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

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.

First report of Strongylidae nematode from pilot whale (Globicephala macrorhynchus) by molecular analysis reveals the cosmopolitan distribution of the taxon

This study investigates the identification, genetic composition, and placement in the evolutionary tree of a particular nematode species found in a short-finned pilot whale in the Gulf of Thailand. To accomplish this, we utilized various methods, including microscopic observations, molecular techniques, and comparative analyses to better understand the characteristics of this parasite. Initially, we concentrated on studying the 18s rDNA sequence through nested PCR, resulting in a 774-bp product. After conducting a BLASTn analysis, we discovered that there were only a few sequences in the GeneBank that shared similarities with our nematode, particularly with Cyathostomum catinatum, although the percent identity was relatively low. To confirm the uniqueness of our sequence, we constructed a phylogenetic tree that demonstrated a distinct branch for our nematode, suggesting significant genetic differentiation from C. catinatum. Additionally, we sequenced a 399-bp section of the ITS2 gene using PCR, and the resulting data showed a close association with the Strongylidae family, specifically with Cylicocyclus insigne. This was further confirmed by BLASTn and CD-HIT-est results, which indicated a 99 and ~94% sequence homology with C. insigne, respectively. The ITS2 phylogenetic tree also supported the position of our isolated sequence within the Strongylidae family, clustering closely with C.insigne. Our findings shed light on the genetic connections, taxonomy, and evolutionary trends within the Strongylidae family, with a particular focus on the widespread nature of the Cylicocyclus genus. This study emphasizes the importance of utilizing molecular techniques and interdisciplinary approaches to gain insight into nematode diversity, evolution, and ecological dynamics in marine environments.

Prevalence and genotype of Toxoplasma gondii in stranded Hawaiian cetaceans

Toxoplasma gondii is a significant threat to endangered Hawaiian wildlife including birds and marine mammals. To estimate the prevalence of T. gondii in stranded cetaceans from 1997 to 2021 in Hawai'i, we tested tissues from 37 stranded spinner dolphins Stenella longirostris and 51 stranded individuals that represented 18 other cetacean species. DNA from cetacean tissue extracts were screened using a nested polymerase chain reaction (PCR) assay targeting the Toxoplasmatinae internal transcribed spacer 1 of the nuclear ribosomal DNA. A positive result was obtained in 9 tissues examined for each of 2 spinner dolphins out of 525 tissue samples analyzed by PCR. The PCR-positive spinner dolphins had disseminated acute toxoplasmosis with necrosis, inflammation, and intralesional protozoal cysts and tachyzoites in multiple organs. Discrete positive immunostaining for T. gondii was observed in all tissues tested including the adrenal gland, brain, liver, and lung. Both positive spinner dolphins were negative for cetacean morbillivirus. The T. gondii genotyping was performed by restriction fragment length polymorphism (PCR-RFLP) based on 10 genetic markers. The PCR-RFLP analysis revealed the T. gondii belonged to PCR-RFLP-ToxoDB genotype #24, previously detected in wild pig Sus scrofa in O'ahu, bobcats Lynx rufus from Mississippi, USA, and chickens Gallus gallus from Costa Rica and Brazil. These cases represent the first report of this genotype in aquatic mammals and the second and third reports of fatal disseminated T. gondii infection in stranded spinner dolphins from Hawai'i. Nearshore species, like spinner dolphins, may be at increased risk of mortality from this parasite in marine coastal waterways via sewage systems, storm water drainage, and freshwater runoff.

A Field-Deployable Insulated Isothermal PCR (iiPCR) for the Global Surveillance of Toxoplasma gondii Infection in Cetaceans

Simple Summary

Since high trophic levels marine mammal species share the coastal environments and diets with humans, cetaceans provide an indication of contaminant bioaccumulation in humans and may serve as sentinels for public health problems. Parasite monitoring in marine sentinels can assist in evaluating the quality of the aquatic ecosystem’s health. T. gondii infection in cetaceans is an indicator of land-to-sea coastal pollution. Although T. gondii infection cases in cetaceans have been reported in several countries, an information gap still exists in some areas. The present study employs a portable insulated isothermal PCR (iiPCR) with an automatic extraction device as a rapid, affordable, user-friendly, and field-deployable platform to rapidly detect nucleic acid of T. gondii in stranded cetaceans. The platform utilizes duplex iiPCR designed to simultaneously detect T. gondii and a housekeeping gene of cetacean on the samples, which can prevent the false-negative results of pathogen detection and improve the accuracy of surveillance. This study would contribute to improving the environment through the warning of the sentinel animals and building new strategies by detecting the occurrence of land-based biological pollution.

