Kingdom Protista:
INTRODUCTION.
Protista is a group of comparatively simple organisms. Most protists are unicellular (consisting of a single cell) and can only be seen with a microscope, although there are some that are composed of more than one cell (e.g. Volvox).
There are a wide variety of protists, and they inhabit many different environmentsBfresh water, seawater, soils, and the intestinal tracts of animals, where they perform crucial digestive processes.
Like plants, some species of protists can make their own food by the process of photosynthesis (e.g. Euglena discussed below).
Like animals, many protists can move around under their own power.
Unlike plants and animals, however, protists do not have cells organized into specialized tissues.The protists include such familiar organisms such as amoeba and Paramecium which are often studied in high school biology.
The kingdom Protista contains many economically important members, including organisms that cause diseases, such as malaria, Chagas disease, and African sleeping sickness.A convenient division of protista based on method of locomotion is as follows:
Sarcodina: Locomotion by means of pseudopodia (e.g.s Amoeba, Entamoeba histolytica)
Ciliata: Locomotion by means of cilia (e.g.s Paramecium, Balantidium coli)
Mastigophora: Locomotion by means of flagella (e.g.s Euglena, Trypanosoma, Trichomonas vaginalis)
Sporozoa: No organs for locomotionBparasitic (e.g. Plasmodium and Toxoplasma)
SOME IMPORTANT MEMBERS OF SARCODINA:
Amoebas
Amoebas are characterized by their locomotive method of extending cytoplasm outward to form pseudopodia (false feet).
The amoeboid group includes hundreds of different organisms, ranging in size from about .25 to 2.5 mm (about 0.0098 to 0.098 in).
All amoeboid organisms have thin cell membranes, a semirigid layer of ectoplasm, a granular, jellylike endoplasm, a contractile vacuole, and an oval nucleus.
Some species live on aquatic plants and some in moist ground; others are parasitic in animals.
Amoebas also use pseudopodia for feeding. Chemical stimuli from smaller organisms, the amoeba's food, induce the formation of pseudopodia, pairs of which envelop the organism, at the same time forming a cavity, or vacuole.
A digestive enzyme secreted into the cavity breaks down this food into soluble chemical substances that then diffuse from the cavity into the cytoplasm.
Undigested food and wastes are excreted through the plasma membrane, which also absorbs oxygen from the surrounding water and eliminates carbon dioxide, a by-product of metabolism, in a form of respiration.
After a period of growth, the amoeba reproduces by splitting into two equal parts in an asexual process called binary fission. Duplicates are formed with the same genes.
At least six forms of amoeba are parasitic in humans. Most important of these is Entamoeba histolytica, which causes amebiasis and dysentery.
Entamoeba histolytica: (A parasitic amoeba)
The diseases often occur in epidemics when raw sewage contaminates water supplies or when soil is fertilized with untreated human wastes.Amebiasis is a widespread human disease in tropical regions, resulting from infection by the amoeba Entamoeba histolytica, however it is estimated that 10% of the world=s population carries the cysts.
It is sometimes found in the United States (lettuce or other vegetables not washed adequately or occasionally due to plumbing problems or septic tanks contaminating wells).
The life cycle of Entamoeba histolytica involves trophozoites (the feeding stage of the parasite) that live in the host's large intestine and cysts that are passed in the host's feces.
Note that the cysts are formed only within the large intestine of the host, and do not form after the trophozoites are passed from the body.
Humans are infected by ingesting cysts, most often via food or water contaminated with human fecal material.
The trophozoites can destroy the tissues that line the host's large intestine, so of the amoebae infecting the human gastrointestinal tract, E. histolytica is potentially quite pathogenic.
In most infected humans the symptoms of "amoebiasis" (or "amebiasis") are intermittent and mild (various gastrointestinal upsets, including colitis and diarrhea).
In more severe cases the gastrointestinal tract hemorrhages, resulting in dysentery.
In some cases the trophozoites will enter the circulatory system and infect other organs, most often the liver (hepatic amoebiasis), or they may penetrate the gastrointestinal tract resulting in acute peritonitis; such cases are often fatal.
