Appendix THE LOGISTICS OF WORKING WITH POISON OAK This appendix is part of my dissertation, which I wrote before I changed my name to Barbara Lachenbruch. Gartner, Barbara L. 1992. Consequences of the vine vs. shrub growth forms for biomechanics, growth, and hydraulic architecture of western poison oak, Toxicodendron diversilobum. Ph.D. Dissertation, Stanford University.
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Appendix
THE LOGISTICS OF WORKING WITH POISON OAK
This appendix is part of my dissertation, which I wrote before I changed my name to Barbara Lachenbruch.
Gartner, Barbara L. 1992. Consequences of the vine vs. shrub growth forms for biomechanics, growth, and hydraulic architecture of western poison oak, Toxicodendron diversilobum. Ph.D. Dissertation, Stanford University.
133
"The poisonous weed, being in shape but little different from our
English ivie; but being touched causeth reddness, itchings, and lastly
blysters, the which howsoever, after a while they pass away of
themselves without further harme; yet because for the time they are
somewhat painefull, and in aspect dangerous, it hath gotten itselfe an
ill name, although questionless of noe very ill nature."
Smith 1609, as quoted in Kligman 1958)
(Captain John
In choosing to study the ecology of western poison oak
(Toxicodendron diyersilobum (T. & G.) Greene, Anacardiaceae, also known
as~ diyersiloba), I was aware that I was at risk of contracting
dermatitis and of causing other people to contract dermatitis. Here I
describe the nature and seriousness of the dermatitis, and discuss my
personal experiences with the allergen: my changing sensitivity over
time, and practical methods I employed to minimize exposure to the
allergen and to decrease the severity of my reaction after exposure. I
would like to caution that these methods worked well for me, a person of
low to moderate sensitivity, but that because of the complexity of the
immune system's reaction, these methods may not be successful for other
people.
THE DERMATITIS CAN CAUSE SERIOUS DISCOMFORT
More cases of allergic contact dermatitis are caused in the United
States by plants of the genus Toxicodendron than all other
"provocatives" combined (Fisher 1986) . At any one time, about half of
the U. S. population is sensitive to poison oak (reviewed in Epstein
1987), and more people would become sensitive if exposed over a period
134
of time (Fisher 1986) . Almost a quarter of the workers who are flown to
California, Oregon, and Washington to fight fires have to leave the
fireline because of poison oak dermatitis (Oltman and Hensler 1986).
Poison oak and poison ivy dermatitis is the biggest single cause of
injuries for USDA Forest Service employees, and accounts for more than
10% of all lost-time injuries for their forestry workers (Oltman and
Hensler 1986). In California about 0.3% of the occupational injury
reports in agricultural workers are due to poison oak dermatitis
(Gellin, Wolf, and Milby 1971), and this costs about 0.1% of the state's
Workman Compensation budget (Epstein 1974) . Because Toxicodendron is
distributed over most of the contiguous United States (Gillis 1971),
people involved in recreational activities such·as hiking and mountain
biking frequently encounter poison oak or ivy and suffer the
consequences.
RELATIONSHIP OF EXPOSURE TO SENSITIVITY
The type of allergic contact dermatitis caused by Toxicodendron is
termed type IV delayed hypersensitivity. The basic mechanism of
sensitization is believed to work as follows (Breathnach 1986, Epstein
1989). The allergens, called urushiols, are a class of ortho catechols
with side chains of 15-17 carbons and various numbers of double bonds.
In the presence of oxygen, urushiols become quinones and bind to
proteins on certain cells of the skin surface. These cells are believed
to present signals related to the urushiol on their outer membrane
inside the body. Also presented are certain proteins that flag the cell
as an active part of the immune system. Helper T-cells react to these
signals by initiating production of at least four classes of cells or
135
factors: effector T-cells (also called killer T-cells) which circulate
in the body and kill the flagged skin cells, memory T-cells which enable
the body to have a reaction to the flags should they be presented some
time in the future, suppressor cells, and circulating suppressor
factors, both of which inactivate the effector T-cells. One's
sensitivity to urushiol, then, depends upon the relative population
levels of these immune system fa c tors. The first time one is exposed to
poison oak there are no killer cells, and so one will not react (unless
one has memory cells resulting from previous sensitization through
cross-reactive allergens. All members of the genus Toxicodendron are
cross-reactive, as are several other members of the Anacardiaceae, such
as mango, cashew, and probably Schinus; Fisher 1986) . With time, the
relative populations of effector T-cells and suppressor T-cells will
probably change, resulting in different sensitivity of the individual as
a function of quantity and frequency of his or her exposure to
urushiols.
At present, the best way to predict one's reaction to poison oak
with time is to gauge from an one's previous experience. Some
individuals will become less sensitive the more they are exposed to
urushiols and others will become more sensitive (Epstein 1974) . About
15% of individuals are truly tolerant : they can not be sensitized even
with very high doses of urushiol (Kligman 1958, Epstein 1959) .
Epidemiological studies can predict the proportion of the population
that is sensitized to poison oak or ivy at any time, but these studies
do not control for amount of exposure or a patient's history of exposure
(Epstein 1974) .
