lect 10: vector-borne diseases // plasmodia

Introduction

  • usually done by arthropods

  • focus is on plasmodium as a pg - causes diff types of malaria

  • vectors act as carrier and the pg goes thru some part of its life cycle in the vector

    • can be passive (carried on body that is transferred to host) or direct (involves bite to transfer)

  • ex of diseases that’re vector borne: malaria, plague, sleeping sickness, yellow fever

  • ex of vectors: ticks, mites

Malaria

  • protist disease caused by plasmodium

  • mosquitoes are vectors - specifically anopheles mosquito

  • disease usually found in tropical and subtropical areas

  • relatively easy to treat and not that expensive BUT usually abundant in low income / less dev countries so not “economically incentivized” to help

  • diagnosed via blood smears to ID plasmodium infected erythrocytes (RBCs)

  • can recur years after the infection was treated

Plasmodium

  • complex life cycle:

    • infected mosquito dev sporozoites in it

    • releases them into blood stream into host, then go to liver

    • goes thru cycle of dev to become schizont and infect phagocytes

    • get into blood stream again

    • infect erythrocytes and grow inside them, then change their morphology and physiology

    • lyse cells and release more merozoites → infect more cells

    • some of them differentiate into male and female gametocytes (haploid) that are picked up by other mosquitoes to pass on

    • get fertilized in mosquito and cont cycle

  • has T dept fertilization and humans too warm for fertilization, so only happens in mosquitoes

  • diff species of plasmodium have varying age of RBCs they prefer, fever periodicity, and if they have a dormancy period or not

  • vaccines target the major life stages: sporozoite, merozoite, or gametocyte

Disease Manifestations

  • parasite changes:

    • morphology → surface changes, affects behavior and ability to circulate, form clots, etc → tissue anoxia (damages)

    • metabolism → anemia, Fe imbalance → tissue anoxia

    • lyses RBCs → anemia

  • infection affects RBCs behavior and where they go → cause issues with peripheral tissues, kidney, and random clot formation

  • become less flexible and more likely to bind to the endothelial cells in the capillary beds

  • normal RBCs can form a “rosette” around infected RBCs → clots in microvasculature → tissue anoxia, inflammation

Prevention

  1. vector control - spraying for mosquitoes, using bed nets, braining standing water that they use to lay eggs, insecticides

  2. access - test for malaria, vector control items, meds, disease surveillance

  3. chemoprevention - monthly treatments when pregnant, seasonal treatments for kids

Future Challenges

  • resistance to insecticides and parasite treatments

  • controlling the vector

  • inc mobility - disease introduced to US, inc exposure of previously immune indiv to new versions of disease

Focus On

  • life cycle

  • pros and cons of vaccine strat for 3 major targets

  • pg of malaria