Human Culture Freshwater Vectors and Disease

Cultural practices may make humans more susceptible to certain diseases with freshwater vectors.

For example, fish and other organisms can be hosts to parasites, some of which can be transmitted to humans through eating raw or partially cooked fish such as salmonids, pike, perch, and burbot, carp and other cyprinids. Jewish women have had higher rates of infection by the broad fish tapeworm (Diphyllobo-thrium latum) than women of other cultures. This is because they often ingested infective stages of this tapeworm while tasting raw fish during the preparation of a traditional dish, gefilte fish. The tendency of restaurants to cook fish 'rare' and the consumption of more raw fish may lead to an increase in the rate of other such parasites in humans.

Many Asian cultures use aquatic insects as part of their diet. Ingestion of uncooked caddis fly larvae while working in rice paddies is known to pass parasites on to humans. Likewise, eating uncooked freshwater prawns (Macrobrachium) may pass on parasites as well.

The creation of cities has certainly affected the prevalence of freshwater vectors and human diseases. For example, when early Africans were hunters and gatherers, malaria was likely to have been far less of a problem to the human population than it is today because of their continual movements and migrations to other areas to find food. However, when people settled in villages and cities with the onset of agriculture and animal domestication, the transmission of the protozoan and its cycling within the population increased greatly. Likewise, the introduction of root crops in agriculture created ideal habitat in which mosquitoes can propagate.

The modification of cultural practices may have disease consequences as well. For example, river blindness was likely less of a problem in West Africa before European colonization because people tended to live some distance (1km) from the rivers and avoided going there during hours of peak black fly biting. However, when the European colonists and missionaries encouraged settlement close to the river, these long-standing cultural taboos disappeared and the infection rate greatly increased.

Finally, the enhancement of global biodiversity has become a cultural goal of many developed countries. The issue of biodiversity in human disease has been a major topic in the conservation biology literature; however, it is invariably about the loss of biodiversity from large-scale disease control programs (loss of fish in OCP and nontarget terrestrial and riparian fauna in tsetse control programs). However, biodiversity is also an important component in the control of freshwater vectors of human diseases as well. For example, all major malaria vectors consist of species complexes, and differences are evident among Anopheles strains in their vector competency, resting-site choice, biting behavior, and development of insecticide resistance. In cost-effective control of schistosomiasis, knowledge of snail diversity, distribution, and the epidemiology of parasite susceptibility by different snail species have been essential.

Onchocerciasis may provide the best example of how biodiversity relates to freshwater vectors and the diseases that they transmit. For example, cryptic species or strains, with varying competence in transmitting the disease or influencing its severity, are characteristic of both the black fly vector and the parasitic roundworms. Likewise, much of the success of OCP was also based on biodiversity. For example, the choice of insecticides used was based on maintenance of fish and nontarget invertebrate biodiversity. But even more unusual, the drug used to control oncho-cerciasis was also based on biodiversity. It was derived from a natural strain of Streptomyces avermitilis, a fungus discovered while screening a soil core from a golf course in Japan for potential nematocidal toxicity.

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