Viral Protozoan And Helminthic Diseases Of The


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24.11.2010
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Viral, Protozoan, And Helminthic Diseases Of The Cardiovascular And Lymphatic Systems Essay, Research Paper

Viral, Protozoan, and Helminthic Diseases of the Cardiovascular and Lymphatic Systems

Koch s postulates are guidelines for determining that a specific microorganism causes a specific disease. Koch s postulates are as follows: 1. The same pathogen must be present in every case of the disease. 2. The pathogen must be isolated from the diseased host and grown in pure culture. 3. The pathogen from the pure culture media must cause the disease when it is inoculated into a healthy, susceptible laboratory animal.

4. The pathogen must be isolated from the inoculated animal and must be compared to the original pathogen.

Microorganisms can enter the body in a variety of ways. They can penetrate the mucous membranes of the respiratory, gastrointestinal, genitourinary systems and the conjunctiva, the membrane that covers the eyes. Microbes can easily be inhaled through the respiratory tract. They can also be ingested in contaminated food. Some microorganisms enter the body through the skin. Some microbes, such as fluke worms, can burrow through the skin into the bloodstream. Bacteria, viruses, and protozoan can go through the skin via a bite, cut, or other wound; this is called parenteral entry.

Bacteria have several devices which they use to penetrate the host s defenses. Some have capsules or proteins in the cell wall that prevent them from being phagocytized. Some can even reproduce in a phagocyte. Bacteria can also produced enzymes such as leukocidins to destroy neutrophils and macrophages and hemolysins that cause lysis in red blood cells.

Bacteria damage host cells and induce illness in two ways: direct damage and the production of toxins. Bacteria damage and destroy the host cells as they multiply. Bacteria also produce toxins, which are substances poisonous to the host. They release exotoxins, which produce disease symptoms. Cytotoxins kill host cells or affect their functions. Neurofunctions interfere with nerve transmissions. Enterotoxins affect cells lining the gastrointestinal tract. The death of the bacterial cell or the presence of antibodies or antibiotics can trigger the release of endotoxins. They can lead to fever and shock.

Plasmids are DNA molecules in bacteria that may carry genes for antibiotic resistance, toxins, capsules, and fimbriae. Lysogeny is bacteria infected with viruses that can change the virulence by altering the toxins or the capsule.

Viruses evade the immune system by growing inside the host cells, where the body s defenses cannot reach. They can easily invade host cells because they have attachment sites for receptors on the host cell. Viruses can causes cytocidal and noncytocidal effects (cell death and cell damage, respectively). Other effects include the stopping of mitosis, lysis, cell fusion, antigenic changes, and transformation of cells.

Fungus cause problems in the host with capsules, toxins, and allergic responses. Protozoan and helminths cause disease by damage the host tissue or by the wastes they produce. Some protozoa can change their surface antigens while growing so that the host s antibodies do not kill the protozoa. Algae can be harmful to the host as some can produce neurotoxins.

Nonspecific defense mechanisms are the body s defenses against any pathogen. The first defense of the body is the skin. Intact skin is impenetrable for most microorganisms. The protein keratin in the skin makes it resistant to microbial invasion. Mucous membranes line the respiratory, gastrointestinal, and genitourinary tracts and are also a barrier for invading pathogens; these can readily trap microbes attempting to enter these systems.

Phagocytosis is the ingestion of microorganisms by a cell. It is performed by phagocytes and white blood cells. White blood cells, or leukocytes, are divided into three groups: granulocytes, lymphocytes, and monocytes. During an infection, the number of white blood cells increases, which is called leukocyosis. During an infection, leukocytes kill or attempt to kill foreign microbes through phagocytosis. The phagocyte attaches itself to a microbe; this can be achieved through opsonization, or the coating of the microbe with plasma proteins. The phagocyte extends its pseudopods around the other microbe, engulfing it in a phagocytic vessel. The microorganism is then killed by lysosomal enzymes or oxidizing agents.

Inflammation is the body s response to the cell damage caused by a pathogen. Signs of inflammation include redness, pain, heat, swelling, and numbness.

Fever is a high body temperature that results from a bacterial or viral infection. Bacterial endotoxins can induce fever. A rising body temperature is called a chill, and falling body temperature is called crisis and is marked by sweating.

Antimicrobial substances are produced by the complement system. It is made up of a group of serum proteins that activate one another to destroy invading pathogens. The entire process can result in cell lysis, inflammation, and oponization.

Interferons are another anitmicrobial substance. They are antiviral proteins that are produced during a viral infection. They induce uninfected cells to produce antiviral proteins that will prevent viral replication. Interferons do not specifically kill a certain type of virus.

