Educating youth swine exhibitors on influenza A virus transmission at agricultural fairs

Influenza A virus (IAV) is a major zoonotic pathogen that threatens global public health. Novel strains of influenza A viruses pose a significant risk to public health due to their pandemic potential, and transmission of influenza A viruses from animals to humans is an important mechanism in the generation and introduction of IAVs that threaten human health. The purpose of this descriptive correlational study was to develop real-life training scenarios to better inform swine exhibitors of the risks they may encounter when influenza A viruses are present in swine. Educational activities were implemented in five Ohio counties where exhibition swine had historically been shedding influenza A viruses during the county fair. A total of 146 youth swine exhibitors participated in the educational programme, and an increase in the knowledge base of these youth was documented. It is expected that educating youth exhibitors about exposure to influenza A virus infections in the swine they are exhibiting will result in altered behaviours and animal husbandry practices that will improve both human and animal health.

Prevalence of Influenza A Virus in Exhibition Swine during Arrival at Agricultural Fairs

The exhibition swine at agricultural fairs provides a critical human-swine interface that allows for the bidirectional transmission of influenza A virus (IAV). Previous IAV surveillance at the end of fairs has resulted in frequent detection of IAV-infected swine; little is known, however, about the frequency with which swine arrive at fairs already infected with IAV. We investigated the IAV prevalence among exhibition swine entering fairs to better understand the epidemiology of IAV in this unique human-swine interface. In 2014, snout wipes were collected from 3547 swine during the first day of nine agricultural exhibitions in Indiana and Ohio. Samples were screened for IAV using rRT-PCR and positive samples were inoculated into cultured cells for virus isolation. The overall IAV prevalence detected among swine arriving at exhibitions was 5.3% (188/3547) via rRT-PCR and 1.5% (53/3547) via virus isolation, with IAV being detected and recovered from swine at 5 of the 9 exhibitions. Within the fairs with IAV-positive swine, the individual exhibition IAV prevalence ranged from 0.2% (1/523) to 34.4% (144/419) using rRT-PCR and 0.2% (1/523) to 10.3% (43/419) with virus isolation. Single IAV subtypes were detected at three of the fairs but subtype diversity was detected among the pigs at two fairs as both H1N1 and H3N2 were recovered from incoming swine. At two of the exhibitions, a temporal relationship was observed between the order of the individual swine in sampling and the associated IAV rRT-PCR results, indicating the fomite transmission of IAV through common contact surfaces may occur. With the knowledge that a small proportion of swine arrive at fairs shedding IAV, resources should be directed towards preventive strategies focused on limiting transmission during fairs to protect swine and humans during exhibitions.

The Inability to Screen Exhibition Swine for Influenza A Virus Using Body Temperature

Agricultural fairs create an unconventional animal-human interface that has been associated with swine-to-human transmission of influenza A virus (IAV) in recent years. Early detection of IAV-infected pigs at agricultural fairs would allow veterinarians to better protect swine and human health during these swine exhibitions. This study assessed the use of swine body temperature measurement, recorded by infrared and rectal thermometers, as a practical method to detect IAV-infected swine at agricultural fairs. In our first objective, infrared thermometers were used to record the body surface temperature of 1,092 pigs at the time of IAV nasal swab collection at the end of the exhibition period of 55 agricultural fairs. IAV was recovered from 212 (19.4%) pigs, and the difference in mean infrared body temperature measurement of IAV-positive and IAV-negative pigs was 0.83°C. In a second objective, snout wipes were collected from 1,948 pigs immediately prior to the unloading of the animals at a single large swine exhibition. Concurrent to the snout wipe collection, owners took the rectal temperatures of his/her pigs. In this case, 47 (2.4%) pigs tested positive for IAV before they entered the swine barn. The mean rectal temperatures differed by only 0.19°C between IAV-positive and IAV-negative pigs. The low prevalence of IAV among the pigs upon entry to the fair in the second objective provides evidence that limiting intraspecies spread of IAV during the fairs will likely have significant impacts on the zoonotic transmission. However, in both objectives, the high degree of similarity in the body temperature measurements between the IAV-positive and IAV-negative pigs made it impossible to set a diagnostically meaningful cut point to differentiate IAV status of the individual animals. Unfortunately, body temperature measurement cannot be used to accurately screen exhibition swine for IAV.

Simultaneous infection of pigs and people with triple-reassortant swine influenza virus H1N1 at a U.S. county fair

Influenza-like illness was noted in people and pigs in attendance at an Ohio county fair in August 2007. The morbidity rate in swine approached 100% within 1-2 days of initial clinical signs being recognized, and approximately two dozen people developed influenza-like illness. Triple-reassortant swine H1N1 influenza viruses were identified in both pigs and people at the fair. The identified viruses (A/Sw/OH/511445/2007, A/Ohio/01/2007, and A/Ohio/02/2007) were similar to H1N1 swine influenza viruses currently found in the U.S. swine population. This case illustrates the possibility of transmission of swine influenza in settings where there is close human/swine interaction.

