In recent decades, there has been a significant increase in studies on emerging diseases and pathogens in marine environments. Cetaceans are recognized as environmental sentinels due to their longevity, role in the trophic chain and ability to bioaccumulate contaminants. As such, they play an important role as indicators of the changes that occur in the aquatic ecosystem over time, from short-term alterations to transformations of a more lasting nature. This increase in disease is directly linked to habitat degradation and fragmentation, which intensifies the interaction between domestic, wild and human species. The data used is generally obtained from dead stranded animals or through image bank evaluations for photo identification. Among the main emerging diseases reported in cetaceans, toxoplasmosis has received special attention from researchers, generating growing concerns.
Toxoplasmosis is caused by the coccidian protozoan of the phylum Apicomplexa, known as Toxoplasma gondii. This parasite has a high morbidity rate and is one of the most prevalent parasitic diseases among endothermic animals. T. gondii is an obligate intracellular parasite that manifests itself in various infectious forms: tachyzoites, bradyzoites and oocysts. Its geographical distribution is global and its incidence rate is high. The presence of this protozoan in cetaceans can be linked to the release of its T. gondii oocysts, which are eliminated by the feces of felids, or to contact with soil contaminated by the parasite. This contamination can occur due to river drainage, dumping or ship run-off, which eventually compromises seawater.
Assessing the prevalence of toxoplasmosis in marine animals, especially cetaceans, is extremely important for the following reasons: the route of infection is still unknown, since most of these mammals ingest little or no water; infection with this pathogen can be fatal for cetaceans; and its detection can serve as a tool for assessing contamination of the marine ecosystem. Some studies show the occurrence of toxoplasmosis associated with co-infection with other immunosuppressive agents, such as morbillivirus. A case of toxoplasmosis was reported in a guiana dolphin (Sotalia guianensis) off the Brazilian coast (GONZALES-VIEIRA et al., 2013). During necropsy, the animal showed extensive areas of necrosis in organs such as the liver, lymph nodes, lungs, adrenals and pancreas, as well as the presence of opportunistic fungi in the pulmonary bronchi. Similar records include cases of death in two other dolphin species: the striped dolphin (Stenella coeruleoalba) (DI GUARDO et al., 2010) and the hector's dolphin (Cephalorhynchus hectori), in New Zealand (ROE et al., 2013). These findings suggest that toxoplasmosis may be a significant factor in the mortality and stranding of these animals.
Despite advances in understanding this pathogen, there is still limited knowledge about various aspects of infection by this parasite and the disease. It is therefore crucial to persist in investigations and studies to improve the understanding and assessment of the marine ecosystem. Collecting information on the causes of mortality related to infectious diseases of parasitic origin is considered a priority in the National Action Plan for the Conservation of Marine Mammals, which aims to increase knowledge about data-deficient species and develop effective conservation actions to safeguard species with imminent threats.
Author: Ana Carolina Prado Sordi - Director of the GEAS Brazil Association
Proofreading: Iago Junqueira - Partner of GEAS Brasil through The Wild Place platform
April/2024 Wild Panel
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