Parasites Flashcards
define parasite
Organisms which lives upon or within another living organism at whose expense it gains some advantage. (By tradition, the discipline of parasitology is concerned with pathogenic protozoa (unicellular eukaryotes) and pathogenic metazoa (multicellular eukaryotes), including worms and insects)
Explain the importance of parasitic diseases for human health from a global perspective
Parasites are very prevalent on a worldwide basis, they have important impact on morbidity, disability adjusted life years (DALYs) and mortality. Parasites have mechanisms to avoid immune response (encapsulation, intraluminal location, immunosuppression and acquisition of host antigens). Few vaccines are available. More drugs used against parasites differ from those used for bacteria/viruses
Definitive Host:
species in which the parasite undergoes sexual reproduction
Intermediate Host:
species in which asexual reproduction occurs
Explain why the life cycles of parasites are important for the geographic distribution, diagnosis, and control of parasitic diseases
- Most protozoan parasites can replicate in humans. Worms develop, but DO NOT replicate in humans (the worm burden reflects the intensity of exposure to infection by the parasite)
- Ability for parasites to infect specific tissues (tropism) is essential for their life cycles
- The geographic distribution of parasites is often restricted by the availability of host species. Understanding the life cycles -> prevent transmission
Worms (helminths)
a. Roundworms/Nematodes: Ascaris, pinworms, whipworms, hookworms, Strongyloides, Echinococcus, Trichinella
b. Flatworms (Flukes): Schistosomes, lung fluke
c. Tapeworms/Cestodes: beef tapeworm, pork tapeworm, fish tapeworm
Protazoa
a. Amebas: Entamoeba histolytica
b. Flagellates: Giardia, Trichomonas, Trypanosoma, Leishmania
c. Ciliates: Balantidium coli
d. Sporozoa: Cryptosporidium, Cyclospora, Plasmodium, Toxoplasma
e. Microsporidia: Enterocytozoon, Septata
Shistosomiasis is caused by _______ parasites and invasion of the ______ causes _______ within _______ days
- metazoa
- skin
- dermatitis (swimmer’s itch)
- 2-3
The acute phase of shistosomiasis
occurs 4-8 weeks after skin invasion and involves serum-sickness. This phase is coincident with worm maturation in liver
The chronic phase of shistosomiasis
involves granulomatous and fibrotic changes in the liver or bladder as a consequence of host reaction to deposited eggs. The lead to the formation of large numbers of eosinophils that eventually scar the liver or urinary bladder
Malaria is caused by _______ parasites and symptoms are primarily associated with the _______ and ________
- protozoa
- rupture of infected erythrocytes and release of merozoites (mature malaria parasites in the blood)
protozoa typically seen in Malaria
P. falciparum invades erythrocytes of all ages while P. vivax and P. ovale invade only young erythrocytes. P. malariae invades only old erythrocytes
Malaria sx
- Onset of fever begins 36-72 hours after infection
- Anemia results from lysis of RBCs, their phagocytosis, sequestration in the spleen, and depressed bone marrow function
- hemolysis can occur in the extreme (hemoglobiuria – Blackwater fever)
- Jaundice, hypotension, and tachucardia are common symptoms along with fever and hepatosplenomegaly
- P. falciparum has been known to cause vasodilation which causes hypotension leading to inadequate blood supply to major organs. This can result in the multi-organ failure which is the major cause of death in malaria.
immune response to malaria
A person mounts an immune response which make future bouts of the disease less severe. The response involves both T and B cells. Within a few weeks of infection, anti-plasmodium antibodies are produced. However, natural immunity is short lived and continual re-infection is required to maintain it. People who return to endemic areas after long absences are very susceptible to re-infection.
Describe some of the major current challenges to treatment and prevention of schistosomiasis
- public health edu
- of molluscisides and environmental modificiation to control snail populations (intermediate hosts)
- Mass treatment programs with anti-schistosome drugs such as praziquantel and research on improved therapeutics and diagnostics are currently ongoing
- –the worm is nearly impossible to completely eradicate evidenced by the fact that in regions of schistosomiasis control the parasite still continues to cause a low frequency of infection