Defining the concept of 'tick repellency' in veterinary medicine

Although widely used, the term repellency needs to be employed with care when applied to ticks and other periodic or permanent ectoparasites. Repellency has classically been used to describe the effects of a substance that causes a flying arthropod to make oriented movements away from its source. However, for crawling arthropods such as ticks, the term commonly subsumes a range of effects that include arthropod irritation and consequent avoiding or leaving the host, failing to attach, to bite, or to feed. The objective of the present article is to highlight the need for clarity, to propose consensus descriptions and methods for the evaluation of various effects on ticks caused by chemical substances.

Transcriptome analysis of the synganglion from the brown dog tick, Rhipicephalus sanguineus

Tick control strategies rely heavily on chemicals (acaricides), most of which target the central nervous system. With increasing resistance, new acaricides are urgently needed but knowledge of tick neurobiology is surprisingly limited, notably the number of neural-specific gene sequences. One thousand and eight expressed sequence tags (ESTs) were obtained from a normalized cDNA library from Rhipicephalus sanguineus synganglia. Putative functional identities were assigned to 44% whereas 34% were unknown/novel sequences. Of particular interest were ESTs encoding a chitinase-like enzyme, an acetylcholinesterase and four transmembrane receptors including two glutamate-gated chloride channel receptors, a leucokinin-like receptor and a nicotinic acetylcholine receptor alpha-subunit. This study highlights the benefits of using both neural tissues and normalized libraries in an EST-approach for identifying potential acaricide targets expressed as rare transcripts.

Tick salivary glands: function, physiology and future

The salivary glands are the organs of osmoregulation in ticks and, as such, are critical to the biological success of ticks both during the extended period off the host and also during the feeding period on the host. Absorption of water vapour from unsaturated air into hygroscopic fluid produced by the salivary glands permit the tick to remain hydrated and viable during the many months between blood-meals. When feeding, the tick is able to return about 70% of the fluid and ion content of the blood-meal into the host by salivation into the feeding site. This saliva also contains many bioactive protein and lipid components that aid acquisition of the blood-meal. The salivary glands are the site of pathogen development and the saliva the route of transmission. The importance of the multifunctional salivary glands to tick survival and vector competency makes the glands a potential target for intervention. Here we review the cell biology of tick salivary glands and discuss the application of new approaches such as expressed sequence tag projects and RNA interference to this important area in the field of tick and tick-borne pathogen research.

Tick salivary prostaglandins: Presence, origin and significance

Prostaglandins (PGs) are oxygenated metabolites of polyunsaturated fatty acids, most notably arachidonic acid, that act as 'local hormones', regulating a plethora of physiological processes in mammals and other vertebrates. For a long time, PGs were reported only in higher vertebrates, but more recently they have been reported in lower organisms such as bacteria, yeasts and protozoa, and much information is now available on PGs in insects. Prostaglandins are increasingly reported to exist at the host-parasite interface and are thought to aid the parasite by modulating the inflammatory and immune response. Ticks secrete saliva containing extremely high concentrations of PGs into the host, and in this article Alan Bowman, Jack Dillwith and John Sauer provide a synopsis of the information, to date, on the presence, synthesis and proposed roles for these tick salivary PGs.

Identification of SNARE and cell trafficking regulatory proteins in the salivary glands of the lone star tick, Amblyomma americanum (L.)

Prostaglandin E(2) (PGE(2)) stimulates secretion of tick salivary gland proteins via a phosphoinositide signaling pathway and mobilization of intracellular Ca(2+) (). Highly conserved intracellular SNARE (soluble NSF attachment protein receptors) complex proteins are associated with the mechanism of protein secretion in vertebrate and invertebrate neuronal and non-neuronal cells. Proteins in the salivary glands of partially fed female lone star ticks cross-react individually with antibodies to synaptobrevin-2 (vesicle (v)-SNARE), syntaxin-1A, syntaxin-2 and SNAP-25 (target (t)-SNAREs), cytosolic alpha/beta SNAP and NSF (N-ethylmaleimide-sensitive fusion protein), Ca(2+) sensitive synaptotagmin, vesicle associated synaptophysin, and regulatory cell trafficking GTPases Rab3A and nSec1. V-SNARE and t-SNARE proteins form an SDS-resistant, boiling sensitive core complex in the salivary glands. Antibodies to SNARE complex proteins inhibit PGE(2)-stimulated secretion of anticoagulant protein in permeabilized tick salivary glands. We conclude that SNARE and cell trafficking regulatory proteins are present and functioning in the process of PGE(2)-stimulated Ca(2+) regulated protein secretion in tick salivary glands.

