Confirmed spread of Vibrio parahaemolyticus by aerosols is a risk factor in the infection of shrimp ponds

Infection with Vibrio parahaemolyticus carrying a plasmid encoding two Pir-like toxins results in a rapid, progressive degeneration of the hepatopancreas of Penaeus vannamei leading to morbidity and mortality. Here we investigate the potential spread of V. parahaemolyticus (Vp_AHPND) aerosols to enhance understanding of biosecurity requirements at the farm level and to minimise the risk of infections. Using air stones to create aerosols from 20 L tanks inoculated with 1 × 10⁶ cfu/mL⁻¹ V. parahaemolyticus, and electric fans to deliver a 9.81 km/h⁻¹ lateral flow of air at source, the spread of bacteria was determined using TCBS agar plates set out over an experimental arena extending to 20 m (34.0–30.7 °C air temperature, 63.3–71.9 % relative humidity). From several experimental trials, aerosols cast into the lateral airflow at 43 or 220 cm above the ground contained viable bacteria and were detected on TCBS plates as far as 20 m, marking the maximum perimeter. By extrapolation of colony counts on TCBS, we predict bacteria released 43 cm and 220 cm above the ground could spread 24.49–28.96 m (27.38 m ± 95 % C.I.) and 72.40–73.68 m (72.92 m ± 95 % C.I.) from the source, respectively. Putative protection provided by a 1.5 m high tarpaulin positioned 5 m from the infection source, failed to stop bacteria, which spread round the barrier and colonised TCBS plates positioned immediately behind, i.e., within 50 cm, and readily up to 5.5 m. A fourth trial using a combination of a protective screen placed over the aeration point to limit the spread of aerosols and two layers of 85 % protective shade netting positioned at least 1 m apart resulted in a ca. 20–30-fold reduction in bacteria penetrating the netting and colonising plates. Finally, detection of Vp_AHPND-laden aerosols was confirmed on a commercial shrimp production site using TCBS plates strategically positioned around a Vp_AHPND-positive pond. Altogether, we highlight the role that aerators play in generating bioaerosols, and how infections might be minimised in indoor culture settings, including the management of airflow and flying insects.