Interaction between ticks (Acari: Ixodidae) and pathogenic nematodes (Nematoda): susceptibility of tick species at various developmental stages

The virulence of entomopathogenic nematodes (Steinernematidae and Heterorhabditidae) to tick species under laboratory conditions is reported. The susceptibility of larval, nymphal, and adult stages of the ticks Hyalomma excavatum (Koch), Rhipicephalus bursa (Canestrini & Fanz), and R. sanguineus (Latereille) to 2 strains of Steinernema carpocapsae and 3 strains of Heterorhabditis bacteriophora were compared in laboratory assays. Preimaginal stages of ticks were found to be more resistant to the nematodes than were adult ticks which exhibited 80-100% mortality in a dish containing 5,000 infective juveniles of H. bacteriophora IS-3 or IS-5 strains isolated in Israel. These 2 strains were found to be much more virulent to unfed adult ticks than were the other isolates. No marked difference was found between engorged ticks and unfed adults of R. sanguineus or H. excavatum in terms of mortality, whereas engorged males and unfed females of R. bursa were significantly more susceptible than unfed males or engorged females.     

Ultrastructural Analysis of the Oocytes of Female Rhipicephalus sanguineus (Latreille, 1806) (Acari: Ixodidae) Ticks Subjected to the Action of Azadirachta indica A. Juss (Neem)

The present study provides ultrastructural information about the acaricidal effects of neem (Azadirachta indica A. Juss) on the ovaries of R. sanguineus engorged females. In general, the main damage caused in the oocytes was alteration in the shape of the cell and of the germinal vesicle, ring-shaped nucleolus, cytoplasmic vacuolation, and disorganization of the organelles and of the cell membranes (including the chorion), all of which indicate that these cells could be in the process of death. The results showed that azadirachtin would be an efficient acaricide agent for inhibiting and/or neutralizing the reproduction process of R. sanguineus females, impairing the reproductive ability of this species.     

Comparison of methods for introducing and producing artificial infection of ixodid ticks (Acari: Ixodidae) with Ehrlichia chaffeensis.

Only 29.5 +/- 8.91% of engorged Amblyomma americanum (L.) nymphs that we inoculated with Ehrlichia chaffeensis molted successfully to adults compared with 75.8 +/- 7.46% of engorged nymphs that were not inoculated. However, 65.4 +/- 6.02% of unfed nymphs of this species were exposed for 2 h to E. chaffeensis suspension introduced to them through glass capillaries gained weight. These nymphs were placed on rabbits, and approximately 50% of them completed their feeding and molted successfully to adults. Weight gained was higher (71.8 +/- 17.33% and 69.8 +/- 23.26%) for unfed A. americanum females that fed from capillaries for 2 and 24, h respectively, than for nymphs. Similar values were recorded for Dermacentor variabilis (Say) (61.0 +/- 16.23%) and Rhipicephalus sanguineus (Latreille) (59.0 +/- 18.62%) females after 24 h of capillary feeding. The amount of E. chaffeensis suspension taken in by females of A. americanum, D. variabilis, and R. sanguineus during 24 h of feeding was 11.2 +/- 3.56, 10.9 +/- 4.29 and 6.3 +/- 2.35 microliters, respectively. This volume is equivalent to approximately 12,969, 12,622, and 7,295 infected cells ingested by the species mentioned above. Positive correlation between the volume taken in by the ticks and the weight gained by the females was found, but the initial weight of the unfed females did not effect the weight they gained. The pathogen was found in the females of all 3 species by polymerase chain reaction procedures for at least 7 d, indicating that the capillary feeding method can be successfully used for infecting unfed ticks. The potential use of this method is discussed.     

