Schmallenberg disease

• Cause: Orthobunyavirus of the Simbu serogroup.
• Signs: mostly unspecific; fever, drop in milk yield, diarrhea, abortions, birth of malformed fetuses.
• Diagnosis: clinical diagnosis can be difficult due to the unspecific nature of the signs and the lag period between infection and birth of fetal malformations; laboratory diagnosis consists of virology, pathology and serology.
• Treatment: supportive treatment only; preventative treatment via inactivated vaccines.
• Prognosis: variable; mostly good for adult animals, poor for fetuses due to abortion and/or malformations.

Presenting signs

• The combination of fetal malformations, presence of the vector species and history of unspecific malaise for example, milk drop, in the months prior, should all raise suspicion of the disease.

Acute presentation

• Unspecific symptoms of malaise lasting up to 6 days (duration of the viremia).
• Fever.
• Inappetence.
• Loss of body condition.
• Drop in milk yield.
• Diarrhea.
• Fetal malformations.
• Abortions/barren animals/returns to estrus.

Geographic incidence

• First identified in a triangular region bordering Germany, The Netherlands and Belgium; the disease was named after the town in which the first cases were confirmed.
• As this is a vector borne disease, its incidence is confined to areas in which the biting midges Culicoides spp are present, closely overlapping their spatial, temporal and temperature distribution.

Age predisposition

• Fetuses especially at risk. Experiments showed that in pregnant cattle the at-risk period might be quite extended, between day 13 and 162. In these studies, the teratogenic effects were uncommon, but the virus was able to efficiently cross the placental barrier. The exact period of highest risk remains unclear and further studies are necessary. However, during Akabane Virus infection (AKAV; another Orthobunyavirus of the Simbu serogroup) fetuses are at highest risk of developing malformations between day 80-150 of pregnancy.
• As Schmallenberg virus (SBV) induces long term immunity following natural infection, animals born after the initial European outbreak of 2011-12 and out with the areas of low-level circulation since, are considered most at risk of infection due to their naïve status.

Gender predisposition

• Both sexes are equally susceptible though the largest losses would occur in females due to loss of pregnancies, fetal mortality and decreased milk yield. In the male, a transient period of subfertility may be experienced following pyrexia as a syndrome of acute infection.
• Seasonal breeders such as beef cattle herds (block calving) and sheep flocks are most at risk of losses if mating occurs on or shortly before the peak vector active period.

Breed/Species predisposition

• Any breed of cattle or sheep.

Public health considerations

• Schmallenberg does not appear to be a zoonotic disease. Farm workers in contact with infected animals did not seroconvert, SBV genetic material could not be isolated, and they did not report any unusual illness during an outbreak.

Cost considerations

• The overall economic losses in the whole of Europe were considered of limited importance, however, for those farms that reported high disease incidence the losses have been significantly high. Costs associated with the disease have been:
  • Abortions and malformed fetuses Abortion and stillbirths: overview. Seasonal (spring) calvers have been reported to be worse hit due to loss of large proportions of the calf crop.
  • Cost of treatment: non-steroidal anti-inflammatory drugs (NSAIDs) Anti-inflammatory drugs: overview and labor costs to treat the affected animals. Dystocia Dystocia requiring veterinary assistance and cesarean sections Cesarean section have been necessary when fetuses were severely malformed. Cost of antibiotics when concomitant bacterial infections were present.
  • Decreased milk yield Investigating milk drop: dairy herd.
  • International trade restrictions of live animals and semen affected local economies.

Special risks

• General anesthetics and surgical procedures are not recommended in clinically unwell, pyrexic animals; the attending veterinarian should carry out a full assessment with regards to animal welfare before commencing surgery.