Cockroaches are cosmopolitan insects distributed across tropical and subtropical regions worldwide, thriving in toilets, kitchens, sewers, and drains. With a fossil history spanning over 300 million years and more than 4,600 described species, they rank among the most evolutionarily successful organisms on Earth. Their feeding habits—on decaying organic matter, human faeces, food waste, garbage, and sewage—make cockroaches significant reservoirs of parasites, pathogens, bacteria, viruses, nematodes, and protozoa, allowing them to function as mechanical vectors of disease transmission. Pathogens associated with cockroaches have been linked to conditions including asthma, allergic rhinitis, skin allergies, bronchitis, balantidiasis, amoebiasis, ulcerative colitis, Crohn's disease, and bacterial dysentery, highlighting their considerable public health relevance.

This study examined the gut parasite composition of domiciliary Periplaneta americana collected from four districts of West Bengal, India: Kolkata, Howrah, Purba Medinipur, and South 24 Parganas (15 specimens per district, 60 total). Specimens were dissected under laboratory conditions, and gut smears were stained with methylene blue for microscopic examination.

Six pathogen taxa were identified: three nematodes (Thelastoma attenuatum, Leidynema appendiculatum, Hammerschmidtiella diesingi) and three protozoa (Gregarina blattarum, Nyctotherus ovalis, Balantidium blattarum). Infection prevalence was highest in Kolkata (93.33%), followed by Howrah (80%), South 24 Parganas (66.67%), and Purba Medinipur (60%). Of the identified parasites, Gregarina blattarum, Nyctotherus ovalis, Balantidium blattarum, and Leidynema appendiculatum were associated with respiratory, allergic, and gastrointestinal disorders in humans, whereas Thelastoma attenuatum and Hammerschmidtiella diesingi showed no known pathogenic association.

These findings establish a baseline for the gut parasite fauna of domiciliary cockroaches in West Bengal and confirm their role as potential vectors of human intestinal parasites. The notably high infection prevalence in Kolkata underscores an urgent need for targeted pest control and public health surveillance in urban households across the region.