Bronchoalveolar Eosinophilia in Guinea Pigs Harboring Inapparent Infections of Paraspidodera uncinata

Abstract

During the course of experiments examining the changes in cell populations in bronchoalveolar lavage (BAL) fluid in 3-11-wk-old guinea pigs, a marked increase in the numbers of eosinophils was observed in BAL fluid in untreated control animals from historical levels (observations made over the previous 2 yr) of 8.8 +/- 1.5% to levels greater than 16% and up to 44%. Repeated occurrence of this phenomenon in several different groups of guinea pigs that appeared clinically normal and the impact on our experimental studies led us to attempt to identify the cause of increased inflammatory cell numbers in these guinea pigs. Examination in 2 groups of animals of whole blood and lung tissue for the presence of bacteria or fungi revealed minor bacterial infections in one group but not the other, whereas both exhibited elevated eosinophil numbers. At necropsy, 41.7% and 60% of the animals in the 2 groups harbored the nematode Paraspidodera uncinata. Guinea pigs exhibiting eosinophil numbers in BAL fluid comparable to our historical levels were then inoculated with approximately 100 embryonated eggs of P. uncinata and developed elevated eosinophilia in BAL fluid compared to sham-inoculated animals (significant at 2 of the 3 examination times postinoculation). These findings suggest that P. uncinata is capable of causing changes in inflammatory cell populations in the lungs of guinea pigs and illustrate the importance of subclinical or inapparent infections in experimental design and interpretation.