Pathology L28 - Protozoal Infections Flashcards Preview

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Flashcards in Pathology L28 - Protozoal Infections Deck (28):
1

What are Protozoa?

Generally single celled, motile eukaryotes

2

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

3

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
-Accomodation
-Sexual activity
-Proximity to animals
-Needle and blood exposure
-Food and beverages

4

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

5

What are some of the common travellers diseases?

Malaria, Dengue fever, mononucleosis, typhoid

6

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

Severe anaemia, hepatitis, hypoglycaemia

7

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

8

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

9

What is the vector for malaria?

Anopheles mosquito - female only

10

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.

11

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

12

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

13

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

14

What are the four classes of anti-malarial drugs?

Quinolone derivatives
Antibiotics like doxycycline
Anti-folates
Artemisinin derivatives

15

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

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

16

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

If they had bloody diarrhoea - dysentery instead of normal diarrhoea

17

Which two Entamoeba species are morphologically identical?

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

18

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

19

How do you diagnose Entamoeba histolytica?

Stool microscopy, antigen test, look at serology

20

What are some other Protozoa species?

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

21

Where in the human body are Enteric Protozoa found?

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

22

How are Protozoa transmitted?

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

23

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

24

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

Pathogens:
Giardia intestinalis and Dientamoeba fragilis

Non-pathogens:
Chilomastix mesnili, Trichomonas hominis, Retortamonas intestinalis and Enteromonas hominis

25

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

26

What is a pathogen in the Ciliates classification?

Balantidium coli

27

What are some Sporozoan pathogens?

Sarcocystis spp., Isospora belli and Microsporidium spp

28

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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