There are three main classes of parasites that can cause disease in humans: protozoa, helminths, and ectoparasites.
Here's a more detailed breakdown:
Main Classes of Parasites
Parasites are organisms that live on or in a host organism and get their food from or at the expense of their host. They are classified into three major groups based on their characteristics:
- Protozoa: These are single-celled eukaryotic organisms. Many are free-living, but some are parasitic. They can multiply in humans, contributing to severe infections.
- Helminths: These are multicellular parasitic worms. They are generally visible to the naked eye in their adult stage. Helminths do not multiply in humans.
- Ectoparasites: These are parasites that live on the host, typically feeding on blood.
Protozoa
- Description: Single-celled, microscopic organisms.
- Reproduction: Can multiply within the human host.
- Examples:
- Giardia lamblia (causes giardiasis)
- Plasmodium species (causes malaria)
- Cryptosporidium (causes cryptosporidiosis)
- Entamoeba histolytica (causes amebiasis)
- Toxoplasma gondii (causes toxoplasmosis)
Helminths
- Description: Multicellular worms, often macroscopic (visible to the naked eye when adult).
- Reproduction: Do not multiply in humans. Disease occurs via infection by eggs or larvae.
- Types:
- Nematodes (Roundworms): Examples include Ascaris lumbricoides, Enterobius vermicularis (pinworm), and hookworms.
- Cestodes (Tapeworms): Examples include Taenia solium (pork tapeworm) and Taenia saginata (beef tapeworm).
- Trematodes (Flukes): Examples include Schistosoma species (cause schistosomiasis) and liver flukes.
Ectoparasites
- Description: Parasites that live on the surface of the host.
- Examples:
- Ticks: Can transmit Lyme disease, Rocky Mountain spotted fever, and other diseases.
- Fleas: Can transmit plague and other diseases.
- Lice: Cause pediculosis (infestation of the hair and skin).
- Mites: Cause scabies.
- Mosquitoes: While technically vectors, they feed on blood and can transmit diseases like malaria, Zika virus, and West Nile virus.
In summary, human parasitic diseases are caused by protozoa, helminths (worms), and ectoparasites (external parasites). These organisms exhibit diverse life cycles and mechanisms of infection.
