JOURNAL OF MEDICAL ENTOMOLOGY J. Mad. Entomol. VoL 14, no. 1: 1-9

20 August 1977

Published bimonthly by Department of Entomology, Bishop Museum, Honolulu, Hawaii, U.S.A. Editorial committee: F. J . Radoviky and J. M. Tenorio, Co-editon, J. L. Gressitt, Managing Editor, A. R. Barr, G. F. Bennett, J . M. Brennan, C. M. Clifford, R. H. Dadd, M. Daniel, D. P. Furman, T. D. C. Grace, G. P. Holland, H. Hoogstraal, N. Kumada, G. C. LaBrecque, F. S. Lukoschus, D. E. Sonenshine, A. Spielman, R. Traub, M. G. R. Vanna, R. Zeledon. Devoted to all branches of medical entomology from the world standpoint, including systematic! of injects and other arthropods of public health and veterinary significance.

REVIEW ARTICLE^ ACARINE SALIVARY GLANDS -PHYSIOLOGICAL RELATIONSHIPS 2 By J. R. Sauer 3 Abstract: The evidence for the many key functions of the salivary glands in both feeding and nonfeeding acarines is reviewed. The salivary glands of most slowly feeding ixodid ticks secrete cement to insure firm attachment of the mouthparts to the host. Much tissue destruction associated with tick feeding is probably caused by host reaction to materials in tick saliva, which produces trauma in the host vascular system near the feeding lesion. Ixodid salivary glands participate in excreting excess fluid while the tick is attached and feeding. There is growing evidence that ixodid salivary fluid secretion is under nervous control and that cyclic AMP and calcium may play important roles in the fluid secretory process. Better understanding of the physiology of acarine salivary glands should contribute significantly to a better understanding of the role of the glands in the development and release of pathogens.

Many ectoparasitic acarines transmit pathogens and cause considerable host discomfort (Sasa 1961, Arthur 1962, Philip 1963, Hoogstraal 1966, 1967). Thus, interest has focused on mechanisms of acarine

feeding. Results of these studies have identified the salivary glands as having an essential role in the feeding process. Glandular functions identified in various feeding acarines include secretion of a cement substance and/or feeding tube, secretion of anticoagulants, cytolysins, enzymes, and pharmacological agents, and secretion of toxic substances. As a result of the transillumination and electrical methods employed by Gregson (1967, 1969) and the direct observations of Balashov (1965), it became clear that the salivary glands are essential for eliminating excess fluid from the ingested meal in feeding ixodid ticks. This finding has been confirmed by Tatchell (1967a) and Kaufman & Phillips (1973a). Recent findings suggest important functions for l

This is the 14th Review Article to appear in the series published in the Journal of Medical Entomology. a Journal article No. 3110 of the Agricultural Experiment Station, Oklahoma State University, Stillwater, Oklahoma. This research was supported in part by NSF Grant Nos.: GB36420, BMS-74-24140 and PCM 74-24140 AO1 from the National Science Foundation. 'Department of Entomology, Oklahoma State University, Stillwater, Oklahoma 74074, U.S.A.

the salivary glands in other than feeding processes. Included in this category are salivary secretion by male ticks during copulation (Feldman-Muhsam et al. 1970) and possible involvement of the glands in processes enabling nonfeeding ticks to take up water from unsaturated air (Rudolph & Kniille 1974, McMullen et al. 1976). Secretion of cement substances.

T h e secretion of a

cement substance is characteristic of most genera of slow-feeding ixodid ticks. This phenomenon was observed by Cowdry & Danks (1933), Foggie (1959), Gregson (1960), Moorhouse & Tatchell (1966), Moorhouse (1969), Balashov (1972), and Chinery (1973). Exceptions are some Jxodes species which do not produce cement but insert the mouthparts deeply into the host skin tissues (Moorhouse 1969, Arthur 1970, Moorhouse 1973). Another tick, Haemaphysalis spinigera, has short mouthparts but is capable of penetrating quite deeply into the host dermis with the aid of an elongated internal cement tube. The cement secreted by H. spinigera is proteinaceous and apparently derived from precursors in the cells of type II and type I I I alveoli (Chinery 1973). Moorhouse & Tatchell (1966) describe the cement secreted by the salivary glands of Boophilus microplus as consisting of 2 main components: a cortex of carbohydrate containing protein, which is stabilized by quinone tanning and disulfide linkages, and an internum which is lipoprotein. Moorhouse (1969) studied the attachment of several species in 7 different ixodid genera. In genera in which the mouthparts penetrate superficially (Rhipicephalus, Boophilus, Haemaphysalis, a n d Dermacentor), a second-