Additional instances of human parasitism by the brown dog tick (Acari: Ixodidae)

Nine cases of humans parasitized by the brown dog tick, Rhipicephalus sanguineus (Latreille), are reported. Eight cases occurred during 1989. Seven of the individuals were from an apparent focus of human biting in northern Texas and southwestern Oklahoma, one case was from San Antonio, Bexar County, Tex., and one case was from Homestead Air Force Base, Dade County, Fla. These cases suggest that the role of R. sanguineus in the transmission of the etiologic agent of canine ehrlichiosis and other pathogenic organisms to humans may be underestimated and warrants investigation.     

Focus of human parasitism by the brown dog tick, Rhipicephalus sanguineus (Acari: Ixodidae)

Throughout most of its range, the brown dog tick, Rhipicephalus sanguineus (Latreille), prefers dogs as a host, but human bites occasionally occur in the Mediterranean region and Central America; historically, this species has rarely bitten humans in the United States. A focus of 15 human bite cases by this tick is reported from four Air Force bases located within 200 miles of each other in north central Texas and southwestern Oklahoma. The sudden appearance of numerous documented bite cases indicates that either the species is becoming more anthropophilic in this area or than an introduction of a more human adapted population of R. sanguineus has occurred. The species is a known reservoir and vector of Ehrlichia canis, the causative agent of canine ehrlichiosis in dogs. The presence of an anthropophilic strain of R. sanguineus in the United States may lead to increased exposure to E. canis and thus an increase in the incidence of human ehrlichiosis.     

Rhipicephalus sanguineus (Acari: Ixodidae) female ticks exposed to castor oil (Ricinus communis): an ultrastructural overview

Tick control has been accomplished through the use of synthetic acaricides, which has created resistant individuals, as well as contaminating the environment and nontarget organisms. Substances of plant origin, such as oils and extracts of eucalyptus and neem leaves, have been researched as an alternative to replace the synthetic acaricides. Ricinoleic acid esters from castor oil have recently been shown as a promising alternative in eliminating bacterial contamination during ethanol fermentation, by acting as an effective biocide. The same positive results have been observed when these esters are added to the food given to tick-infested rabbits. This study tested the effect of these substance on the reproductive system of Rhipicephalus sanguineus females, added to rabbit food, more specifically on oogenesis. For this, four groups were established: four control groups (CG1, CG2, CG3, and CG4) and four treatment groups (TG1, TG2, TG3, and TG4) with one rabbit in each (New Zealand White), used as hosts. After full 4 days feeding (semi-engorgement), the females were collected and had their ovaries extracted. In this study, it was observed that R. sanguineus females exposed to esters had their ovaries modified, which was demonstrated through transmission electron microscopy techniques. The addition of ricinoleic esters to the diet of tick-infested rabbits revealed how toxic such substances are for the cytoplasmic organelles of oocytes and pedicel cells. These compounds can change the morphophysiology of germ and somatic cells, consequently influencing their viability and, therefore, confirming that the ricinoleic acid esters from castor oil are a promising substance in the control of R. sanguineus.     

Quantitative studies of host immunoglobulin G in the hemolymph of ticks (Acari)

A radioimmunoassay was used to measure the concentration of host immunoglobulin G (IgG) in the hemolymph of female hard and soft ticks. Hyalomma excavatum Koch, Rhipicephalus sanguineus Latreille, Ornithodoros tholozani (Laboulbene and Megnin), and O. moubata (Murry) were fed on rabbits immunized with ovalbumin; Argas persicus (Oken) was fed on chickens immunized with cytochrome 'C.' At 24 h after feeding, the concentration of antiovalbumin IgG in the hemolymph was 7 micrograms/ml for H. excavatum, 5 micrograms/ml for R. sanguineus, and 0.15 micrograms/ml for O. moubata; the percentage of intact IgG molecules was 30, 44, and 100%, respectively. Host IgG was not detected in the hemolymph of O. tholozani and A. persicus. There was no increase in the concentrations of host IgG in the hemolymph of the soft ticks during the first week following the blood meal. The potential contribution to the resistance of hosts against ticks by host antibodies that cross into the tick hemocoel is discussed.     

