Tag: Aspergillus

Occupational Health and the Law: UK vs. US; I ask a question


A UK case report on Occupational Health and Safety, published in August, came to my attention today. Two NHS Occupational Health investigators from UK, Charles Poole of the Northern General Hospital, Sheffield, and M Wong of the Dudley & Walsall NHS Trust Health Center, presented two clinical cases associated with a relatively new occupational industry in that nation: “The separation of garden waste from domestic waste, its collection and processing in industrial composting sites, so as to reduce biodegradable waste going to landfill“.

It is well known that any kind of disturbance created in a given environment, for any reason, can often potentially release harmful substances in air in form of aerosols, or minute particles capable of floating in air. We have seen that with the yeast-like fungal pathogen, Cryptococcus gattii, which was found, via environmental studies, to be present in high concentrations in the soil of Vancouver Island (British Columbia, Canada), and to spread during dry summer weather likely as airborne particles (a.k.a. “propagules”). Release and dispersal of spores of various molds during large-scale air-disturbing activities such as construction, renovation and/or demolition of buildings is a well-studied phenomenon in the fields of Infection Control and Epidemiology; for example, see Krasinski et al., 1985; Streifel et al., 1983. The waste separation, collection and processing appear to be no different. The investigators write:

The process of composting organic matter encourages the production of bacteria, fungi, spores and endotoxins, which may be released to air in bioaerosols. Levels of bacteria and fungi up to 106 colony forming units/m3 in ambient air have been reported in relation to composting…

The problem has not been studied well at all in the population of waste-composting workers, because – as the investigators indicate – reports of illness in these workers are relatively rare. As a result, no safe levels of exposure to such potentially hazardous aerosols have been defined in this context, nor have been the exact conditions conducive to exposure; we don’t know if, and/or how much of, the exposure depends on variables such as composition of the compost, weather conditions, steps and systemic controls engaged during the separation and collection process.

In the existing clinical literature, one of the major culprits implicated in these environment-related diseases is the ubiquitous, spore-producing mold, Aspergillus, in form of its various species, mostly commonly Aspergillus fumigatus which is the etiological agent behind various diseases involving the upper (nose and upper part of the air-tube) and lower (lower part of the air-tube and the lungs) respiratory tract. Untreated or incompletely treated, these diseases can be severe and chronic. One particularly important manifestation is the Allergic Broncho-Pulmonary Aspergillosis (ABPA, in short), which is a complex or multi-component, immunologic, inflammatory response similar to allergies or hypersensitivities – which if not detected and treated early (with antifungals and steroid immune-suppressants) can lead to serious lung damage. ABPA is generally observed in people with certain debilitating conditions, such as cystic fibrosis, or immunosuppression, but rarely in otherwise healthy individuals. In ABPA, apart from classical respiratory symptoms, reduction in lung functions, and lung abnormalities observed under X-ray, certain allergy-related responses are noted in blood (more precisely, serum) – such as:

  • Type I hypersensitivity to bits and pieces of Aspergillus (all recognized as antigens by the immune system), leading to the excessive generation of allergy-associated antibody, called Immunoglobulin E (IgE). By its action, IgE causes release of highly inflammatory mediators, such as histamine, leukotriene, and prostaglandin, from immune cells, which have both immediate and long term deleterious effects.
  • Type III hypersensitivity to Aspergillus antigens, in which small complexes of these antigens with antibody run amok through the body, depositing in blood vessels, kidneys and joints – eventually leading to immune-mediated destruction of tissues at those sites.
  • Eosinophilia, in which eosinophils, a type of white blood cells, markedly increase in number in blood and/or tissues, a common occurrence in allergy and asthma, and in parasitic (worm) infections. Activated eosinophils, a member of immune defence, are capable of causing tissue damage by various mechanisms.

The UK case report describes two late-thirties, early-forties patients, both garden waste collectors by profession, and both diagnosed with ABPA at occupational health clinics; both responded to treatment and were released with the advice not to work with waste and compost. Another member of their team, who though not ill had symptoms of asthma and tested positive for high serum IgE to Aspergillus antigens (indicating exposure) was given the same advice.

The investigators go on to make some recommendations at the end of the report. They write:

Until the results of large epidemiological studies of garden waste collectors and industrial compost workers are known, the few case reports of ABPA […] would indicate that workers with asthma who are sensitized to A. fumigatus or who have cystic fibrosis, bronchiectasis or are immunosuppressed should not work with garden waste or compost, unless their exposure to airborne fungi can be controlled. Whether asthmatics who are SPT positive or specific IgE positive to A. fumigatus will go on to develop ABPA is unknown, but they should be made aware of the theoretical risk.