ary production of cement occurs during the final stages of engorgement. In B. microplus, the cement secretion and cutting of the host tissues by the chelicerae are initiated simultaneously. The final rapid engorgement period of larval and adult B. microplus is also preceded by secondary secretion of

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cement into a fluid-filled cavity forming directly of salivary secretions can be distinguished in ixodid beneath the mouthparts and providing additional ticks. The 1st secretion occurs during the initial support for the tick (Moorhouse & Tatchell 1966). attachment phase and forms the cement sheath. These authors found that the cement in this species The 2nd (and later) secretion, which is elaborated is inert and unable to provoke the development of after attachment, is more transparent and is postuhost-parasite factors inimical to the tick. Balashov lated to contain a component that prevents blood (1972) mentioned a 2-layered cement sheath coagulation. Balashov further speculated, based structure. The outer layer consists of a polysac- upon physical and chemical investigations of whole charide-protein complex and the inner layer is tick homogenates by Markwardt and his structural probably lipoprotein. Lamellate layers of cement and histochemical data, that the active salivary near the mouthparts were also observed in feeding anticoagulants may be glycoprotein, mucoprotein, Dermacentor andersoni by Gregson (1967), but he wasor another protein-carbohydrate complex inhibiting unable to differentiate 2 cement components. In enzymatic activity of thrombokinase and having contrast to the findings of others (Moorhouse & high thermostability. The saliva of Boophilus Tatchell, 1966), Gregson (1970) found the cement microplus lacks anticoagulants (Tatchell 1969a, material secreted by D. andersoni to have antigenic Tatchell & Binnington 1973), and Gregson (from properties. Theis & Budwiser (1974) found no Tatchell 1969a) was unable to demonstrate an anticoagulant in Dermacentor andersoni. reliable evidence of a secondary major production of the cement substance in Rhipicephalus sanguineus.

The secretion of cement material is thought by most investigators to be salivary in origin, but Kirkland (1971) cautiously stated that "although the material is probably contributed by the salivary glands, the exact source has not been determined." Most authors believe that rapid-feeding argasid ticks, in contrast to ixodid ticks, do not secrete a cement substance (Balashov 1972, Chinery 1974). Another acarine, the trombiculid mite, builds a cement tube similar in structure to that secreted by the early developmental stages of immature ixodid ticks. This enables the trombiculid to obtain blood from inner skin layers where its short mouthparts cannot penetrate (Balashov 1972), but the tube is not part of the salivary secretion (Wharton & Fuller 1952).