Abstract

Toxoplasmosis is a zoonotic disease with veterinary and public health importance worldwide. Toxoplasma gondii infection in cetaceans is an indicator of land-to-sea oocyst pollution. However, there is a critical knowledge gap within the distribution of the T. gondii infection in cetaceans. To facilitate the global surveillance of this important zoonotic pathogen, we developed a field-deployable duplex insulated isothermal PCR (iiPCR) with automated magnetic bead-based DNA extraction for the on-site detection of T. gondii in stranded cetaceans. It targets the B1 gene of T. gondii combined with β2-microglobulin (B2M) gene of cetaceans as an internal control. Compared with the conventional qPCR assay, B1/B2M duplex iiPCR assay showed comparable sensitivity (21~86 bradyzoites in 25 mg of tissue) to detect spike-in standard of T. gondii DNA in cerebrum, cerebellum, skeletal muscle and myocardium tissues. Moreover, the overall agreement between the duplex iiPCR and qPCR was in almost perfect agreement (92%; 95% CI: 0.78–0.90; κ = 0.84) in detecting a synthetic spike-in standards. The B1/B2M iiPCR assay coupled with a field-deployable system provides a prompt (~1.5 h), feasible, highly sensitive and specific on-site diagnostic tool for T. gondii in stranded cetaceans. This platform provides one approach to evaluating aquatic ecosystem health and developing early warnings about negative impacts on humans and marine animals.

Bacteriological and histopathological findings in cetaceans that stranded in the Philippines from 2017 to 2018

The relatively high frequency of marine mammal stranding events in the Philippines provide many research opportunities. A select set of stranders (n = 21) from 2017 to 2018 were sampled for bacteriology and histopathology. Pertinent tissues and bacteria were collected from individuals representing eight cetacean species (i.e. Feresa attenuata, Kogia breviceps, Globicephala macrorhynchus, Grampus griseus, Lagenodelphis hosei, Peponocephala electra, Stenella attenuata and Stenella longirostris) and were subjected to histopathological examination and antibiotic resistance screening, respectively. The antibiotic resistance profiles of 24 bacteria (belonging to genera Escherichia, Enterobacter, Klebsiella, Proteus, and Shigella) that were isolated from four cetaceans were determined using 18 antibiotics. All 24 isolates were resistant to at least one antibiotic class, and 79.17% were classified as multiple antibiotic resistant (MAR). The MAR index values of isolates ranged from 0.06 to 0.39 with all the isolates resistant to erythromycin (100%; n = 24) and susceptible to imipenem, doripenem, ciprofloxacin, chloramphenicol, and gentamicin (100%; n = 24). The resistance profiles of these bacteria show the extent of antimicrobial resistance in the marine environment, and may inform medical management decisions during rehabilitation of stranded cetaceans. Due to inadequate gross descriptions and limited data gathered by the responders during the stranding events, the significance of histopathological lesions in association with disease diagnosis in each cetacean stranding or mortality remained inconclusive; however, these histopathological findings may be indicative or contributory to the resulting debility and stress during their strandings. The findings of the study demonstrate the challenges faced by cetacean species in the wild, such as but not limited to, biological pollution through land-sea movement of effluents, fisheries interactions, and anthropogenic activities.

