Why This Matters:
- Leptospirosis is a globally distributed zoonotic disease affecting humans and numerous animal species.
- L. interrogans serovar Canicola remains an important canine-associated serovar and vaccine target.
- Dogs can develop severe disease, including acute kidney injury, hepatic dysfunction, pulmonary hemorrhage, and death.
- Companion animal outbreaks may indicate environmental contamination and potential human exposure risk.
- Traditional serology and PCR confirm infection but provide limited information on transmission pathways; WGS enables higher-resolution outbreak investigation.
Key Findings: Randolph et al. investigated a 2021 canine leptospirosis outbreak involving 201 reported cases in Los Angeles County. Detailed clinical and laboratory data were available for 59 dogs evaluated at two specialty veterinary hospitals.¹
Clinical and Lab Findings:
- Common signs included lethargy (76%), hyporexia (54%), vomiting (47%), polyuria/polydipsia (32%), anorexia (20%), and diarrhea (17%).
- Laboratory abnormalities included anemia, neutrophilia, thrombocytopenia, azotemia, and evidence of hepatic injury.
Risk Factors: Cases were more likely to be younger (<6 years), larger-bodied (≥15 kg), and male. Cases clustered during July–August 2021. More than half of affected dogs (53%) had recent exposure to boarding kennels or dog daycare facilities, with illness typically developing within 5 days of attendance. Among dogs with known vaccination histories, 87% had never been vaccinated against leptospirosis; none had completed an effective vaccine series before illness onset.
Diagnostic Testing and Genomics:
- Microscopic Agglutination Test (serology) showed strong evidence of infection in 66% of tested dogs, with highest titers directed against serovar Canicola.
- Point-of-care serologic assays demonstrated sensitivities of 74% (WITNESS Lepto) and 89% (SNAP Lepto).
- Urine PCR was markedly more sensitive than blood PCR (91% vs. 27%).
- WGS identified L. interrogans serovar Canicola ST34 in all five genetically characterized cases. Phylogenetic analysis demonstrated a related Canicola lineage sharing common ancestry, but isolates differed by 12–224 core-genome SNPs, suggesting multiple related transmission sources rather than a single clone.
Treatment and Outcomes
- Most dogs (73%) required hospitalization and antimicrobial therapy; two required hemodialysis.
- Survival was high (92%); 5 dogs were euthanized. Mortality was associated with severe renal failure or suspected leptospiral pulmonary hemorrhage syndrome.
- Renal function improved significantly during treatment and follow-up.
Bigger Picture: The study demonstrates the growing value of genomic epidemiology in veterinary and public health investigations. While traditional diagnostics such as serology and PCR remain essential for case detection, whole-genome sequencing provides strain-level resolution that can distinguish related transmission events, identify circulating lineages, and improve understanding of outbreak dynamics. As sequencing technologies become more accessible, genomic surveillance may become an increasingly important tool for investigating zoonotic disease outbreaks in companion animals.
(Image Credit: iStock/quantic69)