Cytolysin secretion, pharmacological agents, and extra-

oral digestion. Tatchell (1969a) stated that saliva obtained from Boophilus microplus by Gregson's capillary tube technique (1957) or pilocarpine stimulation (Tatchell 1967b) lacks destructive enzymes and anticoagulants. However, cytolysins in the saliva of some ixodid ticks were reported by Foggie (1959) and Arthur (1965). Balashov (1972) speculated that ixodid saliva hinders host blood coagulation and also causes lysis of surrounding cells and tissues. Others (Tatchell & Moorhouse 1970, Tatchell & Binnington 1973) take issue with the hypothesis that these feeding lesions result from extra-oral digestion through the action of cytolysins in the salivary secretions. They suggest that much of the tissue destruction associated with ixodid feeding may be due to host reaction to feeding. Anticoagulant secretion. There are varying reports When dogs were infested with adult Rhipicephalus concerning the existence of anticoagulating sub- sanguineus and given nitrogen mustard to reduce stances originating from acarine salivary glands. leukocyte numbers, tick lesions were insignificant, Anticoagulating properties of Argas persicus saliva lacking the collagen destruction found in untreated hosts, even though the ticks engorged normally. were reported by Nuttall & Strickland (1908), and Chinery (1974) suggested that carbohydrate and The saliva of B. microplus contains a pharmacologprotein in the i cells of the type II alveoli are the ically active material which caused contraction of a precursors of the anticoagulant contained in the rat fundus preparation and an increase in capillary A. persicus salivary secretion. Other reports are of permeability after intradermal injection into a saline extracts of salivary glands of Ornithodoros bovine host (Tatchell & Binnington 1973). Tatchell moubata (Hawkins & Hellmann 1966), a marked (1969b) also found 6 pharmacologically active anticoagulant action in salivary gland extracts of substances (other than histamine) in tick saliva and Ixodes ricinus (Foggie 1959), an anticoagulant in salivary gland extracts of B. microplus. Activity was salivary glands of Ixodes holocyclus (Ross 1926), and tested by noting the effects of the substances on anticoagulant properties of whole tick homogenates cockroach heart preparations. The role of the of /. holocyclus and /. ricinus (Markwardt, from substances remains to be determined, but dilation Balashov 1972 and Gregson 1973). of adjacent superficial bovine skin capillaries occurs very soon after the attachment of larval ticks, Balashov (1972) suggested that 2 different types

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suggesting that pharmacologically active material is being injected by the tick. Of possible relevance to the above is the discovery of a prostaglandin in the saliva of recently detached engorged female cattle ticks (B. microplus). Ticks were stimulated to salivate following topical application of pilocarpine (Dickinson et al. 1976). Saliva collected from feeding B. microplus after pilocarpine injection was analyzed by gel electrophoresis and histochemical techniques by Tatchell (1971). The saliva was found to be very dilute. Four very faint protein bands were found together with 2 further slow-running components containing polysaccharides. Also, a number of esterases and acid phosphatases were present with the major component in each case running just behind the tracer band. An earlier analysis showed that enzymes such as phospholipase, proteinase, or hyaluronidase which might participate in tissue destruction were absent (Tatchell 1969b). Geczy et al. (1971) also studied the saliva of B. microplus and found a carbohydrate-splitting enzyme and a macromolecule with esterase activity. The authors suggested that the esterase may increase vascular permeability in the skin of sensitive cattle by hydrolyzing the cholesterol esters in the membrane of sensitive cells (e.g., mast cells), thereby releasing various pharmacological mediators. In ascribing the presence of cytolysins and enzymes in ticks, Tatchell (1969a) suggested that the salivary secretions of the more primitive argasids appear to be markedly more vigorous and destructive in their actions than those of the ixodids. Tatchell based these suggestions on the work of Lavoipierre & Riek (1955), who observed the feeding habits of 29 species of argasid ticks. Similarly, Moorhouse (1975) noted that because the onset of lysis of the epidermis and the cellular elements in the upper dermis of host tissues occurs 30 min. after infesting the hosts (chickens) with larvae of Argas persicus, these larvae must produce a cytolysin. This destruction, according to Moorhouse, long preceeds any leucocytic infiltration of the area and so cannot be a result of damage induced by the host's own inflammatory response. In addition, preliminary investigations conducted by Howell et al. (1975) indicated the presence of proteolytic and cholinesterase activities in the oral secretions of Ornithodoros savignyi. On the other hand, Tatchell (1969a) reasoned that if the saliva of any ixodid tick is shown to contain active proteolytic enzymes or other cytolytic properties, then it would be found in those genera with deeply inserted mouthparts. Such secretions might imperil attachment in the

more superficially attached genera. Conversely, dermatitis or trombiculosis caused by the bites of chiggers must result from a reaction of the host to the salivary secretion of the mites (Wharton & Fuller 1952). Saliva causes a disintegration of the contents of cells with which it comes in contact. The result of disintegration is a disorganized cytoplasm and fragmented nuclei on which the mites feed (Jones 1950). Toxic components. Howell (1966) suggested that a toxin might be present in saliva of the argasid tick Ornithodoros savignyi, and later Neitz et al. (1969) purified a toxic component from the same species. These authors found the toxic principle to be a protein. Mice demonstrated toxic symptoms after being injected with oral secretions obtained from 0. savignyi (Howell et al. 1975). The oral secretions were collected after stimulating ticks to secrete with pilocarpine hydrochloride. Electrophoresis and chromatography of the secretion showed the presence of at least 10 different protein fractions, only 1 of which was toxic. The toxic principle was found to be heat stable to approximately 80 °C. The authors hypothesized that the remaining fractions, although not toxic as such, may play an important role in the syndrome produced by the secretion. Nuttall & Strickland (1908) were unable to find a toxic component in the saliva of Argas persicus.