As with most of the amoebae, infections of E. histolytica are often diagnosed by demonstrating cysts or trophozoites in a stool sample.
Amebiasis is easily dealt with by drugs, but if untreated it can lead to abscesses of the liver, the lungs and, less frequently, the heart; rarely, it may even reach and damage the brain.Cellular Slime Molds Cellular slime molds constitute a large portion of the soil amoebae population, feeding separately on bacteria.
When they have cleared an area of food, the starving amoebae stream together into central collection points, attracted by a chemical that they themselves give off.
This results in the formation of a multicellular organism (called a slug) which seems remarkably well organized: It has anterior and posterior ends, moves toward light, and orients toward or away from heat, depending on the temperature.
When it comes to rest, the amoebae at the anterior end start producing a delicate stalk, while those at the posterior end turn asexually into spores that form a terminal ball at the tip of the new stalk. (The stalk raises the ball into the air.)
The spores are released and can then develop into new amoebas. Classification: There is debate as to where the slime molds should be classified since they share some characteristics with amoebas and others with fungi. For this class, they are classified in the Kingdom Protista with the amoebas, where they form two phyla.
CILIATA:
There are 7000 known species of ciliates, which may range in size from 10 micrometers to 2 millimeters.
Found in all water environments, ciliates are characterized by a mouthlike cytostome (an area of the cell for ingesting food) andCCat least in some stage of their life cycleCCby many hairlike projections (cilia).
They are unique in having two nuclei in their single cell: a macronucleus involved in feeding and a micronucleus involved in reproduction, which takes place either by binary fission or by conjugation.
Paramecium: (Free-living ciliate)
Paramecium is a genus often called slipper animalcules because of their slipperlike shape.
The pellicle is a rigid outer covering which gives them a definite shape.
Paramecia are unicellular organisms usually less than 0.25 mm (0.01 in) in length and covered with minute hairlike projections called cilia.
Cilia are used in locomotion and during feeding. When moving through the water, paramecia follow a spiral path while rotating on the long axis.
When a paramecium encounters an obstacle, it exhibits the so-called avoidance reaction: It backs away at an angle and starts off in a new direction.
Paramecia feed mostly on bacteria, which are driven into the cytostome and then into the gullet by the cilia. At this point, food vacuoles are formed for circulation in the cytoplasm.
Two contractile vacuoles with radiating canals regulate osmotic pressure by removing excess water.
The cytopyge is the cell Aanus@ which eliminates solid wastes.
A paramecium has a large nucleus called a macronucleus, without which it cannot survive, and one or two small nuclei called micronuclei, without which it cannot reproduce sexually.
Reproduction is usually asexual by transverse binary fission, occasionally sexual by conjugation.
Conjugation (sexual reproduction) in Paramecium:
Paramecia of opposite mating types come together and adhere at their oral grooves.
In each the micronucleus divides by meiosis, resulting in 4 haploid cells.
Three of the nuclei disintegrate.
The remaining nucleus divides by mitosis to form Amale@ and Afemale@ pronuclei.
Male pronuclei are exchanged between the conjugating Paramecia.
In each Paramecium, male and female pronuclei use to form a diploid nucleus.
The Paramecia now separate.
In each exconjugant, the diploid nucleus divides three times to form 8 micronuclei.
The old macronucleus is gradually disintegrates.
Four of the micronuclei fuse to become a new macronucleus.
Three disintegrate.
One remains as the micronucleus.
The Paramecia are Arejuvenated@ by this process and continue to divide asexually by transverse binary fission.
Paramecia are found in large numbers in freshwater ponds throughout the world; one species lives in marine waters. They are easily cultivated in the laboratory by allowing vegetable matter to stand in water for a few days.
Balantidium coli: (Parasitic ciliate)
Balantidium coli is a parasite of many species of animals, including pigs, rats, guinea pigs, humans, and many other animals.
It appears that the parasite can be transmitted readily among these species, providing the appropriate conditions are met (i.e., fecal contamination).
Humans (often farmers who raise hogs) are infected when they ingest cysts via food or water contaminated with fecal material.
