Ticks associated with wild animals in the Nhecolândia Pantanal, Brazil.

A study of ticks associated with wild animals was carried out from September 1996 to April 1998 at the Fazenda Alegria (21,000 ha), in the Nhecolândia Pantanal, State of Mato Grosso do Sul, Brazil, a sunken plain bordering the upper Paraguay river, located 19 x 08'S; 56 x 46'W. A total of 81 wild animals (13 species, 6 orders) were captured with the aid of nets, and ticks were found on 63 (78%). Tick species identified included Boophilus microplus (Canestrini), Amblyomma cajennense (F.), A. parvum (Aragão), A pseudoconcolor (Aragão), A. scalpturatum (Neumann), A. nodosum (Neumann), A. ovale (Koch), and A. tigrinum (Koch). Dragging from grasslands (campos) yielded negative results compared to the high concentration of ticks, mainly nymphs, that were collected from leaves in the forests (capão). Predominance of immature instars (Amblyomma genera) was observed in the end of winter (August-September). Ticks were associated mainly with coatis, deer (Mazama gouazoubira) and anteater, and these animals may play a role in the epidemiology of tick-transmitted pathogens in the Pantanal if one considers their co-existence with local domestic animals.

Seasonal abundance of Muscidae (Diptera) associated with cattle on a northern Transvaal farm.

Face flies were collected from cattle over a 14-mo period in an area where Parafilaria bovicola Tubangui was prevalent. Three species of Musca known to be vectors of P. bovicola were found. Two of the species (Musca lusoria Wiedeman and M. xanthomelas Wiedeman) were collected throughout the year, and M. nevilli Kleynhans was abundant only in autumn.

A case of gynandromorphism in Amblyomma hebraeum (Acari: Ixodidae).

A gynandromorph specimen of Amblyomma hebraeum was found on a goat on which adult ticks were bred in the laboratory.

Seasonal abundance of the tortoise tick Amblyomma marmoreum (Acari: Ixodidae) on the leopard tortoise, Geochelone paradalis.

A survey of Amblyomma marmoreum Koch ticks recorded from the leopard tortoise, Geochelone paradalis Bell, in the National Zoological Gardens, Pretoria, South Africa, was carried out over a 19-mo period. No significant differences were found between the tick burdens on male and female tortoises. A. marmoreum showed a clear seasonal pattern of abundance. Larvae were present on the tortoise host during late summer, with a peak in February and March; nymphs were abundant during winter, with a peak in June and July. Male ticks were found throughout the year, but females were present only during spring and early to midsummer with a peak in October. It was demonstrated that each developmental stage of A. marmoreum showed only one peak of activity per year.

Immunization of rabbits against nymphs of Amblyomma hebraeum and A. marmoreum (Acari: Ixodidae).

Himalayan rabbits immunized with homogenates prepared from nymphs of Amblyomma hebraeum Koch and A. marmoreum Koch ticks developed humoral and probably also cell-mediated immunity to their respective homogenates. Beta and gamma globulin levels and numbers of eosinophils and neutrophils increased significantly in inoculated rabbits. The recipient animals developed resistance to homospecific nymphal infestations. Cross resistance between the two species was not evaluated. Nymphs of both species that fed on inoculated rabbits demonstrated slightly shorter feeding periods, and their mean weights were significantly lower than nymphs that fed on Quil 'A' adjuvant-inoculated rabbits or on naive rabbits. Significantly higher proportions of nymphs from immunized animals failed to moult when compared with nymphs that fed on the two control groups. These parameters indicate that the inoculated rabbits had acquired protective immunity against nymphs of both ticks.

Laboratory studies on the life cycle of Amblyomma marmoreum (Acari: Ixodidae) on two different hosts.

A comparative study was made of the life cycle of the tortoise tick, Amblyomma marmoreum Koch, on tortoises and guinea pigs under laboratory conditions. At 25 degrees C and 85% RH with natural day length, duration of off-host stages (preoviposition, oviposition, incubation, and premolt) was similar for ticks fed on both hosts. Delay in preoviposition (up to 90 d) was observed in some gravid females. Larvae, nymphs, and adults had longer feeding periods on tortoises than on guinea pigs. Adult females fed on tortoises had greater engorgement wieght and ovipositional capacity than ticks fed on guinea pigs. It is suggested that the shortened feeding period of immature stages on mammalian hosts together with the occurrence of morphogenic diapause may be more important than previously recognized in determining whether the life cycle of A. marmoreum is completed in 1 or 2 yr under natural conditions.

