Leptospira spp. and Toxoplasma gondii in stranded representatives of wild cetaceans in the Philippines

Abstract

Background: The stranding events of cetaceans in the Philippines provide opportunities for gathering biological information and specimens, especially from the pelagic forms. As part of an effort to monitor the health of wild cetaceans, this study detected Leptospira spp. and Toxoplasma gondii, causative agents of the emerging zoonotic diseases leptospirosis and toxoplasmosis respectively, in their stranded representatives. From October 2016-August 2018, 40 cetaceans (representing 14 species) that stranded nationwide were sampled for brain, cardiac muscle, skeletal muscle, kidney, and blood tissues, urine, and sera. These were subjected to molecular, serological, culture, and histopathological analyses to detect the target pathogens.

Results: T. gondii was detected in 20 (71%) of the 28 cetaceans with biological samples subjected to either molecular detection through RE gene amplification or IgG antibodies detection through agglutination-based serological assay. On the other hand, Leptospira was detected in 18 (64%) of 28 cetaceans with biological samples subjected to bacterial culture, molecular detection through 16S rDNA amplification, or IgM antibodies detection through ELISA-based serological assay.

Conclusions: There is the plausibility of toxoplasmosis and leptospirosis in cetacean populations found in the Philippines, however, acute or chronic phases of infections in sampled stranded individuals cannot be confirmed in the absence of supporting pathological observations and corroborating detection tests. Further studies should look for more evidences of pathogenicity, and explore the specific mechanisms by which pelagic cetacean species become infected by Leptospira spp. and T. gondii. As there is growing evidence on the role of cetaceans as sentinels of land-sea movement of emerging pathogens and the diseases they cause, any opportunity, such as their stranding events, should be maximized to investigate the health of their populations. Moreover, the role of leptospirosis or toxoplasmosis in these stranding events must be considered.

Keywords: Cetaceans; Leptospira spp.; Philippines; Stranding events; Toxoplasma gondii.

Fig. 1

Cetacean stranding sites. Forty individuals confirmed to belong to 13 cetacean species that stranded in Philippine waters from October 2016 to August 2018, were sampled for biological materials

Fig. 2

Interstitial nephritis in the kidney of a melon-headed whale (S6). The kidney tissue exhibited leptospirosis-associated tubulointerstitial nephritis, characterized by mild-thickening of basement membrane capillaries and necrosis of convoluted tubular epithelium

Fig. 3

Hemosiderosis: brown granular pigments (black arrows). Hemosiderosis was observed in the kidney tissue of a melon-headed whale (S6), characterized by the presence of hemosiderin pigments from hemoglobin degradation