In many respects this parasite resembles Entamoeba histolytica --- an important difference that can have a significant impact in disease transmission is that trophozoites of B. coli will encyst after being passed in stools, trophozoites of E. histolytica will not.
In humans this parasitic species resides most often in the large intestine, and it can invade the mucosa (or invade lesions caused by other organisms) causing serious disease.
Extra-intestinal infections can also occur.
MASTIGOPHORA:
Euglena is a free-living flagellate.
A typical euglena has a flagellum, or whiplike appendage used in swimming, at the front end.
It also executes a kind of crawling movement by changing the shape of its body.
An eyespot enables it to move toward or away from light.
It is photosynthetic and contains several organelles, called chloroplasts, that give them a greenish color.
Some euglens feed by absorbing dissolved substances, and many can ingest larger materials such as other euglenoids.
The animals reproduce asexually by longitudinal fission, sometimes extending even to the tip of the flagellum.
No evidence of sexual reproduction exists.
Trypanosoma is a parasitic mastigophoran.
All Trypanosomes are blood parasites.
They are the cause of two major diseases: African sleeping sickness and Chagas' disease. i
The African sleeping sickness trypanosome is transmitted from one human to another via the tsetse fly, a blood-sucking fly found only in Africa.
The trypanosome starts as a parasite in the blood, but in the later stages of the infection can invade the central nervous system, causing an inflammation of the brain and spinal cord that is responsible for the characteristic neurological symptom of sleeping.
The disease was spread throughout Africa during the 1800 by European explorers, causing hundreds of thousands of death of natives.
The light-skinned Europeans are usually not bitten by tsetse flies.
The trypanosome is never transmitted directly from one person to another, but only if the tsetse fly bites.
Because of this, the spread of the disease is prevented by destroying the tsetse fly.
The introduction of powerful pesticides such as DDT has resulted in the elimination of sleeping sickness from many parts of Africa.
Domestic animals in Africa are affected by this disease, but not the wild animals.
Chagas disease is found in South America:
Chagas disease, named after the Brazilian physician Carlos Chagas who first described it in 1909, exists only on the South American Continent.
It is caused by a flagellate protozoan parasite, Trypanosoma cruzi, transmitted to humans by insects known as assassian bugs
The geographical distribution of the human T.cruzi infection extends from Mexico to the south of Argentina.
The disease affects 16 - 18 million people and some 100 million, i.e. about 25% of the population of Latin America is at risk of acquiring Chagas disease.
There are two stages of the human disease: the acute stage which appears shortly after the infection and the chronic stage which appears after a silent period that may last several years.
The lesions of the chronic phase irreversibly affect internal organs such as the heart, esophagus and colon and the peripheral nervous system.
After several years of an asymptomatic period, 27% of those infected develop cardiac symptoms which may lead to sudden death, 6 % develop digestive damage mainly enlargement, and 3% will have peripheral nervous involvement.
The risk of infection with Chagas disease is directly related to poverty.
The blood-sucking assassin bug which transmits the parasite finds a favorable habitat in crevices in the walls and roofs of poor houses in rural areas and in urban slums.
Chagas disease can be transmitted by blood transfusion. The figures of infection of blood in blood banks in some selected cities of the South American continent vary between 3.0% and 53.0 % thus showing that the prevalence of T.cruzi-infected blood is higher than that of HIV infection and Hepatitis B and C.
Trichomonas vaginalis:
What is trichomoniasis?
Trichomoniasis is one of the most common sexually transmitted diseases (STD) that affects both women and men, although symptoms are more common in women.
What causes trichomoniasis?
Trichomoniasis is caused by the single-celled protozoan parasite Trichomonas vaginalis.
The vagina is the most common site of infection in women, and the urethra is the most common site of infection in men.
How do people get trichomoniasis?
Trichomoniasis is a sexually transmitted disease that is spread through penis-to-vagina intercourse or vulva-to-vulva contact with an infected partner.
Women can acquire the disease from infected men or women, whereas men usually contract it only from infected women.
