0
0
Malaria
This is a mosquito borne infection which injects the parasite Plasmodium into the blood.
There are 4 main variants of the parasite and the natural vector is the female anopheles’ mosquito
Pre-erythrocytic stage
Mosquito injects sporozoites into human blood
These migrate to liver and infect hepatocytes, multiplying by mitosis
They can stage in the liver for up to 2 years remaining immature as hypnozoites
These differentiate into merozoites which are released from the liver into the bloodstream
Erythrocytic stage
Trophozoites infect RBCs, feeding on haemoglobin using the enzyme haem polymerase
These form a schizont and multiply asexually, and are released when the RBC ruptures
Some merozoites produce gametocytes instead which are uptaken by the mosquito
Mosquito stage
The mosquito ingests the gametocytes which fuse to form an oocyst
This matures to gives sporozoites which migrate to the salivary glands and can be reinjected into human
Symptoms
Severe
Usually caused by Plasmodium falciparum, the most common variant of the parasite.
Cyclical fever > 39ÅãC
Metabolic acidosis
Severe anaemia
Hypoglycaemia
Headache
Splenomegaly
Benign
These occur mostly due to non-falciparum strains
Cyclical fever, headache, and splenomegaly
P. vivax and P. ovale gives intermittent shivering with fever every 2 days
P. malariae gives cyclical fever every 3 days and can cause nephrotic syndrome
Infected RBCs display adhesion proteins making them stick to the inside of small vessels, causing blockages. This can lead to complications including:
Complications
Key tests
Microscopy of thick and thin blood smear shows parasite on blood film
Rapid diagnostic test (RDT) of parasite antigen
Management
Uncomplicated P. falciparum – 1st line is artemisinin combination therapy (e.g., artemether-lumefantrine)
Severe P. falciparum – artemisinin therapy with IV Artesunate
Non-falciparum strains – chloroquine or artemisinin combination therapy (if resistant)
If P. ovale or vivax, it is important to also give primaquine after to destroy hypnozoites and prevent relapse of the disease
Prophylaxis
If not drug resistant or little resistance, can give chloroquine and proguanil
If chloroquine resistant, mefloquine or doxycycline are used for prophylaxis
Threadworm Infection
This is due to the worm Enterobius vermicularis (pinworm), primarily seen in children.
Children swallow eggs from the environment.
These hatch in the intestines and grown into worms.
Female worms move to perianal region to lay eggs.
Eggs are then transferred to mouth by hands restarting the cycle.
Symptoms
Most children do not experience any symptoms
Perianal itching worse at night
Vulval itchiness in females
Key tests
Usually a clinical diagnosis.
Can apply adhesive tape over the perianal region to collect eggs, which are then examined under a microscope
Management
Mebendazole for the child and everyone else in the house
Wash all sheets as mebendazole kills the parasites but not the eggs
Toxoplasmosis
This is an infection due to the parasite Toxoplasma gondii, found in cats.
Cats acquire the infection by eating cysts in infected tissue.
These then grow and release trophozoites and form tissue cysts.
The trophozoites release gametes which form oocysts, which are released in faeces.
The faeces are eaten by rats and birds, which are then consumed by cats again.
The problem is that humans acquire oocysts via the GI tract (infected animals and water) or through breaks in the skin.
The trophozoites spread to organs and can cause development of tissue cysts, producing symptoms.
Symptoms
Most immunocompetent patients are asymptomatic
Can resemble infectious mononucleosis with fever, lymphadenopathy, fatigue
Meningoencephalitis – this is usually seen in HIV-infected patients, giving symptoms of fever, headache, and pain on neck movement
In pregnancy, it increases risk of miscarriage, stillbirth and foetal abnormalities
Key tests
Blood test to check for antibodies
Sab-Feldman dye test (tests for antibodies stopping dye enter T. gondii)
CT head shows ring-enhancing lesions
Management
Antiparasitic drugs such as sulfadiazine and pyrimethamine
Schistosomiasis
This is a parasitic flatworm infection found in freshwater snails, common in Africa.
Eggs hatch in freshwater and release miracidia which infect snails.
They multiply and release cercariae which penetrate human skin in rivers.
In humans, they migrate to the portal circulation and mature into adult worms.
Depending on the variant, they then stay there or migrate elsewhere.
Adult worms lay eggs which are released into the stool/urine restarting the cycle.
Symptoms
Specific variants are associated with particular symptoms:
Schistosoma haematobium
This species deposits eggs in the bladder causing irritation.
Symptoms starts as “swimmer’s itch” in the legs of travellers from Africa
It causes urinary frequency, haematuria and dysuria. The subsequent inflammation gives bladder calcification which is a risk factor for squamous cell bladder cancer.
Schistosoma mansoni/japonicum
These worms mature in the liver giving portal vein congestion.
Can lead to progressive liver cirrhosis and portal hypertension.
Management
Oral praziquantel
Neurocystericosis
This is caused by the worm Taenia solium, a tapeworm found in pigs.
Pigs acquire the eggs from faeces which then hatch in their intestines.
The larvae migrate to the pig muscle where they form cysticerci.
Humans ingest cysticerci by eating undercooked meat from infected animals.
The problem is that cysticerci can then develop in human organs, like the brain.
This leads to CNS dysfunction, causing symptoms such as seizures and meningitis.
Symptoms
Most common cause of epilepsy worldwide
Neurological – Headaches, blindness, dementia, meningitis
Key tests
CT scan shows cysticerci in brain
Management
Anti-epileptics
Praziquantel and Mebendazole
