Medical Entomology II: Arthropods and Human Health

Effects of Arthropods on Human Health

• Arthropods can cause direct effects on human health through bites, which can lead to inflammation or toxic effects (e.g., mosquitoes and fleas)
• They can also cause indirect effects by transmitting pathogens, such as bacterial, viral, or parasitic infections
• Arthropods can act as vectors of infectious diseases, which can be classified into two types: biological vectors and mechanical vectors

Biological Vectors

• Biological vectors acquire pathogenic agents during blood feeding, and the parasites multiply and develop inside the arthropod's body (e.g., malaria)

Mechanical Vectors

• Mechanical vectors transmit pathogens through contaminated external surfaces of their bodies, without multiplication or development inside their bodies (e.g., Ascaris)

Modes of Disease Transmission by Arthropods

• Direct Contact: Direct contact between hosts allows arthropod vectors to transmit diseases (e.g., pediculosis and scabies)
• Mechanical Transmission: Arthropods mechanically transmit pathogens through contaminated external surfaces (e.g., diseases transmitted by houseflies, such as diarrhea, dysentery, cholera, and hepatitis A & E)
• Biological Transmission: Arthropods can transmit pathogens through biological transmission, which can be categorized into three types:
  • Cyclo-developmental: The agent undergoes cyclical changes but doesn't multiply in the arthropod's body (e.g., W. bancrofti in Culex female)
  • Cyclo-propagative: The agent undergoes cyclical changes and multiplies in the arthropod's body (e.g., Plasmodium spp. in Anopheles female)
  • Propagative: The agent grows and multiplies in the arthropod's body (e.g., plague bacilli in rat flea)
  • Transovarian (Vertical Transmission): The organism passes to the offspring (e.g., Zika virus in female Aedes)

Control Measures of Arthropods

• Mechanical Measures:
  • Handpicking and destroying insect pests
  • Using screens, bands of heavy oil, or sticky substances as temporary barriers
  • Employing metallic barriers
• Physical Measures:
  • Using energy factors (heat, cold, light, sound, x-rays, and infrared rays) to kill pests or attract them to a killing mechanism
• Biological Control:
  • Introducing, producing, and releasing parasites, predators, and diseases that attack and reduce or control populations of harmful arthropods
• Chemical Measures:
  • Using appropriate pesticides to kill arthropods with reduced toxicity to humans