Infection with equine herpesvirus 1 (EHV-1) strain HVS25A in pregnant mice.

The study investigates how the strain HVS25A of Equine Herpesvirus 1 (EHV-1), affects pregnant mice, primarily focusing on its abortigenic effects. The results reveal significant signs of EHV-1-induced disease and abortion, especially in BALB/c mice. The study also notes that the abortion caused by EHV-1 infection might be due to detrimental vascular effects on the placenta.

Methodology

• The study made use of three types of pregnant mice: BALB/c, C57BL/6J, and Quakenbush. These mice were infected with the EHV-1 strain HVS25A through their noses on the 16th day of pregnancy.
• Another group of BALB/c mice were infected on the 15th day of pregnancy and then killed on various days post infection (1 – 5). This was done to observe changes before the occurrence of potential abortions.

Findings

• Post infection, all mice from the BALB/c strain showed typical signs of an EHV-1-induced disease along with evidence of abortion.
• There were instances of fetal and neonatal deaths among the litters of the C57BL/6J and Quakenbush mice, but the respiratory and systemic effects of the EHV-1 infection in these mice were inconsistent.
• BALB/c mice infected with EHV-1 indicated a significant drop in rectal temperature between the first and second day post infection and underwent weight loss for the first four days following infection. This provided a noteworthy average difference in weight gain compared to the control group.
• Death in utero was identified in five out of 90 fetuses of the EHV-1 infected mice group but was not observed in fetuses from the control group that were inoculated with a rabbit kidney (RK) cell lysate.
• In comparison to the fetuses from the RK-inoculated group, those from the EHV-1-infected dams were significantly smaller from days 1 to 5 post infection.
• Infected dams displayed congestion and necrosis of the middle trophoblast layer and chorionic necrosis in the placentae, all quantitively assessed via a scoring system.

Conclusion

• The presence of the virus was infrequently isolated from the fetuses, placentae, and uteri of the EHV-1 infected dams, and only those who were killed on the first or second day post infection.
• The study concludes that, similar to horses, abortion in mice due to the EHV-1 infection may not necessarily be a result of fetal infection. Instead, it might be due to compromised fetal health because of vascular effects inflicted on the placenta by the virus.