Exam 4 Flashcards
Plasmodium spp.: Form and Function
Stages
Sporozoite: daughter cell resulting from sporogony
Trophozoite: active, feeding stage of a protozoan, in contrast to a cyst
Schizogony: form of asexual reproduction in which multiple mitoses occur, followed by simultaneous cytokineses, resulting in many daughter cells at once
Schizont: in schizogony when nuclear divisions have occurred but not cytokinesis
Merozoite: daughter cell resulting from schizogony
Plasmodiidae : Plasmodium spp.
Processes
Gametogony: process by which gametes are produced in protozoa; occurs when merozoites entering red blood cells transform into gametocytes
- macrogametocyte (egg): cell that gives rise to macrogamete
- microgametocyte (sperm): cell that gives rise to microgametes
- microgamete fertilizes macrogamete
- ookinete: motile, elongated zygote
Sporogony: multiple fission of a zygote
- sporogonous phase begins when ookinete begins to develop
oocyst:
- cystic form resulting from sporogony
- gives rise to many sporozoites
Plasmodiidae : Plasmodium spp.
- female anopheles mosquito bites infected human and ingests blood
- RBC contains either female or male gametocyte
(1) microgametocyte produces 8 microgametes; exflagellation
(2) macrogametocyte matures to macrogamete - zygote elongates to form ookinete, and penetrates mosquitoes gut
- rounds up and transforms to oocyst; produces numerous haploid sporozoites
- sporozoites break out and wander to mosquitoes salivary glands
- sporozoites injected into human bloodstream via mosquito blood meal
- sporozoites invade parenchymal cells of liver (exoerythrocytic schizogony), asexual multiplication occurs (schizogony)
- tiny merozoites rupture out of each schizont from liver cell and invade RBC
- within RBC erythrocytic schizogony occurs; RBC ruptures releasing merozoites
- merozoites can infect new RBCs
- after patient becomes clinically ill merozoites invade RBC and give rise to gametocytes
- gametocytes continue to circulate in blood stream with RBCs
- ingested by Anopheles mosquito, gametocytes transform into gametes (gametogony), followed by sexual fusion (drop in temperature)
- finally, subsequent development into sporozoites (sporogony) in mosquito
Plasmodiidae : Plasmodium spp.
Different symptoms
- Quotidian malaria: 24 hour fever cycle (erythrocytic cycle); overlapping infections
- Tertian malaria: 48 hour fever cycle
- Quartan malaria: 72 hour fever cycle (P. malariae)
- Febrile: having or showing signs of fever
- Paroxysms: rapid onset or return of symptoms or increased intensity of symptoms
- Relapse: reappearance of symptoms when dormant hypnozoites in liver activate (P. vivax and P. ovali)
- Recrudescence: reappearance of the disease after remission; sequestration
- Parasitemia: presence of parasites in the circulating blood
Plasmodium vivax (benign tertian malaria): 48 hour fever cycle
- most vivax malaria in Asia, Latin America; common in North Africa, but drops off in tropical Africa
- accounts for about 43% of all malaria cases
- invades young erythrocytes with Duffy blood groups; 2 codominant alleles & a third
- no Duffy blood group receptors on RBC, no infection
- hypnozoites in liver can cause relapse up to 8 years after initial infection
- oocyst produces up to 10,000 sporozoites
- 10,000 merozoites released from liver cell
- erythrocytic schizogony yields on average 16 merozoites
Plasmodium falciparum (malignant tertian malaria): 48 hour fever cycle
Plasmodium falciparum (malignant tertian malaria): 48 hour fever cycle
- most virulent of Plasmodium spp. in humans; always serious
- worldwide in tropics and subtropics, accounts for about 50% of al malaria cases
-can invade RBCs by at least 4different pathways, unlike P. vivax - sickle cell trait confers resistance to P. falciparum
- higher levels of parasitemia; more than 65% of RBCs; 25% usualy fatal
- trophozoite produces proteins, get deposited on RBC surface (cytoadherence)
- sequestration occurs along venular endothelium and other RBCs (cerebral malaria)
- 30,000 merozoites released from liver cel
- erythrocytic schizogony yields on average 22 merozoites
-recrudescence of disease may folow remission up to 3years
Plasmodium malariae (quartan malaria): 72 hour fever cycle
- found worldwide ni tropics and subtropics, but distribution not continuous
- accounts for 7% of malaria cases
- merozoites can only invade aging RBCs, soon to be removed from circulation - recrudescence up to 53 years after initial infection
- most important cause of transfusion malaria because of recrudescence
- erythrocytic schizogony yields on average 8 merozoites
Plasmodium ovale (mild tertian malaria): 48 hour fever cycle
- found mostly in Africa (especially West Africa) and the islands of the western Pacific
- rarest of the 4 malaria parasites in humans
- difficult to diagnose because of similarity to P. vivax
- hypnozoites ni liver can cause relapse up to 4 years after initial infection
- erythrocytic schizogony yields on average 8 merozoites
2 general factors leading to most major clinical manifestations
(1) host inflammatory response producing characteristic chills and fever, etc.
