Immunity and the level of neutralization antibodies in foals and mares vaccinated with a modified live-virus rhinopneumonitis vaccine.

The research conducted evaluates the effectiveness of a rhinopneumonitis vaccine in foals and mares, identifying the antibody levels and assessing protection against natural infections. The study finds notable variations in antibody levels, along with differences in infection and abortion rates amongst the test subjects.

Subject and Methodology

• This study primarily focused on foals and mares that were vaccinated with a commercially available rhinopneumonitis vaccine.
• These subjects were divided into separate groups housed at different farms and were assessed individually based on a number of factors.
• The research experiment aimed to measure the level of antibodies and gauge the protection against natural infections that the vaccine offered.

Key Findings

• The serum-neutralization (SN) antibody titers against equine herpesvirus type 1 were 1:8 or less in the majority of foals, signifying a low level of antibodies produced. On the other hand, around 10% of foals showed a higher antibody titer of 1:16 or more.
• The level of nasal secretory antibody in the foals was also recorded to be less than 1:4, showing relatively low amounts of these antibodies as well.
• Among the vaccinated foals, respiratory tract infection remained absent for approximately six months. After this period, a spread of the disease was observed in farm 1, affecting three foals.
• The disease was associated with the isolation of the herpes virus from each of these affected foals.

Effects on Pregnant Mares

• The effects of the vaccine were also studied in pregnant mares. On farm 1, about 50% of vaccinated mares ended up aborting their fetuses.
• The aborted fetuses, 5 of the 6, had isolations of the herpes virus, indicating a connection between the disease and the abortions.
• On the other hand, farm 3, where vaccinated mares were also kept, reported no instances of abortion.
• Interestingly, the SN antibody levels of the pregnant mares in both the farms at the time of foaling were high, suggesting the potential for better immunity after childbirth.