The Tropics Flashcards
1
Q
General rules re fevers in the returning traveller and country/region of travel, incubation period, activities and most common causes of fever in the returning traveller
A
Region
- Malaria → Sub-Saharan Africa
- Dengue → SEA, Latin America
- Enteric fever → South Central Asia
Incubation period
- <10 days → dengue, influenza, zika
- 10-21 days → malaria, viral haemorrhagic fever, typhoid
- >21 days → malaria, hepatitis, TB
Activities
- Fresh water/white water rafting → schistosomiasis, leptospirosis
- Caves → histoplasmosis
- Contact with birds/animals → avian influenza, q fever, rabies
2
Q
Physical findings as clues in fever in the returning traveller
A
- Eschar → rickettsia (e.g African tick bite fever), plague, trpanosomiasis
- Jaundice → hepatitis, malaria, yellow fever, leptospirosis, typhoid, fascioliasis, ALA
- Lymphadenopathy → dengue, rickettsia, brucellosis, HIV, syphilis, visceral leishmaniiasis, TB, trypanosomiasis, filariasis, monkey pox. Malaria not associated with lymphadenopathy
- Conjunctivitis → zika, measles
- Conjunctival suffision and subconjunctival haemorrhage → leptospirosis
3
Q
Fever in the returning traveller with rash → potential differentials
A
4
Q
Investigations for fever in the returning traveller
A
5
Q
How many thick and thin films required to rule out malaria
A
- 3
- If initial smear negative and malaria suspected - additional smears should be testing every 12-24 hours for a total of three sets before ruling out malaria
6
Q
Notes on amoebiasis
A
Amoeibic liver abscess
- 10x more common in men than women
- Diarrhoea only present at time of innoculation - stool microscopy for E. histolytica not sensitive
- Radiological features can persist for up to 2 years following erradication therapy
7
Q
Malaria basic facts and epidemiology
A
- Parasitic amoeba that infeects erythrocytes
- Plasmodium falciparum, P vivax, P malariae, P knowlesi
- Incidence falling
- Most cases in sub-Saharan Africa but transmission intensity also very high in some Pacific countries
8
Q
Life cycle of the Malaria parasite
A
- Female Anopheles mosquito injects malaria parasites into the bloodstream by biting human → at this stage the parasite is called a sporazoite
- Sporazoites move to the liver → invade liver cells → replicate into mature Schizont (usually asymptomatic at this stage)
- Liver schizonts rupture after 6-30 days → releases “daughter” merozoites which can infect red cells → replicate in red cells forming new schizonts and rupturing in infected red cells → develop symptoms when red cells infected
- Some merozoites differentiate into male or female gametocytes. If these gametocytes are ingested by a female during feeding they can then complete their life cycle in the gut before migrating back to the salivary glands
9
Q
Clinical features malaria infection
A
- Suspect in anyone with a fever >37.5 who has recently visited a malaria endemic area
- Clinical features limited value in distinguishing malaria from non-malarial causes of fever
- Patients who have had repeated malaria exposure through living in an endemic area will have partial immunity and can have asymptomatic paristaemia → there is no test that can differentiate symptomatic from asymptomatic parasitaemia
10
Q
Diagnosis of malaria
A
- Clues on CBC → thrombocytopaenia non specific
- Microscopy → thick films (screening) and thin films (density and speciation) → in patients with a high clinical suspicion, repeat testing for 3 days required before excluding disease
- Antigen based rapid diagnostic tests (RDTs)
- Some genus specific, and some able to distinguish P. falciparum from P. vivax
- Unable to determine parasite density
- RDTs can stay positive for several weeks after successful treatment
- Increases reports of mutations in antigen encoding genes
11
Q
Notes on severe anaemia
A
Features
- Anaemia
- Jaundice
- Seizures
- Kidney injury
- Shock
- Impaired consciousness
Causes
Most P. falciparum, P vivax and P knowlesi also cause severe disease
Medical emergency
Management
Artemisinin combination drugs clear parasitaemia faster than quinine and reduce mortality
Supportive care → hypoglycaemia common, careful treatment of shock as excess IV fluids → pulmonary and cerebral oedema
12
Q
Notes on P. knowlesi
A
- Human infection typically acquired in forest areas or forest-fringe areas in SE Asia
- Can cause uncomplicated infection and severe disease
- Jaundice, AKI, respiratory distress and shock
- Coma and seizures rare
- Diagnosis requires microscopy
- Parasite density lower than other species for severity of disease → beware false negative slides
- Requires confirmatory PCR for species
- RDTs have poor sensitivity
13
Q
Notes on artemisinin resistance in malaria
A
- Increasingly common in SEA - Thai-Cambodian border
- Artemether monotherapy driven mutations in Kelch 13 gene
- Clonal spread through SEA, also development of parallel resistance
- Resistance = slower parasite clearance → requires prolonged courses of treatment (not necessarily associated with treatment failure)
- Avoid artemether monotherapy
14
Q
Notes on P. vivax/P. ovale malaria and erradication of hypnozoites
A
- Life cycle of both contain dormant hypnozoites → can cause relapse months to years after initial infection
- Should consider erradication in all patients with P. vivax or ovale → primaquine 7-14 days (must have normal G6PD or → life threatening haemolysis)
- New data on tafenoquine as single dose, also need G6PD assay showing >70% function
15
Q
Notes on malaria vaccine
A
- Recombinant fusion protein from P.falciparum sporozoite and an antigen derived from the Hepatitis B surface antigen → roll out 2022 Malaria endemic countries