Annual health surveillance by way of a respiratory questionnaire and skin prick testing is also recommended for these workers. Other cases of ABPA or EAA in garden waste and compost workers should be sought and reported, until such time that the results of a national study of UK compost workers are known.

The recommendations gave rise to some germane questions in my mind. These are, of course, valid from a clinical standpoint, and made keeping the health and welfare of the patients in mind. But given that these are related to occupational health, how do these situations play out from the perspective of the employer? How are these situations different in the UK as opposed to in the United States? For example:

  • Can/should the employers (say, a waste management firm) mandate pre-employment testing for Aspergillus-specific IgE and skin prick hypersensitivity testing?
  • Can/should the employers refuse employment to a person who tests positive for IgE and hypersensitivity because of a theoretical risk? Relatedly, can/should such an employee be made aware of this theoretical risk?
  • Should such an employee choose to ignore this theoretical risk and accept the job (or continue on the job after a diagnosis) and become inflicted with ABPA, can/should the employee be able to claim occupational exposure and Worker’s Compensation?
  • Specifically in the US context, can a Health Insurance company demand the results of these surveillance tests for a person engaged in the waste management profession, and if positive, treat this as a pre-existing condition and refuse payment in the event the employee becomes ill and needs treatment?

I don’t have the answers to any of these questions. Perhaps someone conversant with labor and/or occupational health-related laws would care to illuminate me in the comments?

Poole CJ, & Wong M (2013). Allergic bronchopulmonary aspergillosis in garden waste (compost) collectors–occupational implications. Occupational medicine (Oxford, England) PMID: 23975883

Alcohol pwns inflammation; Or, saga of alcohol dehydrogenase from Aspergillus

Aspergillus fumigatus and various other Aspergilli are ubiquitous molds. These are hardy aerobic saprotrophs, growing as easily on breads and potatoes as on plants and trees. However, many Aspergilli are capable of growing in nutrient-deficient or nutrient-absent environments, and surviving in extreme conditions, such as high temperature (up to 55oC) and pH; for example, A. niger, the Black Mold, can grow happily on damp walls. I have observed A. fumigatus grow on the surface of a highly alkaline buffer (pH9; one of the pH meter standards).

In addition, A. fumigatus has been found to be highly tolerant of a wide range of oxygen levels, from atmospheric (21%) to moderately aerobic (~14% as in the lung alveoli), low (2-4% as in tissues), or hypoxic (<1.5% as found in compost piles), even to as low as 0.1% (Source: References available with the article under review). For an obligate aerobe, A. fumigatus has evolved remarkably robust mechanisms that allow it to tolerate and thrive in extremely hypoxic conditions. Needless to say that such mechanisms are likely to come mighty handy when causing disease.

Many of the Aspergillus species are known to cause disease in human and animals; of these, A. fumigatus is the most common causal agent of invasive pulmonary aspergillosis, a frequent and life-threatening complication in several immunosuppressed patient populations. Microscopic airborne spores (‘conidia’) of the mold, produced copiously, are inhaled by the host (human and animals). Immunocompetent hosts mount an innate immune response that eliminates the conidia; however, both immunocompromised hosts (such as cancer and transplant patients), who cannot mount an efficient enough response, and patients of other chronic lung/airway diseases (such as allergic asthma), who mount an excessive and unmitigated inflammatory immune response, are both vulnerable to the disease produced by A. fumigatus conidia.

In order to cause disease, the conidia primarily colonize airways or the lungs and, if successful in breaching the innate immune defence, germinates into hyphae, long finger-like projections, that invade the tissues and blood vessels. The mechanisms by which A. fumigatus is able to survive and grow in the host environment are not all well-understood. Based on previous studies which demonstrated that inability of certain mutants of A. fumigatus and the yeast pathogen, Cryptococcus neoformans, to grow under hypoxic conditions correlated with their reduced virulence in mouse models, Grahl et al., leading a multi-institutional group of investigators, set out to discover if A. fumigatus encountered such hypoxic conditions in the host lung and how it dealt with it while infecting the host.

They found that
(a) hypoxic microenvironments do occur in three distinct immunosuppressed murine models; they discovered this by using a chemical hypoxia detection agent, pimonidazole hydrochloride, that enabled cool, visual estimation of hypoxia in tissue via immuno-fluorescence (Figure 2). From the observed extent of hypoxia, fungal growth, and host immune responses in different immunosuppressive models, the authors inferred that “the host inflammatory response plays an important, but not exclusive, role in the generation of the hypoxic microenvironment.”
(b) alcohol is involved (perhaps not surprisingly, since hypoxia must be a stressful situation!).