136
Over the course of my study of poison oak, Dr . William Epstein
(UCSF Medical Center) monitored my sensitivity to urushiol in order to
give me an objective indication of my status . Had tests shown that I
was becoming increasingly sensitive, I would have needed to find ways to
decrease my exposure, and had my sensitivity decreased, I could have
dispensed with some of the time-consuming precautions I was taking . The
tests consisted of placing four known quantities of urushiol on my inner
forearm, then monitoring reactions two days later (method described in
Epstein 1989). Dr. Epstein applied 2 . 50, 1.25 , 0.50, and 0.25 ~g of
urushiol in acetone to an area 1 . 2 em in diameter, where pure sap
generally corresponds to a dosage of 2-2.5 ~g of urushiol (Epstein
1990) . For the first trial, he used a larger range of quantities in
order to bracket my sensitivity.
I am relatively insensitive to poison oak ; some peop l e react to
urushiol at less than 0 . 004 % the dosage necessary to cause a reaction in
me (Epstein 1984) . My sensitivity to urushiol remained relatively
constant throughout the study, although it was higher at the outset,
before I had had any but recreational exposure for the previous several
years (Fig. 1). It also rose towards the middle of 1989, when my
exposure to poison oak had been steady and high . Since ceasing to
handle poison oak , my sensitivity has remained constant , but lower than
at the outset of the study . Note that the vertical a x is in Fig . 1a
shows only the bottom quarter of Dr . Epstein's grading system, which
spans from no reaction (0) to 4+ , and my strongest reactions were 1+ .
For a person with my level of sensitivity , desensitization is not
feasible. The oral preparations sold over-the-counter until the late
1970s have been shown to be ineffective , for the quantities o f urushio l
2.50 1+
0.50 +1- .. -- .... - ---.. ------
Q) ... :I
high
en moderate 0 Q. >< Q)
low
none
1987
r--1 i I
I
I I I I
' I
' I I I
' I
' I
' I
' I
' I
' I
' I I
1988
r--1 i l I ' I ' r ' ' ' ' ' ' ' ' , L
I I
'
137
\ .. ----A)
1989 1990
I I
I : I
' ' I ' ' ' ' I
' I
' I I I I I I I B) I
Figure 1a) . My sensitivity to poison oak throughout this study at four
levels of urushiol, 2.50 ~g, 1.50 ~g, 1.25 ~g, and 0.50 ~g applied on
1.2 em diameter spots on my forearm. Severity of reaction increases
with numerical value. b). My exposure to poison oak throughout this
study, (subjectively determined) .
138
were much too low to cause any real effect (Epstein 1974). Oral
urushiol preparations are used successfully, however, to induce some
level of desensitization in extremely sensitive individuals (Epstein
1984, Watson 1986). Unfortunately, the procedure is quite inconvenient:
desensitization only decreases a person's sensitivity to the level of a
moderately sensitive person, it takes two to four months to become
desensitized, a person must continue on the medication to remain
desensitized, and the treatment itself often causes uncomfortable side-
effects.
HOW I LESSENED MY CHANCES OF CONTRACTING AND CAUSING OTHERS TO CONTRACT
DERMATITIS
Urushiol is readily transferred from one item to another, and i t
remains stable (in the absence of high humidity) for long periods of
time. One individual is reported to have contracted dermatitis from
handling 100-year old herbarium specimens (Gillis 1975). Therefore, it
was essential that I learned not only how to avoid contracting
dermatitis, but how to keep equipment and other objects free from
urushiols . I highly recommend the pamphlet "Preventing and treating
poison oak and poison ivy" (USDA 1981) . My recommendations for other
people of similar sensitivity are summarized in Table 1 . I used the
following methods .
Avoidance
The best way to avoid dermatitis is to avoid contact with the
plant. However, almost all of my work required contacting the plant, so
the next best alternative was to handle the plant gently .
139
Table 1 . Recommendations to minimize reactions to poison oak in a
person of low to moderate sensitivity. Urushiols are the class of
substances that cause allergic reactions.
Avoidance :
Cl othing :
Chemical barriers :
Solvents :
Learn to recognize the plant in all seasons , and
avoid it .
If you touch the plant, do not break its surface :
move through it slowly and carefully .
Decontaminate all objects that have contacted
poison oak to avoid re-exposing yourself o r
e xposing other people.
Cover parts of your body that are likely to contact
the plant .
Wrists are particularly sensitive areas, and if you
will be handling the plant , wear long socks on
your arms (provide cut - outs for your finge r s).
Apply spray antiperspirant to your skin before
e xposure.
Soaps and detergents are effective emulsifiers but
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Appendix
THE LOGISTICS OF WORKING WITH POISON OAK
Citation: Gartner, Barbara Lachenbruch. 1990. Appendix, The logistics of working with poison oak. Pages
132-162, in Consequences of the vine vs. shrub growth forms for biomechanics, growth, and hydraulic architecture of western poison oak, Toxicodendron diversilobum. PhD Dissertation, Dept. ofBiological Sciences, Stanford University. 162 pp.
Other articles related to the dissertation: Gartner, B. L., C. Wasser, E. Rodriguez, and W. L Epstein. 1993. Seasonal variation of urushiol
content in poison oak. American Journal of Contact Dermatitis 4:33-36. Gartner, B. L. 1991. Structural stability and architecture of vines vs. shrubs of poison oak,
Toxicodendron diversilobum. Ecology 72 :2005-2015. Gartner, B. L. 1991. Relative growth rates ofvines and shrubs ofwestern poison oak,
Toxicodendron diversilobum (Anacardiaceae). American Journal of Botany 10:1345-1353. Gartner, B. L. 1991. Is the climbing habit of poison oak ecotypic? Functional Ecology 5:696-704. Gartner, B. L. 1991. Stem hydraulic properties of vines vs. shrubs of western poison oak,