This week we continue our series on bird diseases by diving into a fungal bird disease: Aspergillus fumigatus. We will begin by characterizing the physical and genetic qualities of Aspergillus fumigatus and move into a more detailed analysis of how it is spread. Finally we will wrap up by discussing what precautions you can take to keep our favorite holiday bird safe and healthy for the days to come.
Aspergillus fumigatus is a type of fungus that is commonly found in decaying matter and produces spores from the conidiophores during asexual reproduction that are 2-3 microns in size. Its optimal growth range is 37-50 degrees Celsius which is critical for the carbon and nitrogen cycle for breaking down plant and animal matter. It has a filamentous structure under the microscope and its fruiting bodies appear grey during spore release. A study in Nature found 29.4 million base pairs and 5,000 noncoding regions in its genome (Galagan et al., 2010).
A. fumigatus is an opportunistic pathogen that typically attacks immunocompromised individuals, such as those suffering from previous infections, or the very young. The most typical route of infection is pulmonary where the spores germinate in the warm moist areas of the lungs. The fungi evade immune systems attack through macrophages and lactoferrin (iron scavenger molecule) by overwhelming macrophages and lactoferrin production (Ben-Ami et. al., 2005). After successful germination, the fungi penetrate the pulmonary cell walls and in severe cases spread in the blood system for nutrient acquisition. The nutrients include iron, nitrogen, polypeptides, and byproducts, including gliotoxin, that suppress neutrophil activation through superoxide and apoptosis (Ben-Ami et. al., 2005).
In birds, A. fumigatus is spread principally through contaminated feed products or in unsanitary bedding conditions, however, it has been documented that spores can come through improperly cleaned air vents. Air sampling techniques have found seasonal variation among the types of Aspergillus with variations being significantly higher in the winter than the summer (Ben-Ami et. al., 2005). This may be a result of more spore production in drier conditions—there is an inverse relationship between humidity and spore production. Additionally, poults can be exposed to asymptomatic adult carriers and contract it through mechanical interaction. It typically attacks poults 5 days to 8 weeks of age, however, it has been found in birds with underlying genetic or other disease related conditions. Because the fungus mainly attacks the lungs, symptoms can include heavy or rapid breathing and yellow or grey nodular lesions in the respiratory tract, especially lungs and air sacs.
Currently there are no vaccinations or cost effective cure for A. fumigatus infections, therefore once an infection has been identified the bird must be isolated and culled. Vaccine trials have shown no immunity and in some cases a second exposure has proven fatal. The best protection against A. fumigatus infection is delivered through the preparation of clean bedding, food, and air and the prompt culling of infected animals (Ben-Ami et. al., 2005). In addition, increasing the humidity levels and a light spraying of germicide when the poluts are of sufficient size will also keep the risk of contracting the spores lower (Larson et al., 2007).
In summary, there is a lot of work that goes into creating healthy turkeys but with some simple steps and proactive work flocks will not be overrun by pathogenic A. fumigatus. The fungus is very necessary in the carbon and nitrogen cycle and only causes opportunistic disease in immunocompromised birds. So, enjoy your holiday turkey and next week we will continue our series and investigate more illnesses that plague our avian friends.
Image Credit: Champoeg Farm
Ben-Ami, R., Lewis, R. E. and Kontoyiannis, D. P. (2010), Enemy of the (immunosuppressed) state: an update on the pathogenesis of Aspergillus fumigatus infection. British Journal of Haematology, 150: 406–417. doi: 10.1111/j.1365-2141.2010.08283.x
Galagan, J. (2005, October 5). Sequencing of Aspergillus nidulans and comparative analysis with A. fumigatus and A. oryzae. Retrieved November 16, 2014, from http://www.nature.com/nature/journal/v438/n7071/full/nature04341.html
Larson, C., Beranger, J., Bender, M., & Schrider, D. (2007). Common Diseases and Ailments of Turkeys and Their Management. In How to Raise Heritage Turkeys on Pasture (pp. 35-52). American Livestock Breeds Conservancy.