PART X — ENVIRONMENTAL CONTAMINANTS 



These latter reactions, although so far 

 few in number, often terminate in 

 death. It is suspected that they may 

 be related to decomposition products 

 in aged stores of the drug. 



Diagnosis — The classical proce- 

 dure of diagnosing malaria on the 

 basis of finding the parasite remains 

 unchallenged. The paucity of tech- 

 nicians able to apply the established 

 procedures accurately reflects the lack 

 of interest in most medical schools 

 and training centers in tropical medi- 

 cine in general and malaria in par- 

 ticular. 



Direct immunofluorescence using 

 tagged immunoglobulins to signal the 

 malaria parasites in blood smears is a 

 workable procedure, but it is not ex- 

 tensively used, and not likely to be. 



Indirect immunofluorescent proce- 

 dures utilizing prepared malaria 

 smears, sera being examined for pres- 

 ence of antibody, and tagged anti- 

 globulins to the host serum have 

 shown much promise, particularly in 

 permitting study of the immune status 

 of populations. It is not probable, 

 however, that such techniques will 

 find application in the diagnosis of 

 the immediate malarial illness in a 

 human. 



Further refinements are to be an- 

 ticipated, involving the application of 

 newer techniques to obtain purified, 

 or separated, parasite and serum frac- 

 tions. Practical application of such 

 methodology by routine diagnostic 

 laboratories will come slowly, if ever. 



Vectors — The maintenance of ma- 

 laria in the human community is a 

 reflection of vector-host-parasite in- 

 teraction, as well as environmental 

 factors. (See Figure X-19) The vector 

 must have an association with hu- 

 mans, and the parasite must be avail- 

 able. This relationship is highly com- 

 plex put nonetheless subject to analy- 

 sis by construction of models which 

 can be adapted to computer analysis. 

 Macdonald's contributions to such a 

 model are well known. 



It becomes apparent that many or 

 most of the variables introduced into 

 the equation are ill defined, and that 

 many of these relate to the mosquito 

 vectors. A single model can only ap- 

 ply to a single vector, and there are 

 several dozen well-recognized vectors. 

 For each vector, field information is 

 necessary relating to distribution, 

 densities, longevity, flight range, feed- 

 ing habits vis-a vis humans as con- 

 trasted to other blood or food sources, 

 resting habits, frequency of refeeding, 

 susceptibility to insecticides, and sus- 

 ceptibility to the malaria parasite in 

 question. As such questions are ex- 

 plored, there is frequently need for 

 more specific taxonomic detail, and 

 certain of the earlier recognized vec- 

 tors, such as Anopheles gambiae, 

 have been split into a series of recog- 

 nizable entities (races? species?) with 

 distinctly different biology. 



Control — This topic must be con- 

 sidered with respect to the several ac- 

 cessible components: the parasite, the 

 host, and the vector. 



The finding of drug-resistant para- 

 sites complicates greatly the already 

 complex problem of control through 

 direct attack on the parasite through 

 mass chemotherapy of human popu- 

 lations. Drug-resistant parasites have 

 thus far not been recognized in Africa. 

 Should they be transplanted there 

 through migrations of parasitemic hu- 

 mans, or through development locally, 

 the result would be disastrous. 



The host can be approached through 

 immunization procedures. Recent 

 work in rodent malaria systems on 

 developing immunogens derived from 

 sporozoites is encouraging enough to 

 merit extension of such studies to hu- 

 mans. Other approaches to the host, 

 apart from such obvious measures as 

 use of protective clothing, bed nets, 

 and insect repellents — all of limited 

 effectiveness unless conscientiously 

 employed — have centered largely on 

 the insect-repellent aspect. An ap- 

 proach through development of sys- 

 tematic insecticides or repellents, 

 which have had some success in pro- 



Figure X-19 — AREAS OF MAJOR MALARIA POTENTIAL 



Malaria mosquitos cannot survive in areas where temperatures fall below 15° centi- 

 grade and annual rainfall is less than 1,000 millimeters. By combining the 15° 

 centigrade isotherm (broken line) and the 1,000-millimeter isohytel (solid line), 

 one can determine the areas where mosquito survival is continuous (shaded sec- 

 tions), with consequent heavy risk of malaria, and the areas (hatched sections) 

 where unusually heavy rainfall can permit mosquitos to survive and malaria to 

 spread. 



366 



