Identification and Control of an Ornithonyssus Bacoti Infestation in a Rodent Vivarium by Using Molecular Diagnostic Techniques

Abstract

Ornithonyssus bacoti, commonly known as the tropical rat mite, is a zoonotic ectoparasite that occasionally infests research rodent colonies. Most infestations have been attributed to wild rodents that harbor the mite and spread it to research animals, often during building construction or other activity that disrupts wild rodent populations. Although infestation may be clinically silent, severe outbreaks have been reported to cause pruritis, dermatitis, decreased reproductive performance, and anemia in rodents. In mid-2020, our institution experienced increased activity of wild mice, which were found to be infested with O. bacoti, diagnosed by microscopic exam and confirmed by fur swab PCR analysis. We elected to add O. bacoti to our quarterly health monitoring exhaust air dust (EAD) testing PCR panel, increase wild mouse control measures, and treat the environment with a sustained-release synthetic pyrethroid spray in an attempt to prevent colony animal infestation. Initial quarterly EAD health monitoring results in September of 2020 were negative for O. bacoti. However, in early 2021, multiple IVC racks tested positive for O. bacoti at quarterly testing. Treatment consisted of providing permethrin-soaked nesting material and surface spray treatment of the room and hallway with a sustained-release synthetic pyrethroid. Historically in the literature, O. bacoti outbreaks of research mice were not identified until mite burden was high enough to cause dermatitis on animal care workers. Due to modern molecular diagnostics and proactive PCR-based health monitoring surveillance, we were able to identify the outbreak earlier than would have otherwise been possible. To the best of our knowledge, this is the first report to successfully identify O. bacoti using environmental health monitoring PCR techniques. This outbreak demonstrates the importance of screening for O. bacoti in facilities with the potential for wild rodent infestation and highlights unique considerations when managing O. bacoti infestations. In addition, a novel permethrin-soaked enrichment item was developed for cage-level treatment.

Figure 1.

O. bacoti with and without a bloodmeal. 10× microscopic view of adult O. bacoti mite: recently fed (A) and not recently fed (B), measuring approximately 1.0 mm in diameter.

Figure 2.

O. bacoti on cage filter top. Arrow indicates naked eye view of O. bacoti mite crawling over IVC filter top.

Figure 3.

Facility map with initial PCR results. Map showing the original 3 racks that tested positive for O. bacoti at quarterly health monitoring in December 2020. The plenum swab results of all racks in the facility (tested in January 2021) are also shown. The map does not accurately represent the layout of racks in the room, only the total number of positive and negative racks per room. Rooms not used for animal housing (that is, rooms used for cage wash, procedure spaces, storage, etc.) are shaded in blue.

Figure 4.

Timeline of O. bacoti PCR testing. Timeline of the outbreak from testing of wild mice to most recent health monitoring results. Rooms with at least one positive rack are counted as positive. Any positive room that tested negative on confirmatory testing is considered negative.