Ubiquitin-proteasome-dependent proteolysis in rainbow trout (Oncorhynchus mykiss): effect of food deprivation

The ubiquitin-proteasome proteolytic pathway is a major route of protein degradation and of particular importance in muscle proteolysis in mammals. In this study, the beta proteasome subunit N3 and polyubiquitin genes of the rainbow trout, Oncorhynchus mykiss, were sequenced and tissue distribution of gene expression was examined. The effects of 14-day food withdrawal were assessed on the N3 subunit and polyubiquitin gene expression in terms of mRNA, 20S proteasome proteolytic activity and ubiquitin protein abundance in trout liver and muscle. Both sequences are highly conserved, and the rainbow trout ubiquitin amino acid sequence is identical to the mammalian protein. The proteasome beta subunit N3 has 92% similarity to the Xenopus sequence. Starvation halved the polyubiquitin mRNA level in liver but had no effect on muscle levels. No significant effect of food withdrawal was observed on the proteasome mRNA in liver or muscle. Food withdrawal decreased the 20S proteasome proteolytic activity and the abundance of ubiquitin protein in both muscle and liver. Co-regulation of the proteasome and ubiquitin was indicated by the high correlation ( R=0.924) between 20S activity and ubiquitin abundance. Overall, this study demonstrates that starvation down-regulates the ubiquitin-proteasome pathway, possibly highlighting differences in the regulation of protein turnover in poikilothermic and endothermic animals.

Identity and synthesis of prostaglandins in the lone star tick, Amblyomma americanum (L.), as assessed by radio-immunoassay and gas chromatography/mass spectrometry

High concentrations of PGE(2) and PGF(2alpha) were identified by radio-immunoassay (RIA) and/or gas chromatography/mass spectrometry (GC/MS) in the hemolymph, salivary glands and saliva of the lone star tick Amblyomma americanum (L.). Binding studies indicated that PGE(2) was free and not bound to any proteins in the hemolymph. A small amount of 6-keto-PGF(1alpha) (breakdown product of PGI(2); prostacyclin) was also found in the salivary glands but not in the hemolymph or saliva. Neither PGD(2) nor PGA(2)/B(2) was detected in any tick material investigated. Although PGE(2) was found in the gut contents, only small amounts of label crossed the gut into the hemolymph during artificial feeding with labeled PGE(2), indicating that the high amounts of PGE(2) in hemolymph and salivary glands are not sequestered from the host blood meal. Isolated salivary glands and salivary gland homogenates demonstrated robust synthesis of PGE(2) at high concentrations of exogenous arachidonic acid. Synthesis by the salivary glands was monitored by measuring increasing PGE(2) with increasing arachidonic acid by RIA, GC/MS and labeled PGE(2) in the presence of labeled arachidonic acid. Synthesis was inhibited in a dose-dependent manner by indomethacin indicating that the cyclooxygenase synthesizing prostaglandins in ticks shares similarities to the enzyme found in mammals.

Salivary fluid secretion in the ixodid tick Rhipicephalus appendiculatus is inhibited by Thogoto virus infection

Adult Rhipicephatus appendiculatus ticks, infected with Thogoto (THO) virus or control, were fed on guinea pigs and removed at intervals throughout the feeding cycle. Salivary fluid secretion was measured by an in vitro technique. The salivary glands of infected, partially-fed ticks secreted fluid in vitro at about 75% the rate of controls, but the difference between infected and controls among engorged ticks was not statistically significant. Basal and DA-stimulated levels of cyclic AMP (cAMP) were determined in isolated glands and were significantly affected by THO virus infection. The differences in secretory rate among control and infected ticks could not be explained in terms of altered cAMP levels. Haemolymph volume was measured by a tracer-dilution technique using 3H-inulin. The mean haemolymph volume for both THO-infected and control groups was between 23-24% body weight throughout the feeding cycle, indicating that infection by this arbovirus did not influence salivary fluid secretion via altered haemolymph volume. The mechanism by which THO virus affects secretory activity of its tick vector remains unknown.

Prostaglandin E(2)-stimulated secretion of protein in the salivary glands of the lone star tick via a phosphoinositide signaling pathway

Previous studies identified a prostaglandin E(2) (PGE(2)) receptor in the salivary glands of partially fed female lone star ticks, Amblyomma americanum (L.). In the present studies, protein secretion from dispersed salivary gland acini was shown to be specific for PGE(2), as compared with PGF(2alpha) or the thromboxane analog U-46619, in accordance with their respective binding affinities for the PGE(2) receptor. Furthermore, the selective PGE(2) EP1 receptor agonist, 17-phenyl trinor PGE(2), was as effective as PGE(2) in stimulating secretion of anticoagulant protein. Calcium ionophore A-23187 (1 to 100 microM) stimulated secretion of anticoagulant protein in a dose-dependent manner but the voltage-gated Ca(2+)-channel blocker verapamil (1 to 1000 microM) and the receptor-mediated Ca(2+)-entry antagonist, SK&F 96365 (1 and 10 microM), and 5mM ethylene glycol bis(beta-aminoethyl ether)-N,NN', N'-tetraacetic acid (EGTA) had no appreciable effect on inhibiting PGE(2)-stimulated secretion of anticoagulant protein. PGE(2) (0.1 microM) and the non-hydrolyzable analog of guanosine triphosphate (GTP), GTPgammaS (10 microM), directly activated phospholipase C (PLC) in a membrane-enriched fraction of the salivary glands after PLC was first incubated with the PGE(2) EP1 receptor antagonist AH-6809, which presumably antagonized endogenous PGE(2) (0.3 microM) in the broken-cell-membrane-enriched fraction. TMB-8, an antagonist of intracellular inositol trisphosphate (IP(3)) receptors, inhibited PGE(2)-stimulated secretion. The results support the hypothesis that PGE(2) stimulates secretion of tick salivary gland protein via a phosphoinositide signaling pathway and mobilization of intracellular Ca(2+).

