Carriage of Brachyspira hyodysenteriae on common insect vectors

• Published in: Veterinary microbiology 2022-06, Vol.269, p.109417-109417, Article 109417
• Main Authors: Blunt, R., Mellits, K., Corona-Barrera, E., Pradal-Roa, P., McOrist, S.
• Format: Article
• Language: English
• Subjects: Animals; Brachyspira - genetics; Brachyspira hyodysenteriae; Brachyspira hyodysenteriae - genetics; Cockroach; Fly; Gram-Negative Bacterial Infections - veterinary; Insect Vectors; Mice; Mice, Inbred C3H; Mouse; Pigs; Swine; Swine Diseases; Vectors
• ISSN: 0378-1135; 1873-2542
• DOI: 10.1016/j.vetmic.2022.109417

The interactions of likely insect and murine vectors of the causative agent of swine dysentery, Brachyspira hyodysenteriae, were investigated. Insects were collected and analysed from 3 pig farms positive for B hyodysenteriae. Within these farms, several Musca domestica and Orphyra adult fly, Blatta sp. cockroach digestive tracts and hover fly (Eristalis sp) pupal form contents were positive in a standard PCR assay for B hyodysenteriae, whereas all other insect samples on these and case control farms were negative. In challenge exposure studies, B hyodysenteriae DNA was detected in the digestive tract of cockroaches and M domestica flies from day 1 post-inoculation with cultured B hyodysenteriae, for up to 5 days or 10 days respectively, while control non-inoculated insects remained negative. Isolates consistent with B hyodysenteriae were only cultured from frass samples of these inoculated cockroach and flies on days 1–3 post-inoculation. Isolates consistent with B hyodysenteriae were detected by analysis of agar plates exposed to live B hyodysenteriae-inoculated adult flies wandering and feeding on these plates for 20 min per day. In generational challenge inoculation studies, B hyodysenteriae was detected in the adult emergent flies, and internal components of fly pupae on days 1–7 of the pupation period, after being inoculated with B hyodysenteriae as larvae. Five-week-old conventional mice (C3H) that consumed 2 meals of B hyodysenteriae-infected flies remained negative for B hyodysenteriae throughout the next 10 days. The results indicated that pathogenic Brachyspira sp have a limited ability to internally colonise likely insect vectors and do not readily transmit infection to mice. However, the insect vectors analysed were demonstrably capable of mechanical carriage and likely on-farm involvement in consequence. •On pig farms positive for swine dysentery due to Brachyspira hyodysenteriae, samples of some on-farm Blatta sp cockroaches and Musca domestica and Orphyra adult flies were also positive.•In challenge exposure studies, B hyodysenteriae DNA was only detected post-inoculation in cockroaches and M domestica flies for up to 5 or 10 days respectively.•Mice challenged with B hyodysenteriae-infected flies remained negative for B hyodysenteriae post-inoculation.•Pathogenic Brachyspira sp have a limited ability to internally colonise likely insect vectors and do not readily transmit infection to mice. However, the insect vectors analysed were demonstr