In this article, literature records of argasid and ixodid ticks feeding on humans worldwide are provided in view of increased awareness of risks associated with tick bites. Ticks can cause paralyses, toxicoses, allergic reactions and are vectors of a broad range of viral, rickettsial, bacterial and protozoan pathogens. Approximately 12 argasid species (Argas and Ornithodos) are frequently found attached to humans who intrude into tick-infested caves and burrows. Over 20 ixodid tick species are often found on humans exposed to infested vegetation: four of these are Amblyomma species, 7 Dermacentor spp., 3 Haemaphysalis spp., 2 Hyalomma spp. and 6 Ixodes species. Personal protection methods, such as repellents and acaricide-impregnated clothing are advised to minimize contact with infected ticks. Acaricidal control of ixodid ticks is impractical because of their wide distribution in forested areas, but houses infested with soft ticks can be sprayed with acaricidal formulations. Attached ticks should be removed without delay. The best way is to grasp the tick as close to the skin as possible with fine tweezers and pull firmly and steadily without twisting. Finally, despite the fact that most people who are bitten destroy the offending tick in disgust, it is recommended that they preserve specimens in ethanol for taxonomic identification and detection of pathogens by molecular methods.

Ticks feeding on humans: a review of records on human-biting Ixodoidea with special reference to pathogen transmission.

Publisher Summary Ticks are highly specialized obligate parasites of a wide variety of terrestrial and flying vertebrates and a few marine snakes and lizards. During the one to several long periods that most tick species spend off the host and on the ground, their survival depends on a delicate interplay among physiological and structural properties and functions and ecological factors. Thus, tick-host and tick-environmental factors are both of paramount importance in understanding the role of the individual tick species as a parasite and a vector. This chapter focuses on ticks and tick-borne diseases and reviews tick structures and physiology. It discusses the tick cuticle; humidity relationships and water balance; sensory basis of feeding behavior, attachment, and feeding (role of the mouthparts, feeding apparatus, salivary gland secretions, and host response); immunological basis of host resistance; blood digestion; ion and water balance during feeding and mechanisms of excretion; reproduction (sperm development, cytogenetics, oogenesis, and oviposition); structure and functions of the circulatory, nervous, and neuroendocrine systems; endocrine mechanisms (effects of insect hormones and their mimics on development and reproduction); pheromone mechanisms; and diapause and biological rhythms.

Argasid and nuttalliellid ticks as parasites and vectors

Six genera and 27 species of hard ticks (Ixodidae) currently are recognized in the United States east of the Mississippi River as follows: Amblyomma (4 species), Boophilus (1), Dermacentor (3), Haemaphysalis (2), Ixodes (16), and Rhipicephalus (1). We present a diagrammatic couplet key to the adults of the six genera and 27 species of Ixodidae found in the eastern portion of the United States.

Pictorial Key to the Adults of Hard Ticks, Family Ixodidae (Ixodida: Ixodoidea), East of the Mississippi River

A portion of mitochondrial 12S rDNA sequences (337–355 base pairs) and 63 morphological characters of 36 hard-tick species belonging to 7 genera were analyzed to determine the phylogenetic relationships among groups and species of Rhipicephalus and between the genera Rhipicephalus and Boophilus. Molecular and morphological data sets were first examined separately. The molecular data were analyzed by maximum parsimony (MP), maximum likelihood, and neighbor-joining distance methods; the morphological data were analyzed by MP. After their level of congruence was evaluated by a partition homogeneity test, all characters were combined and analyzed by MP. The branches of the tree obtained by combining the data sets were better resolved than those of the trees inferred from the separate analyses. Boophilus is monophyletic and arose within Rhipicephalus. Boophilus species clustered with species of the Rhipicephalus evertsi group. Most of the clustering within Rhipicephalus was, however, consistent with previous c...

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Analysis of the systematic relationships among ticks of the genera rhipicephalus and boophilus (acari: ixodidae) based on mitochondrial 12s ribosomal dna gene sequences and morphological characters

Interest in tick-borne pathogens has been enhanced by the emergence of Lyme disease and, more recently, human and animal ehrlichioses. In order to facilitate investigations of the vector phase of tick-borne disease agents in vitro, several new cell lines derived from embryonated eggs of northern (IDE lines) and southern (ISE lines) populations of the tick Ixodes scapularis were developed. The establishment and characteristics of 4 IDE (IDE1, 2, 8, and 12) and 2 ISE (ISE5 and 18) lines were described. Primary cultures were initiated in L-15B medium at 31 C from a single egg mass each and established lines developed a morphologically distinct phenotype. Myoblasts were present during the first year after isolation in several lines as isolated clusters or sheets covering the whole flask. Cell line extracts resolved by isoelectric focusing were characterized for 3 isozymes (lactate dehydrogenase, malate dehydrogenase, and malic enzyme). The combined banding patterns allowed discrimination between Ixodes cell lines and a Rhipicephalus appendiculatus cell line. Two lines, i.e., ISE5 and ISE18, had unique isozyme bands. Chromosome numbers and morphology conformed to those described from tissue squashes of I. scapularis.

