Parasites

A parasite is an organism that lives in or on a host and obtains nutrients at the host's expense. Parasites may cause mild to severe harm but generally do not kill the host directly. Examples include Plasmodium (malaria parasite) and Taenia solium (pork tapeworm).

Types of Parasites

Parasites are classified based on their lifestyle, host specificity, and mode of transmission.

1. Based on the Life Cycle

A. Temporary Parasites

• Remain attached to the host only for a short period while feeding.
• Example: Mosquitoes (Anopheles spp.) – suck blood temporarily.

B. Permanent Parasites

• Live on or inside the host throughout their life.
• Example: Tapeworms (Taenia spp.) remain in the intestines for a lifetime if untreated.

2. Based on Host Specificity

A. Host-Specific Parasites

• Can infect only a specific host species.
• Example: Head lice (Pediculus humanus capitis) – infect only humans.

B. Generalist Parasites

• Can infect multiple species.
• Example: Leeches (Hirudo medicinalis) – feed on the blood of different vertebrates.

 

3. Based on the Mode of Transmission

A. Directly Transmitted Parasites

• Spread through physical contact, contaminated food/water, or direct exposure.
• Example: Giardia lamblia (causes giardiasis, spreads through contaminated water).

B. Vector-Borne Parasites

• Require an intermediate organism (vector) for transmission.
• Example: Trypanosoma brucei (causes sleeping sickness, transmitted by tsetse flies).