Response to pulmonary challenge of various feedlot dust associated fungal spores in a caprine model

Many genera of fungi are found in the dust of feedlots. Several of these fungi are capable of inducing infections or toxic reactions in animals. Animals raised in feedlots are continually challenged by the dust containing these fungi. The hypothesis of this study was that fungal conidia from various genera differ in their virulence in the lungs of goats following feedlot dust exposure.

Nine groups of six goats were used in these experiments, one pen control group that received neither dust nor saline, one tent control group that received dust and saline containing no conidia, and seven groups each challenged transtracheally with dust and spores from one fungus. The seven fungi, Aspergillus fumigatus, Chaetomium globosum, Monotospora lanuginosa, Mucor ramosissimus, Penicillium chrysogenum, Stachybotrys chartarum, and Trichoderma viride, were administered weekly in 30 ml of physiological saline.

In order to determine the virulence of the fungi, the body temperatures and white blood cell counts were evaluated throughout the challenges, and measurements of the atelectatic surface area and histopathological examinations were made at necropsy. The fungi were placed into 4 categories of virulence based primarily on the diagnoses, which were then supported by the other parameters. The first category contained the most virulent fungus, M. ramosissimus. Category two contained the second most virulent fungi, S. chartarum and T. viride. The least virulent fungi, C. globosum, P. chrysogenum, and A. fumigatus were placed in the third category. Finally, M. lanuginosa was considered to be avirulent and was placed in the last category, as challenge with this organism resulted in the least observable pathology.

Resultant antibody production by these animals was also determined and was correlated with the virulence of various fungi. It was found that antibody production against the fungi was independent of virulence.

A tenth group was added and challenged with S. chartarum in order to determine the catabolism and detectability of macrocyclic trichothecene mycotoxins. It was found that these mycotoxins were detectable at a level of 1.63 ng/ml of serum 6 days after challenge, and in the lymph node at 340 ng/g of tissue after 24 hours.