- single acute day of fever requires approx. 5,000 calories = 2 days hard manual labor
(2) anemia, arising from the enormous destruction of RBCs (iron bound in hemozoin)
Plasmodiidae : Plasmodium spp.
Pathology
- chills and fever, anemia, splenomegaly (enlargement of the spleen), and often fatal complications
- timing of paroxysms of fever follows maturation of each generation of merozoites
- entire paroxysm is 6 to 10 hours; patient sleeps well until next episode
Cold Stage
- typical atack begins with feeling of intense cold as hypothalamus si activated
- temperature rises rapidly to 104’F to 106°F
- teeth chatter and intense shivering; nausea and vomiting are usual
Hot Stage
- hot stage begins 30 min to 1hour later, with intense heat and headache
- often a mild delirium stage lasts for several hours
Sweating Stage
- copious perspiration signals the end of the hot stage
- temp drops back to normal in 2 to 3 hours
Plasmodiidae : Plasmodium spp
Epidemiology
- reservoir; tolerant individuals and primates
- vector; anopheline mosquitoes
- human to human transmission via blood transfusion or sharing needles
- rare, infection of newborn from an infected mother
Babesiidae : Babesia microti
- in US occurs ni parts of Northeast and upper Midwest; peaks during warm months
- definitive hosts is blacklegged tick (Ixodes scapularis)
- intermediate hosts is primarily white-footed mouse; zoonosis
- sporozoites exit salivary glands of infected tick during blood meal
- sporozoites enter white-footed mouse RBC and forms trophozoite
- erythrocytic schizogony gives rise ot merozoites; cycle repeats
- some intraerythrocytic parasites wil form gametocytes; then ingested by tick
- fertilization between male and female gamete, called ray bodies, occurs ni tick gut
- the zygote, called a kinete, migrates to salivary glands
- kinete develops into sporoblast that produce sporozoites
Babesiidae : Babesia microti
Pathology
- healthy people usually asymptomatic; some experience “flu-like” symptoms
- Babesiosis can result in severe pathogenicity in the following people:
- splenectomized
- compromised immune system (Ex. Cancer, lymphoma, or AIDS)
- elderly
- complications include severe hemolytic anemia (hemolysis)
Babesiidae : Babesia microti
Epidemiology
- avoiding exposure ot tick infested habitats
- use repellent on skin and clothing
- limit the amount of skin exposure
- walk in the center of hiking trails
Cryptosporidiidae : Cryptosporidium parvum
- worldwide distribution; opportunistic infection
- low host specificity (Ex. cattle, sheep, human, etc.)
- occurs mainly in brush border of epithelial cells of intestine and respiratory tract
- infective stage is oocysts containing 4 sporozoites
- ingested oocyst excysts in host intestine and sporozoites are released
- sporozoites parasitize epithelial cells of GI tract or respiratory tract
- asexual reproduction (schizogony)
- (gametogony) produces microgamont and macrogamonts
- microgamete fertilizes macrogamete and oocysts develop; sporulates in host
- thick-walled oocyst excreted in feces; thin-walled oocyst involved in autoinfection
