Pathology L28 - Protozoal Infections Flashcards Preview

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What are Protozoa?

Generally single celled, motile eukaryotes


What is the main aim of taking a history from a traveller who presents with illness?

Find out risk factors, timing of symptoms and most importantly, whether you need to discharge or admit your patient


What are four good points to find out from a travel history?

Any of:

-Geographical region of travel
-Dates of travel
-Activities - hiking/water contact
-Vaccines and Prophylaxis
-Sexual activity
-Proximity to animals
-Needle and blood exposure
-Food and beverages


Why do we want to know where they went travelling if they present to the doctor?

Has a high impact on likelihood of disease:
Sub-saharan Africa - Malaria in 42% of presenting, whereas if you went to Southeast Asia, you're more likely to have Dengue or respiratory illness than Malaria


What are some of the common travellers diseases?

Malaria, Dengue fever, mononucleosis, typhoid


What are some blood parameters that could suggest a worrying problem in a traveller?

Severe anaemia, hepatitis, hypoglycaemia


What are some investigations you would consider in the investigation of a febrile traveller returning from a tropical area?

- Full blood count (FBC)
- Liver function test (LFT)
-Urea, Electrolytes and Creatine (UEC)
-Malaria - thick and thin films
-Coaguation tests


What are some of the known Plasmodium species infectious to man and which regions are they usually found in?

P. falciparum
P. knowlesi
P. vivax
P. malariae
P. ovale

Usually found in tropical and subtropical areas


What is the vector for malaria?

Anopheles mosquito - female only


Give a brief description of the lifecycle of Plasmodium in a mosquito

Mosquito takes blood from infected person, containing gametocytes. These turn into Ookinetes, then Oocysts, which rupture and release sporozoites in the mosquito. When the mosquito takes a blood meal from someone, these sporozoites are injected into the victim.


Give a brief description of the lifecycle of Plasmodium in a human

Sporozoites are released into blood stream when mosquito takes a bite. These move to the liver very quickly - so fast that there is no time to mount an immune response. The sporozoites reproduce in the liver, forming merozoites (which are haploid), contained in vesicles called Schizonts. These then rupture, releasing the merozoites into the blood stream.
Red blood cells become infected by the merozoites, and ring stage trophozoites mature into Schizonts again. These eventually rupture the RBC's, releasing merozoites which go on to infect more RBCs

Note that some of the ring stage trophozoites become gametocytes, which infect a mosquito if they bite the infected human host


Describe an uncomplicated clinical presentation of Malaria

Non specific fever with chills, malaise, cough, anorexia, nausea, diarrhoea and myalgais. A palpable spleen is often found. In less than 0.1% parasitaemia will occur, causing slight changes to blood


Describe a clinical presentation of complicated Malaria

Unable to take oral medications or sit upright
May have an altered conscious state, with renal failure, acidosis, severe anaemia or hypoglycaemia


What are the four classes of anti-malarial drugs?

Quinolone derivatives
Antibiotics like doxycycline
Artemisinin derivatives


What are the most clinically important causes of bacterial gastroenteritis in travellers?

Enterotoxigenic E. coli
Enteroaggregative E.coli
Campylobacter jejuni
Salmonella species
Shigella species


Why would you suspect Entamoeba histolytica in a returned febrile traveller?

If they had bloody diarrhoea - dysentery instead of normal diarrhoea


Which two Entamoeba species are morphologically identical?

histolytica and dispar
histolytica is the only pathogenic one and will show ingested erythrocytes


Describe clinical symptoms of Entamoeba histolytica

Incubation of 2-4 weeks with a subacute onset
The majority of patients are asymptomatic

There are two forms of disease:
Intestinal - will have amoebic dysentery, and fever in 10-40% of patients.
Extra-intestinal - more common in men, will have right upper quadrant (RUQ) pain with a fever, as well as a cough, sweating, anorexia and hiccough. Diarrhoea is only seen in 1/3 cases. Bloods will show white cell count and eosinophilia as raised


How do you diagnose Entamoeba histolytica?

Stool microscopy, antigen test, look at serology


What are some other Protozoa species?

Leishmania, Trypanosoma (causes african sleeping sickness), Sarcocystis, Trichomonas


Where in the human body are Enteric Protozoa found?

Gastrointestinal tract, either as commensals, pathogens or in asymptomatic carriage of pathogen


How are Protozoa transmitted?

Direct, Faecal-Oral, Vector-Borne or Predator-Prey


What do cysts enable Protozoa to do?

Survive in the environment after being shed in the faeces. They are the infective form of the host, from which Trophozoites emerge after the host ingests them


Name two pathogens, and two non-pathogens in the Flagellate classification of Enteric Protoza?

Giardia intestinalis and Dientamoeba fragilis

Chilomastix mesnili, Trichomonas hominis, Retortamonas intestinalis and Enteromonas hominis


What are the four ways enteric protozoa are classified?

1. Flagellates: move with flagella
2. Amoebae: move by pseudopodia
3. Sporozoans: lack specialized movement organelles
4. Ciliates: use rows of cilia to move


What is a pathogen in the Ciliates classification?

Balantidium coli


What are some Sporozoan pathogens?

Sarcocystis spp., Isospora belli and Microsporidium spp


Describe the lifecycle of Entamoeba histolytica

Cyst = infective form
Trophozoite = motile, invasive form

Cysts are ingested in food/water which has been contaminated by faeces. In the small bowel, excystation may occur, releasing trophozoites, which have the potential to invade the colonic mucosa. Dysentery and colitis are a result of the ability of the parasite to invade and damage the colonic mucosa.
Trophozoites can then enter portal circulation and be carried to the liver where they produce abscesses with 'anchovy sauce' pus. Abscesses are also seen in the spleen, lung or brain.

However, trophozoites can also undergo encystation in the large intestine, forming cysts which exit the host in the stool

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