MicroBio Notes 25.4

Paroxysm

After 2 or 3 weeks of these vague malarial symptoms, the pattern changes and symptoms fall into three phases: (1) cold phase—the patient feels cold and develops shaking chills that can last for as much as an hour; (2) hot phase—the temperature then begins to rise sharply, often reaching 40°C (104°F) or more; and (3) wet phase—the patient's temperature falls, and drenching sweating occurs. This cycle of intense symptoms—chills, fevers, and sweats—is called a paroxysm

What is the sixth stage of the plasmodium life cycle?

After the ingested gametocytes are ingested, the male gametocyte transforms into about six tiny, whip-like gametes that swim about until they unite with the female gamete (in much the same way as the sperm and ovum unite in animals), forming a zygote.

What is Malaria in humans caused by?

Human malaria is caused by protozoa of the genus Plasmodium, which are transmitted by infected female mosquito species of the genus Anopheles. Five species of Plasmodium are involved—P. vivax, P. falciparum, P. malariae, P. ovale, and P. knowlesi (this last is a simian species that is more frequently being identified as a cause of human malaria now that molecular testing is available). These species differ in microscopic appearance and sometimes in life cycle. They also cause various types of disease, which differ in severity and treatment.

What is the third stage of the plasmodium lifecycle? (Trophozoite) (Schizont)

In an RBC, the malarial parasite develops first into a ring form, then into a larger motile trophozoite (feeding stage) and then a schizont (reproducing stage). The schizont gives rise to merozoites that are released when the RBC ruptures. The merozoites then enter new RBCs and multiply, repeating the cycle.

How do malarial parasites cause anemia?

Malarial parasites cause anemia by destroying RBCs and converting the iron in hemoglobin to a form not readily recycled by the body. The large amount of foreign material in the bloodstream strongly stimulates the immune system. In some cases, the overworked immune system fails and immunodeficiency results. In addition, the spleen enlarges to cope with the high levels of foreign material and abnormal RBCs that it removes from the circulation. The spleen may rupture, which can occur with or without trauma.

Which of the five organisms results in the worst malarial infection?

P. falciparum infections are typically more severe than other types of malaria. One reason for this is that P. falciparum can infect all RBCs (leading to very high levels of parasitemia), whereas the other common Plasmodium species infect only either young or old RBCs. In addition, P. falciparum causes the infected RBCs to stick to the walls of capillaries. When this happens, the RBCs block the blood flow in the capillaries and thereby deprive the nearby tissues of O2. If this occurs in the brain, it leads to a life-threatening outcome called cerebral malaria. The RBCs can also clog the capillaries in the placenta of a pregnant woman, leading to devastating outcomes for the developing fetus. P. falciparum infected RBCs stick to the capillaries because the parasite produces a protein that inserts into the membrane of the infected RBCs.

Why does Malaria often relapse?

P. vivax and P. ovale malaria often relapse because the parasites form hypnozoites (dormant forms) that survive in the liver in a treatment-resistant state. Months or even years later, hypnozoites can begin growing in the liver, starting new erythrocytic cycles of infection after the earlier bloodstream infection has been cured.

What protein does P. falciparum produce?

Plasmodium falciparum erythrocyte membrane protein (pfEMP1) is an important virulence factor for P. falciparum. By causing the infected RBCs to stick to the capillaries, pfEMP1 prevents those cells from circulating and being cleared by the spleen. P. falciparum has over 60 different genes that encode pfEMP1, and this antigenic variation allows the parasite to evade the actions of the adaptive immune system. A given infected RBC will only have one variety of pfEMP1 inserted into the membrane, but different infected RBCs could have different varieties. Recent studies suggest that only some of the varieties of pfEMP1 cause cerebral malaria, and others cause the complications in pregnancy

What is the fifth stage of the plasmodium lifecycle?

The mosquito digests the RBCs of an infected person, releasing the gametocytes. Shortly after entering the intestine of the mosquito, and stimulated by the drop in temperature, the male and female gametocytes change in form to become gametes.

Gametocytes

Some merozoites that enter RBCs develop into gametocytes (specialized sexual forms), rather than becoming schizonts. Gametocytes differ from the other forms in both their appearance and susceptibility to antimalarial medications. These sexual forms do not rupture the RBCs. They cannot develop further in the human host and are not important in causing the symptoms of malaria. They are, however, infectious for certain species of Anopheles mosquitoes and are thus ultimately responsible for transmitting malaria from one person to another.

Why are some people resistant to malaria?

Some people of black African heritage are genetically resistant to P. vivax malaria because their RBCs lack an antigen called the Duffy antigen that the parasite uses to enter the RBC. Also, people with certain genetically determined blood diseases such as sickle cell anemia are partially protected against the disease.

What is the first stage of the Plasmodium life-cycle? (Sporozoite)

The Plasmodium life cycle is complex, consisting of a liver stage (exoerythrocytic stage; exo- means "outside of," -erythrocytic refers to red blood cells) and a red blood cell (erythrocytic) stage. The exoerythrocytic stage begins when the infectious form of the protozoan is injected into the human host. This form—called a sporozoite—is carried by the bloodstream to the liver, where it infects hepatocytes (liver cells).

Why do recurrent paroxysms occur?

The characteristic feature of malaria—recurrent paroxysms followed by feeling healthy again—results from the cycle of growth and release of malarial parasites from RBCs. Interestingly, the infections in all the millions of RBCs become nearly synchronous. Thus, all the infected RBCs rupture to release merozoites at about the same time, causing a rapid increase of antigens in the bloodstream that triggers a fever.

What is the eight stage of the plasmodium lifecycle?

The previously formed cyst enlarges as the diploid nucleus undergoes meiosis, dividing asexually into numerous offspring.

What are the signs and symptoms of Malaria?

The first signs and symptoms of malaria are flu-like, with fever, headache, and pain in the joints and muscles. These generally begin about 2 weeks after being bitten by an infected mosquito, but in some cases they start many weeks later.

What is the ninth stage of the plasmodium life cycle?

The previously formed cyst ruptures into the body cavity of the mosquito, releasing sporozoites that then find their way to the mosquito's salivary glands and saliva, from which they may be injected into a new human host.

What is the seventh stage of the plasmodium lifecycle?

The previously formed zygote transforms into a motile form that burrows into the wall of the midgut of the mosquito and forms a cyst

What is the biological vector of malaria?

The reservoirs for malaria are infected mosquitoes and humans. Human-biting mosquito species of the genus Anopheles are biological vectors of malaria, but only the females transmit the disease because males do not feed on blood. Malaria can also be transmitted by blood transfusions or among intravenous drug users who share syringes. Malaria contracted in this manner is easier to treat because it involves only red blood cells and not the liver—only sporozoites from mosquitoes can infect the liver.

What is the second stage of the plasmodium life cycle? (Merozoites)

There, each parasite enlarges and divides asexually, producing thousands of merozoites, which are then released into the bloodstream. Some species of Plasmodium are able to form hypnozoites, which can live in the hepatocytes for years before reproducing to form merozoites. The merozoites released from liver cells infect red blood cells (RBCs), beginning the red blood cell stage of the protozoan's life cycle.

What is the fourth stage of the plasmodium lifecycle

When a mosquito feeds on an infected person's blood, it ingests the infected RBCs.