Lecture 35: Fever in travellers Flashcards
What are some common infections obtained from contaminated air?
Influenza
Tuberculosis
What are some common infections obtained from contaminated water and food?
Salmonella typhi
Salmonella enteritidis
Campylobacter jejuni
Hepatitis A virus
What are some common infections from infected vectors?
Malaria
Dengue
What taking a history from a traveller with a fever what are some important questions?
Where, when, what, does?
Where have you been 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 timeline fit the incubation period?
What are the incubation periods of some common infections? - that dont take days…
TB - Months
Salmonella typhi - Days to weeks
Hep A - Weeks
Malaria - Weeks
Influenza, salmonella enteriditis, campylobacter jejuni, dengue - all take days
What are the pathogens that cause malaria?
Plasmodium falciparum - Potentially fatal
Plasmodium vivax - Relatively benign
There are others but rare.
Why do mosquitos matter with malaria?
Only the anopheles mosquito is capable for transmitting plasmodium falciparum
Describe the replication cycle of plasmodium falciparum and vivax?
- Infected female anopheles mosquito feeds on blood and injects saliva containing sporozoites
- Sporozoites invade liver cells and replicate
- Merozoites are released from liver and invade erythrocytes (Activating immune system)
- Merozoites replicate in erythrocytes and rupture erythrocytes causing fever
- Some merozoites mature into male or female gamecytes which are the source of sexual replication in mosquito salivary gland (i.e are taken back up by subsequent mosquito)
Whats the difference between the sporozoite and merozoite?
Sporozoite: Form that infects new host (present in mosquito saliva)
Merozoite: Form that results from replication in liver cells, released from liver and replicate in RBC
What are the relative proportions of pathogen in the plasmodium reproductive cycle:
~10 sporozoites infected per bite
~10 liver cells invaded
~10^5-6 merozoites released to infect RBC
~10 merozoites released from each infected RBC
What are the signs/symptoms/history thats used to diagnose malaria?
- Residence in a malarious area
- Fever, rigors, malaise, headache, coma
- Blood film examination
- Antigen detection in blood
Whats the complications of P. falciparum infection?
- Able to infect any RBC, and has a high parasite load <1% RBC infected
- Inserts a protein into RBC membranes that adheres to CD36 and ICAM1 on capillary membranes THUS leading to sequestering of RBC in cap. esp. kidneys and brain
= Death from coma or renal failure because vessels become occluded.
Whats the complications of P. vivax infection?
- Only infects young RBCs
- Low parasite load
- Does not cause RBC sequestration
- No risk of severe disease
Relapse can occur from repeated release of liver hypnozoites
Whats the treatment for P. falciparum?
- Quinine and doxycycline
or
Artemether and lumefantrine
= To kill merozoites in erythrocytes
Whats the treatment for P. vivax?
- Chloroquine
= TO kill merozoites in RBC
Then primaquine to kill hyponozoites in liver
How can malaria be prevented?
- Avoid malarious areas
- Mosquito control; Bed nets, long sleeves etc, insect repellant
- Doxycycline, mefloquine as prophylactics
What is denque fever? how is it spread? where is it found?
- RNA virus
- Transmitted by Aedes moquito
- Found in tropics
Describe the replication process of dengue fever in the body and symptoms:
- Multiplies in macrophages
- Incubation period of 2-7 days
- “breakbone fever” ; Fever, malaise, headache, myalgia, bone pain (recovery ~ 1 week).
How is dengue fever detected and treated?
- Virus antigens in blood
- No effective treatment
What are the two most common types of salmonella we are concerned with?
Salmonella enteriditis
Salmonella typhi
Salmonella enteriditis:
- Where from
- Where it infects
- What it causes
- Acquired from animals and birds
- Infectes colonic mucosa
- Causes colitis
- Common cause of gastro
Salmonella typhi:
- Where from
- Where it infects
- What it causes
- Acquired from people (must be in large numbers)
- Infects peyers patches in terminal ilium
- Causes bacteraemia and septiceamia
- Common cause of persistent fever in travellers
What is typhoid fever and what are the symptoms and risks?
Typhoid fever = enteric fever
Symptoms:
- Fever, rigors, sweats, cough, headache, confusion, Not usually diarrhoea
Risks:
- Perforation of peyers patches -> peritonitis
- Risk of erosion of ileal blood vessels resulting in catastrophic intestinal bleeding
- ~10% mortality without treatment
What happens to a minority of people infected with salmonella typhi?
Minority of infected people have long term gall bladder colonisation and excrete S. typhi in faeces - source of infection for others
How is typhoid diagnosed and treated?
Blood cultures: May be required before the organism is isolated
Treatment: Ceftriaxone IV or Ciproflaxacin O
Vaccine ~70% effective
How is Hep A spread, what are its symptoms and is there a treatment?
Hep A: RNA virus only infects humans, associated with poor sanitation.
- Ingested virus infects hepatocytes and is excreted in faeces
- Causes Hepatitis: Jaundice, malaise, anorexia, fever
Recovery: Elimination of infection, no treatments, but excellent vaccine
What is the major cause of travellers diarrhoea and how does it cause illness?
Enterotoxigenic E. Coli
- Produce toxins which act on small bowel; Abdo cramp, diarrhoea
- 1-5 days
- Antibiotics give minor reduction in incidence and severity
