Types of Parasitic Helminths

Characteristics of Helminths

• Helminths are multicellular eukaryotic invertebrates with tube-like or flattened bodies exhibiting bilateral symmetry.
• They are parasitic worms that can be divided into two major groups: nematohelminths (nematodes) and platyhelminths (flatworms).

Nematohelminths

• Nematohelminths can be further divided into intestinal nematodes and filarial or tissue nematodes.
• Examples of intestinal nematodes include Ascaris lumbricoides (large roundworm), Enterobius vermicularis (threadworm), Trichuris trichiura (whipworm), Strongyloides stercoralis, Ancylostoma duodenale (hookworm), and Necator americanus (hookworm).
• Examples of filarial or tissue nematodes include Wuchereria bancrofti, Brugia species, Loa loa, Onchocerca volvulus, Drancunculus medinensis (Guinea worm), and Trichinella species.

Platyhelminths

• Platyhelminths can be further divided into trematodes (flukes) and cestodes (tapeworms).
• Examples of trematodes include Schistosoma species, Paragonimus species, Fasciolopsis buski, Fasciola hepatica, Opisthorchis sinensis, and Opisthorchis viverrini.
• Examples of cestodes include Taenia species, Echinococcus granulosus, and Diphyllobothrium latum.

Geohelminths

• Geohelminths, also known as soil-transmitted helminths (STHs), are a group of intestinal parasites that cause human infection through contact with parasite eggs or larvae in warm and moist soils.
• Examples of geohelminths include roundworms (Ascaris lumbricoides), whipworms (Trichuris trichiura), and hookworms (Ancylostoma duodenale and Necator americanus).
• Geohelminthic infections are prevalent among poor human populations living in low- and middle-income countries.

Persistence of Geohelminths

• The persistence of geohelminths is influenced by factors such as the absence of safe drinking water, lack of hygienic behavior, improper sanitary habits, poor fecal disposal systems, poor socioeconomic status, and wide dispersion of parasites within human communities.

Characteristics and Impact of Geohelminths

• Geohelminths often co-infect the host, and approximately 3.5 billion people are infected with one or more of the most common STHs.
• Co-morbidity causes more marked morbidity and disability than death.

Acute Clinical Outcomes of Geohelminths

• The acute morbidity caused by helminths includes malnutrition, iron deficiency anemia, malabsorption syndrome, intestinal obstruction, chronic dysentery, rectal prolapse, respiratory complications, and poor weight gain.

Chronic Clinical Outcomes of Geohelminths

• Chronic helminthiasis can lead to insidious and debilitating disease, especially in children and women of child-bearing age.
• Chronic helminth infections induce T-cell hyporesponsiveness, which may affect immune responses to other pathogens.
• STH infections may increase susceptibility to other important tropical diseases such as malaria, human immunodeficiency virus (HIV), and tuberculosis (TB).