What is the context of this research?
Life in marshy habitats in South Africa
has both advantages and limitations. These nutrient-rich environments create a bounty for the organisms that live in them. However, warm waters also provide favorable conditions for the parasites that rely on an aquatic medium to complete their life cycle. Snails and crabs flourish at the land-water interface in Africa, and these invertebrates are often parasitized by trematode flatworms. Trematodes have a complex life cycle that involves several different host species including, a mollusc, a crustacean or fish, and, finally, a bird or a mammal.
The disease that is the focus of our current investigation is paragonimiasis, a lung disease that has symptoms similar to tuberculosis. It is estimated that over 20 million people are infected worldwide. Our project aims to understand the basis for paragonimiasis transmission. Over one hundred years ago, it was discovered that the trematode Paragonimus is the cause of the paragonimiasis lung disease. But the molluscan host of Paragonimus—and the mechanism of transmission between the mollusc and crab—remains unknown in Africa.
What is the significance of this project?
Paragonimiasis occurs primarily in western and central Africa, and it is acquired through the consumption of raw or undercooked crabs. The low incidence of the disease in South Africa could be a result of cultural practices (not eating raw meat), misdiagnosis (confusion of paragonimiasis with tuberculosis), or climate (it is a more temperate region). Trematode parasites respond positively to higher temperatures, and this could increase the infection rate in southern Africa as the climate warms. Our research will help to identify human populations in southern Africa at risk for this disease.
Several mammal species in addition to humans are affected by paragonimiasis, including mongooses and otters. These animals also acquire the disease through consumption of crabs. Although paragonimiasis was discovered in otters and mongooses over a century ago, the transmission cycle of the parasite remains mysterious. It is essential that we study the invertebrates that serve as intermediate hosts of the parasite in order to understand the mechanics of disease transmission. Our research in southern Africa under controlled conditions will shed light on the etiology of paragonimiasis in the tropics where incidence rates are much higher.
What are the goals of the project?
We are studying the ecology of African molluscs and crabs, as well as the infection rates of Paragonimus in the tissue of these hosts, to better understand the basis for the propagation of paragonimiasis in Africa today.
We will collect crabs and snails in several locations in South Africa, and we will study the behavior of the crabs in their natural habitat using underwater video, in an attempt to discover how the crabs are infected by Paragonimus cercaria (the larval parasites that are shed by the molluscan host). Dissections of crabs and snails will take place in the field, and the tissues of infected individuals will be taken to museum laboratories for comparative study and long-term preservation.
You will be kept up-to-date on our expedition with exciting imagery from the field in South Africa and with Twitter updates (@potamon_crab). If you have any questions about our work, feel free to contact us!