malaria Flashcards
What are parasites?
These are organisms which live feed or grow on another organism at the expense of the host’s metabolism and can be divided into three classes:
- Helminthes or worms which includes nematodes (roundworms), trematodes (flukes) and cestodes (tapeworms)
- Ectoparasites which include insects such as bed bugs and mites leading to infestations of diseases such as scabies
- Protozoa which are unicellular eukaryotes found in a wide range of habitats
How are protozoa classified/
According to the presence or type of organ of locomotion
Amoebae have pseudopods, flagellates have flagellum and sporozoites have no organ of locomotion
What are the different hosts involved in parasitic infections?
Parasitic infections often involve more than one host
There is a definitive or primary host in which mature parasites (sexual forms which are reproducing) are present and one or more intermediate host in which immature parasites undergo various stages of maturation
What are zoonoses/
This is a term used to diseases of animals transmitted to humans where the definitive host is an animal and the human is accidentally infected
What are the two major ways in which protozoan parasites can infect the human host?
Ingestion and vector borne transmission
What are the features of giardiasis?
This a disease caused by giardia lamblia where humans are the definitive host (as well as many animals) and commonly infected through the faecal oral route causing severe diarrhoea
What are the features of amoebiasis?
This a disease caused by entamoeba histolytica where the definitive host is humans who become infected through drinking contaminated water causing amoebic dysentry severe diarrhoea which can be fatal
What are the features of cryptosporidiosis?
This a disease caused by cryptosporidium parvum where the definitive host is poultry and live stock where humans are infected through ingestion causing severe diarrhoea
What are the features of toxoplasmosis?
This a disease caused by toxoplasma gondii where the definitive host is cats and humans are infected through contaminated soil infecting livestock and under cooked meat
What are the features of leishmania?
This a disease caused by 20 of the 30 leishmania spp where the definitive host is dogs and rodents where humans are infected through the sandfly vector causing skin ulcers and fatal infection of the liver, spleen, bone marrow and lymph nodes
What are the features of trypanosomiasis?
This a disease caused by trypanosoma brucei and cruzi where the definitive host is cattle, wild game and humans who are infected through either the tsete fly or reviuld bug vectors causing invasion of the central nervous system and mengio encephalitis, heart failure and toxic megacolon
What are the features of babesiosis?
This a disease caused by babesia microti where the definitive host is mice where humans are infected through the deer tick vector leading to anemia, jaundice and fevers
What is malaria?
This is an infection with a protozoan sporozoite, called plasmodium which is an olbligate intracellular eukaryotic parasite which is transmitted by mosquitoes
What are the plasmodium species which have humans as a primary host/
Falciparum, vivax, ovale and malaria with the severity of the symptoms and the timing of the symptoms differing with each species as well as the time between infection of the liver and the start of symptoms
What is the life cycle of the plasmodium parasite/
Plasmodium infection is transmitted by the bite of a female anopheles mosquito resulting in 15-123 sporozoites being transmitted under the skin which rapidly travel to the liver and infect hepatocytes
Here the sporozoites develop into merozoites in a symptomatically silent process which results in the presence of thousands of merozoites in each hepatocytes termed a schizont body between 2-16 days later these will be released into the bloodstream where they will invade an erythrocyte observed as a trophozoite in a blood smear these will replicate in the rebd blooc ell using hemaglobin as a nutrient, this will eventually rupture the cell in an almost simultaneous cycle of 48-72 hours
Some of the new merozoites will transform into gametocytes which can be taken up when the mosquito has a blood meal where they will mature and be able to infect another human
What is the consequence of plasmodium infection of erythrocytes?
More than half of the cytosol in the RBC will be converted to the parasite with parasitemia occurring when an individual has more than 10% of the circulating Red blood cells infected
Due to the use of hemaglobin as a nutrient this can lead to severe anemia
What are the initial symptoms of malaria?