How common is trichomoniasis?
Trichomoniasis is the most common curable STD in young, sexually active women.
An estimated 5 million new cases occur each year in women and men.
What are the signs and symptoms of trichomoniasis?
Most men with trichomoniasis do not have signs or symptoms.
Men with symptoms may have an irritation inside the penis, mild discharge, or slight burning after urination or ejaculation.
Many women do have signs or symptoms of infection.
In these women, trichomoniasis causes a frothy, yellow-green vaginal discharge with a strong odor.
The infection may also cause discomfort during intercourse and urination.
Irritation and itching of the female genital area and, in rare cases, lower abdominal pain can also occur.
The symptoms of trichomoniasis in infected men may disappear within a few weeks without treatment.
However, an infected man, even a man who has never had symptoms or whose symptoms have stopped, can continue to infect a female partner until he has been treated.
Therefore, both partners should be treated at the same time to eliminate the parasite. Persons being treated for trichomoniasis should avoid sex until they and their sex partners complete treatment and have no symptoms.
When do symptoms appear?
Symptoms usually appear within 5 to 28 days of exposure in women.
What are the complications of trichomoniasis?
Trichomoniasis in pregnant women may cause premature rupture of the membranes and preterm delivery.
The genital inflammation caused by trichomoniasis might also increase a woman's risk of acquiring HIV infection if she is exposed to HIV.
Trichomoniasis in a woman who is also infected with HIV can increase the chances of transmitting HIV infection to a sex partner.
How is trichomoniasis diagnosed?
To diagnose trichomoniasis, a health care provider must perform a physical examination and laboratory test.
In women, a pelvic examination can reveal small red ulcerations on the vaginal wall or cervix.
Laboratory tests are performed on a sample of vaginal fluid or urethral fluid to look for the disease-causing parasite.
The parasite is harder to detect in men than in women.
Who is at risk for trichomoniasis?
Any sexually active person can be infected with trichomoniasis.
What is the treatment for trichomoniasis?
Trichomoniasis can usually be cured with the prescription drug metronidazole given by mouth in a single dose.
Metronidazole can be used by pregnant women.
Giardia:
Found in human intestine of infected person.
Diarrhea, abdominal cramps, gas, malaise, and weight loss are the most common symptoms caused by Giardia.
Vomiting, chills, headache, and fever may also occur.
These symptoms usually surface six to 16 days after the initial contact and can continue as long as one month.
Giardia is usually cleared from healthy people without treatment within a month.
Anti-parasitic drugs are available and are particularly helpful for immunocompromised people in whom the illness could otherwise develop into a persistent state.
Giardia are often found in human, beaver, muskrat, and dog feces.
Drinking water sources become contaminated when feces containing the parasites are deposited or flushed into water.
If treatment is inadequate, drinking water may contain sufficient numbers of parasites to cause illness.
Other sources include direct exposure to the feces of infected humans and animals, eating contaminated food, and accidental ingestion of contaminated recreational water.
The comparative importance of these various routes of exposure is unknown.
SPOROZOA:
Malaria is a debilitating infectious disease characterized by chills, shaking, and periodic bouts of intense fever.
Caused by single-celled parasites of the genus Plasmodium, malaria is transmitted from person to person by the bite of female Anopheles mosquitoes (The males do not feed on blood, but rather on the nectar of flowers).Although malaria was once widespread in North America and other temperate regions, the last major outbreak of malaria in North America occurred in the 1880s.
The disease today occurs mostly in tropical and subtropical countries, particularly sub-Saharan Africa and Southeast Asia.
According to the World Health Organization, malaria is prevalent in over 100 countries.
Each year, between 400 million and 600 million cases of malaria are diagnosed, and 1.5 million to 2.7 million people die of the disease.
In recent years, malaria has become more difficult to control and treat because malaria parasites have become resistant to drugs, and mosquitoes that transmit the disease have become resistant to insecticides.
Malaria in humans is caused by four species of Plasmodium parasites.
Plasmodium falciparum is the most common species in tropical areas and is transmitted primarily during the rainy season. This species is the most dangerous, accounting for half of all clinical cases of malaria and 90 percent of deaths from the disease.
