Pathogenic Protozoa II Flashcards
In the mitotic cycle, trophozoites grow and undergo multiple nuclear division cycles without cytokinesis to produce large multinucleate forms called
Schizonts
These then cleave (schizogeny) to produce multiple uninucleate infective progeny cells, released by
Host cell lysis
In apicomplexa, what are
- ) Rapidly-multiplying trophozoites
- ) Slow-multiplying trophozoites
- ) Semi-dormant trophozoites
- ) Tachyzoites
- ) Bradyzoites
- ) Hypnozoites
Kills more people than any infectious disease
Malaria
Malaria plasmodia are transferred to humans by which three mechanisms?
- ) Bite of female anopheles mosquito
- ) Blood transfusion
- ) Maternal-fetal route
What are the 4 species of plasmodium that infect humans with malaria?
- ) Falciparum
- ) Malariae
- ) Ovale
- ) Vivax
Monkey parasite recently shown to infect humans
Plasmodium knowlesi
Found in all subtropical and tropical areas of the world except deserts, usually found below 1800m elevation
Malaria
Was once endemic in the eastern and central United States, but extensive mosquito control efforts have eradicated it as an epidemic disease
Malaria
What are the three diseases that give heterozygotes immunity to malaria
- ) G-6-P deficiency
- )Thalassemia
- ) Sickle-cell anemia
In mammals plasmodia first replicate in the liver. This is followed by multiplication and then gamete formation in
Red cells
After transmission to humans, plasmodia first infect and multiply in
Liver cells
The form of plasmodium most infectious to humans is the
Sporozoite
Each infected liver cell releases thousands of merozoites into the bloodstream and these infect and multiply in
Erythrocytes
Are not infectious for hepatocytes so there is no re-infection of the liver
Merozoites
Merozoites are infectious for
Erythrocytes
The only part of plasmodium that is infection to mosquitos is the
Gametocytes
Microgametocytes produce flagella (exflagellation) and produce
Motile gametes
In the gut these fertilize the larger macrogametocytes to form motile zygotes (ookinetes) which invade the gut wall and
Encyst (Oocysts)
Oocysts then undergo sporogeny: they first grow and then divide to produce multiple sporozoites (the infectious form for mammals), which move to the mosquitos
Salivary glands
Undergo only a single cycle of replication in the liver
P. falciparum and P. malariae
Remain in liver as dormant hypnozoites which can persist long after erythrocytic forms have disappeared
P. vivax and P. ovale
Can produce recrudescent infection of the liver and bloodstream for several years after the initial infection has lapsed
P. vivax and P. ovale
By the time symptoms appear, P. falciparum and P. malariae have no liver stage, and therapy can be targeted to the bloodstream forms alone. This is called
Suppressive cure
The other species require therapy sufficient not only to remove bloodstream infection but to eradicate slow-replicating hypnozoites from the liver and prevent relapse. This is called
Radical Cure
In the erythrocytic cycle, a merozoite infects an erythrocyte and becomes a
Vacuolated ring form
This enlarges [trophozoite], undergoes nuclear division [developing schizont] and finally cleaves [schizont] to produce numerous new
Merozoites
Plasmodia degrade and catabolize hemoglobin. The released hematin precipitates to form granules of
Malaria pigment
In P. vivax/ovale infections the granules are coarse and known as
Shuffner’s dots
After erythrocyte lysis this pigment is phagocytosed by reticuloendothelial cells and produces
Gray/black tissue discoloration
Malaria transmission is followed by an incubation or prepatent period, before the onset of symptoms. This period lasts
1-4 weeks
Cycles of erythrocyte infection and release of merozoites may become highly synchronized. Waves of erythrocyte destruction produce waves of
Chills and fever
-Then sweats as fever relapses
Malaria diagnosis is by
Blood smear
Bouts of fever are often accompanied by headache, nausea/vomiting, and malaise. As disease continues, we see anemia, cachexia, and
Enlargement of liver and spleen
In severe cases, especially of falciparum malaria, there may be extensive hemolysis with hemoglobin in the urine. This is called
Blackwater fever
In falciparum malaria infected red cells at post-ring stages adhere to
Endothelium
Are both involved in recovery from anemia
Humoral and cell-mediated immunity
Produces some degree of immunosuppression, as measured by decreased response to vaccine antigens
Malaria
There is also polyclonal B cell activation. These can interact with latent infection with Epstein-Barr virus to promote development of the B-cell tumor known as
Burkitt’s lymphoma
Bloodstream infection with a given strain of Plasmodium produces a state of low level immunity to
Antigenically similar strains (premunition)
Requires the continued presence of plasmodia; once bloodstream infection lapses, immunity wanes and re-infection can occur
Premunition
The origin of the gin and tonic because the drink was used to mask the taste of
-Could cure malaria
Quinine
Act by inhibiting the enzyme heme polymerase
-Still used in the treatment of CNS malaria
Quinine
Contain a non-photosynthetic plastid with a genome like that of chloroplasts
Plasmodia
What are the three genera of Microsporidia that infect humans?
Encephalitozoon, Enterocytozoon, and Nosemia
Transmission is via contaminated food or water. Life cycle is similar to that of Apicomplexa
Microsporidia
Microsporidia multiply intracellularly. The infectious form is the
Spore
When a spore contacts a host cell the filament everts and pierces the host-cell plasma membrane. Osmotic flow of water into the spore forces the cytoplasm of the parasite through the polar filament and into the
Cytosol of host cell
Have the smallest genomes of any eukaryotes, about 2 mb, smaller than many bacteria
Microsporidia
Mostly intestinal, eye, or systemic infections, although any tissue can become infected
Microsporidia Infection
