Vertical transmission of Rift Valley fever virus without detectable maternal viremia

Area of Science:

• Veterinary Virology
• Zoonotic Diseases
• Ruminant Health

Background:

• Rift Valley fever virus (RVFV) is a zoonotic pathogen causing significant economic losses in livestock, particularly through abortions in ruminants.
• Exotic sheep breeds are known to be highly susceptible, but the susceptibility of native breeds, especially during gestation, requires further investigation.

Purpose of the Study:

• To assess the susceptibility of a native Dutch sheep breed to RVFV infection during different stages of gestation.
• To determine the potential for vertical transmission of RVFV in sheep, even in the absence of overt maternal illness.

Main Methods:

• Experimental inoculation of gestating ewes with RVFV during the first, second, or third trimester.
• Monitoring of clinical signs, viremia, and serological responses (IgG, IgM).
• Post-mortem examination of maternal and fetal tissues for viral RNA and infectious virus.

Main Results:

• High mortality was observed in ewes that developed viremia.
• A subset of inoculated ewes (4/11) did not exhibit detectable viremia or clinical signs, nor did they seroconvert.
• Despite the lack of maternal viremia, viral RNA and infectious RVFV were detected in maternal and fetal organs, indicating vertical transmission.

Conclusions:

• Native Dutch sheep breeds are susceptible to RVFV infection.
• RVFV can be transmitted vertically from ewe to fetus, even when maternal viremia is not detectable.
• This finding has significant implications for disease control and risk assessment in non-endemic regions.