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Is "Parasites" the Correct Word?

Posted Nov 01 2008 2:41am
Following my post on Amanda Peet's calling parents who don't vaccinate their kids "parasites," I've pondered about the technical applicability of the term.
In ecology, there are three basic categories of symbiosis, or dependant ineractions with members of another species. The definitions, according to the MadSci Network, are as follows:

PARASITISM:
(+/-) Where one organism benefits (the parasite) and the other is
negatively affected (the host). Fleas on a dog are a great demonstration of Parasitism at work.

COMMENSALISM:
(+/--)Where one organism benefits and the other neither benefits nor is
negatively affected. An example is barnacles on a whale - the barnacle gets
a place to live and relative safety, and the whale seems unaffected.

MUTUALISM:
(+/+)Where one or more organisms benefit from the partnership occuring
between them. Clown fish in anemonies and photosynthetic zooxanthallae
algae in corals are both examples of an "intimate" relationship occuring
between two species.


Technically, these terms apply only to interactions among different species, not within a single species, but the term "parasite" is often used colloquially to refer to fellow humans.

However, according to these definitions, Peet should have accused non-vaccinators of being "commensalists." Such people don't generally harm others, yet enjoy the benefits of herd immunity, or the fact that infectious microbes have little chance to spread when there is such a small number of potential human hosts. And if you, like me, understand that vaccines pose virtually no harm, then the only "benefit" extracted is the ability to avoid an extra trip or two to the doctor, and to spare a kid from a shot.

There are circumstances, however, in which refusing vaccination can cause considerable harm to others. Inoculations do not work on immunosuppressed people, because the process requires a functioning immune system. Caccinations work by introducing a "fake" microbe that has similar protein markers to an actual pathogen, but is really a benign imposter. This leads your immune system to copy many lymphocytes (B and T white blood cells) that can recognize and attack any pathogen with the specific protein marker.

Why can't your body just do this to fight the real pathogens when they really attack? They do, but the difference between beating a virulent pathogen and falling prey to it is simply a matter of timing.
Having once been introduced to what the immune system "thinks" is the pathogen, the body creates "Memory" B and T cells. The process of recognition, proliferation, and attack by the immune system would normally take about two weeks, which would often be too late. By having the memory B and T cells immediately always ready on standby, your body can now beat the polio, measles, or other virus before it gets very far. Vaccination is the boy scout of medicine: it does nothing directly to fight or kill any bacteria or virus. It simply allows your body to "be prepared" for the future.

Because the success of a vaccination is dependent on the body's ability to respond to the vaccine and create functional "memory lymphocytes," people with poorly-functioning immune systems (whether due to a congenital deficiency, uncontrolled HIV, certain leukemias, etc.) are non-responsive (or much less responsive) to vaccination. In other words, their white blood cells will be "underenthused," when meeting the "antigen," or specific protein marker, presented by the vaccine for the first time, and their bodies will not create the memory cells ready to respond quickly to the actual attack.

Thus, theoretically, if a non-vaccinated child exposes a pathogen to an immunosuppressed child, then this can no longer be considered "commensalism." The non-vaccinated child (well, his parents) caused others unecessary harm. I do not know how common this possibility is; it may have a very low incidence, and therefore have little practical relevance. If, however, many parents suddenly decided not to vaccinate their children, the incidence would surely increase, could cause major harm to immunocompromised people.

Would this be considered parasitism? The non-vaccinators injured others because of their decision. Then again, they didn't actually injure the same people from whom they extracted benefit. In fact, the non-vaccinators presumably contracted and suffered from the illness, and did not benefit from herd immunity, altogether. However, they still affected others. A world of inusfficient communal vaccination is most dangerous to those for which vaccination is not an option.

Should we force people to vaccinate their children?
On the one hand, I don't believe in forcing people to do much of anything. Also, because of herd immunity, not every one actually requires vaccination, provided that the non-vaccinated children are roughly randomly distributed in the population, and don't live in vulnerable pockets.

On the other hand, while adults can do what they want, parents are required to provide minimum care for their children (not just caring as an emotion, which I'm sure people like Jenny McCarthy possess. Intentions don't always count). Additionally, as explained above, non-vaccinated children are in a position to potentially harm others. Perhaps we should consider this a "tort" issue. That way, parents could do what they want, but must understand that they are responsible (i.e. can be sued) if this decision negatively impacts others.
Even this presents its own complications. Unlike a "slip and fall" or medical malpractice, it is very difficult to determine who directly caused an immunosuppressed person to contract an illness. It could be anyone with whom she came into contact. Additionally, this contention raises the question: Do immunosuppressed have any personal responsibility to avoid place in she might contract a dangerous illness?

I suppose the only good strategy to avoid these problems is to maintain good education and PR about the benefits of vaccination.

I think some of these benefits are plainly apparent through the following charts:

TEN PRINCIPAL CAUSES OF DEATH IN MASSACHUSETTS - 1900
1. CARDIOVASCULAR-RENAL DISEASES
2. INFLUENZA & PNEUMONIA
3. TUBERCULOSIS
4. GASTROENTERITIS
5. MALIGNANT NEOPLASMS
6. DIPHTHERIA
7. TYPHOID & PARATYPHOID
8. MEASLES
9. WHOOPING COUGH
10. SYPHILIS

TEN PRINCIPAL CAUSES OF DEATH IN United States - 2005
1. HEART DISEASES
2. CANCER
3. CEREBROVASCULAR DISEASES
4. CHRONIC LOWER RESPIRATORY DISEASES
5. ACCIDENTS (UNINTENTIONAL INJURIES)
6. DIABETES MELLITUS
7. ALZHEIMER’S DISEASE
8. INFLUENZA & PNEUMONIA
9. NEPHRITIS, NEPHROTIC SYN. & NEPHROSIS
10. SEPTICEMIA
Sources:
1900 Massachusetts data was obtained from one of my pathology lecture notes handouts. I can ask my instructor for the specific source, for anyone who is interested. 2005 U.S. Mortality Data taken from National Center for Health Statistics, Centers for Disease Control and
Prevention, 2008.
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