Salivary glands in ixodid ticks: control and mechanism of secretion

The salivary glands are vital to the biological success of ixodid ticks and the major route for pathogen transmission. Important functions include the absorption of water vapor from unsaturated air by free-living ticks, excretion of excess fluid for blood meal concentration, and the secretion of bioactive protein and lipid compounds during tick feeding. Fluid secretion is controlled by nerves. Dopamine is the neurotransmitter at the neuroeffector junction regulating secretion via adenylate cyclase and an increase in cellular cAMP. Dopamine also affects the release of arachidonic acid which is subsequently converted to prostaglandins. Prostaglandin E(2) (PGE(2)) is secreted at extremely high levels into tick saliva for export to the host where it impacts the host physiology. Additionally, PGE(2) has an autocrine or paracrine role within the salivary gland itself where it interacts with a PGE(2) receptor to induce secretion (exocytosis) of bioactive saliva proteins via a phosphoinositide signalling pathway and an increase in cellular Ca(2+). Regulation of fluid secretion has been extensively studied, but little is known about the mechanism of fluid secretion. Continuing advances in tick salivary gland physiology will be made as key regulatory and secretory gland proteins are purified and/or their genes cloned and sequenced.

Phospholipase A2 activity in salivary glands and saliva of the lone star tick (Acari: Ixodidae) during tick feeding

Phospholipase A2 (PLA2) activity levels in tick [Amblyomma americanum (L.)] salivary glands and saliva were examined during tick feeding by using 14C-phosphatidylcholine as the substrate. Saliva produced by stimulating female ticks to salivate with dopamine contains PLA2 (ts-PLA2) activity. The ts-PLA2 activity level in saliva did not change significantly during tick feeding except for a decrease in the last rapid feeding phase (> 200 mg) and in replete ticks. Phospholipase A2 activity was higher in salivary glands of fed than unfed ticks, both in males and females; activity increased during tick feeding correlating with salivary secretory rates during tick feeding suggesting that much of the PLA2 activity measured in whole salivary glands is synthesized for subsequent secretion. During the time course of in vitro salivation, the first 10 microliters of saliva contained higher ts-PLA2 activity than saliva secreted thereafter. Phospolipase A2 was identified in the saliva of artificially fed ticks indicating that ts-PLA2 is a physiological component of tick saliva.

Prostaglandin E2 in the salivary glands of the female tick, Amblyomma americanum (L.): calcium mobilization and exocytosis

A cholera toxin-sensitive, prostaglandin E2 (PGE2) specific receptor has been identified in the plasma membrane fraction of tick salivary glands. In the present study, we report that stimulation of dispersed salivary glands of the lone star tick Amblyomma americanum (L.) with 1 nM to 10 microM PGE2 increased the intracellular concentration of inositol trisphosphate (IP3) in a dose-dependent manner. Incubation of dispersed tissue with 1 nM to 10 microM PGE2 also stimulated release of 45Ca2+ from preloaded tissue. PGE2 (10 microM) did not stimulate an influx of 45Ca2+. Therefore, the PGE2 receptor in the salivary glands appears to activate a phosphoinositide phospholipase C signalling pathway to increase formation of intracellular IP3 and, thus, mobilize Ca2+ from intracellular stores. Incubation of dispersed salivary glands with 1 nM to 1 microM PGE2 stimulated secretion of anticoagulant protein, but not at < 1 nM or > 1 microM PGE2. In addition, the mammalian PGE2 EP1 receptor antagonist AH-6809 affected secretion of anticoagulant by dispersed salivary gland tissue at a low concentration supporting the hypothesis that the PGE2 receptor in tick salivary glands is EP1-like. We propose that a major function for PGE2 in tick salivary glands is to mobilize Ca2+ and stimulate secretion (exocytosis) of bioactive proteins into the tick's saliva during feeding.

A novel phospholipase A2 activity in saliva of the lone star tick, Amblyomma americanum (L.)

