Science and Medicine: New Disease Discovery
Tuesday, February 5, 2008; 11:00 AM
Washington Post staff writer David Brown, and Michael T. Osterholm, director of the Center for Infectious Disease Research and Policy at the University of Minnesota, were online Tuesday, Feb. 5 at 11 a.m. ET to discuss a new illness that has surfaced among workers at a pork factory.
Read about it in the Monday Science Page story: Inhaling Pig Brains May Be Cause of New Illness (By David Brown, Feb. 4)
A transcript follows.
David Brown: Greetings chatters! We have a pretty interesting subject today, the appearance of what seems to be a new disease of the nervous system that has been found in a dozen slaughterhouse workers in Minnesota.
We are very lucky to have with us a distinguished epidemiologist, public health authority, and scientific investigators, Michael T. Osterholm. He is the former state epidemiologist of Minnesota who has been involved in many interesting invesigations in the past. He is now director of the Center for Infectious Disease Research and Policy at the University of Minnesota. He is an expert on pandemic planning and has been an advisor to the federal government on that issue.
So let's begin.
Cincinnati, Ohio: Can we see any similarities between the lesions found in the brain of slaughterhouse workers and other human diseases such as MS?
David Brown: The neurologist at the Mayo Clinic with whom I spoke said that the MRI of the patients show nerve-root thickening suggestive of inflammation. They have not seen abnormalities of the white matter in the brain, which I believe is characteristic of multiple sclerosis. There have been no brain biopsies of the slaughterhouse workers. At least one has had a nerve in the foot biopsied and it shows mild inflammation but is apparently not terribly abnormal. In general, this condition appears to be a disease of the peripheral nervous system, in other words the nerves outside the brain and spinal cord.
1) Are there any similarities of the patients (other than they are Spanish-speaking immigrants) such as their previous jobs or home communities?
2) Do any of the pigs come from herds with commonalities (we assume the pigs are American and not from some other country such as Canada)?
3) Why the MN and other pig processing plant in Indiana and not elsewhere (and how much investigation is going forward among other plants/employees)?
4) Are there any reports from Chinese and Korean epidemiologists about workers handling the brain matter (or consumers eating it)? 5) What are the MN and IN Agriculture Health folks doing with these data?
David F. Goldsmith, PhD
Department of Environmental & Occupational Health, George Washington University, School of Public Health
Michael T. Osterholm: A very detailed and well condcuted case-control study of ill and non-ill workers was conducted by the MN Dept of Health. There were occupational, social, ethnic, demographic or economic factors were associated with illness status other than working at the head table (i.e. where the brain extraction occurs) or performing other procedures at that work area.
More than 90% of the pigs come from an area of approxiamtely 100 miles of Austin, MN. There is no evidence of any relationship between specific hogs processed and human illness. And there are no reports of any illness in the pigs processed over the past several years that can be related to this illness or even ones posibley associated with any foodborne disease. This is why there is no concern about the saftey of the pork leaving this plant.
The final answer on why not elsewhere except the QPP and Indiana plants is still under investigation. However, its investigators to date have only identified 3 plants in the US that used high pressure air for brain extraction. These include the QPP and Indiana plants. There is an active effort to identify other plants around the world that may have used this procedure.
David Brown: QPP is Quality Pork Processors, the company that owns the slaughterhouse and processing plant where the ill workers are employed.
Washington, D.C.: Are there any similarities with this and Mad Cow disease?
David Brown: Mad cow disease is caused by a prion, which is an infectious protein, a very mysterious entity. Prion diseases are characterized by slow onset and a relentless downhill course. There is no evidence of prions or any other infectious agents (such as bacteria, viruses, parasites) in the people this new condition. Plus it comes on more quickly than mad cow disease, which takes years to appear. This condition also gets better to some extent when people are removed from their usual jobs in the plant, suggesting that some exposure there brings it on or exacerbates it. This also is unlike an infection, and particularly unlike mad cow disease.