Establishment, maintenance and description of cell lines from the tick Ixodes scapularis.

Dermacentor ticks (Acari: Ixodoidea: Ixodidae) of the New World: a scanning electron microscope atlas

Growth of Colorado tick fever (CTF) virus in primary tissue cultures of its vector, Dermacentor andersoni Stiles (Acariña: Ixodidae), with notes on tick tissue culture.

A Dermacentor andersoni bilateral gynandromorph, removed from a laboratory-reared colony, was studied morphologically using scanning electron microscopy and cytogenetically by means of the aceto-orcein squash technique. The morphological sexual dimorphism was correlated with the chromosomal constitution usually found in each sex [i.e., the morphologically male side had a testis with spermatogonial cells containing 2n = 21 (20 + X) chromosomes and the female side had ovaries with oogonial cells containing 2n = 22 (20 + 2X) chromosomes]. The dimorphism, therefore, is the result of unequal distribution of sex-linked chromosomes rather than control at the gene or physiological level.

Bilateral gynandromorphism in Dermacentor andersoni (Acari: Ixodidae): morphologic and cytogenetic analysis.

Relative abundance of larval Rocky Mountain wood ticks, Dermacentor andersoni Stiles, in mountainous terrain of western Montana was measured by release and recapture of radiolabeled ticks. Laboratory-reared larvae tagged with 14-Carbon or 125-Iodine were released in equal numbers at selected points within 1 of 2 study areas during the natural larval activity periods of 1967–1969. Tagged larvae subsequently recovered on small rodent hosts trapped in these areas and identified provided an estimate of tick population size per acre (ha) (±2 S.E.): 119,163 ± 50,864 (294,333 ± 125,633) and 388,622 ± 212,750 (959,896 ± 525,214) in 1967 and 1969, respectively. Hosts from which most of the ticks were obtained were Neotoma cinerea (40.9% of larvae; 30.6% of nymphs), and Spermophilus lateralis (35.1% of larvae; 60.3% of nymphs). Other hosts were Peromyscus maniculatus (17% of larvae; 4.9% of nymphs), and Eutamias amoenus and E. ruficaudus (7.0% of larvae; 6.6% of nymphs). Larval activity was restricted to a 9- to 11-week period between mid-June and early September, peaking once in late July or early August. Nymphal activity, already evident when trapping began, remained constant until it declined after mid-August. Labeling of larval ticks by exposure to radioactive iodine vapor appears to be at least as efficient as labeling them through inoculation of ovigerous parents with 14-Carbon.

Contributions to the ecology of Colorado tick fever virus. 2. Population dynamics and host utilization of immature stages of the Rocky Mountain wood tick, Dermacentor andersoni.

Midway virus, a new tick-borne virus isolated from two species of Ornithodoros (Alectorobius) ticks of the capensis group (O capensis, O denmarki), is described from Midway, Kure, and Manana islands in the Central Pacific (Hawaiian Archipelago) and from northern Honshu (Japan). Midway virion is enveloped, unusually large, acid and temperature sensitive, and its type of nucleic acid is RNA. Complement-fixation (CF) tests show a close relation of Midway to Nyamanini virus, which has been isolated from ardeid birds and Argas ticks in Africa, the Indian subcontinent, and Southeastern Asia. However, cross-box tests (CF, mouse and tissue culture neutralization, immunofluorescence) show that these two viruses are quite distinct. Midway virus is lethal for newborn Swiss mice inoculated by intracerebral, but not intraperitoneal route. It fails to kill four-week-old mice by either route. Midway virus causes cytopathic effects in BHK-21 cells and titerable plaques in Vero cells. Antibodies to it were prevalent among nestlings of Larus crassirostris (Black-tailed Gull) on Aomatsushima I., but were scarce among those of Nycticorax nycticorax (Black-crowned Night Heron) of the same island.

Conrad E. Yunker

Papers

Dermacentor ticks (Acari: Ixodoidea: Ixodidae) of the New World: a scanning electron microscope atlas

Growth of Colorado tick fever (CTF) virus in primary tissue cultures of its vector, Dermacentor andersoni Stiles (Acariña: Ixodidae), with notes on tick tissue culture.

Bilateral gynandromorphism in Dermacentor andersoni (Acari: Ixodidae): morphologic and cytogenetic analysis.

Contributions to the ecology of Colorado tick fever virus. 2. Population dynamics and host utilization of immature stages of the Rocky Mountain wood tick, Dermacentor andersoni.

Isolation and characterization of Midway virus: a new tick-borne virus related to Nyamanini.