Leptospirosis in marine mammals: An in-depth look at an underexplored ecosystem

Marine mammals are a diverse group that live in, or are fully dependent upon, the ocean and marine food chain. Infection by Leptospira bacteria has been documented in this group of animals and may cause renal pathology, which for some species can lead to morbidity and mortality. Despite its impact on animal health and relevance as a zoonotic pathogen, important aspects of leptospirosis in marine mammals are still minimally explored. In this context, we conducted a systematic review to better understand this infection in marine mammals worldwide. A systematic review of scientific databases was conducted, resulting in 72 papers. They were classified into twelve categories, such as clinical signs, serologic and molecular identification, geographical localization, and other relevant information. North America stands out as the focus for most of the global research on this topic (70.8 % of publications). The most common clinical signs were depression, anorexia, polydipsia, dehydration, vomiting, muscle tremors, abdominal pain, and sometimes seizure-like neurologic signs. Many of these clinical signs can be attributed to Leptospira-related renal failure and electrolyte imbalances. While severe disease and death were often reported, reports of an asymptomatic state in some individuals suggest a potential asymptomatic infection and highlight the possible role of marine mammals as disseminators of Leptospira spp. in a highly fluid ecosystem. Serology was the most used diagnostic method (77.8 %), and Pomona, Gryppotyphosa, and Icterohaemorrhagiae were the most frequently identified serogroups. Regarding direct detection methods, PCR was the most commonly used (38.8 %), while culture was used in 25 % and IHC in 23.6 % of studies. Based on genetic characterization, Leptospira interrogans was the most commonly detected species. To understand the epidemiology of this complex disease, a review of multiple studies demonstrated the importance of an integrative approach, including pathological, biochemical, molecular and phylogenetic analyses, not only to enrich knowledge about marine microbiological biodiversity but also to clarify important key points on the epidemiology and pathophysiology of this important zoonosis in an ecosystem that is still so little explored.