Washington, D.C.: I wanted to know were there any investigations carried out at Korea and China where the meat was exported. Did people consuming it suffer any illness
Michael T. Osterholm: The consumption of pig brains is a very common and long standing practive in many areas of the world, including Asia and South America. There is no evidence that consuming pig brains is at all associated with this outbreak. If in fact it is caused by an immune reaction of the human to exposure to very small particles of the aersolized pig brain, the inhalation route is the only important route of exposure. The typical foodhandling practices that occur in the home or resturants would not be a source for aersolizing the brain material and thus not a risk factor. This is not a foodborne disease and thus we should not confuse food consumption with this situation.
Michael T. Osterholm: I have been a consultant to the Hormel company for almost 10 years, assisting them with their program in food safety and quality. Hormel has been an international leader in the area of food safety. When this outbreak was first detected they asked me, because of my almost 30 years of leading many internationl/national outbreak investigations, to assist them and QPP with this situaiton. While none of us ever want to "have to work up an outbreak," this outbreak investigation been a very positive experience due to the wonderful collaboration between all the investigators, QPP, the workers and their union.
Arlington, Va.: How serious is this new disease to the general population? Since it seems specific to the workers, can it be controlled?
David Brown: As both The Post's story and the one today in The New York Times make a point of saying, there is no threat to the general population from this "outbreak." There is no evidence it is a transmissible (that is, contagious or infectious) disease. (Since it seems to arise from inhalation of pig brain material, people might want to keep away from school science projects and home activities that aerosolize brain matter, but that shouldn't be hard to do!) The three slaughterhouses that use compressed air to "harvest" pig brains have stopped doing that, which appears to have prevented any more cases. Only the plant in Minnesota have confirmed cases; the few cases in Indiana are suspected only at this point.
Alexandria, Va.: Since we're at what appears to be an early stage of discovering this disease, are researchers learning anything from this situation that may help prevent future outbreaks? or help existing disorders or conditions that may have similarities to what these workers are experiencing?
David Brown: There are dozens of tests and studies underway or being planned. It seems likely that some interesting immunology will come out of this weird story. In particular, scientists want to find out what material in the pig brain is stimulating the immune system, which aspects of immunity are involved (antibodies certainly, but perhaps more), and what part of human nerves are being attacked by the immune response. There's a lot more to the story that will come out in months, and probably years, ahead.
Alexandria, Va.: Were the affected workers wearing masks of any type? If not, would a basic mask prevent the inhalation of these "aerosoled brain matter"?
Michael T. Osterholm: The workers were not wearing masks at the time of exposure as this type of process has never been considered an inhalational risk situation by public health officials, occupational risk experts or the pork industry. Now of course the procedure of using high pressure air to remove brains is no longer used in the QPP plant. In fact, brains are not being harvested at all at the plant.
Alexandria, Va.: Are you satisfied with the speed by which this illness surfaced onto the public health radar? What lesson should we take from this so as to improve our awareness of emerging diseases?
Michael T. Osterholm: I believe this situaiton was detected as quickly as could be hoped for given the rarity of the illness and the atypical illness presentation. The QPP nursing staff first noted the commonality between 3 ill worker late last summer and encouraged them to seek medical care. Shortly there after the local medical clinic (a Mayo Clinic facility) noted a similar pattern of illnesses through an interpreter who worked with the same patients. As more cases were detected shortly there after the MN Dept of Health was alerted and an investigation begun.
Washington D.C.: I understand that the etiology of this disease is still uncertain, but is there any alternative explanation to the symptoms? What I mean to ask is if there is any infectious agent that is present within the slaughtered pigs that may cause these novel neuropathies?
Michael T. Osterholm: An exhaustive study has been done looking for infectious agents in the patients and there is no evidence that this condition is directly related to an infection or a post-infectious disease immune response. In addition, the epidemiology of the case ilnesses does not at all fit with an infectious disease spread. The only cases in the QPP plant are associated with exposure at the head bench area. If this was an infectious disease in the pigs we would expect to see employee cases in other areas of the plant not related to the brain extraction process or other exposures not related to inhalation. Finally, there is no disease in pigs identified that is similar to the human disease seen in the workers. And the pig herd health is confirmed for each pig sent to the processing plant before it is slaughtered.
Rochester, Minn.: Have anti-inflammatory interventions, such as corticosteroids, improved clincal status?
David Brown: High-dose steroid (Solumedrol) has been given to numerous patients, with improvement. Those who have not improved have also gotten intravenous immunoglobulin. I believe at least a couple of people have not had much improvement with either, or at least not lasting improvement.