Specific defenses of the host are defenses designed to prevent an infection from a specific microorganism. This defense is called immunity. It is the ability of the body to counteract the effects of foreign microorganisms called antigens; this is done through the production of specialized lymphocytes and antibodies. It can be acquired after the patient has already contracted the disease, to a newborn child from a mother through the fetus, and artificially through a vaccine.

The humoral or antibody-meditated immune system involves the production of antibodies by B cells in response to a specific antigen. Antibodies defend against bacteria, viruses, and toxins in the blood and lymph.

The cell-mediated immune system relies on T cells and does not involve antibody production. Cellular immunity is a response to intracellular bacteria and viruses, multicellular parasites such as helminths, transplanted tissue, and cancer cells.

The cardiovascular system is responsible for circulating blood throughout the body to deliver cells nutrients and to transports wastes away. It is made up of the heart, blood, and blood vessels. The heart is a muscle that pumps the blood throughout the body. Blood is made plasma, red blood cells, or erythrocytes, and white blood cells, or leukocytes. Plasma transports dissolved nutrients to cells and takes away wastes. Red blood cells carry oxygen to cells. White blood cells play a role in the body s defense against foreign microorganisms. Arteries, veins, and capillaries comprise the network of blood vessels in the body, which transport blood away from the heart, bring blood back to the heart, and distribute materials to and from blood to cells respectively. The cardiovascular system has no normal microbiota.

The lymphatic system is made up of the lymph, lymph vessels, lymph nodes, and lymphoid organs: tonsils, appendix, spleen, and thymus gland. Its main function is to transport the plasma that leaks out to the spaces in between cells back to the bloodstream. Lymph vessels pick up this plasma, which is called lymph, and transport it back to the bloodstream right before the blood reenters the heart. All the proteins in the plasma is returned to the blood. As the lymph flows back to the blood, it flows through round structures called lymph nodes. Lymph nodes contain macrophages that help clean the plasma of infectious microorganisms. Lymph nodes also play a role in the immune system in that pathogenic microbes will also face two kinds of lymphocytes: the B cell which produces humoral antibodies and the T cell that destroys foreign microbes. The lymphatic system also has no normal flora.

Many of the viral, protozoan, and helminthic diseases are found in tropical climates. These include yellow fever, malaria, and, more recently, ebola. Many of them are also transmitted through vectors such as mosquitoes and other insects.

One of the more well known viral diseases is infectious mononucleosis, or commonly called mono. This disease is transmitted through the ingestion of infected saliva, whether by kissing or sharing drinks. The virus which causes mono, the Epstein-Barr or EB virus, reproduces in the parotid glands, which produce saliva. The EB virus has an incubation period of 4 to 7 weeks before symptoms begin to appear. Symptoms include fever, sore throat, buboes, or swollen lymph nodes, in the neck, and a general feeling of weakness. Symptoms, however, do not appear when young children contract the disease. The EB virus infects solely B cells; the infection causes them to transform into plasma cells. Cytotoxic T cells consider these plasma cells to be foreign invaders and attack them. This causes the symptoms in patients. Infectious mononucleosis is largely non-fatal; death can be caused if the enlarged spleen associated with the disease is ruptured during vigorous activity. There is no specific treatment for mono. Recovery is complete within a few weeks with the patient having complete immunity to the disease thereafter. Testing for mono is comprised of the detection of antibodies against the EB virus. Mono can be found all over the world including the United States.

Burkitt s lymphoma is another disease that is related to the Epstein-Barr virus. It is a cancerous tumor of the jaw that is most commonly found in children. Although the cancer is not directly caused by the EB virus, research shows that it is closely associated with the tumor. Scientists still do not know how the virus could start the tumor. Burkitt s lymphoma occurs as mosquitoes infect a person with malaria. The malarial infection in turn weakens the immune system, making the person more susceptible to the EB virus, which is commonly found. Burkitt s lymphoma can only be found in Africa, where malaria is endemic. However, AIDS patients have also been known to contract the disease because of their weakened immune systems

Yellow fever is a viral hemorrhagic fever. It is a zoonotic disease; it appears only in humans from contact with its normal animal host. It is caused by an arbovirus, the yellow fever virus, that is injected into the skin by a mosquito, Aedes aegypti. Early symptoms of this disease are fever, chills, and headache followed by nausea and vomiting. A stage called jaundice follows. Jaundice is the yellowing of the skin which is caused by liver damaged resulting in the deposit of bile pigments in the skin. This stage, evidently, gives yellow fever its name. Twenty percent of the disease s victims die. Yellow fever can be identified from either the symptoms or the presence of antibodies in the blood. There is no treatment for the illness. There is however a vaccine for yellow fever; it is a attenuated live viral strain. Yellow fever can only be found in such tropical climates as Central America, South America, and Africa. It can be controlled by mosquito control and immunization of the population.

