Malaria, worms and leishmaniasis (BSH 2022, 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 by 2 staff, from examination of 200 high power fields each

Thin film

• Giemsa or Leishman stain

• For species identification

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

malaria morphology summary

image bank

Image bank from the CDC

other tests

Immunochromatographic test (Rapid Diagnostic Test (RDT))

• Detects malaria antigen

• Confirmatory test only, must never replace microscopy (lots of detail in guideline)

• Able to give species identity to falciparum and vivax

?Negative RDT in presence of intracellular red cell parasites - think babesiosis and send samples to reference laboratory for further investigation. CDC Babesiosis pages.

Nucleic-acid detection

• Turnaround time 2-72 hours depending on method.

• Cannot always distinguish current from past infection

• PCR

  • 10x more sensitive than microscopy

  • Better at determining species in cases of mixed infection

• LAMP

  • Methodoligically far simpler. Originally developed for use in the field.

Drug sensitivity testing

• Research tool only at present

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

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