LaPaz, Bolivia: Does this disease come with loss of legs's muscular mass?
David Brown: I have not heard whether there is loss of muscle mass. I frankly didn't ask the two physicians I spoke to. I suspect that if loss of muscle was a prominent part of the illness they would have mentioned it. But obviously that's just a guess on my part.
Cincinnati, Ohio: What are the most likely specific components of the pig brain that are affecting these workers? Why do you think this hasn't been recognized previously in these workers?
David Brown: The scientists are looking at a wide array of molecules and structures on the nerve fibers and axons that may be stimulating the immune response. There are a huge number of possibilities and no results are available yet.
The "why now?" question is always an interesting one for new diseases. If the past experience with other new diseases holds here, we can be quite certain that a few cases occurred before the "index" (or first case) was detected in this cluster. It always takes a while for signal to be detected over noise. Which is to say there were probably some cases in the past, including some that may have come to medical attention. But their work-related nature and the association with the "head table", etc. were not recognized. What happened that made the cases more frequent now--and therefore made the cluster detectable--is not known. It may be there was some subtle change in brain-harvesting technique that was not even recognized by the workers themselves or the plant management. There are people trying to answer this, but it may be hard.
Columbia, MO: So what's the big deal? This isn't an outbreak in a true classical sense with an infectious disease, nor does it seem to be a food safety issue.
Michael T. Osterholm: QPP and the state and federal investigators take this situation very seriously as it is truly an outbreak of a significant disease in workers. For that reason the first order of business was to determine the likely source of exposure to the factor responsible for the cases and eliminate that. So, ending the use of high pressure air extraction of the brains has accomplished this (i.e. no new cases witrh onset of illness since the process was stopped.) This is an example of the classic "pulling the pump handle." That is always the first order of priority in an outbreak investigation-make certain there are no new cases. Then the investigation continues to document what happened so that safeguards can be put into place so that a similar outbreak or ongoing case occurrence never happens again. Finally, every effort is being made to find out what actually caused the illness to try and help the remaining cases that have not fully recovered do so with an approapriate medical treatment.
David Brown: BTW, "pulling the pump handle" refers to the action that ended a cholera outbreak in London in 1854. John Snow, a physician, charted the cases in the epidemic and found that they clustered around a pump on Broad Street, where people went to get water. The authorities took the handle off the pump, preventing people's exposure to the contaminated water there, and the epidemic stopped. John Snow is considered the father of modern clinical epidemiology.
Appleton, Wisc.: During the evaluation process, was there any airborne collection that could quantify "material" in the air? Were there any variations in the sanitation processes?
Michael T. Osterholm: These studies have been undertaken. To date there have been no remarkable findings, particularly that explain the clustering of cases in the head bench area. There were no significant changes in any aspect of plant sanitation; this plant has aways had an outstanding record in plant sanitation as determined by the USDA and even the employee union.
David Brown: It's worth noting that everyone says that everyone is cooperating with everyone else. There are no resports of company resistance to any part of the investigation.
Washington DC: Mr. Brown mentioned an article in the New York Times. What does it cover that was not reported by the Post's article? Have there been any similar findings in European pig producers?
David Goldsmith, PhD
washingtonpost.com: A Medical Mystery Unfolds in Minnesota (New York Times, Feb. 5)
David Brown: There are a few details that I did not have the space to mention, and the NYT reporter talked to one of the workers who is affected. And there are pictures of the outside of the plant. Go The Times site and you be the judge!
Baltimore, Md.: What technique do the other plants use to extract the brain? Should there be a restriction on harvesting of any brain tissue until the etiology is understood?
Michael T. Osterholm:
Other plants do harvest pig brains as there is high demand for them in many areas of the world. However, these plants use a mechanical cutting of the skull for removal. None of these plants have reported a similar humna illness to date however only limted case ascertainment has been done in these plants. If this illness was associated with an infectious diease in pigs we would have expected to see human cases in other plants where these pigs brains are handled. This is one more piece of evidence that these illnesses are not due to an infectious agent.
David Brown: We've come to the end of hour. As I mentioned, there will be more answers, although probably not terribly soon. But stay tuned. I want to thank Dr. Osterholm for spending time here today; we all benefited from his expertise.
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