Ew. Cupp et Ms. Cupp, BLACK FLY (DIPTERA, SIMULIIDAE) SALIVARY SECRETIONS - IMPORTANCE IN VECTOR COMPETENCE AND DISEASE, Journal of medical entomology, 34(2), 1997, pp. 87-94
When blood-feeding, black flies introduce secretions into the feeding
lesion that act in a coordinated manner on the 3 arms of the vertebrat
e hemostatic system (platelet aggregation, coagulation, and vasoconstr
iction). Apyrase activity inhibits platelet aggregation and is ubiquit
ous in the saliva of black flies, although activity per gland varies b
y species and has a positive association with anthropophagy. Anticoagu
lants target components in the final common pathway of the coagulation
cascade, including factors V, Xa, and II (thrombin). The antithrombin
salivary protein may exert a redundant effect by inhibiting the role
of thrombin in platelet aggregation. Antithrombin presence and activit
y also varies among black fly species, supply to the feeding wound app
ears to be an important requirement for Simulium spp., because substan
tial erythema-inducing activity has been demonstrated in salivary glan
ds of all New World species examined. Salivary glands of Simulium ochr
aceum (Walker), a highly anthropophilic vector of Onchocerca volvulus
(Leuckhart), contain greater vasodilator activity than several other s
pecies, including S. metallicum Bellardi, a secondary zoophagic vector
of human onchocerciasis, Simulium vittatum Zetterstedt saliva affects
immune cell responses and cytokine production. The ability of the sal
iva to modulate components of the host immune system provides an oppor
tunity for enhancing transmission of pathogens during bloodfeeding. Th
us, the likely possibility that effective pathogen transmission relies
on vector saliva may complement present efforts aimed at target epito
pes of O. volvulus or identify additional molecules to be investigated
as part of a ''river blindness'' vaccine cocktail. Components in sali
va also may enhance the transmission of other microbial agents either
by a cofeeding process similar to that observed in ixodid ticks or thr
ough rupture of the labrum during escape of Onchocerca infective stage
larvae. In a few instances, saliva of some Simulium spp. also has bee
n associated with extensive tissue and organ pathology, including hemo
rrhagic shock and death. Pathologic signs associated with this syndrom
e indicate an enhanced antihemostatic activity in saliva.