Page 198 - Concise Pathology for Exam Preparation ( PDFDrive )

7 Infections 183

Gametocyte of
P. falciparum

FIGURE 7.16. Peripheral smear showing gametocyte stage of P. falciparum (arrows).

Resistance to Malaria Resistance to Malaria is Seen in Association With:
• Inherited alterations in RBCs (presence of HbS, HbC and absence of Duffy antigen)
• Repeated and prolonged exposure to Plasmodium species which stimulates an immune
response that reduces the severity of malaria.

Histopathology
Spleen:
• Congested and enlarged (may exceed 1000 g in weight)
• Parenchyma is grey-black because of granular, brown-black, birefringent haemozoin
pigment.
• Capsule is thickened and the spleen becomes extremely fibrotic and brittle (fibroconges-
tive splenomegaly).
• Phagocytic activity of reticuloendothelial cells is increased.
• Liver is enlarged and sections show pigmented Kupffer cells, which are heavily laden
with malarial pigment and parasite.
• Kidneys are enlarged with presence of pigment in glomeruli and haemoglobin casts in
tubules.
• Nervous system:
• Brain vessels plugged with parasitized RBCs, each with a dot of haemozoin.
• Perivascular ring haemorrhages due to local hypoxia with vascular stasis and small
focal inflammatory aggregates (malarial or Durck granulomas) is seen.
• Also seen are degeneration of neurons and focal ischaemic softening.

Leishmaniasis
• Leishmaniasis is a chronic inflammatory disease of the skin, mucous membranes and
viscera caused by an obligate intracellular protozoan transmitted through bites of
infected sand fly.
• It is endemic throughout Middle East, South Asia, Africa and Latin America.
• Life cycle involves two forms: promastigotes, which develop and live extracellularly in
the sand fly vector and the amastigote form that multiplies intracellularly in the host
macrophages.
• Mammals including rodents, dogs and foxes are reservoirs of leishmania.
• Parasite specific cell-mediated immunity is the main host immune response.

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