Molecular evidence of SARS-CoV-2 detection on cockroaches in Shiraz, southwestern Iran and potential implications for mechanical carriage

Cockroaches are known vectors of various pathogens due to their unsanitary feeding habits and close association with human habitats. The COVID-19 pandemic has raised concerns about potential non-human transmission routes, including mechanical transmission by insects. This study investigates whether cockroaches can carry SARS-CoV-2 RNA and their potential role in mechanical transmission in Shiraz, Iran. Using real-time RT-PCR (positivity threshold: Ct < 38.0 for both RdRp and N genes), we molecularly examined 200 cockroaches (100 Blattella germanica and 100 Periplaneta americana ) randomly selected from a total of 400 collected specimens. An additional 200 specimens were allocated to insectarium-based vertical transmission experiments. SARS-CoV-2 RNA was detected on external surfaces of 59/200 specimens (29.5%; 95% CI: 23.4–36.3%), with significantly higher detection in P. americana from hospital sewage (35/50, 70%; 95% CI: 55.9–81.2%) than B. germanica from dormitory kitchens (24/50, 48%; 95% CI: 34.2–62.2%; χ 2 = 5.01, p = 0.025). Internal viral RNA was detected in only 11/200 specimens (5.5%; 95% CI: 3.1–9.6%), with significantly lower loads than surface samples (mean surface-to-internal ratio: 15.2:1; p < 0.001). No viral RNA was detected in 200 nymphs or 50 egg capsules from insectarium-reared populations, indicating no evidence of transovarial transmission under experimental conditions. These findings demonstrate that cockroaches can carry SARS-CoV-2 RNA on their external surfaces, suggesting potential for mechanical carriage rather than biological transmission. However, as RT-PCR detects nucleic acids rather than infectious virus, our results do not establish mechanical transmission. Further research incorporating viral viability assays is needed to determine whether cockroaches can transmit infectious SARS-CoV-2 and contribute to COVID-19 epidemiology.