Pathogenicity of entomopathogenic fungi Beauveria bassiana and Metarhizium anisopliae to Ixodidae tick species Dermacentor variabilis, Rhipicephalus sanguineus, and Ixodes scapularis

Nymphal and adult ticks from three different tick species, Dermacentor variabilis Say, Ixodes scapularis Say, and Rhipicephalus sanguineus Latrielle, were treated with conidia and blastospores of the entomopathogenic fungi Beauveria bassiana (Bals.) Vuill. and Metarhizium anisopliae Metschnikoff. Dose-response experiments indicated that a critical concentration of fungal spores is required for infection and mortality. Over a 28-d time course, fungal suspensions of either B. bassiana or M. anisopliae at 10(8) conidia/ml resulted in 50-70% mortality in adult I. scapularis and R. sanguineus, but <20% mortality in D. variabilis ticks. R. sanguineus nymphs were highly susceptible to both entomopathogenic fungi, displaying >60% mortality within 14 d postinfection and >90% mortality within 21-28 d postinfection. D. variabilis nymphs also were more susceptible than their corresponding adults, displaying mortalities ranging from 20 to 40% 28 d postinfection. I. scapularis nymphs, however, seemed to be slightly less susceptible than adults (45% mortality, 28 d postinfection). The addition of nutrients to fungal cell suspensions did not have any noticeable effects on mortality toward any of the tick species tested. Significant mortality against D. variabilis adults (approximately 65%) was noted only when B. bassiana fungal cells with growth media carryover were used as the inoculum against the ticks. Entomopathogenic fungi such as B. bassiana and M. anisopliae may have the potential for controlling populations of I. scapularis and R. sanguineus, and under certain conditions D. variabilis. Our results indicate that inoculum conditions can greatly affect successful virulence and subsequent mortality.     

Cloning and sequencing of putative acetylcholinesterase cDNAs from the American dog tick, Dermacentor variabilis, and the brown dog tick, Rhipicephalus sanguineus (Acari: Ixodidae)

Two putative cDNAs of acetylcholinesterase (AChE), one from Dermacentor variabilis, and the other from Rhipicephalus sanguineus, were amplified and sequenced. The deduced amino acid sequences have high amino acid identities (between 70 and 94%) to known tick AChE sequences deposited in GenBank. Furthermore, these two AChEs also possess common features in their primary AChE structure such as catalytic active sites. A 2,220-bp contiguous sequence, containing a 1,791-bp open reading frame encoding an AChE precursor with 596 amino acid residues, was obtained from D. variabilis. The deduced proteins of R. sanguineus are different in size by 6 amino acids because of alternative splicing at the 5' end. A gene tree deduced from phylogenetic analysis indicates that there are at least three lineages of AChE in arthropods.     

Detection of Ehrlichia platys DNA in brown dog ticks (Rhipicephalus sanguineus) in Okinawa Island, Japan

Thirty-two Rhipicephalus sanguineus females collected from eight free-roaming dogs in Okinawa Island, Japan, were examined for ehrlichial DNA by 16S rRNA-based PCR and subsequent sequencing. Partial sequences of Ehrlichia platys 16S rRNA (678 to 679 bp) were detected in three ticks (9.4%) from two dogs. This is the first report of detection of E. platys in Japan, and also the first report of detection in ticks.     

Detection of Rickettsia rickettsii and Bartonella henselae in Rhipicephalus sanguineus ticks from California

Sixty-two questing adult Rhipicephalus sanguineus (Latreille) ticks were collected by direct removal from blades of turfgrass and adjacent concrete walkways at a suburban home in Riverside County, CA, and tested for the presence of Rickettsia, Bartonella, and Ehrlichia DNA. Polymerase chain reaction (PCR) was used to amplify fragments of the 17-kDa antigen gene and the rOmpA gene of the spotted fever group rickettsiae. One male tick contained R. rickettsii DNA; its genotype differed from R. rickettsii isolates found in Montana and Arizona that cause Rocky Mountain spotted fever and from Hlp#2 and 364D serotypes. One male tick and one female tick contained B. henselae DNA. No Ehrlichia platys or Ehrlichia canis DNAs were detected using nested PCR for their 16S rRNA genes. These findings extend the area where Rickettsia rickettsii may be vectored by Rh. sanguineus. Rh. sanguineus also may be infected with Bartonella henselae, a human pathogen that is typically associated with fleas and causes cat scratch disease.     

