Leptospirosis vaccine call after California outbreak study

Vets have called for more widespread vaccination of dogs against leptospirosis after a study led by the University of California, Davis revealed critical gaps in vaccination practices.

In the paper, published in the Journal of Clinical Microbiology, researchers investigated a 2021 outbreak affecting more than 200 client-owned dogs in Los Angeles County.

The scholars gathered data on 59 cases from two major veterinary hospitals in the region, the VCA Animal Specialty and Emergency Center and VCA West LA Animal Hospital, comparing them to the background hospital population of more than 15,000 control patients.

All isolates were found to be Leptospira interrogans serovar Canicola, one of the four strains the canine leptospirosis vaccine protects against.

Days of boarding

Many of the dogs developed the illness within days of being boarded in one of two regional dog daycare facilities in the region, with 31 of the 59 (53%) having had exposure to indoor congregate facilities.

Almost three-quarters (43, 73%) were hospitalised and 54 (92%) survived to discharge, although some were said to have remained azotemic.

Of the 47 dogs where leptospirosis vaccination history was known, none were completely vaccinated, with 41 of them never having been administered a single dose.

COVID-19 impact

The authors suggested the COVID-19 pandemic may have impacted the timing of the outbreak, with rising pet ownership and return-to-work activity documented in Los Angeles in mid-2021 leading to overcrowding of dog daycare facilities, as well as increased rodent exposure in large cities.

Lead author Jane Sykes, professor of small animal internal medicine at the UC Davis Weill School of Veterinary Medicine, said: “We know that the boarding itself was a risk factor.

“It might have been rodent problems in those facilities, or it might have just been really overcrowded facilities with lots of dogs in close contact with one another.

“The outbreak was massive. It might have been the biggest outbreak of leptospirosis in dogs that’s ever been recognised.”

Need for vaccination

The researchers argued the findings support the need for vaccination of dogs to reduce the risk to canine and human health, a high index of suspicion for the disease in unvaccinated dogs, the combined use of molecular and serologic tests to optimise diagnosis and early treatment to optimise outcomes.

With the bacteria typically thriving water from heavy rainfall, Dr Sykes noted vets in the LA area “rarely” offered leptospirosis vaccinations at the time as it was considered low risk due to the arid climate.

The researchers are now examining cases in homeless encampments in Berkeley and Oakland, where dogs, wildlife and environmental conditions are said to be creating new pathways for transmission, with early investigations said to show high infection rates in local rat populations.

Rodent exposure

Dr Sykes concluded: “This disease – there’s no boundaries for it. We’re talking about dogs with this disease owned by wealthy people in LA and dogs that are in homeless encampments on the streets of Berkeley dying with this disease because of rodent exposure.

“It’s probably the tip of the iceberg. There are probably more unrecognised cases than we know about.”