Malaria, worms and leishmaniasis (BSH 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

malaria morphology summary

malaria.png

image bank

 

Image bank from the CDC

Rapid Diagnostic Tests

 

Immunochromatographic test

Detects 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

  

Malaria Biology

Geographical distribution

Falciparum     – Global

Malariae         – Global

Ovale              – Sub-Saharan Africa

Vivax               – Rest of Africa

Knowlesi        – SE Asia

Life Cycle

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

  2. Sporozoites infect liver cells and mature into shizonts

  3. Liver shizonts mature then rupture to release merozoites

  4. 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

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

  6. 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.

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

 

worms

 

Sheathed Worms

 

Wucheria bancrofti

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

Mosquito-borne

Clinical Picture

  • Lymphatic filariasis, but often asymptomatic for years

  • Pulmonary eosinophilia syndrome

  • Hydrocoeles

 

Brugia Malayi

South and SE Asia

Mosquito-borne

Clinical Picture

  • Lymphatic filariasis, but often asymptomatic for years

  • Pulmonary eosinophilia syndrome

  • Hydrocoeles

 

Loa Loa

West and Central Africa

Fly-borne

Syn. African Eye worm

Clinical Picture

  • Itchy calabar swellings

  • Eye worm

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

 

No Sheath Worms

 

Mansonella

Africa and tropical Americas

Midge-borne

Clinical Picture

  • Usually asymptomatic

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

 

Worm Summary

Source: This is a paper chart in my local lab with no author given. Will of course amend if anyone recognises this.

Source: This is a paper chart in my local lab with no author given. Will of course amend if anyone recognises this.

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

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