Malaria Flashcards

Question

What are the selective pressure that can alter receptor-ligand expression in Plasmodium?

Answer 1

Selective pressure can alter receptor-ligand expression in Plasmodium through a process of evolutionary adaptation driven by the host immune response. Here's how it happens: Polymorphism of Red Blood Cells: Red blood cells exhibit polymorphism, including variations in surface proteins and receptors. Interaction with Plasmodium: Plasmodium parasites interact with these polymorphic receptors on the surface of red blood cells during invasion. Selective Pressure: The host's immune system exerts selective pressure on Plasmodium parasites, favoring those parasites that can effectively invade specific red blood cell types. Host immunity targets parasite ligands, which are involved in receptor-ligand interactions during invasion. Evolutionary Response: Plasmodium parasites evolve to adapt to this selective pressure by altering the expression of their receptor-ligand pairs. Variation in Ligands: Parasites may switch between different ligands, allowing them to invade different types of red blood cells. Example - EBAs and RHs: For instance, Plasmodium falciparum can use erythrocyte binding antigens (EBAs) or reticulocyte binding proteins (RHs) for invasion. EBAs and RHs interact with different receptors on the surface of red blood cells. Switching Ligand Expression: Under selective pressure, the parasite can switch between using EBAs and RHs, depending on the availability of specific receptor types on the surface of red blood cells. In summary, the interaction between Plasmodium parasites and host red blood cells is dynamic and subject to evolutionary adaptation. Selective pressure from the host immune system can drive changes in receptor-ligand expression in Plasmodium, allowing the parasite to adapt to different host environments and evade immune responses.

Answer 2

Detection of Parasite Antigens: The RDT detects specific antigens produced by the malaria parasite, typically histidine-rich protein 2 (HRP2), lactate dehydrogenase (LDH), or aldolase. Principle of the Test: A small amount of blood is collected from the patient via finger prick. The blood sample is applied to the sample pad of the RDT device. If the sample contains malaria antigens, they bind to specific antibodies on the test strip. This antigen-antibody binding results in the appearance of colored lines on the test strip, indicating a positive result for malaria infection. Interpretation of Results: A positive test result is indicated by the appearance of colored lines in the test and control regions of the test strip. A negative test result is indicated by the appearance of a colored line only in the control region. The absence of any colored lines indicates an invalid test and necessitates retesting. Why New Tests are Required: Emergence of Antigenic Variation: Some strains of Plasmodium falciparum, the most deadly malaria parasite, have evolved to produce reduced or undetectable levels of HRP2. This antigenic variation compromises the sensitivity of HRP2-based RDTs, leading to false-negative results. Impact on Malaria Diagnosis: False-negative results can delay appropriate treatment, leading to increased morbidity and mortality. In areas where HRP2-based RDTs are commonly used, false-negative results can underestimate the true burden of malaria and compromise disease surveillance efforts. Need for Alternative Tests: New diagnostic tests are required to overcome the limitations of HRP2-based RDTs. Alternative tests should be capable of detecting a broader range of parasite antigens, including those not affected by antigenic variation. Ideally, new tests should be affordable, easy to use in resource-limited settings, and provide rapid and accurate diagnosis of malaria infections. In conclusion, while HRP2-based RDTs have been valuable tools for malaria diagnosis, the emergence of antigenic variation in Plasmodium parasites underscores the need for new diagnostic tests capable of detecting a broader range of parasite antigens. These tests should address the limitations of current RDTs and contribute to more accurate and timely diagnosis of malaria infections.