Saliva from female lone star ticks, Amblyomma americanum, contained a novel phospholipase A2 (PLA2) activity that hydrolyzed 14C-arachidonate from 14C-arachidonyl phosphatidylcholine. The tick saliva PLA2 (ts-PLA2) was active over a broad pH range (4.5-11.5) with two distinct pH optima of pH 5.5 and 9.5. Though extracellular PLA2s are reported to be activated by millimolar Ca2+, ts-PLA2 was sensitive to submicromolar Ca2+ and was half-maximally activated by 3.5 microM Ca2+. Tick saliva contains > 500 microM Ca2+ and the feeding lesion in the host is expected to contain millimolar Ca2+. Saliva exhibited a single peak of PLA2 activity corresponding to a molecular weight of 55.7 +/- 1.3 kDa by size exclusion chromatography. The ts-PLA2 was unaffected by a variety of compounds known to inhibit either secreted or cytosolic PLA2s from other sources. However, ts-PLA2 was inhibited by the substrate analog, oleyloxyethyl phosphorylcholine (IC50 = 1.4 microM), and the end product, arachidonic acid (IC50 = 38 microM). Low concentrations of dithiothreitol did not greatly affect ts-PLA2, but activity was reduced at higher concentrations. The PLA2 activity found in A. americanum salivary glands showed many similarities to ts-PLA2, but also some distinct differences. Secreted at the tick-host interface, ts-PLA2 is thought to play an important, but unknown, role during the prolonged tick feeding.

Isolation and characterization of americanin, a specific inhibitor of thrombin, from the salivary glands of the lone star tick Amblyomma americanum (L.)

A thrombin (EC 3.4.21.5) inhibitor (americanin) was isolated from the salivary glands of the lone star tick Amblyomma americanum (L.) using reversed-phase chromatography and anion-exchange chromatography. Americanin did not inhibit any other protease tested, including factor Xa, plasmin, trypsin, chymotrypsin, elastase, papain, pepsin, and carboxypeptidase. The inhibition of thrombin by americanin decreased dramatically with dilution of the reaction mixture including thrombin, its substrate, and americanin. When thrombin assays were performed in the presence of americanin, the reaction curve showed a time-dependent inhibition. Significant inhibition was observed when americanin concentration was approximately equal to that of thrombin, with a Ki of 0.073 nM. The results suggest that americanin is a specific, reversible, competitive, slow, tight-binding inhibitor of thrombin.

Tick saliva: recent advances and implications for vector competence

Secretions of the tick salivary glands are essential to the successful completion of the prolonged feeding of these ectoparasites as well as the conduit by which most tick-borne pathogens are transmitted to the host. In ixodid ticks the salivary glands are the organs of osmoregulation, and excess water from the bloodmeal is returned via saliva into the host. Host blood must continue to flow into the feeding lesion as well as remain fluid in the tick mouthparts and gut. The host's haemostatic mechanisms are thwarted by various anti-platelet aggregatory, anticoagulatory and anti-vasoconstrictory factors in tick saliva. Saliva components suppress the immune and inflammatory response of the host permitting the ticks to remain on the host for an extended period of time and, adventitiously, enhancing the transmission and establishment of tick-borne pathogens. Over the years much work has been done on the numerous enzyme and pharmacological activities found in the tick saliva. The present article reviews the most recent work on salivary gland secretions with special emphasis on how they favour pathogen transmission.

A specific prostaglandin E2 receptor and its role in modulating salivary secretion in the female tick, Amblyomma americanum (L.)

Prostaglandins of the 2-series (e.g. PGE2) are typically synthesized from arachidonic acid (AA) after AA is released from cellular phospholipids after activation of an intracellular phospholipase A2 (PLA2). Treatment of isolated salivary glands with PLA2 inhibitor oleyloxyethyl phosphorylcholine (OPC) or prostaglandin synthetase inhibitors reduced dopamine-induced fluid secretion and cyclic AMP (cAMP) levels in isolated salivary glands. PGE2 and its analog, 17-phenyl trinor PGE2, partly reversed the inhibition of secretion and cAMP level by OPC, suggesting that prostaglandins may have an autocrine effect in modulating tick salivary gland function. A specific PGE2 receptor was identified in the plasma membrane fraction of the salivary glands. The receptor exhibits a single, high affinity PGE2 binding site with a KD approximately 29 nM, is saturable, reversible, and specific for PGE2 and coupled to a cholera toxin-sensitive guanine nucleotide regulatory protein. Assay of adenylate cyclase activity in salivary gland membranes showed that PGE2 neither stimulated nor inhibited adenylate cyclase activity, indicating that the PGE2 effects on cAMP levels and possibly secretion are indirect, and that the PGE2 receptor stimulates an alternate "second messenger" pathway.

