Lecture 28

Question 1

What is a protozoa?

Answer 1

A single celled eukaryote which may be motile

Question 2

What are the common protozoa and what disease do they cause?

Answer 2

Plasmodium falciparum-malaria
Toxoplasma gondii- toxoplasmosis
Giardia Lamblia- giardiasis
Trichomonas vaginalis trichomoniasis
Entamoeba Histolytica- amoebiasis
Leishmania Donovani- Leishmaniasis

Question 3

How does Giardia Lamblia infect humans?

Answer 3

Initially infects the gut of many animals, is then excreted and can contaminate the water through formation of a cyst wall allowing it to survive when not in a host, when this water is drunk by humans it can infect the gut lining under the mucosal layer

Question 4

What are the symptoms of giardiasis and how are they caused?

Answer 4

Mostly people with this infection do not feel unwell, but can produce a watery diarrhoea
This can occurs as the small intestine does not absorb nutrients properly, this occurs as the parasite eats the microvilli of the cell but does not kill or invade the cell

Question 5

How is giardiasis diagnosed and treated?

Answer 5

They are diagnosed via cysts seen in the faeces,
Treated with anaerobic antibiotics
Metronidazole,
500mg TDS orally with a 7 day course

Question 6

How does toxoplasma gondii cause infection in humans?

Answer 6

Initially infects the gut of cat species , oocysts are then excreted by the cat, these are ingested resulting in infection in the tissue of the human , the pathogen then spreads to the blood and can return to cats through cat eating meat with the parasite (typically birds, mice etc)

Question 7

What is the epidemiology of toxoplasmosis?

Answer 7

Infection is in approx. 30% of the population
typically gained during childhood, only very minor symptoms are experienced with a persistent lifelong infection being developed with reactivation only occuring in unusual circumstances

Question 8

What are the unusual circumstances in which toxoplasma gondii can causes severe infection?

Answer 8

Immunosuppression such as in HIV/AIDS

Passing on from the mother to the foetus if the infection is active as it can be passed via the placenta

Question 9

How is toxoplasmosis diagnosed?

Answer 9

Serology IgM= positive acute infection
IgG positive= chronic infection
PCR in CSF to confirm cause of brain abscesses
Radiology
Ophthalmoscopy

Question 10

How is toxoplasmosis treated?

Answer 10

Typically no treatment is required but immunosuppressed individuals are treated with sulphadiazine and pyramethamine for 6 weeks
Some countries will also provide treatment for acute infection in pregnant womens

Question 11

What are the different types of malaria?

Answer 11

Plasmodium falciparum which can potentially be fatal
Plasmodium vivax
Also the rare forms of plasmodium ovale, plasmodium malariae

Question 12

What us the common pathway of infection for both Plasmodium falciparum and Plasmodium vivax?

Answer 12

An anopheles mosquite feeds on blood but injects saliva containing sporozoites
These then invade the liver and replicate
Merozoites are released by the liver and infect red blood cells where they replicate inducing lysis and fever
Some of these will form the male and female gametes which will undergo sexual replication in the mosquitos salivary gland once taken up again via another mosquite fedding

Question 13

What is the key type of mosquito in malaria?

Answer 13

Anopheles mosquito

Question 14

How does malaira affect the thermoregulation of the body?

Answer 14

There are fits of fevere, shivering and sweating which typically coincide with when the red blood cells are being lysed

Question 15

How is malaria diagnosed?

Answer 15

Residence in a malarious area

Blood film examinaton or antigen detection kit

Question 16

What are the symptoms of a malaria infection?

Answer 16

Fever, rigors, malaise, headaches, coma

Question 17

What is the difference between P.Falciparum and P.vivax?

Answer 17

P.falciparum infects any red blood cell leading to a high parasite load and the blocking of capillaries caused by infected red blood cells can induce serious symptoms like coma
P.Vivax only infects young red blood cells resulting in a lower parasite load and therefore less serious disease, it does however have relapses as it maintains a population of hypnozoites in liver cells

Question 18

How is malaria treated?

Answer 18

P.Falciparum= quinine and doxycycline which kills merozoites in red blood cells
P.Vivax= chloroquine to kill merozoites in red blood cells and primaquine to kill hypnozoites

Question 19

How can malaria be prevented?

Answer 19

Avoiding malarious areas
Mosquito control
Bed nets, long sleeved shirts, long pants etc
Insect repellent
Doxycyline,mefloquine, other drugs