In certain ixodid ticks, the saliva is thought to contain a strong toxin which causes paralysis of domestic animals and man (Balashov 1972, Gregson 1973). Ixodid tick paralysis is a motor paralysis induced by the bites of certain species, and there is no evidence of involvement of infectious organisms (Arthur 1962, Gregson 1962, 1973). Gregson (1973) paralyzed a hamster by subcutaneously injecting continuously, for 18 hr, 1 ml of tick saliva collected from Dermacentor andersoni. Although Gregson concluded that tick saliva is a prerequisite for toxin, he recognized 3 possibilities for origin of the toxin: a product of tick tissues per se, a product of metabolic breakdown of host tissues, or a product of an organism within the tick. Salivary gland extracts from Ixodes holocydus, injected into mice, produced signs resembling tick paralysis (Ross 1926). Paralysis does not appear until the ixodid tick has been feeding for approximately 4 days, which is the time when oral secretions become abundant (Gregson 1957). Paralysis produced in the dog by D. andersoni is due to an absence of acetylcholine at the neuromuscular junction and to a conduction block produced by tick toxin in the

J. Med. Entomol.

somatic motor fibers (Murnaghan 1960). Additional details of the effects of tick toxin in causing paralysis of the host may be found in the papers by Emmons & McLennan (1959, I960), McLennan & Oikawa (1972), Esplin et al. (1960), Cherington & Snyder (1968), and Swift & Ignacio (1975).

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and neurosecretory neuron becomes unclear the term neurosecretomotor has been applied. Maddrell (1974) pointed out that the neurosecretomotor substance involved in the control of some insect salivary glands is probably a catecholamine (Klemm 1972, Bland et al. 1973). The effectiveness of catecholamines in stimulating tick salivary fluid secretion, the finding of nerves in close association with the glands, and the presence of noradrenaline and dopamine in tick salivary glands (Megaw & Robertson 1974) suggest that this statement may also apply to the control of tick salivary fluid secretion. Berridge & Prince (1972) have hypothesized a model for the stimulatory effect of 5-hydroxytryptamine (5-HT) on salivary fluid secretion in