Identification of hemolytic activity in saliva of the lone star tick (Acari:Ixodidae)

Hemolytic activity was identified in the saliva of Amblyomma americanum (L.) when red blood cells from sheep were incubated with tick saliva in the presence of phosphatidylcholine and sodium deoxycholate. The hemolytic activity was destroyed by boiling or treating with trypsin. The hemolytic activity in tick saliva was calcium-dependent, and inhibited by a phospholipase A2 inhibitor oleyloxyethyl phosphorylcholine. Phosphatidylserine could replace phosphatidylcholine in the hemolytic assays but phosphatidylethanolamine and phosphatidylinositol were ineffective. Size exclusion chromatography of tick saliva revealed one peak of hemolytic activity, which correlated with the activity of tick salivary phospholipase A2, both having a molecular weight approximately 55,000 daltons. These results suggest that the hemolytic activity in tick saliva results from salivary phospholipase A2. The hemolytic activity in tick saliva may play a role in lysing host red blood cells, thus facilitating the tick digestive process.

Identification and characterization of anticoagulant activities in the saliva of the lone star tick, Amblyomma americanum (L.)

Anticoagulant activities against both the extrinsic and intrinsic coagulation pathways were identified in the saliva of partially fed female lone star ticks, Amblyomma americanum (L.). The activities of factor Xa and thrombin in the common pathway of the coagulation cascade were inhibited by tick saliva. The greatest anticoagulant activities were found in the saliva of ticks weighing more than 200 mg. The anticoagulant activities in tick saliva could be detected without preincubation of tick saliva with sheep plasma, but preincubation significantly increased the activities. Tick saliva anticoagulant activities were abolished by boiling for 15 min or being treated with trypsin for 1 hr. Phosphatidylcholine (3 mM) and phospholipase A2 inhibitor oleyloxyethyl phosphorylcholine (0.2 mM) did not affect the anticoagulant activities significantly, suggesting that the phospholipase A2 activity found in tick saliva does not contribute to the anticoagulant activities. Size exclusion high performance liquid chromatography revealed that the molecular weights of the anticoagulant activities were approximately 16,000 D. The anticoagulant activities in tick saliva are believed to play an important role in facilitating tick feeding by helping overcome the host hemostatic system.

Dietary modification of host blood lipids affect reproduction in the lone star tick, Amblyomma americanum(L.)

The feeding and reproductive performance of female lone star ticks (Amblyomma americanum (L.)) infesting guinea pigs on diets containing 15% fish oil (FO) or safflower oil (SO) were investigated. Replete ticks fed on FO-fed guinea pigs weighed approximately 30% less than those on the SO-fed guinea pigs. The lower engorged weight resulted in a similar decrease in the mass and number of eggs laid and number of larvae hatching. No effect of host dietary treatment was observed upon the reproductive efficiency index, egg weight, or hatchability. Guinea pig blood on the FO-diet contained high levels of eicosapentaenoic acid, which has previously been shown to inhibit the accumulation of arachidonic acid in the tick salivary gland. It is suggested that the ticks on the FO-fed guinea pigs have impaired production and secretion of dienoic prostaglandins in the saliva resulting in poorer feeding performance, possibly by altering the amount of host blood present in the feeding lesion.

Alteration of arachidonate levels in tick salivary glands by dietary modification of host blood lipids

Tick saliva contains prostaglandins of the 2-series, believed to facilitate bloodmeal acquisition. Because ticks cannot synthesize the prostaglandin precursor, arachidonic acid, investigations were undertaken to study the uptake, incorporation, and distribution of arachidonic acid in the salivary glands of the lone star tick in vitro and in vivo. Uptake of [3H]arachidonate by isolated salivary glands was reduced in the presence of low concentrations of arachidonic or eicosapentaenoic acids, but much higher, non-physiological concentrations of oleic and linoleic acids were required to inhibit [3H]arachidonate uptake. The incorporation of [3H]arachidonate into triglycerides increased at high concentrations of arachidonic or eicosapentaenoic acid, but not at any concentration of oleic or linoleic acid. Eicosatetraynoic acid greatly inhibited [3H]arachidonic acid. Guinea pigs fed hydrogenated coconut oil, safflower/primrose oil, or fish oil exhibited altered blood lipids; notably increased levels of eicosapentaenoic acid when fed fish oil. Salivary gland lipids in ticks fed on these hosts were also altered. Ticks parasitizing fish oil-fed guinea pigs contained high levels of eicosapentaenoic acid with a 30% reduction in arachidonate levels. The results demonstrated that eicosapentaenoic acid in the host diet had profound effects on arachidonate assimilation by tick salivary glands, which could lead to altered prostaglandin content in tick saliva.

Biosynthesis of salivary prostaglandins in the lone star tick, Amblyomma americanum

Dopamine-induced saliva from ticks fed [3H]arachidonic acid contained the radiolabelled prostaglandins E2, F2 alpha, D2, and B2, the latter probably derived from PGE2 owing to the alkalinity of tick saliva. Prostaglandin synthetase (PGS) activity in the salivary gland homogenate from the lone star tick, Amblyomma americanum, could not be detected by standard radiometric methodologies successfully employed for tissues from many animal species, including numerous arthropods. Modifications to the assay conditions had no effect. The presence of a PGS-inhibitor in the salivary glands was ruled out. It is postulated that the PGS in A. americanum salivary glands may be considerably different from that found in other animals, including vertebrate hosts.

