Avian pathogen screen in air | bulk (Histoplasma, Cryptococcus & Chlamydophila by PCR) [APS]
Published: July 8th, 2009
Revised: March 21st, 2023
The fungi Histoplasma capsulatum and Cryptococcus neoformans are two agents of serious disease in otherwise healthy, immunologically normal humans and animals. Both agents are endemic in Canada, and both occur in the droppings of certain bird species in addition to other materials. Additionally, the bacterium Chlamydophila psittaci is the causative agent of psittacosis and is associated with bird feces (although in Canada this agent is predominantly restricted to captive parrots).
Histoplasma capsulatum is the causative agent of histoplasmosis, a non-communicable infectious disease that is mostly acquired by inhalation of environmental particulates. Greater than 95% of infections are clinically silent. These cases are detected sporadically by later serological tests or by the observation of small lung calcifications by x-ray. Clinically significant pulmonary histoplasmosis, in general, is often related to inhalation of a large inoculum load, or to the presence of an underlying immunodeficiency in the patient. Secondary blood-borne spread occurs in a small subset of cases, typically in people with serious pre-existing immune dysfunction. When treated, histoplasmosis generally responds well to systemic antifungal drugs. Histoplasma capsulatum occurs in accumulations of bat, pigeon or starling guano, particularly where those materials have come in contact with moist soil, where it grows as a cottony white mould until changing to a budding yeast-like phase in human or animal tissue. Only a few parts of Canada lie within the endemic distribution of H. capsulatum. Scattered cases and moderate to low levels of subclinical exposure are only found in southern areas of Quebec, Ontario, and Manitoba, as well as a few parts of Alberta, New Brunswick and Nova Scotia.
Members of the C. neoformans species complex are widely distributed basidiomycetous yeasts (more closely related to mushrooms than moulds) that occur in bat guano and bird droppings, particularly those of pigeons and chickens. Cryptococcus neoformans is an occasional cause of pneumonia and meningitis in people who inhale typically large quantities of infectious material. Immunocompromised people are more susceptible to cryptococcal disease, developing it occasionally following contact with birds and bird nesting materials.
Chlamydophila psittaci is a bacterium that can cause a respiratory disease in birds known as psittacosis or parrot fever. The bacterium can also infect humans who come into close contact with infected birds or their droppings. Outside of tropical regions, the agent is primarily restricted to captive birds especially parrots. Symptoms of psittacosis in humans include fever, headache, muscle aches, and a dry cough, which can progress to severe pneumonia if left untreated. Although rare, psittacosis can be a serious illness, especially for people with weakened immune systems.
The recognition and elimination of infective reservoirs of these agents is central to prevention. This test uses an extremely sensitive and specific PCR-based method to detect both agents in bulk material samples or large volume, time-integrated air samples collected on polycarbonate membrane filters. Bulk samples should be collected dry in a clean, new, food-grade, zippered freezer bag. Damp or moist samples should be refrigerated after collection prior to delivery to the laboratory. Air samples should be collected on a 25 or 37 mm 0.4 um membrane filter with a minimum volume of 1 cubic metre of air. The value of air sampling for these agents is likely to be low where there is little ongoing mechanical disturbance or aerosolization of dusts. In general, bulk samples are preferred for this test. Samples should be placed individually in a clean, new, food-grade, zippered freezer bag, and delivered to the laboratory within 24 hr of collection.
The detection of H. capsulatum is accomplished using primer sets that target portions of a catalase gene known as the “M-antigen”. Cryptococcus neoformans group is detected by primer sets that target a gene involved in capsular synthesis, CAP59. This method cannot distinguish between living and dead cellular material. Chlamydophila psittaci is detected by targeting a portion of the major outer membrane protein gene cluster (omp1). A negative result does not necessarily refute the presence of potentially infectious material in the area tested, since only a small amount of material is subjected to the test. The testing of multiple replicate samples is helpful to establish confidence on the generalizability of results. A positive result, however, may provide information that is useful in public health interventions.
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Laboratory code: APS
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