Problem: The number and prevalence of diseases found in the marine ecosystem is increasing at a rapid rate. The cause of this increase in not known and the pathways of disease spread is either not known or poorly understood. Some diseases may have an anthropogenic source or their effects made worse by anthropogenic activities e.g. global warming changing distributions, pollutants effecting immune systems Researchers have analyzed recent reports of marine disease occurrences (from 1970 – 2001 publications) [Ward and Lafferty (2004)] Increases in Marine Disease Reports • Disease reports had decreased in fish. • No trends were noted for seagrasses, decapods or sharks/rays. • Increases in disease reports were noted for turtles, corals, urchins and molluscs. • Increases in disease reports were also noted for marine mammals. [Ward and Lafferty (2004)] Emergence of novel diseases The emergence of novel diseases occurs in both the terrestrial and the marine environment. These diseases are facilitated by: - a new combination of hosts and pathogens - creating an environment favoring pathogens & stressing hosts Managing diseases in the marine environment is a lot more difficult than on land however Managing marine diseases Methods for managing disease on land are not easily applicable in marine ecosystems: vaccinations, culling, quarantine or restricting transportation •Many species may be wide ranging and their movements difficult to predict/uncontrolable •Marine species produce copious amounts of eggs/larvae which are adapted for long distance dispersal – aids widespread disease transfer •Many marine species are colonial – lack of genetic diversity [McCallum et al. (2004)] Rapid spread of marine diseases Researchers analysed the rate of spread of marine diseases – extremely rapid: • herpes virus spread through pilchard populations a a rate greater than 10,000km year-1 • morbillivirus spread through whale and dolphin populations at a rate of 3,000km year-1 In comparison, only myxomatosis in rabbits and West Nile Virus in birds, have spread at a rate of greater than 1000km year-1 Conditions favoring outbreaks What causes increased stress on marine organisms? - Changes in environmental conditions - Climate Change - thermal stress in corals - increased pathogen growth - range changes in pathoges & host = exposure to new hosts or pathogens. Conditions favoring outbreaks - Changes in environmental conditions - Anthropogenic causes - Nutrient loading - increased bacteria growth - decrease light (UV) - Partially/untreated sewage outfalls - Chemical pollutants (immune suppressors) - Wildlife trade - Aquaculture - non native species - anti-biotics Black band disease on coral in the Caribbean Case study: Coral disease • Black band disease (BBD) is believed to be caused by Phormidium corallyticum • Healthy corals may get BBD through contact with an infected coral but diseased corals do not always occur in the same site -can be separated by great distances. • BBD can be spread by currents? • Corals under stress are more likely to be infected and BBD has a higher rate of infection in warmer water. Case study: Coral disease • Seasonal temperatures changes may affect the spread of BBD • Anthropogenic warming of ocean water temperatures may also increase BBD. • BBD was also found to be more abundant near anthropogenic disturbances. The fungus Aspergillosis on a sea fan Case study: Coral disease • Experiments were conducted that increased nutrient concentrations up to 10 times around sea fans infected with Aspergillosis. • There was an increase in the spread of the disease (about twice as much) compared with colonies that had no extra nutrients. Case study: Coral disease • A similar nutrient experiment was conducted with a hard coral (Montastrea) • similar results – up to 50% of the coral became infected when nutrients were increased. • The infectious agents that cause the diseases probably feed off the nutrients - which are normally in short supply in tropical waters (oligotrophic). • So the more nutrient input from storm runoff the more stressed the corals become. Source of disease pathogens Sewage: Salmonella spp., Escherichia coli, Streptococcus sp., Staphylococcus aureus, Pseudomonas aeryginosa, Candida fungus enterovirus, hepatitis, poliomyelitis, influenza, and herpes. Terrestrial: - Animal feces - Fungal spores – either air-borne or in storm runoff Animal transport… Marine transportation of livestock • Every year 6 million sheep and 1 million cattle are transported by sea. • The waste of these 7 million terrestrial animals is directly into open ocean. In addition… • 2002 – an estimated 14,500 animals were reported to have died at sea and were thrown overboard • But the actual numbers may be closer to 9% of all transported animals = 630,000 Common terrestrial diseases found in marine ecosystems Measles – Marine mammals Canine distemper – Marine mammals Toxoplasmosis – Marine mammal - sea otters Herpes virus – Sea Turtles San Joaquin Valley Fever – Marine mammals – sea otters Aspergillosis fungus- Corals Brucellosis – Marine mammals - cetaceans Green turtle with fibropappiloma tumors on it. These have been associated with the herpes virus. Case study: Toxoplasmosis in