Submitted to: American Journal of Veterinary Research
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 7/9/2004
Publication Date: 4/4/2005
Citation: Purdy, C.W., Layton, R.C., Straus, D.C., Ayers, J.R. 2005. Virulence of fungal spores determined by tracheal inoculation of goats following inhalation of aerosolized sterile feedyard dust. American Journal of Veterinary Research. 66(4):615-622.
Interpretive Summary: Feedyard dust contains endotoxins, bacteria and fungi and the endotoxins appear to be the most toxic component when inhaled. However, a number of fungi were identified from feedyard dust in past studies that are potentially pathogenic to the ruminant. Seven fungal types (genera) were compared in pathogenicity by injecting fungal spores weekly into the trachea of goats, over a six week time period. Two sets of controls were used, tent controls were injected with sterile saline into the trachea, and pen controls were not confined to a tent or injected into the trachea. Prior to injections into the trachea, eight goat groups were confined to a tent where they inhaled sterilized dust for four hours, the exception being the pen control group. Each group consisted of six goats. The most pathogenic fungi (in order of pathogenicity) were Mucor, Trichoderma, Chaetomium, and Stachybotrys. Pathogenesis was based on the presence of gross atelectatic (collapse of lung tissue) and consolidated lung lesions. Aspergillus, Penicillium and Monotospora fungi lung lesions were not significantly different than the tent control lung lesions. The tent control goats injected with saline had minor atelectatic lesions of the lungs, and the pen controls had no lung lesions. The results of this study alerts the scientist to which fungal types are the most virulent in ruminants, and then begs the question, why are they so pathogenic?
Technical Abstract: The objective of the study was to compare the fungal spore virulence of seven different fungi in goats given via tracheal inoculation following an organic dust aerosol exposure. A prospective randomized controlled study was conducted using 54 weanling Boar/Spanish goats. There were seven fungal treatment groups, a tent control group and a pen control group. Each group was composed of six goats. Experimental goats were injected via the trachea with 30 ml of fungal spore preparation. Tent control goats were similarly injected with 30 ml of physiological saline. The goats were exposed to autoclaved and aerosolized feedyard dust for four hours prior to injections, in a specially constructed tent. These treatments were performed weekly for six-weeks. There were significant differences (P minus/plus 0.0001) in severity of pathology among the seven fungal treatment groups. Pathogenesis was based on the presence of gross atelectatic and consolidated lung lesions, and histological lesions of the lung. The fungi in descending order of pathogenesis were: Mucor ramosissimus, Trichoderma viride, Chaetomium globosum , Stachybotrys chartarum, Aspergillus fumigatus, Penicillium chrysogenum, and Monotospora lanuginosa. Trichoderma viride spores were the most invasive, and were cultured from the bronchial lymph nodes and thoracic fluid of all six goats receiving this organism. Spores were histologically observed in lung tissue from all experimental groups, in tissues harvested 72 hours post inoculation. In summary four of seven fungal spore types induced significantly (P minus/plus 0.05) larger lung lesions compared to those induced by the other spore types and controls.