Fluid elimination. In addition to the pioneering observations of Gregson (1960, 1967, 1969) and Balashov (1965), numerous studies have shown that ticks concentrate the ingested meal by excreting large quantities of excess fluid (Lees 1946, Sutton & Arthur 1962, Arthur 1965, 1970, Seifert et al. 1968, Snow 1970, Sauer & Hair 1972, Koch et al. 1974). The main organs of fluid elimination are the salivary glands in ixodids and coxal glands in most argasids. However, coxal glands are lacking in larvae of the the insect Calliphora erythrocephala. 5-HT, cyclic argasid tick Argas persicus and Moorhouse (1975) AMP, and the phosphodiesterase inhibitor theophylsuggests that concentration of the blood meal may line stimulate fluid secretion. In their scheme 5-HT also be brought about by a salivary secretion in acts on the receptor site at the basal membrane and this stage of an argasid tick. As the blood meal is stimulates the entry of calcium and production of ingested, excess ions and water are moved across cyclic AMP. The increase in the level of cyclic the gut epithelium into the hemocoel and secreted AMP stimulates the pumping of potassium across back into the host via the salivary glands in ixodid the apical membrane. Calcium controls the moveticks (Tatchell 1967a, 1969c, Kirkland 1971, ment of chloride. Water follows the movement of Kaufman & Phillips 1973a, b, c, Meredith & potassium and chloride, resulting in fluid secretion. Kaufman 1973). Chloride is the major anion There are a number of similarities between the constituent of tick salivary secretion and sodium is insect scheme and the control of tick salivary fluid the major cation constituent (Tatchell 1969c, secretion. Both catecholamines and cyclic AMP Kaufman & Phillips 1973a, Hsu & Sauer 1975) and stimulate fluid secretion (Needham & Sauer 1975). an active transport of chloride may be an important However, an important difference is that cyclic driving force for thefluidsecretory process (Kaufman AMP or theophylline alone will not stimulate secre& Phillips 1973c). tion unless the glands have been preconditioned to Kaufman & Phillips (1973b) suggested that secrete with adrenaline [or another catecholamine control of salivary fluid secretion may be neural (Needham & Sauer 1975) ]. However, a comrather than hormonal. This hypothesis is sup- bination of cyclic AMP (4 X 10-3 M) and theophylported by evidence which indicates that cate- line (10"2 M) will stimulate secretion without cholamines rather than "factors" in tick hemolymph preconditions (Sauer et al. 1976). Also, calcium stimulate chloride uptake and fluid secretion by appears to be necessary. Omission of calcium from isolated salivary glands (Kaufman & Phillips 1973b, the bathing medium depresses secretion, which Sauer et al. 1974, Kaufman 1976). resumes upon readministration of a calcium-containing Ringer to the bathing medium (Needham & The suggestion was further strengthened by the Sauer, in prep.) This is also indicated by the observation of a nerve close to the basal surface of and cyclic AMP the group III acinus, the acinus believed to con- fact that both catecholamines (and theophylline) stimulate 36C1 uptake by isolated tribute most of the fluid portion of the saliva in Dermacentor andersoni (Meredith & Kaufman 1973).tick salivary glands (Sauer et al. 1974), which suggests that lower concentrations of cyclic AMP Axons have also been observed in association with granular and agranular acini in Amblyomma ameri- are required to stimulate uptake of the anions than are required to initiate fluid secretion. Results canum, Dermacentor variabilis and Argas arboreus using 3H-cyclic AMP as substrate and assaying for (Coons & Roshdy 1973, Roshdy & Coons 1975). 3 H 5'-AMP indicate that a phosphodiesterase is These authors also observed neurosecretory material present in tick salivary glands (McMullen & Sauer, in axons closely associated with the basal region of in prep.). The combined results of the above the epithelial cells. Miller (1975) stated that where strongly suggest the existence of an adenyl cyclase the distinction between an ordinary motor neuron