An account of the ticks of the northeastern of Spain (Acarina: Ixodidae).

The tick species commonly collected at the Northeast of Spain are reported in this paper. Data on hosts, temperature and humidity requirements, vegetation relationships, altitudinal distribution, and seasonal activity are included. R. sanguineus is commonly collected in areas with Mediterranean vegetation, esteppe, and semi-desertic esteppe, ranging from 190 to 1,000 meters above the sea level. R. sanguineus is related with sparse vegetal areas, and it is absent from areas with dense shrub or forests of every kind; sometimes, small populations may be collected in ecotones between Pinus spp. and esteppe formations. R. pusillus is closely related to areas of Mesomediterranean vegetation, sometimes subordinate to Pinus spp. and Quercus spp. The climate to which the species ally is always of continental type, with a hot and dry summer, and cold winter; although the species is commonly restricted to its main host, Oryctolagus cuniculus, several specimens have been collected from V. vulpes. Our data display the clear affinity of I. ricinus to the Supramediterranean vegetation (Aceri-Quercion faginae), places of Quercetum-Buxetum, as well as the Iberian Oromediterranean vegetation (Pinus sylvestris-Buxus sempervirens). Captures are scarce in forest of Fagus sylvatica, but data suggest that the species may be locally common on such places. Climate for the zones of collection of I. ricinus is Atlantic attenuated, with mild summers and humid winters. D. marginatus is strongly related to the xerophilic vegetation, widely spread through the Mediterranean, Supramediterranean, and hill levels, but does not colonize the true Oromediterranean vegetation. In our captures, the species is commonly collected in pubescent oak formations, but it does not penetrate in true forest associations.(ABSTRACT TRUNCATED AT 250 WORDS)     

Immunocompetent cells requisite for graft rejection in Lineus (Invertebrata, Nemertea)

Antecerebral ends from donors of one Lineus species (L. sanguineus) were grafted onto bispecific recipients previously constructed from two other Lineus species (denoted L. ruber----L. lacteus because the anterior component of chimeras was from L. ruber and the posterior component was from L. lacteus) and onto monospecific controls. Histological examination of areas where the tissues from L. sanguineus and L. ruber had been brought into contact by grafting always showed, at early stages, (6 to 20 days postgrafting), a great deal of difference depending upon whether the recipients were monospecific L. ruber or bispecific L. ruber----L. lacteus: only in grafts onto the former was there lysis of gland cells, connective tissue, muscular fibers, and finally epidermis. We attribute this lytic process to a strongly and rapidly cytotoxic action of lymphocyte-like cells from the L. ruber intestinal segment and the absence of lysis during the same stage in grafts onto composite recipients and monospecific L. lacteus to weak, delayed actions of immunocytes from the L. lacteus intestinal segment. Subsequent phagocytosis of material from lysed cell of grafts in the process of being rejected was effected by wandering amebocytes usually involved in destruction of degenerating "self" components, as in oosorption and resorptive processes after fasting. This work supports the existence of immunocytes at an early phylogenetic level.     

