How do arthropods such as mosquitoes, flies, and ticks spread parasitic diseases?

Arthropods spread parasitic diseases primarily by acting as biological vectors, though some facilitate mechanical transmission.1

Biological Transmission

In biological transmission, the arthropod serves as an essential host in the parasite's life cycle. When a blood-sucking arthropod—such as a mosquito, tsetse fly, or sand fly—bites an infected host, it ingests the pathogen. The parasite then multiplies or matures within the arthropod before being transmitted to a new host during a subsequent blood meal.2345

• Mosquitoes: These are among the most significant vectors, transmitting malaria (Plasmodium) and filarial nematodes like Wuchereria bancrofti.34
• Flies: Tsetse flies transmit African trypanosomiasis (sleeping sickness), while sand flies transmit Leishmania protozoans.32
• Ticks: As obligate parasites, ticks ingest pathogens while feeding on blood. These pathogens can survive through the tick's developmental stages (transstadial transmission) or be passed to offspring (transovarial transmission).5

Mechanical Transmission

Some insects, such as blow flies, spread disease mechanically. They pick up pathogens on their bodies from contaminated sources like feces or decaying matter and deposit them onto food or wounds, rather than serving as a biological host.1