Parasitic Flatworms Essays - Parasitology, Digenea, Helminthiases

Parasitic Flatworms INTRODUCTION Imagine going to the doctor for a simple check up. Sure you've had some minor problems- indigestion, lack of energy, weight loss, and a bit of gas- but that's not out of the ordinary....or is it? In most cases you would be correct...but today is your unlucky day. The doctor has just informed you that you have a tapeworm parasite. PARASITIC CHARACTERISTICS By definition, a parasite is an organism that lives either in or on another organism. Infected organisms that are carrying a parasite are called host organisms- or hosts. This parasitic relationship can vary from benign to harmful- and sometimes even fatal. There are two main types of parasites: endoparasites and exoparasites, however endoparasites will be the focus of this paper, and flatworms in particular. Endoparasites are parasites that live inside the host organism. Endoparasites that inhabit vertebrates or invertebrates live off the nutrients in the food host organisms eat as well as the tissue of the host. These parasites not only live in the cavities of hollow organs but can also live within the tissue. Endoparasites can range from microscopic in size to 25 feet or more in length. Many worms are antiparasitic. Some live in the host's digestive tract feeding off the host's blood. Others, such as trichinosis, enter the host through the digestive tract and then migrate throughout the body tissue. Most microscopic worms secrete toxins into the hosts blood stream which then circulates and often causes damage to surrounding systems and tissue. The life cycle of endoparasites is as varied as the parasites themselves. Some parasites are permanent fixtures in a host's body, while others only live within the host for a limited amount of time. For example, parasitic worms can live within a host for up to 30 years! The host not even being aware of this fact because there are little or no symptoms of the invasion. Not only are life cycles varied for parasites but the number of hosts they live in are as well. Sometimes parasites live in only one host for their entire life- known as autecious - while others change hosts- known as heteroecious. In relation to the life cycle of parasitic worms, there are also different reproductive methods. Many parasites do not reproduce within their host, or reproduce to a limited degree. They are more likely to reproduce eggs that enter another host before they develop in the final host. These parasites just use their fist host as an intermediatory step in completing their life cycle. The species schistosoma ( Refer to Figure 1 ) from the class trematoda is an example of such a parasite. These parasites go through a life cycle in which they use an invertebrate, usually a snail as an intermediatory host. ( Refer to Figure 1a ) FLATWORM CHARACTERISTICS Flatworms from the phylum Platyhelminthes, are parasites that live within the intermediatory host but usually complete their sexual maturity within a vertebrate. They are broken into three major classes: Turbellaria, the most primitive, free-living class that resides either in or on a host, they generally live in a marine environment. Trematoda which is the small parasitic flatworm ( most of which are called flukes) has disk like suckers which attach to the outside or internal organs of their host, and the class Cestoda which consist of the parasitic flatworm known as the tapeworm. ( Refer to Figure 2 ) Tapeworms have no true digestive tract, therefore they live inside the digestive tract of vertebrates and some invertebrates, absorbing food through their body wall. They latch onto the walls of their host's digestive tract with suckers and hooks, located at their head, which is called a scolex. The phylum platyhelminthes are one of interest when discussing parasitic flatworms that in fect vertebrates and invertebrates. INFECTION Humans and animals are in continuous contact with microorganisms, because of this relationship there are numerous ways in which infection of flatworms can occur. Organisms that transmit parasites are known as vectors. Some vectors transmit parasites when they are eaten by the hosts. An example of this would be a flea eaten by a dog or cat. When the animal eats the flea, the immature form of the tapeworm emerges from the fleas body and later develops