Plasmodium vivax is the most widely distributed parasite, existing in temperate as well as tropical climates.
Plasmodium malariae can also be found in temperate and tropical climates but is less common than Plasmodium vivax.
Plasmodium ovale is a relatively rare parasite, restricted to tropical climates and found primarily in eastern Africa.
Malaria Life Cycle
Plasmodium parasites undergo many stages of development, and their complete life cycle occurs in both humans and mosquitoes.
The parasites are transmitted to humans by female mosquitoes of the genus Anopheles.
About 60 of the 390 species of Anopheles mosquito transmit the malaria parasite.
Of these, only a dozen species are important in the transmission of malaria worldwide.
Usually just one or two species play a role in malaria transmission in a particular region where the disease is prevalent.Malaria transmission begins when a female mosquito bites a human already infected with the malaria parasite.
The mosquito ingests blood containing immature male and female gametes (sex cells) of the malaria parasite.
Inside the mosquito's stomach, the gametes quickly mature.
A male gamete fuses with a female gamete to produce a cell known as a zygote.
The zygote enters the wall of the mosquito's gut and develops into an oocyst.
The oocyst multiplies to produce thousands of cells known as sporozoites.
The sporozoites leave the wall of the gut and migrate to the mosquito's salivary glands.
The mosquito phase of the malaria parasite's life cycle is normally completed in 10 to 14 days. This development process occurs more slowly in areas with cooler temperatures.
When the infected mosquito bites another human, sporozoites in the mosquito's saliva transfer to the blood of the human.
Sporozoites travel in the blood to the liver.
In liver cells over the course of one to two weeks, the sporozoites divide repeatedly to form 30,000 to 40,000 merozoites.
The merozoites leave the liver to enter the bloodstream, where they invade red blood cells.
Inside these blood cells, the merozoites multiply rapidly until they force the red cells to burst, releasing into the bloodstream a new generation of merozoites that go on to infect other red blood cells.
Some merozoites divide to form gametocytes, immature male and female gametes.
If another mosquito bites the human and ingests these gametocytes, the life cycle of the malaria parasite begins again.
Symptoms:
The fever that characterizes malaria develops when merozoites invade and destroy red blood cells.
The destruction of red blood cells spills wastes, toxins, and other debris into the blood.
The body responds by producing fever, an immune response that speeds up other immune defenses to fight the foreign invaders in the blood.
The fever usually occurs in intermittent episodes. An episode begins with sudden, violent chills, soon followed by an intense fever and then profuse sweating that brings the patient's temperature down again.
Upon initial infection with the malaria parasite, the episodes of fever frequently last 12 hours and usually leave an individual exhausted and bedridden.
Repeated infections with the malaria parasite can lead to severe anemia, a decrease in the concentration of red blood cells in the bloodstream.
The malaria parasite consumes or renders unusable the proteins and other vital components of the patient's red cells.
The pattern of intermittent fever and other symptoms in malaria varies depending on which species of Plasmodium is responsible for the infection.
Infections caused by Plasmodium falciparum, Plasmodium vivax, and Plasmodium ovale typically produce fever approximately every 48 hours, or every first and third day. Infections caused by Plasmodium malariae produce fever every 72 hours, or every fourth day.
In Plasmodium vivax and Plasmodium ovale infections, some merozoites can remain dormant in the liver for three months to five years. These merozoites periodically enter the bloodstream, triggering malaria relapses.
(Note that malaria can be, and is, transmitted by blood transfusion from an infected person. This is common in Africa, but very rare in the United States.)
Diagnosis and Treatment
Malaria is difficult to diagnose based on symptoms alone.
This is because the intermittent fever and other symptoms can be quite variable and could be caused by other illnesses.
A diagnosis of malaria is usually made by examining a sample of the patient's blood under the microscope to detect malaria parasites in red blood cells.
Parasites can be difficult to detect in the early stages of malaria, in cases of chronic infections, or in Plasmodium falciparum infections because often in these cases, not many parasites are present.