These are non-specific and include recurrent paroxysms of fever and flu-like symptoms such as chills, headache, muscle ache and tiredness there may also be nausea, vomiting and diarrhoea
The initial infection of hepatocytes is symptomatically silent with the symptoms of fever and chills only occurring on rupture of the red blood cells these paraoxysms occur every few days for a number of weeks until an immunological response is mounted this is uncomplicated malaria (in complicated malaria there may be organ failure and/or cerebral malaria which can be fatal
How does erythrocyte destruction lead to fever?
There is release of pyrogenic material along with the RBC being and parasites being phagocytosed by macrophages which initially leads to hyperplasia of these cells but is followed by pancytopenia where further phagocytosis of this material is by the fixed mononuclear pahgocytes in the spleen and liver which causes hepatosplenomegaly
What occurs to the spleen in malaria infection?
This will turn slate grey/black due to deposition of large amounts of hemozoin which is a malarial pigment produces as the end product of parasitic hemaglobin metabolism and is composed of haem r iron protoprphyrin IX crystals
How does malaria lead to hemogloginuric nephrosis?
The destruction of erythrocytes leads to excessive release of hemaglobin causing this condition where there is acute renal failure associated with hemoglobinuria with excretion of large quantities of heamglobin in the urine where the lumen and tubular epithelial cells become packed with hemaglobin
How can malaria cause jaundice?
The excessive release of hemaglobin when the parasite bursts the red blood cell leads to haem oxygenase activity which degrades haem to release iron CO and biliverdin which is then converted to bilirubin which can cause yellow discolouration of the skin
How does malaria cause altered red blood cell adhesion?
Infection of the red blood cell causes it to be remodelled to express knob proteins on the surface which then attach to the endothelial cells of red blood vessels (this can cause circulating parasitemia to appear lower than reality)
This attachment leads to altered blood flow which can form fibrin and thrombi resulting in microinfarcts and obstruction of microvasculature causing congestive heart failure, pulmonary oedema, ecephalopathy and death
Obstruction of capillaries can also cause ischaemia of the kidneys and acute renal failure
What is cerebral malaria?
This occurs in about 10% of plasmodium falciparum (however this causes over 50% of all malarial deaths)
This is impaired consciousness, delirium, convulsions and unrousable coma caused as falciparum infected RBCs adhere particularly to cerebral microvasculature stopping blood flow and leading to a shortage of oxygen and nutrients, if the occlusion occurs diffusely throughout the brain leading to oedema of the cortex, vascular congestion and ischaemia
How is the blood brain barrier involved in cerebral malaria?
The damage to the brain microvasculature in this condition particularly compromises the blood brain barrier with perferin being released from CD8 cells targeting the paratized adherent RBC damaging the microvascular endothelium of the brain
The damage to the blood brain barrier results in elevated intra-cranial pressure and seizures which are cause of death for patients with cerebral malaria being respiratory arrest due to intracranial pressure causing fatal brain stem herniation
What is tertian malaria?
Malaria where the fever occurs every 42-47 hours (or every third day counting the day of occurrence as the first day in the cycle) and is due to infection with plasmodium ovale or vivax, if the infection ends with spontaneous recovery then it is most likely to be ovale
What is quotidian malaria?
Malaira where the fever occurs daily occurring when two broods of vivax lyse RBC on alternate days
What is quartan malaria?
This is malaria where the febrile paroxysms occur every 72 hours or every 4 days and is due to infection with Plasmodium malariae
How frequent are the malaria attacks from Plasmodium falciparum?
This species can cause almost continuous febrile attacks and is the most devastating of the infections
What is unique about P. ovale and P. Vviax?
These are capable of causing relapsing malaria as they have an additional sleeping stage where the merozoites can infect the liver in a dormant form called hypnozoites which may become reactivated later causing relapsing malaria
What may be the fifth human malarial parasite?
Plasmodium Knowlesii which may be a zoonose from macaque monkeys, it is major cause of human malaria in Malaysia and causes severe disease due to the daily fevers and the high levels of parasitaemia but does not lead to cerebral malaria
