Hawaiian monk seals are listed as endangered under the U.S. Endangered Species Act and are protected by Federal and state law. This unique tropical pinniped is found exclusively within Hawaii’s waters, mostly throughout the low-lying atolls of the Northwestern Hawaiian Islands. However, monk seals have been recolonizing the main Hawaiian Islands over the past two decades. This subpopulation is estimated at 200-250 seals, and is growing. With that growth comes the recognition of new threats to the species such as fish hook ingestion, intentional killing, and now, an accumulating number of deaths from toxoplasmosis. This is not surprising, given the increasing geographic overlap between humans, cats, and Hawaiian monk seals.
A total of 8 monk seal mortalities (and 2 suspect mortalities) have been attributed to toxoplasmosis to-date. We arrived at this number by developing a case definition and retrospectively applying it to 306 cases of mortality from 1982-2015. To be classified as a protozoal-related mortality, we required: (a) pathological lesions consistent with protozoal disease and sufficient to cause mortality, and (b) confirmation of the organism in direct association with these pathologic lesions by immunohistochemistry. Supporting data such as serology and molecular analyses were provided when available. The results were recently published in the peer-reviewed journal, “Diseases of Aquatic Organisms.”
While 8 deaths may not sound like a large number, NOAA is growing increasingly concerned about the threat of toxoplasmosis for several reasons. First of all, the number of monk seal mortalities attributed to toxoplasmosis is an underestimate. More seals disappear each year than are found sick or dead. Even when carcasses are found, they may be too decomposed to definitively identify this infection as a cause of mortality. Vertical transmission to fetuses has been documented in monk seals, however failed pregnancies can be difficult to detect in wild animals. The outlook for treating sick seals is poor because of the rapid, severe, diffuse inflammatory response in the infected seal and because drug choices and delivery routes are far from optimal. Only two seals have been assessed prior to death, but both declined rapidly and could not be rehabilitated. Unlike threats such as fish hook ingestion or malnutrition, which can often be mitigated through rehabilitation, our options are severely restricted when it comes to treating seals for toxoplasmosis. Even if there were improvements in treatment modalities, most cases are simply found dead on the beaches. The population level impact of each mortality exceeds the loss of one seal because the future reproductive potential of that seal is also lost.
NOAA is one of a handful of Federal and state agencies that have met in 2016 to discuss the complex problem of cats in Hawaii and the threats (disease, predation) they pose to native wildlife. The group is still formalizing its mission, scope and membership, but for now, it is focused on compiling and disseminating the best available science on this issue. In time, subgroups will be developed to focus on specific topics. The group will seek participation from outside (non-agency) groups, including veterinarians – so stay tuned.
Through some of our ongoing research partnerships, we at NOAA are investigating the prevalence of exposure within the monk seal population using serology and molecular analyses. Evidence of previous exposure to T. gondii has been documented in a few apparently healthy monk seals as well, so we are very interested in this dichotomy. To address that, we are working with external partners and experts in this field to better understand the epidemiology of this pathogen in monk seals and the risk factors related to the host, pathogen and environment. I hope to be able to share the results of these studies with all of you in the years to come and I welcome your questions or dialogue on this topic.
Michelle Barbieri, DVM, MS
Wildlife Veterinary Medical Officer
Hawaiian Monk Seal Research Program
As the primary veterinarian for NOAA’s Hawaiian Monk Seal Research Program, Dr. Michelle Barbieri oversees wild monk seal disease surveillance, population health studies, vaccination, rehabilitation, and provides veterinary support to the program’s other research objectives.
Honnold, S.P., Braun, R., Scott, D.P., Sreekumar, C. and Dubey, J.P., 2005. Toxoplasmosis in a Hawaiian monk seal (Monachus schauinslandi). Journal of Parasitology, 91(3), pp.695-697.
Barbieri, M.M., Kashinsky, L., Rotstein, D.S., Colegrove, K.M., Haman, K.H., Magargal, S.L., Sweeny, A.R., Kaufman, A.C., Grigg, M.E. and Littnan, C.L., 2016. Protozoal-related mortalities in endangered Hawaiian monk seals Neomonachus schauinslandi. Diseases of Aquatic Organisms, 121(2), pp.85-95.