Recent advances have made it possible to detect proteins or genetic material of Plasmodium parasites in a patient's blood.
Malaria is treated with drugs that block the growth of the Plasmodium parasite but do not harm the patient.
Some drugs interfere with the parasite's metabolism of food, while others prevent the parasite from reproducing.
Drugs that interfere with the parasite's metabolism are related to quinine, the first known antimalarial drug.
Quinine is a chemical derived from the bark of the South American cinchona tree and was used as a fever remedy by the ancient Inca in the 15th century.
This drug has a bitter taste and produces severe side effects, such as nausea, headache, ringing in the ears, temporary hearing loss, and blurred vision, and large doses can be fatal.
However, quinine is still sometimes used in treating malaria today, particularly in developing nations, because it is inexpensive and effective.
Variations of quinine and a number of other drugs are widely used today due to resistance.
Immunity
After repeated infections, people who live in regions where malaria is prevalent develop a limited immunity to the disease.
This partial protection does not prevent people from developing malaria again, but does protect them against the most serious effects of the infection.
These individuals develop a mild form of the disease that does not last very long and is unlikely to be fatal.
Deaths from malaraia:
Most of the deaths and severe illnesses caused by malaria occur in infants, children, and pregnant women.
Infants and children are vulnerable because they have had fewer infections and have not yet built up immunity to the parasite.
Pregnant women are more susceptible to malaria because the immune system is somewhat suppressed during pregnancy.
In addition, the malaria parasite uses a specific molecule to attach to the tiny blood vessels of the placenta, the tissue that nourishes the fetus and links it to the mother.
After exposure to this molecule during her first pregnancy, a woman's immune system learns to recognize and fight against the molecule.
This phenomenon makes a woman particularly vulnerable to malaria during her first pregnancy, and somewhat less susceptible during subsequent pregnancies.
Some people have genetic traits that help them resist malaria by preventing the parasites from growing and developing normally, even in people who are infected with malaria for the first time.
Sickle-cell anemia and thalassemia are two inherited blood diseases linked to malaria resistance.
People with two sickle-cell or thalassemia genes become seriously ill and often die in childhood if their disease is untreated.
But people who have only one sickle-cell or thalassemia gene do not develop the genetic disorder and are, in fact, resistant to malaria.
Various sickle-cell or thalassemia genes are widespread among people in Africa, the Mediterranean region, the Middle East, India, and Southeast Asia.
Prevention and Control Malaria can be prevented by two strategies: eliminating existing infections that serve as a source of transmission, or eliminating people's exposure to mosquitoes.
Eliminating the source of infection requires aggressive treatment of people who have malaria to cure these infections, as well as continuous surveillance to diagnose and treat new cases promptly.
This approach has been successful in areas such as North America and Europe where malaria is not common.
However, it is not practical in the developing nations of Africa and Southeast Asia, where malaria is prevalent and governments cannot afford expensive surveillance and treatment programs.
Eliminating exposure to mosquitoes, the second strategy, can be accomplished by several means.
These means include permanently destroying bodies of stagnant water where mosquitoes lay their eggs;
treating such habitats with insecticides to kill mosquito larvae; fogging or spraying insecticides to kill adult mosquitoes;
or using mosquito netting or protective clothing to prevent contact with mosquitoes.
In 1947 the United States initiated a program to eliminate exposure to malaria-carrying mosquitoes.
The program involved applying the insecticide DDT to the interior walls of homes, where female mosquitoes typically rest after feeding.
Within five years, this program virtually eliminated illness and death due to malaria in the United States.
Many of the countries where malaria is prevalent are developing nations where even basic health care is unaffordable for many people and governments lack funds for public health programs.
Some countries that had been willing to make short-term financial commitments for malaria eradication programs were unable to make the long-term commitments necessary to sustain malaria control programs.
A shortage of health care workers trained in malaria surveillance and control further complicated the problem.
During the mid-1960s, insecticide-resistant mosquitoes began to emerge in some regions.
Around the same time, malaria parasites developed resistance to chloroquine and other antimalarial drugs.
