Febrile returned traveller Flashcards
Why is a history important in these scenarios?
Where have you been to and what did you do there?
- what organisms was the person exposed to
When were you there and when did you start to get sick?
- does the timeline fit with the incubation period? e.g. you’d know if you got dengue or pika before you got back to NZ
The types of mosquitoes that carry disease
Anopheles - forest dwelling, night feeding - not present in the pacific to the east of vanuatu - malaria Aedes - Urban dwelling, dry feeding - widespread but not in NZ - Dengue, zika, yellow fever Females and males feed on nectar, but females need blood meal for egg development
Pathogenesis of malaria
infected female anopheles mosquito feeds on blood and injects saliva containing sporozoites
Sporozoites invade liver cells and replicate
Merozoites are released from the liver and invade erythrocytes
Merozoites replicate in erythrocytes and rupture erythrocytes causing fever
Some merozoites mature into male and female gametocytes which are the source of sexual replication in mosquito salivary gland
Sporozoite
form that infects new host (present in mosquito saliva)
Merozoite
form that results in replication in liver cells
Conditions for malaria diagnosis
residence in a malarious area
Fever, rigors, malaise, headache, coma
Blood film examination
Antigen detection in the blood
About P. falciparum
able to infect any RBC
High parasite load >1% erythrocytes infected
Insertes a protein into a RBC membrane that adheres to CD36 and ICAM1 on capillary membranes
Sequestration of erythrocytes in capillaries esp brain and kidneys
Death from coma and renal failure
About P. vivid
Only infects young RBCs low parasite load <1% Does not cause RBC sequestration No risk of severe disease relapses result from repeated release of liver hypnozoites
P. falciparum treatment
quinine and doxycycline
or artemether and lumefantrine
to kill merozoites in erythrocytes
P. viviax treatment
chloroquine
to kill mosquitoes in erythrocytes
then primaquine to kill hypnozoites in liver
Malaria prevention
avoid malarious areas mosquito control Bed nets, long sleeved shirts, long pants etc Insect repellant, doxycycline, mefloquine, other drugs
About dengue fever
Widespread in tropics
Dengue virus (an RNA virus)
transmitted my aides aegypti mosquitoes
multiplies in macrophages
Incubation pared of 2-7 days
“breakbone fever” - fever, malaise, headache, myalgia, bone pain. Recovery after about 1 week
Demonstration of dengue virus antigens in the blood
No effective treatment. vaccines under development
Salmonellae enteritidis
acquired from animals and birds (not humans)
infects colonic mucosa
Causes colitis
Common cause of gastroenteritis in NZ and overseas
Salmonella typhi
acquired from people not animals
Infects peyers patches in terminal ileum
Can cause bacteremia and septicaemia
common cause of persisitnant fever in travellers
approx 10% of people who contract it will die from:
- examination from gut bleeding
- peritonitis from leaving of bacteria through hole in terminal ilium to gut
Typhoid / Enteric fever
Bacteraemic illness arising from intracellular infection in macrophages in peyers patches
Fever, rigors, sweats, cough, headache, confusion, NOT usually diarrhoea, may have constipation
Risk of perforation of peyers patches resulting in peritonitis, risk of erosion of ill blood vessels resulting in catastrophic intestinal bleeding
Minority of infected have long term gall bladder colonisation and excrete S. type in faeces - source of infection for others