No, really. Using a 400 MHz 1H-NMR, Grahl et al. could detect substantial ethanol in 4 out of 10 immunosuppressed mice infected with A. fumigatus at day 3 post-infection, but none in uninfected mice.

Figure S1 Grahl et al., 2011, PLoS Pathog 7(7): e1002145

In order to ensure that the ethanol in the lung was of fungal origin (and not a result of, say, some wild Bacchanalian orgy the mice partook of in the middle of the night), the authors tested and established that A. fumigatus was indeed capable of fermenting glucose to ethanol in vitro in media containing minimal (1%) glucose under hypoxic conditions (1% oxygen, Figure 1) after 48, 72, and 96 hours of growth.

Analyzing fungal genes involved in the alcohol fermentation pathway, the authors zeroed in on the A. fumigatus gene alcC encoding an alcohol dehydrogenase whose expression is enhanced significantly in response to hypoxia. Interestingly, this gene appeared not to be contributing to A. fumigatus‘s ability to grow under hypoxic conditions, nor to the virulence of the mold – since mutants lacking this gene was as virulent as the wild type A. fumigatus in all models of immunosuppressed mice. However, in the model with cyclophosphamide induced neutropenia, as well as the one with corticosteroid induced immunosuppression, the mutant mold strain producing no alcohol had greatly reduced growth with evidence of significant inflammation when compared to the wild type (Figure 8); in the mice infected with the mutant mold strain, increased recruitment of immune effector cells, particularly neutrophils (Figure 9), and associated altered cytokine responses (Figure 10) were observed in the lung.

In other words, the alcohol of fungal origin may modulate the immune response by suppressing the inflammation, which may offer a survival advantage to the mold in the tissue. As always, alcohol makes everything better, especially when the mold brews it by itself.

The authors discuss one important caveat of the study: the observation of ethanol production in only 4 of the 10 infected mice. They offer several possible reasons that may have contributed to this, such as the lack of a more sensitive method of detection, unsuitability of bronchoalveolar lavage fluid as the site of interest and so forth. It’d be of interest to see if better detection methods – which they say they are developing – improve upon these results.

Another important caveat that the authors didn’t discuss lies in the model, particularly the method of immunosuppression. Corticosteroid treatment impairs the antifungal action of immune effector cells; in mice treated with a single dose of the corticosteroid Triamcinolone, it is perhaps not surprising that at day 3 post infection there was a rebound increase in inflammatory cells, led by neutrophils, which are after all the principal effectors against Aspergillus. Unfortunately, the authors didn’t check cellular infiltrate status in mice immunosuppressed with cyclophosphamide which they gave at day -2 and day 3 of infection. Cyclophosphamide causes profound neutropenia – as the authors have noted – and at the given dose, the neutropenia usually lasts for 96 hours. So, by day 3, one would expect a rebound neutrophilia in these mice prior, of course, to the second dose. It would have been interesting to see the cellular composition of the infiltrates in the cyclophosphamide-treated mice. One would expect the inflammation in this case to be largely macrophage/monocyte in nature, perhaps.

Overall, a rather interesting study with some intriguing findings; a good read.

Pathogens&rft_id=info%3Adoi%2F10.1371%2Fjournal.ppat.1002145&rfr_id=info%3Asid%2Fresearchblogging.org&rft.atitle=In+vivo+Hypoxia+and+a+Fungal+Alcohol+Dehydrogenase+Influence+the+Pathogenesis+of+Invasive+Pulmonary+Aspergillosis&rft.issn=1553-7374&rft.date=2011&rft.volume=7&rft.issue=7&rft.spage=0&rft.epage=&rft.artnum=http%3A%2F%2Fdx.plos.org%2F10.1371%2Fjournal.ppat.1002145&rft.au=Grahl%2C+N.&rft.au=Puttikamonkul%2C+S.&rft.au=Macdonald%2C+J.&rft.au=Gamcsik%2C+M.&rft.au=Ngo%2C+L.&rft.au=Hohl%2C+T.&rft.au=Cramer%2C+R.&rfe_dat=bpr3.included=1;bpr3.tags=Biology%2CMedicine%2CResearch+%2F+Scholarship">Grahl, N., Puttikamonkul, S., Macdonald, J., Gamcsik, M., Ngo, L., Hohl, T., & Cramer, R. (2011). In vivo Hypoxia and a Fungal Alcohol Dehydrogenase Influence the Pathogenesis of Invasive Pulmonary Aspergillosis PLoS Pathogens, 7 (7) DOI: 10.1371/journal.ppat.1002145