Lecture 37: Febrile Returned Traveller Flashcards
Where can patients acquire new infections from overseas?
- Contaminated air: influenza, tuberculosis
- Contaminated water and food: salmonella typhi/enteridis, campylobacter jejuni
- large proportion of the reason
- Infected vectors: malaria (mosquitos), dengue from environments different to NZ
- Infected people: HIV, syphilis
A history is extremely important in an infcted traveller! What do you need to ask?
- Where have you been and what did you do there?
- what organisms was the person exposed to?
- When were you ther and when did you start to get sick?
-
does the timeline fit with incubation period:
- influenza = few days
- tuberculosis = months (cough)
- GI tract bugs = days (poops)
- malaria = weeks
- Dengue = days
-
does the timeline fit with incubation period:
Why do we NOT transmit malaria in NZ?
-
Anopheles mosquitos are what transmit malaria! These are not present in the Pacific to the east of Vanuatu (NOT IN NZ). Forest dwelling and night feeding.
- in Papua New Guinea, Africavanuatu, but not Fiji etc
- Culex: “only” species present in NZ, spread worldwide
-
Aedes: urban dwelling, day feeding. Widespread but not in NZ, for dengue, Zika, yellow fever
-
females need blood
Whars the most important illness to consider in travellers and what causes it?
Malaria
- Plasmodium falciparum (potentially fatal)
- Plasmodium vivax (benign)
Complex single cell with cell structure. 1 and 2 are very similar to the ones that infect birds etc. Acquired from mosquito transmission from person to person!
plasmodium ovale and plasmodium malariae are rarer forms
What do the terms Sporozoite and Merozoite mean?
Sporozoite: form that infecs new host (present in mosquito saliva)
Merozoite: form that results from replication in liver cells (merogeny = shizogeny), released from the liver and replicates in RBCs, eventually bursting them
With Malaria, why do we not have symptoms for ten days, and then why do we get ycclical fevers?
- No symptoms for the 10 days the malaria is in the liver
- Once in RBC, the bursting of RBCs will cause fever
- Experimental maralria shows a more defined
Describe how Plasmodium falciparuma and vivax infected people
- Infected female Anopheles mosquito feeds on blood and injects saliva containing sporozoites
- the saliva contains the anti-coagulant (that makes you itchy) and is what is infectious
- Sporozoites leave BS and invade liver cells and replicate
- happens within minutes, completely asymptomatic
- Merozoites are released from liver and invade erythrocytes
- always <10days for the amount to reach a point that it ‘bursts’ from the liver. In the RBC they digest the haemagobin
- Merozoites replicate in erythrocytes and rupture them, causing fever and immune response
- lots of people can have malaria in their blood at a low level, controlled but the patient will be slightly anaemic. Still infectious and can further spread the disease
- Some merozoites mature into male and female gametocytes which are the source of sexual replication in mosquito salivary gland
What do you need to diagnose Malaria?
- Residence in a malarious area
- Fever, rigors, malaise, headache, coma
- Blood film examination
- 2 blood samples enough to diagnose almost everyone with Malaria
- microscopy to examine blood for merozoites in RBCs, and estimate the % of RBC that contain merozoites
- <1% usually, .2% severe, >5% very severe
- can determine species by appearance of merozoites
- Antigen detection in blood
Why is P. Falciparum so dangerous?
-
Able to infect any RBC
- p. vivax can only infect young recentky release from bone marrow RBCs
- High parasite load >1% RBC infected
- Inserts a protein into the RBC mebranes that adheres to CD36 and ICAM1 on capillary membranes
- Sequestration of RBC in capillaries
- sludge up and block flow here (esp. brain and kidneys)
- Death from coma and renal failure whilst febrile and shivering
Why is P. Vivax so benign?
- Only infects young RBCs
- Low parasite load <1%
- Doesn’t cause RBC sequestration
- No risk of severe disease
Relapses result from repeated release of some liver hyponozoites (sleeping parasites) these can stay there for months/years eventually activating in small amounts over time!
What’s the difference in
Salmonella enteridis
Salmonella typhi
*both are very similar to E.coli
Salmonella enteridis:
- Acquired from animals and birds (not humans)
- infects colonic mucosa
- causes colitis
- common cause of “gastroenteritis” in NZ and overseas, not that common overal
Salmonella typhi (typhoid fever)
- Acquired from people (not animals)
- infects macrophages peyers patches →into terminal ileum that are taking it up for IS sampling
- erosion of BV in PP and haemorrage into gut, dying from Blood loss
- full perforation into TI
- Cause bacteraemia and septicaemia from poo
- Common cause of persistant fever in travellers and death of
Malarial Treatment for P.falciparum and P. vivax
P. falciparum:
- quinine and doxycycline
- or artemether and luefantrine
- To kill merozoites in erythrocytes
P. vivax
- chloroquine
- to kill merozoites in erythrocytes
- then primaquine to kill hyponozoites in the liver
Malarial Prevention
- Avoid malarious areas
- Mosquito control
- Bed nets, long-sleeved shirts, long pants etc
- insect repellant
- Drugs: doxycycline, mefloquine
Dengue Fever
- Widespread in tropics
- Dengue Virus (RNA virus)
- Transmitted by Aedes aegypti mosquitos
- multiples in macrophages
- Incubation period of 2-7 days
- “breakbone fever”- fever, malaise, headache, myalgia, bone pain, recovery after ~1 week, no significant unless repeated epsiodes
- Demonstration of dengue virus antigens in blood
- No effective treatment. Vaccines under development.
What are the 2 organisms that cause Salmonellae?
- Salmonella enteridis
- Salmonella typhi
