Detection of Leptospira kirschneri in a short-beaked common dolphin (Delphinus delphis delphis) stranded off the coast of southern California, USA.

BACKGROUND: Pathogenic Leptospira species are globally important zoonotic pathogens capable of infecting a wide range of host species. In marine mammals, reports of Leptospira have predominantly been in pinnipeds, with isolated reports of infections in cetaceans. CASE PRESENTATION: On 28 June 2021, a 150.5 cm long female, short-beaked common dolphin (Delphinus delphis delphis) stranded alive on the coast of southern California and subsequently died. Gross necropsy revealed multifocal cortical pallor within the reniculi of the kidney, and lymphoplasmacytic tubulointerstitial nephritis was observed histologically. Immunohistochemistry confirmed Leptospira infection, and PCR followed by lfb1 gene amplicon sequencing suggested that the infecting organism was L.kirschneri. Leptospira DNA capture and enrichment allowed for whole-genome sequencing to be conducted. Phylogenetic analyses confirmed the causative agent was a previously undescribed, divergent lineage of L.kirschneri. CONCLUSIONS: We report the first detection of pathogenic Leptospira in a short-beaked common dolphin, and the first detection in any cetacean in the northeastern Pacific Ocean. Renal lesions were consistent with leptospirosis in other host species, including marine mammals, and were the most significant lesions detected overall, suggesting leptospirosis as the likely cause of death. We identified the cause of the infection as L.kirschneri, a species detected only once before in a marine mammal - a northern elephant seal (Mirounga angustirostris) of the northeastern Pacific. These findings raise questions about the mechanism of transmission, given the obligate marine lifestyle of cetaceans (in contrast to pinnipeds, which spend time on land) and the commonly accepted view that Leptospira are quickly killed by salt water. They also raise important questions regarding the source of infection, and whether it arose from transmission among marine mammals or from terrestrial-to-marine spillover. Moving forward, surveillance and sampling must be expanded to better understand the extent to which Leptospira infections occur in the marine ecosystem and possible epidemiological linkages between and among marine and terrestrial host species. Generating Leptospira genomes from different host species will yield crucial information about possible transmission links, and our study highlights the power of new techniques such as DNA enrichment to illuminate the complex ecology of this important zoonotic pathogen.

Systemic Erysipelas Outbreak among Free-Ranging Bottlenose Dolphins, San Diego, California, USA, 2022.

We diagnosed fatal Erysipelothrix rhusiopathiae sepsis in 3 stranded bottlenose dolphins (Tursiops truncatus) during summer 2022, in San Diego, California, USA. The previously undetected disease in this relatively small, regional population of dolphins most likely indicates an environmental or biological change in the coastal ocean or organisms.

Renal and vaginal calculi in a free-ranging long-beaked common dolphin Delphinus capensis.

Bilateral nephrolithiasis with a concurrent vaginal calculus was identified in a stranded free-ranging long-beaked common dolphin Delphinus capensis. Necropsy and radiologic examinations of the sexually mature D. capensis revealed multiple small irregularly round nephroliths and a 6.4 × 4.1 × 9.2 cm vaginal calculus weighing 182 g. Nephroliths numbered 68 and 71 in the left and right kidneys, respectively, and ranged from 1.7 to 6.9 mm in diameter. Nephroliths were composed of 100% ammonium urate, which has been found in captive dolphin populations. However, the vaginolith consisted of struvite and calcium carbonate suggesting an alternate etiology. The composition of the vaginolith suggests that bacterial vaginitis could have served as the predisposing condition. Renal lesions included chronic tubulointerstitial nephritis with tubular degeneration and loss, likely secondary to the nephroliths. The pathogenesis of ammonium urate nephrolithiasis in managed care is suspected to be linked to diet and age but in this case may be due to metabolic disruption. However, if environmental changes cause a shift in prey species, the risk of nephrolithiasis in free-ranging cetaceans could increase. Careful surveillance for nephroliths in free-ranging populations should be considered by researchers.

Serum correlation, demographic differentiation, and seasonality of blubber testosterone in common bottlenose dolphins, Tursiops truncatus, in Sarasota Bay, FL.

Blubber and serum testosterone levels were compared among 55 individual common bottlenose dolphins, Tursiops truncatus, in Sarasota Bay, FL during 2011-2019. A significant positive relationship between the matrices was found in male testosterone concentrations in 29 paired samples (r2 = 0.932). Mature males (n = 17) had 300 times greater mean testosterone concentration in serum than immature males (n = 17). A comparison of blubber samples, including 12 females, 24 immature males, and 19 mature males, revealed significant differences in mean blubber testosterone values among all three demographics. Immature males had greater than 6 times the average blubber testosterone concentration of females and mature males had almost 100 times that of immature males. Estimated testis volume was highly correlated with blubber testosterone concentration and mature males had 60 times greater average testis volume than immature males. We observed seasonal variation in blubber testosterone in mature males, consistent with known reproductive patterns. These data suggest males can be distinguished from females and designated as mature or immature via blubber testosterone concentrations, an observation that validates dart biopsy sampling as a means of obtaining demographic data.