Uptake, incorporation and redistribution of arachidonic acid in isolated salivary glands of the lone star tick

The ability of isolated salivary glands from the lone star tick, Amblyomma americanum, to take up, incorporate and redistribute [3H]arachidonic acid was examined. Uptake of arachidonic acid was concentration dependent--a single salivary gland incorporated up to approximately 2.8 micrograms arachidonic acid in 60 min. Over 90% of the [3H]arachidonate entering the glands was esterified and found only in the phospholipid (approximately 80%) and triglyceride (approximately 10%). Essentially no radioactivity was associated with the diglyceride fraction and none with phosphatidic acid indicating de novo phospholipid synthesis was negligible. Phospholipid synthesis via acylation of lysophospholipids (the Lands pathway) was indicated by the rapidity of the synthesis (< 2 min) and the sensitivity to sulfhydryl-blocking agents. Within the phospholipids, [3H]arachidonate was incorporated only into phosphatidylcholine (PC) and phosphatidylethanolamine (PE). Initially [3H]arachidonate was incorporated primarily into PC, but as the incubation proceeded PE contained an increasing proportion of the label. The proportion of [3H]arachidonate incorporated into triglyceride increased at higher media concentrations of arachidonic acid. The roles of lysophosphatide acyltransferase, transacylase and diglycerol acyltransferase in the distribution of arachidonate in tick salivary glands are discussed.

Origin of arachidonic acid in the salivary glands of the lone star tick, Amblyomma, americanum

The contribution of synthesis and dietary sequestration to the high arachidonate content of the lone star tick, Amblyomma americanum, salivary glands was investigated by assessing the salivary metabolites of various radiolabeled fatty acid substrates administered to partially fed females. A portion of each of the fatty acids studied was incorporated into the fatty acid moiety of the phospholipid fraction. [14C]acetate was metabolized only into myristic, palmitic, palmitoleic, steric, and oleic acids. [3H]oleic acid, [14C]linoleic acid, [14C]gamma-linolenic acid and [14C]eicosatrienoic acids were incorporated into salivary gland phospholipids but underwent little change including elongation and/or desaturation to arachidonate. Ingested [3H]arachidonic acid was readily taken up by the salivary gland and distributed among the lipid classes in a pattern markedly different from that of the other fatty acids tested. We conclude that ticks are unable to synthesize arachidonic acid for incorporation into the salivary glands, but rather sequester it from the host bloodmeal.

Tick salivary gland physiology

The multifunctional, morphologically complex salivary glands are essential to the biological success of ticks and are intricately involved in the transmission of pathogens. They are innervated, and there is convincing evidence that dopamine is a neurotransmitter at the neuroeffector junction controlling fluid secretion. As feeding progresses, the rate of salivary fluid secretion increases greatly, enabling the ixodid tick to concentrate the bloodmeal by returning excess water and ions to the host. Saliva in feeding ticks is rich in bioactive components and exhibits a range of pharmacological properties. Factors identified in saliva or salivary glands include cement to help anchor the mouthparts to the host, various enzymes and inhibitors, histamine agonists and antagonists, prostaglandins, antihemostatic factors, and immuno-modulating factors. A secretion from the salivary glands allows ticks to absorb water from the air during the lengthy periods off their hosts. The physiology of this remarkable organ provides a striking example of strategies that have evolved to meet the challenge of a unique parasitic life style.

Regulation of free arachidonic acid levels in isolated salivary glands from the lone star tick: a role for dopamine

An important regulatory step for prostaglandin synthesis is the availability of the precursor, free arachidonic acid (AA). In isolated salivary glands of the lone star tick, Amblyomma americanum (L.), the level of free AA appears to depend on higher phospholipase A2 (PLA2) activity rather than decreased rates of re-esterification by lysophosphatide acyl transferase (LAT). This conclusion is supported by experiments where inhibition of LAT with merthiolate was without effect, while the calcium ionophore A23187, a PLA2 stimulant, increased levels of free AA. The PLA2 activity in A. americanum was reduced by the substrate analog, PLA2 inhibitor, oleyloxyethyl phosphorylcholine in a dose-dependent manner, but was insensitive to the other mammalian PLA2 inhibitors mepacrine (20 microM), aristolochic acid (45 microM), and dexamethasone (50 microM). No substrate preference was observed for the functional group of the phospholipid, with phosphatidylcholine and phosphatidylethanolamine being equal sources of AA in A23187-stimulated glands. Compared to phospholipids containing other fatty acids, only arachidonyl-phospholipid (arachidonyl-PL) was significantly hydrolyzed by PLA2 activity in A23187-stimulated glands. Dopamine was as effective as A23187 as a stimulant of PLA2 activity in isolated glands, but this effect was abolished in the presence of the calcium channel blocking agent verapamil. It is concluded that free AA levels in tick salivary glands are increased through activation of a Type IV-like PLA2 following an increase of intracellular calcium caused by the opening of voltage-dependent calcium channels due to dopamine stimulation.

