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

Definition of Impressment of Sailors

Definition of Impressment of Sailors Impressment of sailors was the practice of Britains Royal Navy of sending officers to board American ships, inspect the crew, and seize sailors accused of being deserters from British ships. Incidents of impressment are often cited as one of the causes of the War of 1812. And while it is true that impressment happened on a regular basis in the first decade of the 19th century, the practice was not always viewed as a terribly serious problem. It was widely known that large numbers of British sailors did desert from British warships, often because of the severe discipline and miserable conditions endured by seamen in the Royal Navy. Many of the British deserters found work on American merchant ships. So the British actually had a good case to make when they claimed that American ships harbored their deserters. Such movement of sailors was often taken for granted. However, one particular episode, the Chesapeake and Leopard affair, in which an American ship was boarded and then attacked by a British ship in 1807, created widespread outrage in the United States. The impressment of sailors was definitely one of the causes of the War of 1812. But it also was part of a pattern in which the young American nation felt like it was constantly being treated with contempt by the British. A press gang of the Royal Navy at work. Getty Images   History of Impressment Britains Royal Navy, which constantly needed many recruits to man its ships, long had a practiced of using press gangs to forcibly recruit sailors. The working of the press gangs were notorious: typically a group of sailors would go forth into a town, find drunken men in taverns, and essentially kidnap them and force them to work on British warships. The discipline on the ships was often brutal. Punishment for even minor violations of naval discipline included flogging. The pay in the Royal Navy was meager, and men were often cheated out of it. And in the early years of the 19th century, with Britain engaged in a seemingly endless war against Napoleons France, sailors were told that their enlistments never ended. Faced with those horrendous conditions, there was a great desire for British sailors to desert. When they could find a chance, theyd leave the British warship and find escape by finding a job aboard an American merchant ship, or even a ship in the U.S. Navy. If a British warship came alongside an American ship in the early years of the 19th century, there was a very good chance that British officers, if they boarded the American vessel, would find deserters from the Royal Navy. And the act of impressment, or seizing of those men, was seen as a perfectly normal activity by the British. And most American officers accepted the seizing of these fugitive sailors and did not make a major issue out of it. The Chesapeake and Leopard Affair In the early years of the 19th century the young American government often felt that the British government paid it little or no respect, and really did not take American independence seriously. Indeed, some political figures in Britain assumed, or even hoped, that the United States government would fail. An incident off the coast of Virginia in 1807 created a crisis between the two nations. The British stationed a squadron of warships off the American coast, with the purpose of capturing some French ships which had put into port in Annapolis, Maryland, for repairs. On June 22, 1807, about 15 miles off the Virginia coast, the 50-gun British warship HMS Leopard hailed the USS Chesapeake, a frigate carrying 36 guns. A British lieutenant boarded the Chesapeake, and demanded that the American commander, Captain James Barron, muster his crew so the British could look for deserters. Capt. Barron refused to have his crew inspected. The British officer returned to his ship. The British commander of the Leopard, Captain Salusbury Humphreys, was furious and had his gunners fire three broadsides into the American ship. Three American sailors were killed and 18 were wounded. Caught unprepared by the attack, the American ship surrendered, and the British returned to the Chesapeake, inspected the crew, and seized four sailors. One of them was actually a British deserter, and he was later executed by the British at their naval base at Halifax, Nova Scotia. The other three men were held by the British and finally released five years later. Americans Were Outraged When news of the violent confrontation reached shore and began to appear in newspaper stories, Americans were outraged. A number of politicians urged President Thomas Jefferson to declare war on Britain. Jefferson chose not to enter a war, as he knew that the United States was not in a position to defend itself against the much more powerful Royal Navy. As a way of retaliating against the British, Jefferson came up with the idea of imposing an embargo on British goods. The embargo turned out to be a disaster, and Jefferson faced many problems over it, including New England states threatening to secede from the Union. Impressment As a Cause of the War of 1812 The issue of impressment, by itself, was not cause for war, even after the Leopard and Chesapeake incident. But impressment was one of the reasons given for the war by the War Hawks, who at times shouted the slogan Free Trade and Sailors Rights.