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catecholamines. Yet catecholamines will stimulate and phosphodiesterase closely regulating the cellular secretion in vivo as well (Kaufman & Phillips level of cyclic AMP, which along with calcium is 1973b, Hsu & Sauer 1975). In addition, salivary involved in controlling tick salivary fluid secretion. glands of at least 7 ixodid species (female) are Kaufman (1976) has recently found that modified 3 TC 199 (Morgan et al. 1950) is a far superior nutri- insensitive to acetylcholine (10" M), but very sensitive to dopamine. These include Dermacentor tive medium to previously used Normal Ringerandersoni, D. reticulatus, Boophilus microplus, Rhipicephasaline (NRS) (Kaufman & Phillips 1973b) for bathlus appendiculatus, Ixodes ricinus, I. hexagonus, a n d ing in vitro glands. He observed a shorter latent Hyalomma excavatum (Kaufman 1976). The comperiod between drug application and response, bined results suggest that perhaps in the intact lower threshold concentrations for stimulating drugs animal control of salivary secretion has a cholinergic, (2 X 10' 9 M for dopamine and 5 X 10"8M for adrenaline) and an ability of cyclic AMP (10"2 M) as well as catecholaminergic, involvement. Smallman & Schuntner (1972) extracted and chromatoto stimulate secretion. graphed acetylcholine from the brain of adult Kaufman has also verified the importance of ticks, and Megaw & Robertson (1974) have found calcium to salivary fluid secretion. He found that both dopamine and noradrenaline in the brain the high citrate level (550 mg/liter) in the Normal (synganglion) and salivary glands of Boophilus. Ringer-saline (NRS) originally used by him to bathe Kaufman (1976) reported that homogenates of in vitro glands was partially responsible for the synganglia stimulate fluid secretion. As indicated, glands' relatively low secretory rates by virtue of earlier studies have revealed that the salivary glands its well-known ability to chelate calcium. He of several species of ticks are innervated by nerves tested the effects of adding citrate to TC 199. containing dense core granules, indicating the posCitrate (550 mg/liter) inhibited secretion in glands sible presence of catecholamines (Coons & Roshdy from Amblyomma hebraeum to a level approximating 1973). All of these studies make clear the urgent that expected from NRS. Kaufman (pers. comneed for more information on the control of salivary mun.) found the glands obtained from Dermacentor secretion at the cellular and molecular levels. For andersoni are generally sensitive to many analogues this reason and until adequate information is of phenylethylamine listed in descending order of available, researchers should be cautious about potency: dopamine>adrenaline = noradrenaline> assessing the physiological significance of substances isoproterenol ~ phenylephrine > norphenylephrine > obtained from tick saliva following artificial stimulaphenylethylamine > tyramine > DOPA > octopation with drugs. mine. Kaufman (1976) also found that glands from As indicated earlier, Meredith & Kaufman (1973) fed males can secrete in vitro; however, the threshold the importance of the type III acinus in stressed concentration to dopamine (DA) was 10 X higher fluid transport of the feeding tick. In particular, than in females and the rate of secretion only 1/20 a role for the "water cell" the authors hypothesized the maximum rate observed for females. The ion and water transport because of its in bulk secretory rates of male salivary glands are of interest numerous membrane infoldings and mitochondria. because of their implied correlation between size of Diehl (pers. commun.) has recently observed a meal intake and activity of salivary glands. The similar phenomenon in Amblyomma hebraeum. In results with the use of dopamine are of interest the unfed female the "water cell" is very small, because of the growing belief that dopamine is a with no apparent invaginations and few mitochontransmitter at the salivary gland in a number of dria. During the first 2-3 days of feeding the insects (Robertson 1975). "water cell" increases very much in size and develops Of particular interest in conjunction with the enormous infoldings and mitochondria, which above is the fact that the parasympathomimetic parallels the development and secretory ability of drug pilocarpine has been used by several researchers (Howell 1966, Tatchell 1967b, Purnell et al. 1969) the glands. In an argasid tick (Ornithodoros moubata) Diehl to stimulate tick salivation. Similarly, in the ixodid tick Boophilus microplus, a number of anticholine-found that "water cells" are present, but observed sterases, when injected into the whole tick, cause little development of the cells, which corresponds salivary secretion (Megaw 1974). However, where with the low salivary fluid secretion observed in argasid ticks. In addition, the "water cells" in investigated (Kaufman & Phillips 1973b, Needham & Sauer 1975), pilocarpine even at high concentra- feeding males of the ixodid tick A. hebraeum are poorly developed. This also corresponds well with tions (10"3 M) does not stimulate salivary fluid the much lower fluid secretory abilities observed in secretion in vitro as do lower concentrations of