Distribution of arachidonic acid among phospholipid subclasses of lone star tick salivary glands

The subclass composition of choline- and ethanolamine-containing phospholipids was determined by analysis of acyl-linked fatty acids released by base hydrolysis of diradylglycerobenzoates formed from lone star tick salivary gland diacyl, alkylacyl and alkenylacyl phospholipids. The diacyl subclass comprises 87% of all choline-containing phospholipids, while th alkylacyl subclass comprises c. 9% and the alkenylacyl subclass c. 4%. The diacyl subclass comprises 72-77% of ethanolamine-containing phospholipids and about 14 and 13% of this subclass of phospholipid are alkylacyl and alkenylacyl lipids, respectively. Arachidonic acid (20:4) is the most abundant fatty acid (28% of all fatty acids) esterified in the alkylacyl form of phosphatidylcholine (PC) and it comprises 17% of the fatty acids in alkenylacyl-PC. The alkylacyl form of phosphatidylethanolamine (PE) is also rich in 20:4 (24%) while the alkenylacyl-PE subclass contains only 9% 20:4. Despite the relatively high amounts of 20:4 within the ether-linked phospholipids, the majority of the salivary gland 20:4 (> 83%) is found in the diacyl phospholipid subclass because of the preponderence of this subclass in tick salivary glands. Isolated salivary glands incorporated [3H]-20:4 primarily (> 98%) into the sn-2 position of diacyl PC > PE, with some incorporation into triglycerides. Continued incubation in the absence of labeled 20:4 demonstrated remodeling of [3H]-20:4 from PC into PE, and from the diacyl subclass to the alkylacyl subclass in the choline containing phospholipids.

Regulation of plasma oestrogen by dietary fats in the laying hen: relationships with egg weight

1. Feeding a diet supplemented with maize oil was found to elevate plasma oestradiol concentration in laying hens. 2. In a larger-scale experiment, isoenergetic and isonitrogenous diets containing 10, 20, 40 or 60 g/kg supplemental maize oil, tallow, coconut oil or fish oil were fed for 5 weeks. 3. Egg weights showed very different responses to the different fats. The responses could be described by quadratic functions that all gave optimum responses with supplemental dietary fat concentrations of about 40 g/kg. Egg weight increased the most with maize oil and was decreased with fish oil at the highest inclusion rate. 4. Measurements of egg components showed a relatively larger increase in albumen weights with maize oil than with other fats. 5. Across treatments, mean plasma oestradiol concentrations were very highly correlated (r = 0.96) with the changes in egg weights over the experimental period. 6. It is concluded that oestrogen is important in controlling egg weight and that the effect of dietary fats in influencing egg weight is mediated by an effect of the fats on oestrogen metabolism.

Changes in lipids of the salivary glands of the lone star tick, Amblyomma americanum, during feeding

The lipid composition of salivary glands from male and female lone star ticks, Amblyomma americanum, was investigated at progressive stages of tick feeding. The amounts of fatty acids from both phospholipid and neutral lipid fractions increased dramatically during the initial stage of feeding and peaked in partially fed females weighing 100-250 mg. Percentage compositions of myristic (14:0) and palmitic acid (16:0) decreased, but stearic (18:0), oleic (18:1), linoleic (18:2), and arachidonic acid (20:4) increased during tick feeding. Arachidonic acid, the precursor to eicosanoids including the 2-series of prostaglandins, increased from 1.3% of all fatty acids in salivary glands from unfed female ticks to 8.2% in salivary glands from fully engorged female ticks. Arachidonic acid was found in the triglyceride fraction of unfed and fed virgin females but only in phosphatidylcholine and phosphatidylethanolamine from salivary glands of other fed female ticks. Comparisons between fed and unfed male ticks and fed/virgin, fed/mated, and unfed females demonstrate that feeding is necessary for accumulation of arachidonic acid in salivary gland phospholipids.

The effects of dietary fat and bird age on the weights of eggs and egg components in the laying hen

1. A low-fat diet or an isoenergetic and isonitrogenous high-fat diet containing 55 g maize oil/kg were fed to laying hens at different stages during the laying year in two experiments. 2. Feeding the high-fat diet to young hens resulted in a rapid increase of 2.5 g in egg weight, made up of increases in both yolk and albumen weights. 3. Switching the diets at 50 weeks caused changes in egg weight that were accounted for entirely by changes in egg albumen weight. 4. Feeding the high-fat diet from 46 weeks in a second experiment increased egg and egg albumen weights by 1.26 and 1.34 g respectively. 5. The increase in egg weight with age was associated with a greater increase in the proportion of yolk, at the expense of albumen, compared to egg weight increases related to dietary fat. 6. It is concluded that dietary fatty acids increase egg weight by a mechanism different from that causing age-related increases in weight and that the mechanism involves a stimulation of oviduct protein synthesis.