G. Berton Davis M.D.** and Gordon F. Comstock M.D. *
It has been noted by one of the authors (Comstock, G, unpublished communication) that there was a direct relationship between the incidence of pruritic distal lower-extremity erythematous papules (PDL-EEP) and the number of visits to a small mountainous village and an inverse relationship between these aforementioned PDL-EEPs and the daily use of insect repellant. Based upon references in the literature which imply a direct relationship of pruitis to residence in southern climes (1, Nash, O., The Face is Familiar, 1941***) and the personal experience of the authors (who spent formative years in the State of Georgia), these PDL-EEPs were clinically diagnosed as "chiggers." Chiggers (Trombicula alfreddugesi, Figure 1) are cute little mites that live in the tall grass in the lower latitudes, and when one walks through the grass, the larval chiggers crawl up one's distal lower extremity until they reach a cosy spot, where they bite, inject an anticoagulant fluid, and feed. (2, Ogg, B, University of Nebraska Cooperative Extension in Lancaster County; 5, Comstock, J.H., Insect Life, 1913) Repeated exposure results in a delayed hypersensitivity reaction. (3, Arthus, N.M., 1903) Based upon reviews in the literature (4, "Bug Off," Consumers Reports, July 1993), experimental trials performed previously by one of the authors (Comstock, G, article in contemplation) had determined that daily use of an effective insect repellent such as diethyltoluamide (DEET) would substantially reduce this infestation.
After spending one full week in a small mountainous Honduran village with an abundance of tall grass, the subjects were transported to sea level. After giving informed consent, the study subjects lavaged their distal extremities with 3.5% saline. (6, "Composition of Seawater," Funk & Wagnall's New Encyclopedia) The number of erythematous papules (see Figure 2) was enumerated on each lower extremity below the knee by one of the authors and recorded by the other. Inquiry was made as to whether each subject had used an insect repellant (e.g., DEET) on a daily basis or not. The data were analyzed by commonly used mathematical techniques until the desired result was obtained. (7, Huff, D, How to Lie with Statistics)
The results are shown in Figure 3. The subjects were classified in two groups: those that used insect repellant daily (n=1) vs. those that did not (n=5). For the first group, the mean number of pruritic distal lower-extremity erythematous papules was 8 (range 8 to 8); while for the second group the mean number was 54 (range 14 to 123).
This study demonstrates the value of putting insect repellant on your ankles daily, prior to sallying forth into the underbrush.
(1) Nash, O., The Face is Familiar, Garden City Publishing Co., Garden City, 1941***
(2) Ogg, B, University of Nebraska Cooperative Extension in Lancaster County, http://lancaster.unl.edu/pest/resources/chiggers(008).shtml
(3) Arthus, N.M, "Injections répétées de serum du cheval zhez le lapin," Comptes rendus des séances de la Société de biologie, Paris, 1903; 55:817-820
(4) "Bug Off," Consumers Reports, July 1993
(5) Comstock, J.H., Insect Life, D. Appleton & Co., New York, 1913
(6) "Composition of Seawater," Funk & Wagnall's New Encyclopedia, New York, Vol.18, 1979
(7) Huff, D, How to Lie with Statistics, W. W. Norton & Co., New York, 1954
Figure 1: Velvet Mite Adult (Trombidium sp.) - photo by Jim Kalish, University of Nebraska Department of Entomology, Lincoln (used with permission) http://lancaster.unl.edu/enviro/Images/Insects/velvetmite2.jpg
* From NY/HELP Honduras, a project of the New York Conference of the United Church of Christ and the Disciples of Christ. Address reprint requests to Dr. Comstock at the Centro Medico La Laguna, La Laguna de Mataderos, Yoro, Yoro, Honduras.
** Dr. Davis is of the "Third Age," (i.e., a "Senior Citizen") and therefore under Honduran law is entitled to go to the head of the line.
*** "There was a young belle of old Natchez whose garments were always in patchez. When comment arose on the state of her clothes, she drawled, 'When Ah itchez, Ah scratchez.'"
29 March 2002