By the late 1970s, malaria had reemerged in many countries, such as Sri Lanka and Mozambique, where eradication programs had virtually eliminated the disease just a few years before.
This resurgence was particularly devastating because many people had not been exposed to the disease in years and no longer had protective immunity.
Today continuing difficulties with insecticide-resistant mosquitoes and drug-resistant parasites have led to the abandonment of community-wide mosquito control programs in many countries.
In these areas, the primary means of preventing malaria is the use of insecticide-treated bed nets.
Recent research has shown that these nets are one of the most effective malaria prevention strategies available, but even their modest cost is beyond the means of many families in developing nations.
Lack of access to medical care and to effective antimalarial drugs is also a problem in these countries.
The resurgence of malaria and the widespread problems of drug and insecticide resistance have focused increasing attention on the need for a malaria vaccine.
Developing such a vaccine has been difficult because the malaria parasite has hundreds of different strategies for evading the human immune system.
Many of these strategies are not well understood, and it is difficult to develop a vaccine that will block all of the parasite's ways of getting past the immune system.
To be successful, a vaccine will also need to target several different stages of the parasite's life cycle.
Some pharmaceutical companies have been reluctant to work on a malaria vaccine because malaria is most prevalent in developing nations and the companies fear that sales of the vaccine may not be able to recoup the costs of its development.
Progress has also been slow because the malaria parasite is difficult to raise in the laboratory and study, since it must live inside the cells of another organism.
Despite these hurdles, scientists have developed several possible vaccines that are now being tested in humans. History:
Malaria is an ancient disease that has plagued humans throughout history.
The Greek physician Hippocrates described malaria in his writings during the 400s BC.
Documents from early civilizations in China, the Middle East, and Egypt also show evidence that malaria was known to these cultures.
Throughout history, and even today, outbreaks of malaria have often been associated with warfare, migrations, and other societal disruptions.
More soldiers have been lost to malaria than to bullets in the wars of the 20th century.
Historians believe that malaria was brought to the Western Hemisphere by European explorers.
The first recorded malaria outbreak in the Western Hemisphere occurred in 1493, and the disease was common during the era of European exploration and settlement in the Americas.
The first malaria treatment emerged in 1638, when Spanish Jesuit missionaries brought cinchona bark, the source of quinine, back to Europe from South America.
Tonic water, which contains quinine, was developed in an attempt to make the drug more palatable.Malaria's association with bodies of stagnant water has long been recognized, and civilizations as early as the Etruscans (1st millennium BC) drained marshes and swamps in an effort to combat the disease.
However, the exact cause of malaria was not understood until the closing years of the 19th century. In 1880 the French surgeon Charles Alphonse Laveran identified the malaria parasite in the blood of a patient.
In 1899 Sir Ronald Ross, a British physician, demonstrated that the parasite is transmitted from human to human by the female Anopheles mosquito. Ross was awarded the 1902 Nobel Prize in physiology or medicine for this discovery.
Efforts to develop a better understanding of the malaria parasite's biology continue today with an international program to decipher all the genetic material of Plasmodium falciparum.
Toxoplasmosis is an infection that is caused by the sporozoan parasite, Toxoplasma gondii.
The parasite is carried by cats, birds, and other animals, and is found in soil contaminated by cat feces and in meat, particularly pork.
The parasite can infect the lungs, retina of the eye, heart, pancreas, liver, colon, and testes.
Once T. gondii invades the body, it remains there, but the immune system in a healthy person usually prevents the parasite from causing disease.
If the immune system becomes severely damaged, as in HIV-infected persons, or is suppressed by drugs, T. gondii can begin to multiply and cause severe disease.
In HIV-infected persons, the most common site of toxoplasmosis is the brain.
It is possible for the developing fetus of a pregnant woman to become infected with possibly fatal consequences.
It is unwise for a pregnant woman in her first trimester to empty a cat litter box.
Such women should avoid handling raw meat, especially in the early stages of pregnancy.
The risk is fairly low, but it is now believed that 2% of all mental retardation in the United States is the result of congenital toxoplasmosis. .