Evidence for attachment pheromones in the Cayenne tick (Acari:Ixodidae).

Evidence is presented for the existence of male-produced attachment pheromones in the tick Amblyomma cajennense (F). Unfed males and females attached significantly faster to shaved sides on bovine hosts where preattached males were present than did adult ticks released in control areas. Attached ticks did not form clusters around the preattached males as described for other species of Amblyomma. They attached in areas under bags where they had been released, but were not necessarily close to the feeding males. Males apparently required at least 4 d of feeding before producing the pheromones. Males that fed for < 3 d failed to induce attachment. A significant increase in attachment of newly introduced males and females was observed only on day 4 after the feeding of the preattached male started. This response increased on days 5 and 6 after feeding had commenced. An evolutionary trend in the production of tick pheromones was suggested.

Production of pheromones by artificially fed males of the tick Amblyomma maculatum (Acari: Ixodidae).

Aggregation-attachment pheromones are produced only by male ticks of the genus Amblyomma that have imbibed blood for at least 8 d from their mammalian hosts. This report demonstrates that production and release of aggregation-attachment pheromones by Amblyomma maculatum (Koch) males can be induced in vitro by using nonblood media, artificially introduced through capillary tubes, into the male ticks. The presence of these pheromones is demonstrated by using both biological observations on bovine hosts and in vitro experimentation with petri dishes. The attraction of unfed female ticks to the artificially fed males (using the petri dish method) was significantly higher (P < 0.001) than the attraction of unfed females to unfed males. Similarly, attraction and attachment were recorded on bovine hosts. Only 62.8 +/- 17.5% of the females released attached to the bovine host. Of these, 61.9 +/- 19.37% attached around artificially fed males that were placed on the bovine 24 h earlier. This percentage did not differ significantly from the 81.4 +/- 7.1% of the total that attached around males that fed naturally for 8 d. In comparison, only 33.3 +/- 21.9% of the total number of females placed on the host did so after being fed 1 d (control group). The possibility of using capillary feeding as a new tool for investigating the physiology and reproductive behavior of blood-sucking arthropods is discussed.

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.

Respiratory gas exchange in the tick Amblyomma hebraeum (Acari: Ixodidae).

Respiratory gas exchange was studied in unfed adult Amblyomma hebraeum Koch. Carbon dioxide emission was measured at 25 degrees C using flow-through respirometry to determine standard metabolic rate and the temporal pattern of gaseous emission. The standard CO2 production rate (sVCO2) of inactive ticks was 0.0135 +/- 0.0085 ml g-1 h-1, and the standard O2 consumption rate (sVO2) was 0.0158 +/- 0.0097 ml g-1 h-1. Ventilation was discontinuous and was characterized by periodic bursts of CO2 emissions at frequencies of 0.33 h-1-1.11 h-1. Low metabolic rate coupled with discontinuous ventilation may contribute to the ability of adult A. hebraeum to withstand prolonged periods of starvation and desiccation in the absence of a host.

Ticks (Acari: Ixodidae) associated with wild animals in the Pantanal region of Brazil.

This paper describes the identification of ticks from wild animals of the Pantanal region in Brazil as part of a comprehensive study about established and emerging tick-host relationships and related pathological aspects. Eighty-one animals were captured (representing 13 species, six orders), and ticks were found on 63 (78%). Tick species identified included Boophilus microplus (Canestrini), Amblyomma cajennense (F.), Amblyomma parvum Aragão, Amblyomma pseudoconcolor Aragão, Amblyomma scalpturatum Neumann, Amblyomma nodosum Neumann, Amblyomma ovale Koch, and Amblyomma tigrinum Koch. Dragging from grasslands yielded negative results compared with the high concentration of ticks that were collected from leaves in the forests.

Isotopes as host blood markers to measure blood intake by feeding ticks (Acari: Ixodidae).

