Effects of environmental temperature, relative humidity and vaccination on Pasteurella haemolytica in lungs of mice.
Groups of mice were kept in four combinations of environmental temperature (8 and 20 degrees C) and humidity [50 per cent and 90 per cent relative humidity (RH)]. The mice were anaesthetized and inoculated intranasally with Pasteurella haemolytica growing logarithmically. Groups of 11 mice were killed at 0.5 h intervals for 6 h after inoculation and the number of colony-forming-units (CFU) of Pasteurella haemolytica in the lungs was determined. The CFU in the lungs of mice were affected by a significant interaction of temperature, relative humidity and time after inoculation (P less than 0.01). From 0.05 to 5.0 h after inoculation, fewer CFU were found in the lungs of mice kept in 8 degrees C 50 per cent RH than in mice kept in 8 degrees C 90 per cent RH, 20 degrees C 50 per cent RH and 20 degrees C 90 per cent RH. In each environment, CFU in the lungs of mice increased from inoculation to approximately 3.5 h after inoculation and then decreased (P less than 0.01). In a similar experiment in an environment of approximately 20 degrees C and 50 per cent RH, there were significantly fewer CFU in the lungs of mice vaccinated intranasally 21 days earlier with live P. haemolytica than in the lungs of mice either vaccinated intranasally with formalized P. haemolytica or not vaccinated with P. haemolytica (P less than 0.01).
University of Liverpool, Department of Veterinary Pathology, Cheshire, U.K.
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Woldehiwet
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Rowan
D000818:Animals; D003114:Colony-Forming Units Assay; D006813:Humidity; D008168:Lung / Q000382:microbiology*; D051379:Mice; D008807:Mice, Inbred BALB C; D010325:Pasteurella / Q000302:isolation & purification*; D010326:Pasteurella Infections / Q000517:prevention & control*; D013696:Temperature; D014611:Vaccination