One of the most interesting and fascinating biological characteristics about parasitic organisms is their life cycle. Most parasites have a very specific, complex, yet delicate life cycle. Parasites do not have a straight forward way to mature, reproduce, and survive; most parasites require of specific conditions to thrive. Some parasites require a vector to infect their host, other infect multiple hosts, and other parasites infect only one species. Some parasites reproduce sexually, other asexually, and others reproduce by both sexual and asexual means. The specificity to follow a very unique life cycle is what makes parasites’ survival so intriguing. For decades, scientists have studied life cycles in order to understand the pathogenicity, epidemiology, and biology of the parasites. One would think that by parasites following such unique paths to survive will make them easy to eradicate; and the case is partially true. Research has focused on finding weak points in the parasite’s life cycle in order to truncate its reproduction. An example is the implementation of a very simple measure to reduce transmission of Dracunculus medinensis. The life cycle of D. medinensis, also known as Guinea worm, starts when a person drinks contaminated water with D. medinensis larvae infected copepods. After ingestion, the larvae exit the copepod and migrate to the mammalian’s host intestines where the parasite matures and mates; with the female worm migrating to the skin surface where it forms a blister and upon contact with water, the worm breaks the skin releasing its larvae into the water; which are then eaten by copepods. After understanding the life cycle of this parasite it was possible to start prevention programs to provide safe water. One of the simplest, yet most successful implementation strategies in Guinea worm endemic regions was the use of net filters or cheesecloth to filter the copepods present in the water. The use of cheesecloth has been key in the reduced transmission, and close eradication, of this ancient nematode caused disease. On the other side, other parasites continue to spread and have high infection rates despite years of research on their life cycle and implementation of strategies to halt their life cycle. For example, Plasmodium spp. the causative agent of malaria, infect female mosquitoes as vectors and as intermediate hosts. Despite the use of insecticides to kill the mosquitoes, disease continues to spread and new insecticide resistant mosquitoes have emerged, thus malaria control continues to be a modern science challenge; with the use of bed nets and artemisinin the best approaches to prevent and treat malaria.

Parasitic diseases control rely on different approaches: immunization, therapeutic drugs, education, and public health. All these measures can target different points in a parasite’s life cycle, thus making the study of their biology of such importance in the control of parasitic neglected tropical diseases. On the course of this blog I will dedicate some of the entries on describing the life cycle of different parasites.