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.