S8: travel-related infections & COVID-19

Question 1

List the 5 main species of Plasmodium (in order of most common organism)

Answer 1

Falciparum (most from Africa)
Vivax (most from India)
Ovale (India) 
Malariae 
Knowlesli

Question 2

Describe the signs & symptoms of malaria

Answer 2

Symptoms: fever, headache, vomiting, diarrhoea & muscle pains
Signs: jaundice (due to haemolytic anaemia), haemoglobinuria

Question 3

Describe the pathophysiology of malaria (P. falciparum)

Answer 3

Malaria carried by the female Anopheles mosquito (vector)
Incubation period (different for each strain, minimum 6 days, falciparum: by 4 weeks, vivax/ovale: up to a year)
1) Mosquito bite -> plasmodium moved from mosquito’s salivary gland into the blood stream of the person
2) Bloodstream = plasmodium is in the sporozoite stage of its life cycle – go straight for the liver & get inside the liver parenchyma
3) Asexual multiplication in the liver and mature from sporozoites to merozoites
4) Burst out from liver & attack and enter RBCs
5) Asexual replication & maturation in the RBC & when they are ready to burst out of the RBC, the RBC is called a schizont (what bursts out is a mass of merozoites, which continue the cycle of infection)

Question 4

Describe how a diagnosis of malaria is made

Answer 4

Thick and thin blood films (x3) to test for the presence of parasites
FBC
CXR
CT-head

Question 5

Describe the management of malaria

Answer 5

Artesunate given via IV or via IM

Alongside either quinine (P. falciparum) or chloroquine (p. vivax, ovale & malariae)

Question 6

Describe Legionnaire’s disease

Answer 6

Caused by legionella bacteria (gram negative)
Place of infection = water is at a high enough temperature to help bacteria grow (eg. shower, air conditioning unit)
Transmission = inhaling droplets of water that the bacteria are contained in (once inside the body, L. pneumophilia invades macrophages in the lungs & replicates inside them)

Question 7

Describe the signs, symptoms & treatment of Legionnaire’s disease

Answer 7

Headache, muscle/chest pain, chills, fever > 40
Can progress to: cough, shortness of breath, GI symptoms & confusion/other mental changes
Uncommen cause of pneumonia – readily treated with antibiotics (clarithromycin)

Question 8

Describe schistosomiasis infection

Answer 8

Flatworm common in tropical areas
Humans acquire flatworms through unprotected skin contact in areas of fresh water contaminated with the helminths which have been released from snails

Question 9

Describe the symptoms, diagnosis & treatment of schistosomiasis

Answer 9

Acute schistosomiasis = diarrhoea, coughs, rashes, abdominal pain & muscle/joint pain
Often involves chronic inflammation – causes damage due to host’s immune response
Diagnosis = confirmed by finding eggs in urine/stool sample or blood test for antibodies
Acute symptoms treated with a course of steroids, curative treatment = praziquantel (normally most effective once the worms have matured so patient may not get treatment until a number of weeks post-infection)

Question 10

Describe typhoid fever

Answer 10

Caused by salmonella typhi (gram negative bacilli)
Presentation = fever, abdominal pain & constipation
Most common where there is poor sanitations & limited access to clean water (children are more likely to contract, but their symptoms are less severe than adults)

Question 11

How is typhoid fever treated?

Answer 11

Diagnosed early – treated with a course of antibiotics: IV ceftriaxone
More serious – treated by infections of antibiotics in hospital
Two vaccinations against typhoid fever but neither offer 100% protection (so need to take precautions – most cases come from Bangladesh, India or Pakistan)

Question 12

Describe dengue fever

Answer 12

Caused by the dengue virus, usually transmitted by mosquitos
Most infections only present with mild/asymptomatic infections
After 4-10 days after the bite, someone may suddenly present with – an intense headache, fever, muscle/joint pain, widespread red rash
No specific treatment – resolves itself within a few days

Question 13

What is a fatal complication of dengue infection?

Answer 13

1-2% of infections, progression to severe dengue/dengue haemorrhagic fever
No cure
Symptoms – restlessness, acute/sudden fever, severe abdominal pain, petechiae, nosebleeds & shock
Also, low levels of platelets in the blood (this is why people say papaya can cure dengue fever – accelerates the increase in platelet count with infection infected patients)

Question 14

Describe the structure of the coronavirus

Answer 14

Large, enveloped pleomorphic particles with a distinctive arrangement of spikes projecting from their surfaces
Positive ssRNA
Major surface antigen = Spike (S) glycoprotein -> required for entry into cells

Question 15

Explain how the virus gains entry to the human host and its subsequent uptake and spread from person to person

Answer 15

1) Binding of the virus to host receptor – ACE2 (transmembrane protein, which is widely expressed in lung, heart, kidney & GI tissue) acts as a receptor for coronavirus
2) Invagination of the membrane
3) Formation of an endocytic vesicle – receptor-mediated endocytosis
Transmission from person to person via the respiratory route

Question 16

Describe the clinical symptoms and complications of this infection

Answer 16

Cough
Fever 
Loss of smell/taste
Shortness of breath 
Diarrhoea, myalgia, septic shock etc

Question 17

Describe how you would diagnose COVID-19 in a clinical setting

Answer 17

Sample from a nasopharyngeal swab or saliva
Nasopharyngeal swab – detects the viral RNA using RT-PCR
Lateral flow test (question to reliability and sensitivity)

Question 18

Briefly outline the management of COVID-19 including treatment options and prevention including vaccination

Answer 18

Treatment = dexamethasone & remdesivir
AstraZeneca – genetically modified virus – 2 doses
Pifzer-biotech – RNA – 2 doses
Moderna – RNA – 2 doses

Question 19

Define the concepts of mutation rate and production of variants

Answer 19

Coronavirus is constantly replicating
Viral RNA polymerases have a high error rate
High error rate & lack of proofreading ability leads to mutations -> genetic variation & resistance
Examples = UK variant, South African variant