We have modified an experimental technique in which two different isotopes (Cr51 and I125) were used simultaneously as blood markers for determining the amount of blood removed by feeding ticks. This method enables us to measure separately and directly the volumes of red blood cells and plasma in ticks and to calculate the ratio between the two parameters (concentrating ability). The concentration of red blood cells in nymphs of Amblyomma hebraeum Kock and Rhipicephalus appendiculatus Neumann and in females of these species plus in those of Hyalomma truncatum Kock were found to be twice the amount measured in the labeled blood of goats. Concentrations of plasma in the ticks were approximately two-thirds of that measured in samples taken directly from these same goats. Small nonsignificant differences between the ability of various tick species to concentrate red blood cells and dilute host plasma were found. The advantage of this method is compared with that of the colorimetric and gravimetric methods, and its potential use is discussed.

Changes in the concentration of globulins in naive guinea pigs during feeding by the immature stages of Rhipicephalus evertsi evertsi (Acari: Ixodidae).

The weight of Rhipicephalus evertsi evertsi Neumann nymphs, which as larvae and nymphs completed the entire blood meal on the same individual guinea pig, was significantly lower than the weight of those that as larvae and nymphs fed on two separate naive hosts. Nymphs of the latter category spent 1 wk (from unfed larvae to unfed nymphs) on one animal before their transfer to the second host to complete the blood meal. The albumin concentration of the host blood decreased and was related to the time that the immature ticks spent on the hosts. The albumin/globulin ratio also decreased. The alpha 1 globulin fraction increased soon after the guinea pigs were infested with ticks. No further changes in the levels of the alpha 1 globulin fraction were observed with time. The concentration of serum beta globulins increased only in guinea pigs infested with immature ticks for the entire larval and nymphal feeding period. A second infestation of those guinea pigs with larvae of R. e. evertsi resulted in further increases in the levels of serum beta globulins. The relationships among serum beta globulin levels, the weight of engorged nymphs, and host immunity are discussed.

Life cycle in the laboratory and seasonal activity of the tick Rhipicephalus glabroscutatum (Acarina: Ixodidae).

The life cycle of Rhipicephalus glabroscutatum Du Toit was studied under laboratory conditions at 26 C +/- 1C. The preoviposition period was 6.0 +/- 0.12 days. The mean number of eggs was 2,044 +/- 186 (maximum 3,053, minimum 748), and the greatest production was recorded on day 3 (234 eggs/female). The incubation period was 37.4 +/- 0.32 days (maximum 41, minimum 35). The feeding time of larvae and nymphs of this two-host tick was 20.2 +/- 0.33 days (16-28). Nymphs producing males weighed less (4.09 +/- 0.07 mg) than those producing females (6.62 +/- 0.08 mg). The combined larval-nymphal feeding time of the former was shorter (19.3 +/- 0.90 days) than that of the latter (20.4 +/- 0.90 days). The molting period of nymphs to adults of both sexes was similar. Engorged females weighed (mean +/- SE) 204.0 +/- 10.75 mg and the feeding time was 7.9 +/- 0.34 days. Spermatogenesis was completed on day 5 after the commencement of feeding, and pairing between males and females and mating occurred subsequently. The adult ticks were active during early summer and were much more prevalent on kudu than on angora goats and cattle. Immature stages were not found during this study.

Life cycle of the tick Rhipicephalus evertsi evertsi neumann (acarina: ixodidae) under laboratory conditions.

The preoviposition period of the tick Rhipicephalus evertsi Neumann maintained under laboratory conditions at 26 C was 6.1 +/- 0.38 days. The average number of eggs produced during the oviposition period was 10,400 +/- 397 (max. 13.307, min. 7,558). The greatest daily egg production was recorded on the 3rd day (1.107 eggs/female). The incubation period of eggs at 26 C was 24.8 +/- 1.37 and the feeding time of the larvae and nymphs (a two-host tick) was 17.2 +/- 0.14 days at 26 C. This tick represents the two-host type of cycle and the percentage of larvae, pharate nymphs, and nymphs on the host at various intervals after attachment was recorded. The changes in the weight of the immature stages during the feeding period was examined daily. Nymphs which produce males were lighter in weight (10.3 +/- 0.28 mg), than those which produce females (15.6 +/- 0.33) and males emerge (13.7 +/- 0.10 days of premolting period) before females (14.1 +/- 0.11 days).

