Parasites in the tropics Flashcards
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What are NTDs?
Neglected Tropical Diseases. A group of diseases that cause substantial illness for more than one billion people globally
What is the life cycle of Ascaris lumbricoides?
Adults in intestine void eggs into environment. Eggs mature in the soil, require > 2 weeks. Infection occurs orally
What is the treatment for Ascaris lumbricoides? What is less effective about it?
Oral Albendazole, Mebendazole and/or Ivermectin. Drugs don’t change susceptibility to re-infection and only kills adult worms in intestinal lumen
What is the life cycle of Schistosomiasis?
1) Parasitic eggs in contaminated fresh water
2) Larvae called miracidae hatch and seek out a certain snail
3) the miracidae multiply inside the infected snail and produce cercariae larvae
4) The cercariae penetrate human skin transforming into schistosomulae larvae
5) These mature into worms in the blood supply of the liver, intestines and bladder
6) The worms lay thousands of eggs which are then released into the water
What are the effects of Schistosomiasis?
eggs released in the vasculature become lodged in the liver, causing granuloma formation, fibrosis and hepatomegaly
What is the prevention and cure of Schistosomiasis?
The drug praziquantel clears adult parasites but does not prevent re-infection.
Treatment of snail breeding sites and education and infrastructure.
Describe the Malaria Life Cycle inside a human
Hepatic cells in the liver are infected creating mature liver schizont. Merozoite proteins are then released and attack red blood cells in a cycle known as the Erythocytic cycle of malaria. They are then reorientated and a tight junction formed. Invasion using actin-myosin motor occurs followed by the mature invasion which results in a loss of surface proteins. Adhesive knobs line the outside of the RBC and the parasites multiply within. These erythocytic schizont rupture releasing merozoites and turn erythrocytes into gametocytes.
Describe the malaria life cycle within a mosquito
The mosquito drinks blood from an infected host and inherits the gametocyte. This then transforms into a microgamete to macrogamete to zygote which form oocysts on the mosquito midgut. These then burst releasing sporozoites to the salivary gland for more transmission.
What kind of infectious disease is Malaria
It is a protozoal parasite and is vector borne
What are the symptoms cerebral malaria
-high grade fever
-seizure
-coma
-high mortality (25-50%)
-progresses rapidly (24-72 hrs)
-Tends to effect children and travellers
How can sickle cell disease prevent malaria?
Haemoglobin S carries an amino acid that changes the shape, making it protective against severe malaria. If homozygote then suffer sickle cell disease.
How do you prevent malaria?
mosquito nets, insecticide spraying and genetic strategies such as sterilising males. Malaria keeps adapting resistance to drugs
What is a sporozoite vaccine?
Targets the infection site of malaria. Effective with live
irradiated sporozoites, but not practical for mass vaccination
What is a merozoite vaccine?
Targets the merozoite phase of malaria cycle (just before the erythrocytic cycle) Targets proteins required for cell invasion, but :
(a) only “visible” for < 20 mins
(b) highly variable between strains
What is gametocyte vaccine?
Targets the completed infection to prevent transmission.
blocking vaccine :
(a) can target parasites in mosquito, no
selection for antigenic variation;
(b) but does not benefit recipient (“altruistic”)
Why don’t we vaccinate against worms and mosquito carried diseases
- Complex life cycles, with multiple stages in different tissues
- High level of antigenic variation, e.g. blood stage malaria
- Multiple immune evasion strategies (eg sequestration)
- Parasites are able to suppress the immune system
What are some ways for disease to emerge?
-Reappear after a period of absence (Plague)
-Spreads from an isolated population to naive population
-Mutation and adaptation
-Natural disasters
Give 5 examples of bacterial diseases (PSTTC)
Plague, syphilis, Typhus, Typhoid, Cholera
Give 5 examples of viral diseases
Smallpox, Influenza, Polio, HIV, Ebola
How is smallpox transmitted? What are the symptoms?
Person to person via droplets or contaminated bedding/clothes.
Variola virus, eradicated due to vaccination
High fever, rash with fluid-filled pustules
What did Edward Jenner do?
Developed a working vaccine for smallpox using cowpox as it is antigenically similar
How is Cholera transmitted? What are the symptoms?
It is passed on by through contaminated drinking water or food. Larger epidemics have been caused due to faecal contaminated water supplies.
diarrhea, vomiting and shock.
What did John Snow do?
identified the contaminated water pump in London causing the cholera outbreak.
What is the Reproduction Number?
It is an epidemiologic metric used to describe the contagiousness or transmissibility of an infectious agent.
If R0>1 it is expected to continue
If R0<1 it is expected to end
