CHARACTERIZATION OF EXCRETORY-SECRETORY PRODUCTS FROM LARVAL STAGES OF HAEMONCHUS-CONTORTUS CULTURED IN-VITRO

To determine biochemical changes associated with early parasite develo pment, Haemonchus contortus larvae were cultured in vitro to the fourt h stage (L(4)), Infective larvae developed from third to fourth stage in 48-96 h. Metabolic activity increased following stimulus of infecti ve stages by CO2 but secretion/excretion of significant amounts of pro tein into cultures and larval feeding did not occur until larvae had m olted to the fourth stage. Larval feeding, as monitored by the ability of larvae to ingest fluorescein-labeled albumin, correlated with molt ing to the fourth stage and only fourth stage larvae were observed to feed. Fourth stage larvae secreted/excreted several enzymes into cultu re media including a metalloprotease, an acid phosphohydrolase, a cath epsin C-like enzyme, a phospholipase C-like enzyme and an N-acetyl-bet a-D-glucosaminidase. Excretory-secretory (ES) products produced by L(4 ) had antigenic homologies with parasite products produced during the second molt and with proteins and glycoproteins extracted from third a nd fourth stage larvae, ES products were recognized by sera from sheep infected with H. contortus, The enzymes identified here serve as mark ers for maturation to the fourth larval stage as well as the initiatio n of feeding and are likely to be involved in extracorporeal digestion . Further, they might serve as potential targets for immune or chemica l control of trichostrongyle infections.