Flashcards in Pathology L28 - Protozoal Infections Deck (28)
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?
-Geographical region of travel
-Dates of travel
-Activities - hiking/water contact
-Vaccines and Prophylaxis
-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
What are some of the known Plasmodium species infectious to man and which regions are they usually found in?
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?
Antibiotics like doxycycline
What are the most clinically important causes of bacterial gastroenteritis in travellers?
Enterotoxigenic E. coli
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?
What are some Sporozoan pathogens?
Sarcocystis spp., Isospora belli and Microsporidium spp