The Emergence of Mucormycosis in Free-Ranging Marine Mammals of the Pacific Northwest

Abstract

Primary fungal diseases in marine mammals are rare. Mucormycosis, a disease caused by fungi of the order Mucorales, has been documented in few cetaceans and pinnipeds. In 2012, the first case of mucormycosis in the Pacific Northwest was documented in a dead stranded harbor porpoise (Phocoena phocoena) in Washington state. Since then, mucormycosis has been detected in a total of 21 marine mammals; fifteen harbor porpoises, five harbor seals (Phoca vitulina), and one southern resident killer whale (Orcinus orca). Infected animals were predominately found in the inland waters of Washington and British Columbia, and one harbor seal was recovered in northern Oregon. Fungal hyphae were detected histologically in a variety of tissues, including brain, lung, spleen, pancreas, kidneys, muscle, lymph nodes, and skin. Three fungal species were identified from seven cases by PCR screening or fungal culture; Rhizomucor pusillus (four cases), Lichtheimia corymbifera (two cases), and Cunninghamella bertholletiae. Underlying conditions such as emaciation, current or recent pregnancy, multisystemic parasitism, protozoal infection, and herpesvirus were found in several affected animals. Reasons for the appearance and subsequent increase of these fungal infections in marine mammals are unknown. The emergence of this disease as a source of marine mammal mortality in the Pacific Northwest is of particular concern for endangered southern resident killer whales that spend time in this region. Current population-level stressors such as insufficient prey, high levels of contaminants, and noise pollution, could predispose them to these fatal infections.

Causes of Mortality in a Harbor Seal (Phoca vitulina) Population at Equilibrium

“…Mucormycosis, an emerging fungal disease in marine mammals of the Pacific Northwest (Huggins et al, 2018), was identified in one sub-adult harbor seal in 2009 and one adult in 2019 (the latter was not included in the dataset for this study). During a 2007 Cryptococcus gattii epizootic in Dall's porpoises (Phocoenoides dalli) and harbor porpoises (Phocoena phocoena), a sub-adult harbor seal was diagnosed with multisystemic C. gattii infection.…”

Survival of the fattest: linking body condition to prey availability and survivorship of killer whales

“…2020) and was measured in body condition class 5 the same year; L95 died in 2016 of a fungal infection that may have been associated with a satellite tag attachment (Huggins et al. 2020) and was measured in body condition class 1 the previous year. The condition matrix for those whales was left as unknown (NA) after their last measurements, to prevent them from influencing mortality probabilities for their respective body condition classes prior to death.…”

Return of the Salish Sea Harbor Porpoise, Phocoena phocoena: Knowledge Gaps, Current Research, and What We Need to Do to Protect Their Future

“…Research has revealed additional pathological stressors for harbor porpoises in this region and the Salish Sea was recognized as having the first recorded multi-species outbreak of Cryptococcus gattii with affected species including both harbor and Dall's porpoise (Raverty et al, 2007;Norman et al, 2011). More recently there was emergence of the fungal disease mucormycosis which was found predominantly in harbor porpoises in both United States and Canadian waters of the Salish Sea (Huggins et al, 2020). Despite their status as a top predator, and indicator species, little is known about the potential effects from environmental pollutants on Salish Sea harbor porpoise ontogeny, physiology and longevity.…”

“…The focus on harbor porpoises is also being seen in stranding related research studies. The recent emergence of the fungal disease mucormycosis is a concern for all marine mammals in the Salish Sea, but more so for harbor porpoises that were disproportionately vulnerable (Huggins et al, 2020). A largerscale epizootic may have severe negative consequences for this recently recovered population, thus stranded harbor porpoises are prioritized for collection and necropsy and efforts are underway to identify risk factors that may be associated with mucormycosis for harbor porpoises in Washington (Huggins et al, 2020).…”

“…The recent emergence of the fungal disease mucormycosis is a concern for all marine mammals in the Salish Sea, but more so for harbor porpoises that were disproportionately vulnerable (Huggins et al, 2020). A largerscale epizootic may have severe negative consequences for this recently recovered population, thus stranded harbor porpoises are prioritized for collection and necropsy and efforts are underway to identify risk factors that may be associated with mucormycosis for harbor porpoises in Washington (Huggins et al, 2020). Monitoring of stranded animals has resulted in new information on the growth and development of harbor porpoise (Norman et al, 2018), parasites and disease (Stephen et al, 2002;Gibson et al, 2011;Norman et al, 2011;Kersh et al, 2012;Barbosa et al, 2015;Huggins et al, 2020), causes of mortality (Moore et al, 2013;Huggins et al, 2015;Fenton et al, 2017), and morphology (Piscitelli et al, 2013).…”