Exposure of pelagic seabirds to Toxoplasma gondii in the Western Indian Ocean points to an open sea dispersal of this terrestrial parasite

Toxoplasma gondii is a protozoan parasite that uses felids as definitive hosts and warm-blooded animals as intermediate hosts. While the dispersal of T. gondii infectious oocysts from land to coastal waters has been well documented, transmission routes to pelagic species remain puzzling. We used the modified agglutination test (MAT titre ≥ 10) to detect antibodies against T. gondii in sera collected from 1014 pelagic seabirds belonging to 10 species. Sampling was carried out on eight islands of the Western Indian Ocean: Reunion and Juan de Nova (colonized by cats), Cousin, Cousine, Aride, Bird, Europa and Tromelin islands (cat-free). Antibodies against T. gondii were found in all islands and all species but the great frigatebird. The overall seroprevalence was 16.8% [95% CI: 14.5%-19.1%] but significantly varied according to species, islands and age-classes. The low antibody levels (MAT titres = 10 or 25) detected in one shearwater and three red-footed booby chicks most likely resulted from maternal antibody transfer. In adults, exposure to soils contaminated by locally deposited oocysts may explain the detection of antibodies in both wedge-tailed shearwaters on Reunion Island and sooty terns on Juan de Nova. However, 144 adults breeding on cat-free islands also tested positive. In the Seychelles, there was a significant decrease in T. gondii prevalence associated with greater distances to cat populations for species that sometimes rest on the shore, i.e. terns and noddies. This suggests that oocysts carried by marine currents could be deposited on shore tens of kilometres from their initial deposition point and that the number of deposited oocysts decreases with distance from the nearest cat population. The consumption of fishes from the families Mullidae, Carangidae, Clupeidae and Engraulidae, previously described as T. gondii oocyst-carriers (i.e. paratenic hosts), could also explain the exposure of terns, noddies, boobies and tropicbirds to T. gondii. Our detection of antibodies against T. gondii in seabirds that fish in the high sea, have no contact with locally contaminated soils but frequent the shores and/or consume paratenic hosts supports the hypothesis of an open-sea dispersal of T. gondii oocysts by oceanic currents and/or fish.

Recent epidemiologic and clinical importance of Toxoplasma gondii infections in marine mammals: 2009-2020

Toxoplasma gondii infections are common in humans and animals worldwide. T. gondii causes mortality in several species of marine mammals, including threatened Southern sea otters (Enhydra lutris) and endangered Hawaiian monk seals (Monachus schauinslandi). Marine mammals are now considered sentinels for environmental exposure to protozoan agents contaminating marine waters, including T. gondii oocysts. Marine mammals also serve as food for humans and can result in foodborne T. gondii infections in humans. The present review summarizes worldwide information on the prevalence of clinical and subclinical infections, epidemiology, and genetic diversity of T. gondii infecting marine mammals in the past decade. The role of genetic types of T. gondii and clinical disease is discussed.

Dolphins Stranded along the Tuscan Coastline (Central Italy) of the "Pelagos Sanctuary": A Parasitological Investigation

Parasite monitoring is considered a necessary step for cetacean management and conservation. Between February 2013 and July 2015, 26 dolphins (15 Stenella coeruleoalba, 10 Tursiops truncatus, and one Grampus griseus) stranded along the Tuscan coastline of the protected marine area "Pelagos Sanctuary", were examined. Organs, tissues, and faecal and blood samples taken from all animals were analysed by parasitological, immunological, and molecular techniques. Twenty-one out of 26 dolphins (80.77%) tested positive for at least one parasite species, and 13/15 (86.7%) S. coeruleoalba, 7/10 (70%) T. truncatus, and the single G. griseus were found positive. Identified parasites included the nematodes Skrjabinalius guevarai (7.69%, 2/26), Halocercus lagenorhynchi (3.85%, 1/26), Halocercus delphini (7.69%, 2/26), Stenurus ovatus (7.69%, 2/26), Crassicauda spp. (7.69%, 2/26); the trematodes Pholeter gastrophilus (26.92%, 7/26), Campula palliata (3.85%, 1/26); the cestodes Phyllobothrium delphini (42.31%, 11/26), Monorygma grimaldii (23.08%, 6/26), Tetrabothrium forsteri (7.69%, 2/26), Strobilocephalus triangularis (7.69%, 2/26), and the acanthocephalan Bolbosoma vasculosum (7.69%, 2/26). Moreover, 6/26 (23%) animals scored positive to Toxoplasma gondii at serology, but PCR confirmed the infection (T. gondii Type II genotype) in a single animal. In examined dolphins, obtained results showed a high prevalence of endoparasites, which included species considered as a cause of severe debilitation or death.