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.
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Biomedical subjects
Y Rechav
Publications and source records attributed to Y Rechav.
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.
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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.
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Acquired immunity to larvae of Amblyomma marmoreum and A.hebraeum by tortoises, guinea-pigs and guinea-fowl.
A study of acquired resistance in guinea-pigs, guinea-fowl and tortoises to larvae of the ticks Amblyomma hebraeum Koch and A.marmoreum Koch (Acari: Ixodidae) showed that repeated infestations of the laboratory host resulted in a 29.3-49.4% reduction respectively in weight of engorged larvae. No resistance was induced in guinea-fowl, the natural host for larvae of both species. A small decline in the mean weight of engorged larvae was observed for both species of ticks after three successive infestations on tortoises. The reduction in weight was more pronounced in A.hebraeum (14.5%) which does not naturally feed on tortoises than for A.marmoreum (8.4%), a common tick on this host. The occurrence of acquired resistance in natural tick host relationships as opposed to unnatural tick host relationships is discussed.
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Immunization of guinea-pigs and cattle against adult Rhipicephalus appendiculatus ticks using semipurified nymphal homogenates and adult gut homogenate.
Guinea-pigs inoculated with crude homogenate of unfed nymphs of the tick Rhipicephalus appendiculatus and with three semipurified fractions of the homogenate obtained by gel permeation chromatography, acquired a significant degree of immunity to infestation with adults of this tick. Fraction 2 induced the highest reduction (66%) in mean weight of engorged females followed by crude homogenate and fractions 1 and 3. Calves immunized with crude homogenates of unfed nymphs, fraction 2 of nymphal homogenate, and gut homogenate of unfed females also acquired immunity against adults of R. appendiculatus. The mean weight of engorged females fed on calves inoculated with nymphal fraction 2 was the lowest of all five groups of calves on which females fed. The reduction in weight (38%) was not significantly different from that observed for females fed on calves inoculated with crude nymphal homogenate (31%) or females from third infestation of adult ticks. No differences in the weight and hatchability of egg batches produced by engorged females collected from the five groups of calves were observed. Analysis of sera collected from the five groups of calves showed that the concentration of albumin, alpha-1, alpha-2 and beta-globulins fluctuated and no significant differences between the treated groups were observed. The levels of gamma-globulin increased in treated groups including the group inoculated with adjuvant only, but unlike previous reports no increase in gamma-globulin or a correlation between the level of gamma-globulin and the degree of resistance acquired were observed in calves exposed to repeated tick infestations. However, the increase in the concentration of gamma-globulin in calves inoculated with fraction 2 or crude nymphal homogenate was higher than that observed in the other groups.
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Resistance of indigenous African cattle to the tick Amblyomma hebraeum.
Field collections of Amblyomma hebraeum Koch adults from six breeds of cattle were conducted on two farms in the Northern Transvaal. The density of A. hebraeum adults was highest on Simmentaler cows, followed by Santa gertrudis, Africaner, Bonsmara, Brahman and Nguni. Indigenous breeds, namely Nguni, Bonsmara and Africaner, have the highest level of resistance to A. hebraeum. The relationship between tick abundance and the high level of resistance found in the indigenous breeds is discussed.
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Acquisition of immunity in cattle against the blue tick, Boophilus decoloratus.
It is well known that ixodid ticks have the ability to induce immunity in their host. We demonstrate, for the first time, that the tick Boophilus decoloratus induced immunity in its bovine host, since the mean weight of engorged females fed on naive animals dropped from 201.5 mg, to 173.7 mg and 155.3 mg, for females fed on calves previously exposed once and twice; respectively, to B. decoloratus infestations. Ticks which had been transferred from one individual host to another one were able to complete their feeding period on a sensitive host. Such ticks were significantly heavier (mean 245.2 mg) than those fed on a naive (mean 201.5 mg) host for the entire normal feeding period. A negative correlation between the mean weight of the engorged female ticks and the level of serum gamma globulins in the host was also demonstrated.
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The role of Rhipicephalus appendiculatus and R. evertsi evertsi males in inducing resistance in laboratory animals: preliminary studies.
