Influence of Rack Design and Disease Prevalence on Detection of Rodent Pathogens in Exhaust Debris Samples from Individually Ventilated Caging Systems

Abstract

Sampling of bedding debris within the exhaust systems of ventilated racks may be a mechanism for detecting murine pathogens in colony animals. This study examined the effectiveness of detecting pathogens by PCR analysis of exhaust debris samples collected from ventilated racks of 2 different rack designs, one with unfiltered air flow from within the cage to the air-exhaust pathway, and the other had a filter between the cage and the air-exhaust pathway. For 12 wk, racks were populated with either 1 or 5 cages of mice (3 mice per cage) infected with one of the following pathogens: mouse norovirus (MNV), mouse parvovirus (MPV), mouse hepatitis virus (MHV), Helicobacter spp., Pasteurella pneumotropica, pinworms, Entamoeba muris, Tritrichomonas muris, and fur mites. Pathogen shedding by infected mice was monitored throughout the study. In the filter-containing rack, PCR testing of exhaust plenums yielded negative results for all pathogens at all time points of the study. In the rack with open air flow, pathogens detected by PCR analysis of exhaust debris included MHV, Helicobacter spp., P. pneumotropica, pinworms, enteric protozoa, and fur mites; these pathogens were detected in racks housing either 1 or 5 cages of infected mice. Neither MPV nor MNV was detected in exhaust debris, even though prolonged viral shedding was confirmed. These results demonstrate that testing rack exhaust debris from racks with unfiltered air flow detected MHV, enteric bacteria and parasites, and fur mites. However, this method failed to reliably detect MNV or MPV infection of colony animals.

Figure 1.

Location of mouse cages on ventilated racks containing 5 cages of mice per agent tested. The image on the left is rack 1 and blower. The image on the right is rack 3. Mice were housed with one agent per row, and the numbers 1–5 indicate the location of the 5 cages per agent. Rows: a, uninfected mice; b, uninfected mice; c, MNV; d, MPV; e, MHV; and f, Sencar mice with Pasteurella pneumotropica, Helicobacter ganmani, Helicobacter typhlonius, Myobia musculi, Myocoptes musculinus, Syphacia obvelata, Aspiculuris tetraptera, Entamoeba muris, and Tritrichomonas muris. For rack 2 containing 1 cage of mice per agent, the mice were housed in column 1, with the same rows containing the same agents as rack 1 containing 5 cages.

Figure 2.

(A) Racks 1 and 2 with blower airflow pattern. The white arrows show the direction and pathway of the supply air, and the black arrows show the direction and pathway of the exhaust air. The white arrowhead indicates the prefilter access door on the blower unit. The inset shows the ports through which air enters and leaves through an individual cage. (B) Rack 3 with blower airflow pattern. The white arrows show the direction and pathway of the supply air, and the black arrows show the direction and pathway of the exhaust air. The inset shows the ports through which air enters and leaves through an individual cage. Air enters through an open port on the cage lid but exits through a filtered port on the cage lid.

Figure 3.

(A) An image of the prefilter utilized in racks 1 and 2 with the attached high-efficiency filter. The black arrow indicates the 2-cm sections that were removed for testing. (B) Rack 3 customized with sampling ports at the level of each horizontal plenum. The black arrow indicates an open sampling port. For sampling, the port was opened and a swab inserted into the port; the sample was collected by rubbing the swab on the horizontal plenum surface at the junction of the horizontal and vertical plenum.