[CDHC] Syndrome vs. disease revisited

[Esther Peters]

Dear CDHC List Members,

The Coral Disease and Health Workshop: Developing Diagnostic Criteria that was held in Madison, WI, at the end of April, was an excellent forum in which scientists with diverse backgrounds in the study of corals and diseases came together for many fruitful discussions.  I think we made a lot of progress that week, but I heard about something that happened during the workshop and I felt I should address this topic and express my concerns.  I did not participate in either of the Tuesday afternoon discussion sessions to develop a process to name new coral diseases because I was preparing for the Pathologists' Colloquy.  I understand that in both sessions, use of the terms "disease" and "syndrome" were discussed.  Apparently in both sessions, coral biologists proposed using the term "syndrome" when naming health impairments or lesions when first noticed, i.e., no pathogen (microbial or otherwise) had been identified as the causal agent; then change the name to "disease" when pathogen(s) were identified.  Veterinarians noted that both "disease" and "syndrome" are used interchangeably in the biomedical literature for other organisms; if the coral biologists insisted on this naming convention, they would be the first to do so and pathologists would not necessarily recognize this convention.

I came into the study of diseases of corals and other organisms from the perspective of a biologist/marine scientist, but I have also had the advantage of studying under comparative histopathologists, taking courses in pathology taught by veterinarians (e.g., comparative pathology of laboratory animals at the Armed Forces Institute of Pathology) or human pathologists (at the Foundation for Advanced Education in the Sciences, NIH), I have worked with veterinarians on projects (Registry of Tumors in Lower Animals), and I have had the pleasure of having some of these pathology specialists in my disease courses and slide reading workshops.  They have a lot to teach us and we need to listen.

I was at a professional meeting a couple of years ago and a comparative pathologist came up to me and mentioned reviewing some NSF proposals and journal manuscripts on coral diseases.  This pathologist was appalled at the lack of knowledge of pathology terminology, disease mechanisms, and misuse of terms in the description of coral lesions and diseases. "Why don't they get it?" I was asked.  This pathologist noted that it was difficult for the scientific community to take the coral biologists seriously when they seemed to be incapable of  applying the body of knowledge of pathology and its terminology to the study of another group of animals.

Why not?  Having become trained in field and laboratory investigative techniques and terminology so that we can explore coral biology/ecology, perhaps we are not aware that disease investigations require additional understanding of the field of pathology.  Or perhaps we don't have time to pick up a pathology text or medical dictionary.  As an educator in diseases of corals and other organisms, I emphasize to my students that we must learn new definitions and explore the non-coral pathology literature.  I am guilty also:  when I first started out, I used the term "symptoms" in a published paper because I did not know that only humans can report these subjective feelings, in animals we note signs of disease.  But I was informed by others as to that error and joined in trying to make others aware of this (see "Epidemic misuse," E.H. Williams, Jr., L. Bunkley-Williams, J.M. Grizzle, E.C. Peters, D.V. Lightner, J. Harshbarger, A. Rosenfield, and R. Reimschuessel, 1993, Nature 364:664). 

So, I ask the coral biologists, since we have had a wonderful opportunity to interact with and learn from veterinary pathologists through this CDHC workshop, that we take the time to listen and apply their knowledge to our studies.  This will help others accept and understand our work.  The terms "syndrome" and "disease" are used interchangeably (check any medical dictionary).  Criteria for disease include any two of the following:  recognized etiologic agent(s); identifiable group of signs; or consistent anatomical alterations (gross or microscopic).  Thus, we have Alzheimer's disease, when we have no known agent(s); Down's syndrome, caused by triplication or translocation of chromosome 21; or toxic-shock syndrome, caused by toxin-producing staphlococci.  Because many of the impairments and lesions we are examining in the corals consist of an "aggregate of signs...constituting together the picture of disease" using the term "syndrome" is fine.  But, they can also be termed "disease."  

In e-mail discussions with Pam Parnell and Cheryl Woodley, it was noted that field biologists want to be able to give a name to an observation made on the reef and apply a disease/syndrome diagnosis based only on visual signs.  It is important to have identifiers of health impairments seen in the field, but describing a condition is not the same as diagnosing a condition (presumptive or definitive).  It is rare in veterinary/human medicine that a set of signs clearly identifies a single disease/syndrome; these are pathognomonic signs, such as those for smallpox.  Most signs of disease can be similar for two or more diseases/syndromes, which require application of appropriate diagnostic tests and procedures before the diseases/syndromes can be differentiated.  Thus, the Public Health Service Web site on case definitions (http://www.cdc.gov/nchstp/od/tuskegee/case_def.htm) defines these categories of disease: suspected case, probable case, clinically compatible case, epidemiologically linked case, supportive or presumptive laboratory results, laboratory-confirmed case confirmed case.  When we report diseases/syndromes based on field signs only, we need to be aware that we are identifying "suspected" or "probable" cases, not "confirmed."  Only with more diagnostic work (histopathology, microbiology, biomarkers, etc.) will we be able to confirm cases as this or that.  As Pam said "The dream of being able to discriminate/differentiate diseases based solely on visual signs in the field is one that has not proven to be attainable in human/veterinary medicine and I believe that with the exception of the RARE few select conditions, the same will hold true for diseases of corals and other invertebrates." 

What will be important is to develop case definitions for the signs of impairment we see in the field under whatever "field condition" disease/syndrome name is assigned, realizing these can change as more knowledge from definitive diagnostic tests becomes available.  Preliminary work on the "white syndromes" suggests that these are going to require microbiological and histopathological examinations to distinguish them (white pox, white plague, white band).   Let's listen and learn.

Esther Peters