Malaria & Other Parasites (BCSH 2013, CDC website)

Preparing Films

 

Make 4 thick and 4 thin films --> 2 of each to go to reference lab unstained

 

Thick film

–      Geimsa or Field stain

–      Parasitaemia count made from examination of 200 high power fields

 

Thin film

-       Giemsa or Leishman stain

-       For species identification

 

Negative films should be repeated every 12-24 hours which clinical suspicion remains

 

Rapid Diagnostic Tests

 

-       Immunochromatographic test to detect malaria antigen

-       Confirmatory test only, does not replace microscopy

-       Able to give species identity to falciparum and vivax

 

PCR

-       10x more sensitive than microscopy

-       Better at determining species in cases of mixed infection

 

Quality assurance

 

Internal

-       Dual reporting of all slides

-       New stain batches tested on known vivax and ovale cases

External

-       NEQAS

-       Reference lab confirmation

 

image bank

 

Image bank from the CDC

 

Malaria Biology

 

-       During a blood meal, malaria-infected female anopheles mosquitoes inoculate sporozoites into the human host.

-       Sporozoites infect liver cells and mature into shizonts

-       Liver shizonts mature then rupture to release merozoites

-       Merozoites infect red cells and multiply asexually --> ring form immature trophozoite --> trophozoite --> shizonts --> again rupture (this time from red cells) releasing more merozoites. This is responsible for clinical manifestations of the disease

-       Some parasites differentiate into a sexual stage (microgametocytes (male) and macrogametocytes (female)

-       The gametocytes are ingested by mosquito at next meal. Microgametocytes penetrate macrogametocytes to generate a zygote. The zygote becomes motile and elongated (ookinete) and invade the gut wall of the mosquito.

-       The now oocyst grows, ruptures and release sporozoites, which migrate to the salivary glands and the cycle repeats.

 

Geographical distribution

 

Falciparum     – Global

Malariae         – Global

Ovale              – Sub-Saharan Africa

Vivax               – Rest of Africa

Knowlesi        – SE Asia

 

Summary

malaria.png

 

 

worms

 

Sheathed Worms

 

Wucheria bancrofti

-       Central Africa, Nile, Central/South America & Tropical Asia

-       Mosquito-borne

-       Clinical Pciture

o   Lymphatic filariasis, but often asymptomatic for years

o   Pulmonary eosinophilia syndrome

o   Hydrocoeles

 

Brugia Malayi

-       South and SE Asia

-       Mosquito-borne

-       Clinical Picture

o   Lymphatic filariasis, but often asymptomatic for years

o   Pulmonary eosinophilia syndrome

o   Hydrocoeles

 

Loa Loa

-       West and Central Africa

-       Fly-borne

-       Syn. African Eye worm

-       Clinical Picture

o   Itchy calabar swellings

o   Eye worm

o   But often asymptomatic (More symptomatic if not a native of endemic area)

 

No Sheath Worms

 

Mansonella

-       Africa and tropical Americas

-       Midge-borne

-       Clinical Picture

o   Usually asymptomatic

o   Non-specific fever, angioedema, itch, arthralgia, headache

 

Worm Summary

parasites.png

 

 

Leishmaniasis

 

Tropics, Subtropics and Southern Europe

Sand fly-borne

 

Cutaneous

-       Skin sores

-       Often self-resolving but can take years

Visceral

-       Fever, weight loss, hepatosplenomegaly, pancytopenia

-       Often fatal if untreated

-       Tissue stage of larvae is called an amastigote

o   Often seen inside macrophages, should have a nucleus + rod-shaped kinetoplast