Transmission of Schistosomiasis - mediated by chemical communication
Living organisms use a variety of cues to find their prey, to mate, to move and to hide from their predator. These cues can be visual, auditory or olfactory. Olfactory cues often require a release of chemical from a source towards which an organism could be attracted to or be repelled from. From single celled bacteria to large chordates like sharks use chemical communication for different purposes. However, the most prevalent role of chemical communication is disease transmission. Various insects, bacteria and nematodes rely on their sense of smell to find their host. Chemicals emitted by the host direct these organisms towards the host. Often times, these organisms become parasitic and cause diseases in the host. Chagus disease, Malaria, Dengue, and skin infections are some of the most common diseases associated with chemosensory behaviors (Vinauger, 2014). Schistosomiasis, mediated by the chemosensory behavior of Schistosoma (trematode), is another acute and chronic disease. The parasite exploits the neuroendocrine hormones and nutrients produced by the host for its growth, development and maturation. (Zhou et al, 2009). Nearly 42 million people were reported to have been treated by the disease in 2012.(WHO)
Schistosomiasis can be caused by different species of Schistosoma - S. mansoni, S.japonicum, S. mekongi, S. guineensis, S. intercalatum, S. haematobium. The disease is transmitted through the consumption of contaminated water. There are two major forms of the disease - Intestinal and urogenital. Most cases have been reported in rural and underdeveloped populations as they don’t have access to clean water and sanitation is usually poor in these regions, however, transmission of the disease is increasing in developed areas as infected people are moving to urban settlements. (WHO). Recent eradication measures by WHO have been implemented in over 40 countries, including Brazil, China, Cambodia and Egypt, although moderate to acute transmission has been reported in a total of 52 countries with 90% of infected population living in Africa. (WHO).
The parasite senses the carbon dioxide released by the host and other chemicals that are host specific. The way these parasites find humans is rather complex. Parasite Schistosoma exhibits a life cycle similar to malarial parasite Plasmodium. The juvenile and adult stages of Schistosoma attacks two different hosts. In its larval stage, also called the miracidia, the parasite enters a snail host and develops inside the snail to a free swimming organism, referred to as the cercariae. The cercariae then finds the human host inside which it grows and reproduces to release its eggs. (Keely Ellen, Chaisson, 2013)
The free swimming cercariae penetrate through an aquatic environment. When cercariae are in water, they sense changes in temperature, gravity and light. Presence of a human in the water are sensed by the secretions of...