Life cycles of seven ixodid tick species (Acari: Ixodidae) under standardized laboratory conditions

Studies of transmission, maintenance, infectivity, virulence, and pathogenicity of tick-borne agents require the use of large numbers of live laboratory-raised ticks. Colonies of Ixodes scapularis Say, Ixodes pacificus Cooley & Kohls, Amblyomma americanum (L.), Dermacentor occidentalis Marx, Dermacentor variabilis (Say), Hemaphysalis leporispalustris (Packard), and Rhipicephalus sanguineus (Latrielle) have been maintained in our laboratory at the Centers for Disease Control and Prevention for five to 18 continuous generations. New Zealand White rabbits (Oryctolagus cuniculus) are used as hosts for all tick species and developmental stages. Between feedings, ticks are stored in environmental incubators at 22-24 degrees C and 90% RH with a day/night photoperiod of 16:8 (L:D) h. The duration of feeding, molting, preoviposition, and periods of postmolting development were recorded. Here, we describe the life cycles of these common North American tick species under standardized laboratory conditions. At 22-24 degrees C, the minimal time needed for each species to complete one life cycle was as follows: I. scapularis, 204-219 d; I. pacificus, 214-229 d; R. sanguineus, 162-177 d; H. leporispalustris, 209-224 d; D. variabilis, 176-191 d; D. occidentalis, 180-195 d; and A. americanum, 192-211 d.     

Transmission of Hepatozoon americanum (Apicomplexa: Adeleorina) by ixodids (Acari: Ixodidae)

American canine hepatozoonosis (ACH) caused by Hepatozoon americanum Vincent-Johnson, Macintire, Lindsay, Lenz, Baneth, and Shkap is an emerging, often fatal, tick-borne protozoal disease of dogs in the United States of America. Dogs acquire infection by ingesting ticks that contain oocysts. To understand the invertebrate (definitive) host range of H. americanum, experiments were carried out using four ixodids, Rhipicephalus sanguineus (Latreille), Dermacentor variabilis Say, Amblyomma americanum (L.), and Amblyomma maculatum Koch. Laboratory-reared nymphal ticks were fed on dogs that were either naturally or experimentally infected with H. americanum; when these ticks molted to the adult stage they were either fed to susceptible dogs or were dissected and examined for the presence of oocysts. Mature H. americanum oocysts were found in >90% of A. maculatum (both males and females), whereas oocysts were not found in any of the other three species. These results confirm that A. maculatum is an excellent host and vector for H. americanum and also suggest that this apicomplexan may have a narrow invertebrate host range, at least among ixodid ticks that are likely candidate vectors in the United States.     

Prevalence of Ehrlichia canis (Rickettsiales: Anaplasmataceae) in dogs and Rhipicephalus sanguineus (Acari: Ixodidae) ticks from Brazil

The current study evaluated the prevalence of Ehrlichia canis Donatien and Lestoquard in domestic dogs, Canis familiaris L., and Rhipicephalus sanguineus (Latreille) (Acari: Ixodidae) ticks from different areas of Brazil. In Monte Negro County (state of Rond?nia, Brazilian western Amazon), the indirect immunofluorescence assay detected E. canis-reactive antibodies (titer > or = 40) in 58/153 (37.9%) and 40/161 (24.8%) dogs from the urban and rural areas, respectively. These values were significantly different between the two areas. Ticks from a household in the urban area of Monte Negro, and from households in three other localities (162-165 adult ticks per household) in the state of S?o Paulo (SP) were tested by polymerase chain reaction (PCR) targeting an erlichial dsb gene fragment. The prevalence of infected ticks (given as minimal infection rate) was 2.3, 6.2, and 3.7% for populations 1 (Monte Negro), 2 (Jundiaí, SP), and 3 (S?o Paulo I, SP), respectively, which were statistically similar. In contrast, no infected tick was detected in population 4 (S?o Paulo II, SP). DNA sequences were determined for some of the PCR products generated from ticks and dogs from populations 1-3, being all identical to each other and to available sequences of E. canis in GenBank. These results reinforce previous records of E. canis-infecting dogs in Brazil. Natural infection of R. sanguineus ticks by E. canis is reported for the first time in Brazil, where this tick is the commonest species infesting dogs.