Health Effects of Asbestos | Microorganism of the Month: Aeromonas species
By Dr. Harriet Burge, EMLab P&K Chief Aerobiologist and Director of Scientific Advisory Board
Nature of Asbestos
Asbestos is a mineral with a unique crystal structure. Individual crystals of asbestos are long and thin (needle like) and these crystals occur as a "palisade" in tightly packed bundles. When disturbed, these bundles break and crystals are released individually, either whole or as fragments. This crystal structure is responsible for the health effects of asbestos. The fibers are strong and resemble those of cellulose in that they can be woven and spun. On the other hand, they are silicates and not digestible as are cellulose fibers. There are two overall types of asbestos. The most commonly used in industry is chrysotile asbestos. The second group is amphibole asbestos which is divided into actinolite, tremolite, anthophyllite, crocidolite and amosite.
Health Effects of Asbestos
Health effects of asbestos depend on inhaling the fibers. Most of these fibers are immediately exhaled. However, some are inhaled deeply into the lungs and become lodged in the tissues. Because they are minerals, enzymes that would facilitate their digestion are not present, so they probably remain in the lung throughout life. The amphibole types of asbestos appear to remain in the lungs the longest, which may lead to increased risk of disease. Lung cancer, mesothelioma, asbestosis, and other lung and pleural cavity disorders may result from significant exposure to asbestos. Health effects from asbestos exposure may continue to progress even after exposure is stopped.
Figure 1: Chrysotile bundle from World Trade Center dust.
Source: USGS Denver Microbeam Laboratory
Asbestosis is not a cancer, but rather a result of inflammation and irritation of lung tissue that result from inhaling the fibers. It is a serious disease that leads to lung scarring, difficulty breathing, and an impaired ability to transfer oxygen and carbon dioxide in and out of the lungs. The progress of the disease is slow, with first diagnosis generally occurring 10-20 years following initial exposure. Symptoms of asbestosis include shortness of breath, cough with mucus, chest tightness, chest pain, loss of apetite, and crackling sounds in the lungs. Risks for the development of asbestosis primarily are controlled by the amount of exposure, the length of time over which exposure occurs, and the type of asbestos inhaled.
Lung cancer is a malignant tumor that grows within the lung, invading the air passages and gradually blocking them so that air exchange is not possible. The disease is generally diagnosed 10-15 years following initial exposure. It is most likely in cigarette smoking. Symptoms include cough, wheez, weight los, labored breathing, and coughing up blood. Persistent chest pain and anemia may also be present. The combination of asbestos and smoking create greater risk for lung cancer than the sum of the individual risks for these exposures.
Mesothelioma is a rare cancer of the lining of the lungs and sometimes the peritoneum. Exposure to asbestos is the primary cause for mesothelioma. Diagnosis generally occurs at least 30 years following the first exposure to asbestos. Mesothelioma leads to a build up of fluid in the pleural cavity or peritoneum. In the pleural cavity the fluid leads to shortness of breath and chest pain. In the peritoneum, there may be swelling and pain, and even bowel obstruction, anemia, and fever. All of these symptoms are common to other diseases as well, so it is important to inform the physician of asbestos exposure.
Exposure to Asbestos
Asbestos is a part of the natural environment, and is present in ambient air and water. Concentrations in ambient air range from 1x10-5 to 1x10-4. People are more likely to experience asbestos-related disorders when they are exposed to high concentrations of asbestos, are exposed for longer periods of time, and/or are exposed more often. Disease may result with exposures for 40 years to concentrations of 0.125 - 30 fibers/ml. Inhaling longer, more durable asbestos fibers (such as tremolite and other amphiboles) probably contributes both to the risk and severity of asbestos-related illness.
Disease-causing exposures occur primarily in asbestos miners and in industrial workers that routinely handle asbestos. Asbestos remediators may also be at risk. Building occupants are unlikely to be sufficiently exposed to lead to illness. However, mesothelioma has been diagnosed in family members of asbestos miners, and residents who live close to asbestos mines.
1. National Cancer Institute: Asbestos Exposure - Questions and Answers
2. USGS: Tabulation of Asbestos-Related Terminology (824k PDF)
3. USGS: Denver Microbeam Laboratory - Image Gallery
4. Agency for Toxic Substances and Disease Registry: Asbestos - Health Effects
By Gregorio Delgado, EMLab P&K Analyst
Aeromonas comprises a group of Gram-negative bacteria that inhabit water worldwide. Traditionally, the genus has been included as part of the family Vibrionaceae, which include pathogenic water inhabitants such as Vibrio, the causal agent of cholera. However, molecular studies have demonstrated that these two genera are distantly related, and the family Aeromonadaceae has been proposed to include Aeromonas as the type species as well as other three more genera. The Subcommittee on the Taxonomy of Aeromonadaceae, Vibrionaceae and related organisms of the International Committee on Systematics of Prokaryotes (ICSP) recognize 17 species within the genus based on DNA hybridization groups. The best known of them is Aeromonas hydrophila.
