Health and Disease Program

Two weaned Hawaiian monk seal pups.
Two weaned Hawaiian monk seal pups.

The Health and Disease Program (HDP), part of the Hawaiian Monk Seal Research Program (HMSRP), investigates the role infectious diseases, parasites, and toxins (anthropogenic or human caused, and naturally occurring biotoxins) play in the recovery of the Hawaiian monk seal population.

The Health and Disease Program lead is Michelle Barbieri, DVM.

Surveillance and analysis of Hawaiian monk seal health and disease has been investigated for more than 3 decades throughout the NWHI. Recently, research focus in the MHI has become an increasing priority. In collaboration with veterinarians, studies include gross necropsy and histopathology, parasitology, hematology, serology, morphometrics, microbiology, epidemiology and scat (feces) and spew (regurgitate) analysis to assess population health.

Infectious Disease

Close contact with other animals can spread disease.
Close contact with other animals can spread disease.

Despite the population level benefits of an expanding main Hawaiian Island (MHI) subpopulation, the increased exposure to humans and domesticated and feral animals elevates the possibility of disease exposure and transmission throughout the entire Hawaiian monk seal population. In the MHI, monk seals forage, travel and rest in close proximity to areas of human activity, domestic and feral animals and agricultural areas. This increases exposure to contaminated waters from sewage and land based surface run-off increasing the probability of infectious disease transmission. Monk seal movements throughout the MHI and Northwestern Hawaiian Islands (NWHI) suggest any diseased seal could quickly infect healthy seals with the potential of causing debilitating impacts to the monk seal population including mass mortality.

The potential impact of infectious disease on the health of the population is severe. Diseases are constantly emerging and reemerging, and endemic diseases in terrestrial, avian and other marine mammal species could threaten monk seals. For this reason, the HDP provides vigilant infectious disease surveillance; timely response to hooked, entangled, sick, injured and dead monk seals; provides medical treatment to seals and assesses disease exposure.

Veterinarians and researchers in the HDP monitor for multiple pathogens which are a known risk for other pinnipeds and cetaceans. Some of the infectious diseases endemic to the MHI and considered a great risk for the Hawaiian monk seal population include distemper viruses, Leptospira spp., Toxoplasma gondii and Brucella spp.

Fortunately, distemper virus in Hawaii is rarely diagnosed in domestic pets and antibodies have not been found in the Hawaiian monk seal population. However, monk seals continue to be screened for the presence of distemper antibodies due to the known devastating impact distemper viruses have on other marine and terrestrial species.

Leptospirosis is widespread. In Hawaii, mongoose and rodents are the principle vectors where transmission of the bacteria is made through direct or indirect contact with infected urine. Evaluation of testing methods and monitoring of Leptospira infections are ongoing to determine potential lethal impacts on monk seals.

Toxoplasma gondii oocytes (immature egg cells) are found in domestic and feral cat feces which contaminate the ocean environment via terrestrial run-off leading to contaminated beaches and soil. A seal may become infected either through direct contact or through ingestion of contaminated prey. T. gondii is potentially fatal and is thought to be a cause of mortality in the southern sea otter population along the central California coast. Over the past decade, a few incidences of monk seal mortality have been attributed to T. gondii infection. The potential impact of T. gondii on MHI seals continues to be examined and monitored.

The potential for Brucellosis to affect the survival of Hawaiian monk seals is unclear. However, this bacterium may cause reproductive failure in other species and is thus a cause for concern. Brucella spp. antibodies are found in a significant percentage of the monk seal population and it is unknown if the decline of the monk seal population and low recruitment rates are associated with Brucella spp. infection. Techniques to accurately screen for Brucella spp. antibodies in the Hawaiian monk seal population are currently under investigation and are necessary for rapid diagnosis and treatment of infected seals as well as for the protection of responding biologists. The source of Brucella spp. infection is unknown, though thought to be from infected fish.

The HDP continues to improve infectious disease surveillance and provide rapid response and treatment of infected seals. Future research is aimed to develop more accurate testing methods for existing and emergent diseases specific to Hawaiian monk seals allowing veterinarians and biologists the ability to better mitigate the effects of these diseases.

Further Reading:

Parasites

Emaciated yearling from the NWHI.
Emaciated yearling from the NWHI.

The prevalence of gastrointestinal parasitic infections throughout the monk seal population is significant and the effects on monk seal morbidity and mortality are not fully known. The high rate of infection, concurrent with prey limitation, may be a significant factor affecting the survivorship of Hawaiian monk seals in the Northwestern Hawaiian Islands. Parasitic infections directly contribute to emaciation and starvation by damaging a seal's ability to digest food and absorb nutrients. When prey availability is scarce, the effects of an additional parasite load may further impair a seal's ability to effectively forage, leading to starvation while also increasing susceptibility to shark predation. In collaboration with the Survival Enhancement Program and Population Assessment Program, the HDP is examining parasite loads and testing de-worming medication on juvenile monk seals at Laysan Island. Due to the critically endangered status of the Hawaiian monk seal, reducing parasite burdens in individual seals may be a valuable intervention strategy with the potential to increase growth and survivorship of the population.

Further Reading:

Toxins

Organochlorine (OC) contamination of the marine environment is widespread. In Hawaii, OC pesticides are widely used, particularly in urban areas to control termites and mosquitoes. Contamination of the marine environment occurs from a variety of sources including sewage spills and urban and agricultural run-off. Ingestion of contaminated prey ultimately results in the accumulation of OCs in monk seal tissue and blood. High OC concentrations in tissue and blood may lead to immunosuppression as well as other effects with the potential of having a significant negative influence on monk seal survival.

Recent research conducted in the NWHI measured the levels of OCs in the tissues and blood of monk seals at four of the six breeding colonies. Few seals were found to have high enough levels of OCs in their tissues to possibly have an effect on their health. Current research is focusing on measuring OC levels in MHI seals as well as assessing the potential impact of high OC levels on the species vitality.

A recent study on the potential threat from ciguatoxins, neurotoxins produced by microalgae that accumulate in coral reef associated fish, has shown that some monk seals have significant levels of ciguatoxins in their tissues. However, it is unclear what impacts ciguatoxins have on the health of monk seals.

Further reading: