Session 8 ILOs - Travel related infections and COVID-19 Flashcards
Describe common global and imported tropical infections and their pathogenesis, including malaria, enteric fever, and dengue fever
Malaria
- Risk factor is a mosquito/insect bite
- Pathogenesis: parasites in the form of sporozoites are injected into the bloodstream. The sporozoites travel to the liver, multiplying over the next 7–10 days. The parasites, now in the form of merozoites, emerge from the liver cells in vesicles and travel through the heart to the capillaries of the lungs.
- The vesicles eventually disintegrate, releasing the merozoites to enter the bloodstream where they invade and multiply in erythrocytes and cause the cells to burst
Enteric fever/typhoid fever
- Bacterial infection caused by Salmonella typhi
- Risk factor is contaminated food or drink with faeces
- Pathogenesis: fibriae adhere to epithelium over Payer’s patches (survives gastric acid)
- Reside within macrophages
Dengue fever
- Risk factor is a mosquito/insect bite
- Pathogenesis: The dengue virus attaches to the surface of a host cell and enters the cell by a process called endocytosis. Once deep inside the cell, the virus fuses with the endosomal membrane and is released into the cytoplasm. The virus particle comes apart, releasing the viral genome.
Describe the main symptoms and clinical features of presentation, the process of diagnosis and principles of management
5 main species of plasmodium:
- Falciparum and Vivax are the most common
Main symptoms/clinical features
- Incubation period of 6 days minimum, 4 weeks for Falciparum up to 1 year for Vivax
- History of fever chills and sweats
- Very few clinical features other than fever (+/- splenomegaly)
Diagnosis/investigations:
- Blood film x 3
- Chest Xray
- FBCs, U&Es, LFTs, glucose and coagulation
Management - depends on species:
Supressive treatment (prophylaxis) - aims to kills sporozoites before they infect the liver
Therapeutic treatment - aims at eliminating the merozoites in the RBCs (during active infection)
Falciparum: Artensunate (first line), followed by Quinine and Doxycycline
Vivax: Chloroquine (Primaquine for dormant hypozoites)
Describe common travel related respiratory infections, including emerging infections
Influenza
Coronaviruses
e. g. MERS-CoV
- A respiratory syndrome coronavirus (MERS-CoV) is a virus transferred to humans from infected dromedary camels
- Possible human-human contact, especially in healthcare settings
e. g. SARS
- Severe acute respiratory syndrome (SARS) is a viral respiratory disease caused by a SARS-associated coronavirus.
- First identified at the end of February 2003 during an outbreak that emerged in China and spread to 4 other countries
Describe the structure of the coronavirus
- Large
- Enveloped
- Spike (S) glycoprotein (required for entry into cells)
- Positive single stranded RNA - large genome!
Define the concept of an animal reservoir for coronaviruses (including bats, snakes, pangolin, camels and other animals) & its major surface antigen - spike (S) protein
Animal reservoir - usually a living host of a certain species, such as an animal or a plant, inside of which a pathogen survives, often (not always) without causing disease for the reservoir itself
Civet - SARS
Dromedary camel- MERS
Pangolin/snake or bat - COVID-19?
Explain how the virus gains entry to the human host and its subsequent uptake and spread from person to person
Entry and uptake:
- Mainly uses spike glycoprotein on it’s surface
- ACE2 receptor acts as a receptor for the protein
- Enters the cell via receptor-mediated endocytosis
Spread - 3 main methods:
- Small droplets - airborne
- Large droplets - short distances, onto surfaces
- Larger droplets - onto surfaces, transferred to mucous membranes
Describe the clinical symptoms and complications of this infection
Symptoms:
- Fever
- Persistent cough
- Myalgia
- SOB
- Haemoptysis
- Diarrhoea
Complications:
- Pneumonia
- Septic shock
- Renal failure
Describe how you would diagnose COVID-19 in a clinical setting
Combination of the following:
- Swab test (PCR)
- Clinical history / signs
- Radiological tests
- Blood tests (look at CRP, urea, LDH, neutrophils)
Briefly outline the management of COVID-19 including treatment options and prevention including vaccination
Supportive:
- Lots of fluids
- Proline position (helps with ventilation)
Specific:
- Dexamethasone
- Remdesivir
- Non-invasive ventilation
- Low molecular weight heparin
Define the concepts of mutation rate and production of variants
COVID-19 has a high mutation rate as the ssRNA has a high capacity for errors/mutations to occur (due to poor error-checking mechanisms)
Therefore high production of variants, but we only really care about the mutations in the spike glycoproteins because this is what the vaccines are targeting
Understand and describe the life cycle of malaria
Life cycle:
- Parasites in the form of sporozoites are injected into the bloodstream.
- The sporozoites travel to the liver, multiplying over the next 7–10 days.
- The parasites, now in the form of merozoites, emerge from the liver cells in vesicles and travel through the heart to the capillaries of the lungs.
- The vesicles eventually disintegrate, releasing the merozoites to enter the bloodstream where they invade and multiply in erythrocytes and cause the cells to burst
- A few of the infected cells transform into gametocytes
which can remain in the bloodstream for a few days and can infect another mosquito
