Eddie W. Cupp

Biology of Ticks

Ticks are an ancient group of obligate bloodsucking ectoparasites that has evolved over millions of years. Two general types of ticks are evident today: argasid or soft ticks, and ixodid or hard ticks. Each lineage exhibits distinct patterns of host coevolution and preference. However, about 10% of the approximately 850 species are of medical importance because of their indiscriminate host selection and catholic feeding behavior. As a result, a number of diseases have begun to emerge in the temperate zones, including Lyme borreliosis and several others putatively associated with ticks. Ticks may serve as both pathogens and disease vectors. Because of the unique physiology of the salivary glands and the contents in tick saliva of toxins, feeding alone may cause disease. Ticks also transmit a number of different types of pathogens (viruses, rickettsiae, spirochetes and bacteria, fungi, protozoa, filarial nematodes) and even exceed mosquitoes in this regard. Abatement and control of ticks emphasizes a broad approach because of the differing types of habitats in which pest species may be found. The use of repellents and acaricides as well as cultural and management practices are of primary importance. Other approaches (ivermectin) may be beneficial; with the advent of molecular genetics and its usefulness in immunology, the development of tick vaccines for common pest species appears promising.

Simulidin: a black fly (Simulium vittatum) salivary gland protein with anti-thrombin activity

Abstract A protein purified from the salivary gland lysate of female Simulium vittatum was found to inhibit bovine α-thrombin. This protein is stable to heat, has a mass of 11,334 Da and is rich in threonine. Based on N-terminal sequencing for the first 35 amino acids, no significant sequence similarity with other proteins was detected, indicating that this salivary component may be unique in structure. Because of its source and its anti-hemostatic properties, this protein has been named simulidin.

Salivary gland apyrase in black flies (Simulium vittatum)

Abstract Apyrase enzyme activity was demonstrated in the salivary glands of a colonized strain of Simulium vittatum . Activity was maximum (8.5 ± 0.7 mU/pair of gland equivalents) at pH 8.0, with ADP as substrate and Ca 2+ as the divalent cation. Activity was minimal in newly emerged females (1.6 ± 0.5 mU/pair of gland equivalents) but increased by 48 h. Activity in male salivary glands was marginally detectable (0.7 ± 0.8 mU/pair of gland equivalents), even 72 h after emergence. When newly emerged females were maintained at 4°C, salivary apyrase activity accumulated at a slow rate. Transferring females to warmer temperatures increased the rate of apyrase accumulation, but 27°C did not yield greater activity than 20°C. Apyrase activity was decreased when females engorged on whole bovine blood or on a simulated blood meal. Activity remained low 6 h after feeding, but increased to prefeeding levels by 48 h. During the second, anautogenous gonotrophic cycle, apyrase activity was not greater than during the first, autogenous gonotrophic cycle. Apyrase activity was not related to long term colonization as total salivary gland apyrase activity and pH profile in wild S. vittatum was not different from colonized S. vittatum .

Care and maintenance of blackfly colonies

The availability of vector species on a continuous basis in the laboratory is an important prerequisite for both basic and applied aspects of research. Unlike other types of filariasis vectors (particularly mosquitoes), the immature stages of the Simuliidae (blackflies) are found exclusively in riverine or other types of running-water habitats. In the laboratory, duplicating this unusual aspect of the biology of the immatures (especially the larvae) poses a major obstacle to colonization of most important vector species. Thus, sustained propagation of many medically-important taxa under artificial conditions is difficult, if not impossible, at the moment. While several species of Simuliidae have been reared successfully through multiple generations in the laboratory, there are currently no colonies of a natural vector.