The pathogen
Paratyphoid abortion, a disease affecting sheep, is caused by Salmonella enterica serovar Abortusovis. It causes late abortions, premature lambs and neonatal mortality.
It is a major reproductive problem which can have a huge economic impact and affect animal welfare. Infected animals excrete S. abortusovis through colostrum, milk, faeces and after abortions, through placenta, vaginal secretions and foetuses.
Both attenuated and inactivated vaccines are available to control the disease, but their safety and efficacy, respectively, have always been questioned.
How was the study conducted?
The purpose of this study was to evaluate the efficacy of the new inactivated vaccine against S. Abortusovis (also including Chlamydia abortus).
To this end, results from a vaccinated (n=17) and a control (n=20) group of ewes were compared. The parameters monitored were: incidence of abortions, vaginal excretion (CRP), lamb survival and humoral response (ELISA).
“A recognised feature of inactivated vaccines is their safety”.
What results have been obtained?
The results showed a significant decrease in the number of abortions in the vaccinated ewe group, in which 5/17 (29.4%) animals miscarried; compared to the control group, which had 13/20 (65%) abortions.
Another important point is the survival of the lambs, which was also higher in the vaccinated group.
Fig 1. S. Abortusovis excretion results (Log cfu/ml). Source: ScienceDirect
Promising results were also observed in terms of excretion. Both the percentage of positive PCRs and the amount of S. abortus excreted (Log cfu/mL) were significantly lower in the vaccinated group.
In addition, the vaccine caused no side effects (temperature increase, clinical signs, etc.), except for some mild local reactions.
The vaccine provides adequate stimulation of the humoral response, indicating active immunity.
What can we conclude?
This study has shown that this inactivated vaccine is safe and effective in controlling two main points of an S. Abortusovis infection:
● Reduces the abortion rate.
● Reduces excretion.
Therefore, this vaccine is a valuable tool to prevent and control the disease, and thus reduce its economic impact.