Dengue, or breakbone fever, is a disease very similar to yellow fever. It, too, is transmitted by the Aedes aegypti mosquito. It is, however, a much milder disease, although the symptoms can be painful. Denegue is characterized by fever, severe muscle and joint pain, and rash and is rarely fatal. It can be found in the Caribbean and other tropical environments.

A different strain of the denegue fever virus causes another disease called the denegue hemorrhagic fever. This disease is mainly found in Southeast Asia. It can induce shock in a victim and kill in a few hours. Denegue hemorrhagic fever only attacks those who have antibodies against other strains of the denegue virus.

One emerging viral hemorrhagic fever is caused by the now well publicized ebola virus. Caused by the ebola filovirus, ebola first appeared in an outbreak in Africa in 1976. The natural host is unknown, but the disease is spread by contact with blood, often through unsterilized needles. Ebola has a staggering mortality rate of ninety percent.

American trypanosomiasis or Chaga s disease is a cardiovascular disease caused by a flagellated protozoan called Trkypanosoma cruzi. It occurs in Southern Texas, Mexico, and Central and South America. The microorganism is found on wild animals such as rodents, opossums, and armadillos. The protozoan is then carried to humans by an insect vector called the reduviid bug. The microbe grows on the gut of the insect and are transmitted if the bug defecates while feeding. T. cruzi is rubbed into the bite wound by either the reduviid bug or the bitten human. The parasite damages the heart muscle and the nerves controlling the actions of the esophagus or the colon. These two organs can no longer transport food and become enlarged, which is known as megaesophagus and megacolon. Identification of the disease is done mainly by observing symptoms. An alternative is xenodiagnosis. Parasite-free reduviid bugs are allowed to feed on suspected patients. They look for the protozoan in the intestinal tract of the bug 10 to 20 days later. Treatment of Chaga s disease consists of chemotherapy if the patient is in the disease s early stages. However, if it becomes chronic, the disease becomes difficult to cure.

Toxoplasmosis is a cardiovascular and lymphatic system disease caused by the spore-forming protozoan Toxoplasma gondii. Cats are carriers of the disease. The protozoan can only go through its sexual phase in the intestinal tract of a cat. Oocysts are left in the cat s feces. It is transmitted to humans by direct contact with the feces or by eating undercooked meat from an animal that has contracted toxoplasmosis from contact with infected cat feces. The oocysts invade a host cell and form tachyzoits. These multiply rapidly and eventually cause the host cell to rupture, allowing these parasites to invade more host cells. Eventually, the immune system becomes too overwhelming for the protozoa. Host cells then form a wall protecting the protozoa inside, creating a tissue cyst. These tissue cysts can remain in the body for years. In a healthy person, a toxoplasmosis infection may have only very mild to no symptoms. However, it can become deadly during pregnancy as it can cause still birth or a child with brain damage or vision problems.

Malaria is a protozoan disease marked by the symptoms of chills, fevers, and often vomiting and severe headaches. These symptoms appear for 2 or 3 days, subside, and reappear 2 or 3 days later. The mosquito Anopheles transports the protozoa Plasmodium in its saliva. The vector infects a person with the sporozoite form of the protozoa. The sporozoites travel through the bloodstream and eventually reach the liver. There, they undergo reproduction in the liver cells and release merozoites. These infect red blood cells. The merozoites reproduce. In doing so, the red blood cell ruptures, releasing more merozoites; in addition toxic compounds are released into the blood, causing the paroxysms of malaria. The paroxysms are the intervals of chills and fever a patient experiences. The fever can reach up to 104o F. A sweating stage can occur after the fever. Anemia can result because of the loss of red blood cells, and enlargement of the spleen and the liver can also cause problems. Young children who contract malaria have the highest mortality rates. People who survive malaria can gain a limited immunity; they often have milder symptoms if they get re-infected. A vaccine does not yet exist for malaria. In the past, malaria can be treated with the drug quinine, but newer strains have grown resistant to the drug.

Schistosomiasis is a debilitating disease caused by a small fluke, a helminths. The disease is caused by flukes of the genus Schistosoma. The entire life cycle of this microogranism involves humans. Ova from a Schistosoma from human wastes contaminate water . The egg hatches and becomes a larva, called miracidium. This then enters the body of a snail. The helminths then emerges from the snail in a form called cercaria. These can then penetrate the skin of a swimming or wading human. Then, the microbes are carried by the bloodstream to either the liver or urinary bladder. The cercaria matures into adult form, and a male and female produce ova. The ova can cause tissue damage called granulomas. Adult worms are unaffected by the human immune system. Schistosomiasis occurs in Asia, Africa, South America, and the Caribbean.

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