dolphins • 98% of 141 Atlantic bottlenose dolphins immunologically tested positive for the pathogen Toxoplasma gondii -the pathogen causes marine mammal mortality via encephalitis (toxoplasmosis). • The source of this pathogen is likely to be cat excrement flushed out into the marine environment in sewage or via runoff. Case study: Toxoplasmosis in dolphins • Also, 91% of 47 dolphins tested positive for Neospora caninum - a causes agent of encephalitis in livestock. • The only known host for this pathogen are dogs – pet or stray dog excrement entering the marine environment via sewage or surface runoff is probably the source of the pathogen • Exposure to pathogens in dolphins may be substantial, which are indirectly anthropogenic in source. Case study: Toxoplasmosis in dolphins • Also, 91% of 47 dolphins tested positive for Neospora caninum - a causes agent of encephalitis in livestock. • The only known host for this pathogen are dogs – pet or stray dog excrement entering the marine environment via sewage or surface runoff is probably the source of the pathogen • Exposure to pathogens in dolphins may be substantial, which are indirectly anthropogenic in source. Case study: Brucella in whales • Japanese researchers described testicular lesions in 33% of sampled male North Pacific minke whales – taken in their scientific whaling program [Ohishi et al. (2003)] • Blood serum tests were antibody positive in 38% of minke whales of both sexes for the pathogen Brucella spp. [Ohishi et al. (2003)] • Brucella spp. cause brucellosis in mammals. • Symptoms = joint and muscle pain, and epididymitis and inflammation of the testis in males and the induction of abortion in females. Case study: Brucella in whales • The high rate of pathogen infection has implications for minke whale health and reproductive rate/recovery from exploitation. • But Brucella spp. has also been documented as being capable of causing infections in humans. • The high prevalence of Brucella in North Pacific minke whales has implications for human health – those working with infected carcasses – those consuming contaminated products Another worry… • A study on antibiotics in sewage waters determined that three antibiotics could be detected up to 500 m from the discharge site. • Also bacteria in the treatment plant were resistant to all the antibiotics (n=6) researchers tested on the bacteria. • Bacteria collected from discharge waters displayed resistance to two of the antibiotics tested. • The increasing prevalence of antibiotics and antibiotic-resistant pathogens in the aquatic environment “pose a potential threat to ecosystem functions and…human health”. [Costanzo et al. (2005)] Marine disease research needs Develop rapid response capability to identify, study, and manage disease outbreaks as they occur. Document longevity and host range of infectious stages. Better understanding of environmental facilitators of disease and host immunity. Develop molecular and microbiological diagnostics that can identify and track pathogens - to trace origins and their spread. Develop forecasting models for outbreaks with environmental or climate sensitivity. Determine better management of land-based sources of pollution. References Costanzo, S.D., Murby, J. and Bates, J. 2005 Ecosystem response to antibiotics entering the aquatic environment. Marine Pollution Bulletin 51: 218-223 Dubey, J.P., Zarnke, R., Thomas, N.J., Wong, S.K., Van Bonn, W., Briggs, M., Davis, J.W., Ewing, R., Mense, M., Kwok, O.C.H., Romand, S. and Thulliez, P. 2003. Toxoplasma gondii, Neospora canium, Sarcocystis neurona, and Sarcocystis canis-like infections in marine mammals. Veterinary Parasitology 116: 275-296. Grillo, V., Parcons, E.C.M., Shrimpton, J.H. 2004. A review of sewage pollution in Scotland and its potential impacts on harbour porpoise populations. Paper presented to the Scientific Committee at the 53nd Meeting of the International Whaling Commission, 3-16 July 2001, London. SC53/E13. Harvell, C.D., Kim, K., Burkholder, J.M., Colwell, R.R., Epstein, P.R., Grimes, D.J., Hofmann, E.E., Lipp, E.K., Osterhaus, A.D.M.E., Overstreet, R.M., Porter, J.W., Smith, G.W., Vasta, G.R. 1999. Emerging marine diseases – climate links and anthropogenic factors. Science 285: 1505-1510. Kim, K. et al. 2002. Disease and Conservation. Diseases and Conservation Biology working group of the National Center for Ecological Analysis and Synthesis. McCallum, H., Harvell, D. and Dobson, A. 2003. Rates of spread of marine pathogens. Ecology Letters 6:1062-1067. McCallum, H.I., Kuris, A., Harvell, C.D., Lafferty, K.D., Smith, G.W. and Porter, J. 2004. Does terrestrial epidemiology apply to marine systems? Trends in Ecology and Evolution 19: 585-591 Ohishi, K., Zenitani, R., Bando, T., Goto, Y., Uchida, K., Maruyama, T., Yamamoto, S., Miyazaki, N. and Fujise, Y. 2003. Pathological and serological evidence of Brucella-infection in baleen whales (Mysticeti) in the western North Pacific. Compartative Immunology and Microbiolology of Infectious Diseases 26:125-136 Ward, J.R., Lafferty, K.D. 2004. The elusive baseline of marine disease: Are diseases in ocean ecosystems increasing? PLOS Biology 2: 542-547.
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