Aeromonas cells are straight, rods (bacillary) or elongated spheres (coccobacillary). The cells are 0.3-1 micrometers in length and occur singly or in pairs, rarely in short chains. Some strains are non-motile and others are motile, the latter producing a single polar flagellum or, in some species, lateral flagella are also present (EPA, 2006).
Figure 1: Transmission electron micrograph of an Aeronmonas bacterial cell showing pili (thin fibers) and flagella (thick fibers).
Source: Northwest Fisheries Science Center
Aeromonas grows well on 5% sheep blood agar when incubated at 35°C or ambient laboratory conditions for a minimum of 24 hours, forming large, round, raised, opaque colonies. The organism is a facultative anaerobe, meaning that it can live with or without oxygen. Most species are beta-hemolytic, which means that they can lyse red blood cells. Some species ferment lactose. Aeromonas resembles members of the family Enterobacteriaceae, but notably differ by their positive oxidase test (Forbes et al, 2002).
Aeromonads naturally occur in a wide variety of aquatic environments, mainly freshwater but also in brackish, polluted or chlorinated, ground, surface, estuarine and occasionally marine waters, where they are a normal part of the microflora. Their presence does not indicate that water has been polluted. They can also be found in foods, such as red meats, seafood, raw milk and cheese, in sewage before and after treatment, in biofilms of drinking water distribution systems. They can be associated with the intestinal track of cold and warm blooded animals, including humans, with or without evidence of gastrointestinal disease (EPA, 2006). Aeromonads are not considered part of the normal human flora, although gastrointestinal carriage has been observed in approximately 3% of individuals. Therefore its presence in stool specimens does not indicate disease.
Aeromonas species can infect frogs, reptiles and fishes. They are probably the most common bacterial cause for disease diagnosed in the warm-water aquaculture industry (Francis-Floyd, 2002). However, some researchers consider them as secondary invaders of previously weakened hosts. In humans, Aeromonas species have been associated with gastrointestinal disease and wound infections, although not all strains appear to be pathogenic. The most important pathogens are A. hydrophila, A. caviae and A. veronii biovar sobria, accounting for 85% of all clinical cases of Aeromonas-related gastroenteritis and bacterial septicemia. They are typically acquired through two routes: ingestion of contaminated food or water, or exposure of open wounds or mucosal surfaces to contaminated water or soil, traumatic inoculation by fish fins or fishing hooks (EPA, undated). According to the Center for Food Safety (CFSAN) of the U.S. Food and Drug Administration, two distinct types of gastroenteritis have been associated with A. hydrophila: a cholera-like illness producing a watery diarrhea and a dysenteric illness characterized by loose stools containing blood and mucus. Disease is usually acute in children but in adults tends to be chronic. Immunocompromised patients are also susceptible to systemic Aeromonas infections (Murray et al, 2005).
Figure 2: Scanning electron micrograph of Aeromonas sp. bacteria adhering to human epithelial cells.
Source: Northwest Fisheries Science Center
A. hydrophila is listed on the first and second U.S. EPA Contaminant Candidate List (CCL) of potential waterborne pathogens, the primary source of priority contaminants for the EPA’s drinking water program. It has also been also included in the Revisions of the Unregulated Contaminant Monitoring Regulation (UCMR) for Public Water Systems. The EPA Method 1605 has been validated for detection and quantification of this species in drinking water. This method provides a direct count of the bacterium based on the growth of yellow colonies on the surface of a membrane filter placed on a selective medium that partially inhibits other bacteria and allow Aeromonas species to grow (EPA, 2001).
Usually Aeromonas species are killed by the levels of chlorine-based disinfection used in water treatment facilities. However, single cells associated with particles in raw water may evade disinfection, as well as any break may allow untreated or sewage water to enter the distribution system (EPA, undated). Despite the presence of aeromonads in the drinking water distribution system, no outbreak attributed to them has been reported in the United States (EPA, 2006). Special concerns are users of untreated water in developing countries, mainly those individuals with wounds or underlying diseases.
1. FDA: Center of Food Safety and Applied Nutrition
2. EPA (2001): Method 1605: Aeromonas in Finished Water by Membrane Filtration Using Ampicillin-Dextrin Agar with Vancomycin (ADA-V) (pdf).
3. EPA (2006): Aeromonas: Human Health Criteria Document (pdf).
4. EPA (undated): Aeromonas Detection: What Does It Mean?
5. Francis-Floyd, R. (2002). Aeromonas Infections, FA14 Document. IFAS Extension, University of Florida.
6. Forbes, B. A., D. F. Sahm and A. S. Weissfeld (2002). Bailey & Scott's Diagnostic Microbiology. Eleventh Edition, Mosby, Saint Louis, MO.
7. International Committee on Systematics of Prokaryotes
8. Murray, P. R., M. A. Pfaller and K. S. Rosenthal (2005). Vibrio and Aeromonas. Chapter 32: 339-346. In: Medical Microbiology. 5th Edition, Elsevier.
9. Northwest Fisheries Science Center
This article was originally published on June 2007.