Mycotic Infections in Livestock

(Aspergillus fumigatus)

Pathogenic fungi can affect livestock via infection of the gastrointestinal tract and hematogenous distribution to tissues (1). In humans, nosocomial disseminated mycoses are becoming more prevalent (2). Immunoincompetence is the main predisposing factor for nosocomial infection in humans. Mortality rates in immunocompromised patients are high (>50%; 2). The most common mycotic infections in humans are mediated by Aspergillus fumigatus and Candida albicans (2).

Livestock are also susceptible to mycotic infections (3). A recent survey found mycotic GI lesions in 5% of slaughter cattle with the most common infecting pathogens being A. fumigatus and C. albicans (4). Predisposing factors to mycotic infections included feeding of moldy feed, immunocompromising diseases, acidosis, anti-microbial therapy, reflux of abomasal contents, metabolic disturbances, post-partum stress, viral erosive disearses such as IBR, anti-inflammatory treatment and abortion (4). Primary portals for mycotic invasion included the omasum and the Peyer’s patches. Infection is typically associated with GI hemorrhage. Recent studies have linked jejunal hemorrhage syndrome (JHS, hemorrhagic bowel syndrome, acute hemorrhagic enteritis) and abortion to A. fumigatus infection (3). However, it appears that A. fumigatus may not be the sole cause. Its feeding may require other predisposing conditions, such as stress or immunosuppression, for manifestation of pathogenicity (5).

Research at Oregon State University has determined that JHS (HBS) dairy cows and cows with mycotic abortions have significant amounts of A. fumigatus DNA in their GI tracts, mesenteric lymph nodes, liver, blood and cotyledon (3). Some asymptomatic cows harbor A. fumigatus DNA in their blood, however, these levels of DNA are typically far lower (1/20th to 1/ 50,000th) levels detected in sick cows.

Interpretation of your results

OmniGen’s methods for quantitation of A. fumigatus required almost two years to develop. DNA from your blood / tissue sample(s) was extracted using a standard DNA extraction method (Qiagen) and then purified. The DNA sample was then assayed for the presence of A. fumigatus genomic DNA using A. fumigatus -specific primers and a BioRad MyiQ thermocycler. Primers were designed to hybridize to unique A. fumigatus sequences in the fungal internally-transcribed spacer (ITS-1) domain. A Sybr-Green real-time polymerase chain reaction (PCR) method was then used to amplify the DNA in your sample(s) and determine the concentration of A. fumigatus DNA. A standard curve using purified genomic A. fumigatus DNA was run with all assays.

Results are provided using both a “+” system and by providing actual concentration of A. fumigatus DNA in your sample(s).

ScoreResultGU x 10000/ml
—-negative0no detectable A.fumigatus
+low> 0-1trace
++borderline1 – 3positive
+++positive3 – 10positive
++++strong positive10 – 25strong positive
+++++very strong positive> 25very strong positive

Value > 3×10000 GU/ml are rarely observed in healthy (asymptomatic) cows or in non-HBS downer cows.

Caution: Use results only as an adjunct to other diagnostic indicators. Detection of A. fumigatus alone may not be taken as a definitive diagnosis. Values are expressed in “genomic units” (GU). One hundred GUs are the equivalent genomic DNA present in one A. fumigatus organism (i.e., one spore). In blood, however, not all GUs are viable. A significant proportion of GUs may arise from digestion of A. fumigatus genomic DNA and liberation of intact ITS-1 DNA fragments.

References

  1. Jensen H, Shoenheyder H, Basse A. Acute disseminated aspergillosis in a cow with special reference to penetration and spread. J. Comp Path 1991; 104: 411-417.
  2. Chen SCA, Halliday CL, Meyer W. A review of nucleic acid-based diagnostic tests for systemic mycoses with an emphasis on polymerase chain reaction-based assays. Med Mycol. 2002; 40: 333-357.
  3. Puntenney S, Wang Y, Forsberg NE. Mycotic infections in livestock: recent insights and studies on etiology, diagnostics and prevention of hemorrhagic bowel syndrome. Proc. SW. Nutr Manag Conf. p.49-62, 2003.
  4. Sarfati J, Jensen H, Latge J. Route of infections in bovine aspergillosis. J Med Vet Mycol 1996; 34: 379-383.
  5. Kirkpatrick MA, Timms LL, Kersting KW, et al. Case Report – jejunal hemorrhage syndrome of dairy cattle. Bov Prac 2001; 35: 104-115.