Biologists seek halt to parasitic diseases New attacks on parasitic diseases are desperately needed. But such attacks depend on knowledge of the parasites and their infecting mechanisms. More bits and pieces were added to that knowledge base at a joint meeting of the American Society of Tropical Medicine and Hygiene and the American Society of Parasitologists in Washington, D.C. Biologists and biochemists at the meeting heard of application of the latest investigative methods to an area of hygiene and medicine that sometimes seems hardly to have changed since the nineteenth century. Drugs of choice for human infection by blood flukes are compounds of arsenic and antimony. With D D T and other poisons under attack for their effects on the environment, the old, barely effectual means of control might be on the way out. Extermination of trypanosomebearing flies and bugs and trematodeinfested snails with poisons may be in political and social disfavor in the developing countries. The cercariae forms of one species of human blood fluke,. Schistosoma mansoni, burst from sporocytes inside Planorbis snails and penetrate human skin. Equipped with collagenases and hyaluronidases to dissolve connecting tissue and cementing substances between cells, cercariae infiltrate to the hepatic portal vein, which carries nutrient-rich blood from the intestine to the liver. There they mature, mate, and lay eggs. Human antibodies respond to these foreign organisms. Dr. W. M. Kemp, Tulane University, New Orleans, La.,
Electron scanning micrograph of fluke cercaria snout after immersion in immune serum shows precipitate deposited uniformly over hirsute coat
thinks part of this reaction is triggered specifically by the outer "hirsute coat" of cercariae. But the antibody reaction is not given by mature flukes, says Dr. Kemp, and they lack the hirsute coat. He would like to know at what stage cercariae lose the coats and what it is about them that causes the reaction. The coat seems to be composed of glycoprotein. Immune reaction. A series of electron micrographs, made by Dr. Kemp in work supported by National Science Foundation and National Institutes of Health, show the diaphanous coat alone, then slowly enveloped in a uniform sheath of precipitate. Dr. Kemp says that the precipitate forms around cercariae in immune serum, immobilizing them and causing them to clump together. The technique of electron scanning microscopy enables Dr. Robert M. Lewert and Dr. P. L. Moriearty of University of Chicago, supported by Public Health Service, to see cercariae in a new dimension. Conventional electron microscopy forms images by focusing electrons scattered by very thin specimens. Electron scanning microscopy focuses electrons prior to scanning across the specimen surface of any thickness. As cercariae invade human tissue, moving toward the systemic circula-
Dr. Robert M. Lewert's facial views of blood fluke cercariae show by conventional electron scanning microscopy (right) and in differentiated mode (left) a contrast heightening technique 42 C&EN NOV. 17, 1969
tory system, the victim suffers watery skin eruptions, cough, fever in late afternoon, and diarrhea. When the new-laid eggs use enzymes to dissolve blood vessel walls on their way out to the colon, hemorrhaging begins. The eggs hatch in fresh water outside the body to their miracidium forms, which invade the snail intermediate host. Tanned eggs. If more were known about fluke eggs, ways might be found to poison or prevent them from hatching. Dr. Paul M. Nollen, Western Illinois University, Macomb, notes that Haematoloechus medioplexus eggs are protected by a "tanning" of the outer protein coat, based on oxidation of tyrosine. In other species, the eggs seem to be protected by a keratinlike shell, Dr. Nollen says, based on formation of disulfide bonds between adjacent cysteine residues. Efforts to demonstrate keratinization by this route are not definitive, however, and Dr. Nollen emphasizes the complex variety of protective skins for trematode eggs. As many as 15% of Americans are infected by Trichinella spiralis, though not all show acute symptoms. Dr. Dickson D. Despommier would like, to know how to confer immunity to this parasite in undercooked pork. In work supported by PHS and NIH at Rockefeller University, New York, N.Y., Dr. Despommier isolates stichosome cell granules—organelles of cells—from homogenized whole T. spiralis. Antigens associated with the stichosome granules immunize mice to T. spiralis. Isoelectric focusing. Dr. Despommier detaches antigens from granule membranes with a quaternary ammonium salt and separates fractions on an isoelectric focusing column. This column has a pH gradient from 3 to 10, and an electric potential causes migration of fractions to regions where the pH equals isoelectric points of their proteins—a kind of column electrophoresis. Following the fractions by enzymic analysis as well as column electrofocusing, Dr. Despommier finds two N-acetyl-/?glucosaminidase and six acid phosphatase active fractions.
