Can parasites cause a low red blood cell (RBC) count?

Parasites and Low Red Blood Cell Count

Yes, parasites can cause low red blood cell counts (anemia) through various mechanisms including direct destruction of red blood cells, splenic removal of infected cells, and impaired red blood cell production. 1, 2

Parasitic Causes of Low RBC Count

Blood-Dwelling Parasites

• Plasmodium species (malaria):

  • Directly infect and destroy RBCs during their life cycle 1
  • Can cause severe anemia when parasitemia exceeds 5% in non-immune individuals 1
  • Leads to increased rigidity and adhesiveness of infected RBCs, promoting their removal by the spleen 2, 3
  • Causes destruction of both infected and uninfected RBCs, contributing to anemia 2

• Babesia species:

  • Similar to malaria, infects and damages RBCs 1
  • Can be indistinguishable from Plasmodium on blood films 1
  • May cause hemolytic anemia, particularly in asplenic or immunocompromised patients

Intestinal and Tissue Parasites

• Hookworms and other intestinal helminths:

  • Cause chronic blood loss through intestinal attachment and feeding
  • Lead to iron deficiency anemia over time

• Schistosomiasis:

  • Chronic infection can lead to anemia through various mechanisms including blood loss

Mechanisms of Parasite-Induced Anemia

1. Direct hemolysis: Parasites like Plasmodium rupture RBCs as part of their life cycle 2, 4

2. Splenic removal:

   • Infected RBCs undergo structural and functional changes that trigger splenic clearance 5
   • The spleen can remove parasites from RBCs without destroying the cells (pitting), leaving RESA-positive but parasite-negative RBCs 5

3. Altered RBC membrane properties:

   • Parasites export proteins that interact with RBC membrane proteins 3, 4
   • These interactions cause increased membrane rigidity and reduced deformability 2, 3
   • Changes in RBC structure promote premature clearance from circulation

4. Ineffective erythropoiesis:

   • Chronic parasitic infections can suppress bone marrow function
   • Inflammatory cytokines released during infection can inhibit RBC production

5. Bone marrow suppression:

   • Some antiparasitic medications (like albendazole) can cause bone marrow suppression as a side effect 6
   • This can manifest as pancytopenia or agranulocytosis

Diagnostic Approach

For suspected parasitic causes of anemia:

1. Blood film examination:

   • Thick and thin blood films with Giemsa stain are essential for detecting blood parasites 1
   • Examine at least 100 microscopic fields (300+ for patients without previous exposure) 1
   • Manual screening is required as automated analyzers may miss parasites 1

2. Quantitative assessment:

   • Determine percentage of parasitemia by counting infected RBCs divided by total RBCs 1
   • Parasitemia >2-5% (depending on immune status) indicates severe infection 1

3. Additional testing options:

   • Rapid diagnostic tests (RDTs) for malaria antigens 1
   • Quantitative buffy coat (QBC) method 1
   • Nucleic acid amplification tests (NAATs) for higher sensitivity 1
   • Serologic testing for antibodies to specific parasites 1, 7

Clinical Implications

• Severe anemia (hemoglobin <7 g/dL) with parasitemia is a criterion for severe malaria requiring urgent treatment 1

• Parasitic infections should be considered in patients with unexplained anemia, especially with:

  • Travel history to endemic regions
  • Fever patterns
  • Splenomegaly
  • Eosinophilia (for helminthic infections)

• Prompt diagnosis and treatment are essential to prevent complications from severe anemia

Treatment Considerations

• Treatment should target the specific parasite identified
• Monitor blood counts during treatment, especially with medications that may cause bone marrow suppression 6
• Some patients may require blood transfusion for severe anemia

Important Caveats

• Not all parasitic infections cause significant anemia
• The degree of anemia may not correlate directly with parasite burden
• Co-infections and nutritional deficiencies can exacerbate parasite-induced anemia
• Certain genetic RBC disorders (hemoglobinopathies, hereditary ovalocytosis) may protect against severe malaria-induced anemia 2
• Automated hematology analyzers may miss parasites, leading to false-negative results 1