obstetric events.

Because SBV emerged recently, transmission from animals to human cannot be completely excluded. Knowing whether SBV poses a risk to humans is vital. Therefore, we conducted a seroprevalence study among exposed shepherds in the area in Germany most affected (North Rhine-Westphalia) to determine whether zoonotic or vector-borne infections occur in humans.

Emerging Infectious Diseases
July 10, 2012

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