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not appear to be neutrotrophic and all attempts to male salivary glands. culture it have failed. Megaw (pers. commun.) has recently studied the salivary glands of Boophilus microplus. He observed Role of acarine salivary glands in disease transmission. 3 types of acini in females which are similar to those A better understanding of the physiology of acarine described earlier by Meredith & Kaufman (1973) salivary glands should contribute significantly to a in female Dermacentor andersoni. The type I acini arebetter understanding of the role of these glands in confined to the anterior region of the gland and the development and release of pathogens. For contain pyramidal cells which have extensive in- example, Kaufman (pers. commun.) has been able foldings of the basal membrane. The type II acini to culture salivary glands for up to 14 days in TC contain 3 different granule-secreting cells "a," "b," 199 with 10% calf serum using a near neutral pH, and "c," and 2 types of granular cells "d" and "e" room temperature, and an ambient atmosphere of are found in the type III acini. Little change was O2-CO2 (96:4). This assay permits monitoring observed in type I acini during feeding. However, the ability of the glands to secrete fluid in vitro dramatic changes in type II and type III acini following their culture. Using this technique, were observed. Granules in the "a," "d," and "e" Hadani et al. (1975) were able to sustain developcells were secreted during the early stages of feeding ment of the babesial parasite Nuttallia danii in the at a time corresponding to cement secretion. The salivary gland of Hyalomma excavatum nymphs from "b" and "c" cells were observed to be active throughan immature stage to an infective stage, while in out feeding. As the "a," "d," and "e" cells regresculture, if the nymphs were first slightly fed. sed following secretion of their products, adjacent It is widely believed that disease-causing agents epithelial cells which appeared insignificant in the are transmitted to the host in secretions of the unfed ticks enlarged and developed mitochondria salivary glands (see for example Burgdorfer 1951, and membranes. These cells appeared similar to Varma 1962, 6eha£ek 1965), but detailed informathe "water cells" described by Meredith & Kaufman tion is limited to the relationship between salivary (1973). The "water cells" were most obvious in gland physiology and parasite development and type III acini, but similar but not so pronounced release into the host. Martin et al. (1964) showed changes occurred in type II acini. These morthat type II and III alveoli of the salivary glands phological developments of cells suspected to be of Rhipicephalus appendiculatus are important in the responsible for most, if not all, of the fluid secretion cyclic development and transmission of Theileria which occurs during feeding are reflected by a parva, the agent of East Coast fever. Purnell et al. progressive increase in the secretory capability of (1969) found the greatest number of mature infective in vitro glands. Similar progressive increases until parva in the salivary glands of ticks particles of T. a maximum is reached in the secretory capabilities which had fed for either 4 or 5 days on rabbits. of in vitro glands have been observed in our laboraThese authors found a progressive decrease in the tory (Sauer, unpubl. information) and by Kaufman number of infected acini as tick weight (feeding) (1976). Increases in Na, K-ATPase activity have increased. They harvested infective particles from also been observed with increasing secretory ability saliva obtained from 15 ticks that salivated after of the gland (Kaufman et al. 1976). We have stimulation with pilocarpine which successfully observed a progressive decrease in phosphodiesterase calf. Purnell et al. (1973) further infected a activity that is inversely related to the maximum demonstrated that cattle became infected when secretory ability of the glands (McMullen & Sauer, injected with supernatant fluids from triturated in prep.). This latter finding is significant because ticks that had fed 4-9 days. The most highly of the mounting evidence for an intracellular infective supernatant fluids were prepared from regulatory role for cyclic AMP during fluid secretion 5-day fed ticks and these results were correlated (Sauer et al. 1976). with the histological detection of mature parasites in During the course of Megaw's investigation of Boophilus microplus salivary glands, he found a number the ticks' salivary glands. Howell (1966) had previously stated that transmission of disease is of viral-like particles in the salivary glands. He affected mainly by salivary secretion of ticks, the has since confirmed them as viruses but they remain causal organisms being transferred into the tissues to be classified. The virus appears to damage of the host along with the salivary secretion. salivary gland tissue, and in heavy infections, may affect gland function. In the latter case the ticks Postulated functions assigned to salivary glands of ticks contain large volumes of hemolymph (ca. 100 fxl) in nonfeeding processes. Male argasids and ixodids with elevated ion concentrations. The virus does were observed to secrete saliva during copulation

