Controlling Salmonella Dublin in Dairy Herds

By Andi Anderson

Salmonella Dublin (S. Dublin), a host-adapted serotype of Salmonella in cattle, has increased in prevalence within dairy and calf-rearing facilities across the United States since 2012.

It is particularly concerning because S. Dublin isolates are often multidrug-resistant (MDR), making treatment and control more challenging. With no effective antimicrobial treatments available for use in cattle, preventing the spread of this zoonotic disease is crucial for both animal and human health.

Importance of Salmonella Dublin

S. Dublin is a significant concern in dairy herds, especially as it can cause both respiratory disease and septicemia in cattle.

Infected animals can also act as carriers, shedding the bacteria over extended periods, which complicates control measures. Moreover, the infection is zoonotic, meaning it can be transmitted to humans, causing serious illnesses like gastroenteritis and bacteremia.

Data from the National Animal Health Monitoring System show that S. Dublin was found on 6.7% of dairy farms, highlighting its prevalence.

The pathogen’s resistance to common antibiotics used in both humans and animals further complicates its management, emphasizing the need for effective prevention strategies.

Latent Carriers and Vertical Transmission

One of the key challenges in controlling S. Dublin is the presence of latent carriers—cattle that survive the infection but continue to shed the bacteria asymptomatically.

These cows can transmit the infection to their offspring in utero, leading to vertical transmission of the bacteria. The impact of this transmission route in dairy herds is significant, as it leads to the infection of newborn calves, even in the absence of clinical symptoms in the dam.

In a recent study, researchers explored the impact of vaccinating latent carriers for S. Dublin in late pregnancy. Cows were vaccinated with a commercial live culture vaccine (EnterVene-d) before dry-off, and the results showed a substantial reduction in intrauterine transmission to calves.

Vaccinated cows were five times less likely to give birth to seropositive calves, and the antibody concentrations in the calves born to vaccinated cows were significantly lower compared to calves born to control cows.

Study Results and Conclusions

This study, which took place from June 2022 to June 2023, included four commercial dairy farms and involved screening 1,096 cows for latent S. Dublin infection. The findings revealed that vaccinating latent carrier cows at dry-off reduced vertical transmission of S. Dublin by 81%.

This approach is particularly promising as it directly targets the source of the infection—latent carriers—thereby reducing the risk to newborn calves. 

Interestingly, traditional diagnostic methods like bacterial culture and PCR did not detect S. Dublin in feces or colostrum from latent carriers at the time of calving.

This raised questions about the sensitivity of current diagnostic methods and the actual role of bacterial shedding in transmission.

Further research is needed to understand the dynamics of S. Dublin transmission, particularly the role of vertical transmission and latent carriers in the spread of this disease.

These findings, however, provide valuable insight into managing S. Dublin in dairy herds and highlight the potential of vaccination as a key control measure.

Photo Credit: gettyimages-ahavelaar