The life cycle of the tick Hyalomma marginatum rufipes Koch (Acarina: Ixodidae) under laboratory conditions.

The life cycle of Hyalomma marginatum rufipes Koch was studied under laboratory conditions at 26 +/- 1 C. The preoviposition period was 7.1 +/- 0.23 days. The mean (+/- SE) number of eggs was 6,867 +/- 2,609 (max. 13,180, min. 3,184). The greatest egg production was recorded on day 3 (avg 1,170 egg/female). The incubation period was 29.3 +/- 2.96 days. The feeding time of larvae and nymphs of this 2-host tick was 22.8 +/- 0.13 days. Nymphs producing males weighed less (23.1 +/- 0.748 mg) than those producing females (26.8 +/- 1.19 mg); the combined larval-nymphal feeding time of the former was shorter (21.9 +/- 0.1 days) than that of the latter (22.9 +/- 1.12 days). The premolting period of nymphs to adults of both sexes was similar.

Persistent Ehrlichia chaffeensis infection in white-tailed deer.

Four white-tailed deer (Odocoileus virginianus) were inoculated intravenously with a deer-origin isolate (15B-WTD-GA) of Ehrlichia chaffeensis. The course of infection was monitored using indirect fluorescent antibody (IFA), polymerase chain reaction (PCR), and culture over a 9 m period. All deer became rickettsemic within 24 days post inoculation (DPI), and all developed antibody titers >1:64 to E. chaffeensis by 17 DPI. Titers in all deer fell below 1:64 during 87 to 143 DPI. One deer exhibited a second period of seropositivity (peak titer of 1:256) from 207 to 271 DPI but was culture and PCR negative during this period. Rickettsemia was confirmed by reisolation of E. chaffeensis as late as 73 to 108 DPI in three deer. Positive PCR results were obtained from femur bone marrow of one deer and from rumenal lymph node of another (leer at 278 DPI. None of the deer developed clinical signs, hematologic abnormalities, or gross or microscopic lesions attributable to E. chaffeensis. Two uninoculated control deer were negative on all tests through 90 DPI at which time they were removed from the study. Herein we confirm that white-tailed deer become persistently infected with E. chaffeensis, have initial rickettsemias of several weeks duration and may experience recrudescence of rickettsemia, which reaffirm the importance of deer in the epidemiology of E. chaffeensis.

A bioassay technique for the pheromone emitted by Amblyomma hebraeum males.

Attachment of Amblyomma hebraeum females, either around feeding males or in areas in which extracts of fed males had previously been placed, was studied. The percentage attachment of female ticks around feeding males was significantly higher than that inside extract-treated areas. It was also found that the percentage attachment around the males increases with time, but there is little or no increase in attachment with time inside the treated areas. The amount of pheromone released by 1 feeding male was enough to stimulate attachment of females, although the rate of attachment accelerated as the number of males increased.

Relative resistance of six cattle breeds to the tick Boophilus decoloratus in South Africa.

Adult females of the tick Boophilus decoloratus were removed from 6 breeds of cattle on 2 farms in the Northern Transvaal. Highest numbers of female ticks were collected from Simmentaler, followed by Santa Gertrudis, Bonsmara, Afrikaner, Brahman and Nguni. Resistance levels of each breed to B. decoloratus was positively correlated with the amount of Bos indicus genes in the breed, with the exception of Nguni, which is a sanga type but not pure B. indicus.

The ecology of the African vectors of heartwater, with particular reference to Amblyomma hebraeum and Amblyomma variegatum.

The hosts, sites of attachment, life cycle, habitat requirements and seasonal abundance of Amblyomma astrion, Amblyomma cohaerens, Amblyomma gemma, Amblyomma hebraeum, Amblyomma lepidum, Amblyomma marmoreum, Amblyomma pomposum, Amblyomma sparsum, Amblyomma tholloni and Amblyomma variegatum, the 10 potential vectors of heartwater in Africa, are listed. Factors influencing the distribution and abundance of the ticks as well as interactions with other species and the role of predators and pathogens are discussed.