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(Feldman-Muhsam et al. 1970). These authors uptake. Additional research is needed to fully postulated that the secretion insures the smooth clarify this possibility. The salivary glands of most slow-feeding ixodids transfer of the spermatophore to the mouthparts of secrete cement substances to insure firm attachment the male where the spermatophore is held during of the tick mouthparts to the host. Exceptions are transfer. Chemical analysis of saliva from male Ornithodoros savignyi showed the presence of proteins,Ixodes species which do not produce cement but neutral sugars, and uronic acid (Feldman-Muhsam insert the mouthparts deeply into host skin tissues. Much of the tissue destruction associated with et al. 1970). ixodid tick feeding may be due to host reaction to Of utmost importance to many acarines is their pharmacologically active materials in tick saliva, ability to absorb water from unsaturated atmospheres which causes trauma in the host vascular system (Lees 1946, Wharton & Kanungo 1962, Kniille near the feeding lesion. 1965, 1966, Hafez et al. 1970, Sauer & Hair 1971). Salivary glands of ixodid ticks participate in The level of humidity above which this can occur is referred to as the critical equilibrium humidity excreting excess ions and water while the tick is attached and feeding on the host. Catecholamines (CEH), or critical equilibrium activity (CEA) by Wharton & Arlian (1972). Rudolph & Kniille stimulate salivary secretion both in vivo and in vitro, (1974) identified the mouth of ixodid ticks as the leading some investigators to suggest that the glands site of vapor uptake and suggested the possible role are under nervous control. Results suggest that both cyclic AMP and calcium are important of salivary glands in the uptake process. These intracellular regulators of fluid secretion. authors suggested that this role may well be related The precise role of acarine salivary glands in to hygroscopic properties of salivary secretion. disease transmission is not known in sufficient detail, Preliminary chemical analysis of the crystalline but few researchers doubt that many disease orsubstance in the region of the mouthparts identified ganisms are inoculated into the host body by direct high concentrations of sodium and potassium introduction of the agent with tick saliva. Studies (Rudolph & Kniille 1974). More recently the related to this problem are urgently required. mouth has been reconfirmed as the site of water vapor uptake in the ixodid tick Amblyomma americanum ADDENDUM ADDED IN PROOF (McMullen et al. 1976). Furthermore, chloride Subsequent to completion of this review paper, another was found to increase in the mouthparts of desiccated Higgs et al. (1976) has reported finding a prostaglandin ticks. The highest levels of chloride were found in group, in the saliva of the cattle tick Boophilus microplus. Ticks were the mouthparts, salivary glands and gut tissue during stimulated to salivate with subcuticular injections of pilocarpine rehydration. A hypothesis was proposed whereby hydrochloride and the authors suggested that prostaglandins ions are secreted by the salivary glands into the could be an important factor in the initiation and maintenance of the host lesion. In another paper of interest, Chinery & mouth where water is picked up hygroscopically. Ayitey-Smith (1977) have found that salivary gland homoIt was further proposed that water and ions are genates of Rhipicephalus sanguineus sanguineus antagonize and then swallowed and absorbed from the lumen of potentiate, respectively, the action of histamine and acetylcholine on guinea pig ileum. the gut. In a communication pertinent to the problem of tick paralysis, Megaw (pers. commun.) believes the pyramidal Cooper & Spence (1976) demonstrated that the paralysis procells of the type I salivary gland acini are suitable duced in mice by nymphal Ixodes holocyclus is due to a teminhibition of evoked release of acetylcholine candidates for the source of the hygroscopic fluid. perature-dependent at the neuromuscular junction. The authors hypothesized that His hypothesis is supported by the straight apical the toxin might block the influx of calcium ions which seem to membranes and infolded basal and lateral mem- be essential before evoked release can occur. This latter hypobranes of the cells, cellular features common to thesis remains to be investigated, however. epithelia involved with hyperosmotic secretions. CONCLUSIONS

The salivary glands are obviously vital to many key processes in acarines, involving both feeding and nonfeeding functions. Much of the relevant research has focused on the physiology of the glands in attached ectoparasitic ticks. However, recent findings also suggest important roles for the glands in nonattached ticks. Foremost within the latter category is the possible participation in water vapor

Acknowledgments: I would like to thank the following for their helpful comments: G. R. Needham, J. A. Hair, Robert L. Burton, D. C. Peters, and Richard C. Berberet. I am also grateful to W. R. Kaufman, P. A. Diehl, and M. W. J. Megaw for permission to quote from their unpublished work and to W. R. Kaufman and Harry Hoogstraal for critically reviewing the manuscript. LITERATURE CITED Arthur, D. R. 1962. Ticks and disease. Pergamon Press, Oxford. 445 p. 1965. Feeding in ectoparasitic Acari with special reference to ticks. Adv. Parasitol. 3: 249-98.

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Acarine salivary glands--physiological relationships.

JOURNAL OF MEDICAL ENTOMOLOGY J. Mad. Entomol. VoL 14, no. 1: 1-9 20 August 1977 Published bimonthly by Department of Entomology, Bishop Museum, Hon...
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