Guinea-pigs infested with male ticks of the species Rhipicephalus appendiculatus, and rabbits infested with R. evertsi evertsi, acquired immunity to conspecific female ticks. The hosts were first infested with male ticks and thereafter were challenged with males and females of the same species. The mean weight of the engorged females of R. appendiculatus fed on guinea pigs previously infested with male ticks was 509.0 (+/- 41.4) mg compared with that of females fed on control guinea pigs (651.2 +/- 31.8 mg). Similar weight differences were observed for R.e. evertsi females which fed on rabbits previously infested three times with male ticks. The mean weight of the female ticks which fed on these rabbits was 520.1 (+/- 29.8) mg compared with 640.7 (+/- 30.2) mg of R.e. evertsi females which fed on control hosts. The concentration of gammaglobulins in the sera of rabbits was monitored at various intervals after the first infestation. It was found, for the first time, that infestation of laboratory animals with male ticks conferred immunity, but to a lesser degree than infestation with both sexes. It was also shown that the level of gammaglobulins increased from 3.4 +/- 0.28 g l-1 to 7.3 +/- 0.24 g l-1 in sera of rabbits hosts as a result of the feeding activity of males, but to a lesser extent than in sera of rabbits on which both sexes had fed (10.8 +/- 2.4 g l-1).
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Development of resistance in laboratory animals to adults of the tick Rhipicephalus evertsi evertsi.
Acquired resistance to adults of the two-host tick Rhipicephalus evertsi evertsi Neumann has been demonstrated in guinea-pigs and rabbits. Four infestations of both hosts with R.e.evertsi adults resulted in a significant reduction in the mean weight of the engorged females. A decline in the mean weight of the female ticks was also observed in ticks which fed on a rabbit previously injected with serum taken from a rabbit resistant to R.e.evertsi. This suggests that humoral immunity may have an important role in the acquired resistance to ticks. In both hosts an increase in the level of serum globulins was recorded. In rabbits the level of gamma globulin was affected, while in guinea-pigs an increase was observed in the concentration of alpha 1 and beta globulins. The differences in host responses to the R.e.evertsi adults are discussed.
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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.
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Seasonal abundance of ticks associated with indigenous goats on a northern Transvaal farm.
The 3 most abundant tick species on indigenous goats on a northern Transvaal farm were found to be Rhipicephalus evertsi evertsi, Rhipicephalus appendiculatus and Amblyomma hebraeum. Three other tick species were present in small numbers. The economical and ecological importance of the ticks found on the goats, mainly in rural areas where chemical control of ticks is practically non-existant, is discussed. The high number of goats in the study area and the shift towards alternative methods of tick control, such as the use of resistant hosts, are important factors in the livestock industry of southern Africa.
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Some aspects of the life cycle of the tick Ixodes pilosus under laboratory conditions.
Some aspects of the life cycle of the tick Ixodes pilosus were studied under laboratory conditions. The preoviposition period was 7,2 +/- 0,6 d. Maximum egg production was on Day 4 after oviposition commenced, with total egg production of 2,395 +/- 128,7 eggs per female. The mean feeding time of larvae was 3,3 +/- 0,1 d. The life cycle could not be completed due to the specific requirements of this species.
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Resistance of Brahman and Simmentaler cattle to southern African ticks.
Field collections of ticks from two breeds of cattle in the North Western Transvaal showed the common tick species to be Rhipicephalus appendiculatus, Amblyomma hebraeum, Rhipicephalus evertsi evertsi and Hyalomma marginatum rufipes. The number of these ticks was higher on Simmentaler than on Brahman cattle. Correlation was found between the number of ticks on the cattle and their serum gamma globulin levels indicating an increase in the production of antibodies. Similar correlation was also found between the number of ticks on the cattle and the number of eosinophils in their blood. Resistance was probably acquired by the hosts and, it appears, to a higher degree in Brahman than in Simmentaler.
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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.
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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.
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Resistance and cross-resistance in guinea-pigs and rabbits to immature stages of ixodid ticks.
Infestation of guinea-pigs and rabbits with larvae of any one of five species of ticks, Rhipicephalus appendiculatus Neumann, Rhipicephalus evertsi evertsi Neumann, Amblyomma hebrauem Koch, Amblyomma variegatum Fabricius and Ixodes ricinus L., conferred resistance in the animals when exposed to subsequent infestations with the same tick species. Resistance to infestations by other tick species was not observed.
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Expression of acquired immunity to immature stages of the tick Rhipicephalus evertsi evertsi by rabbits and guinea-pigs.
Acquired immunity in guinea-pigs and rabbits to immature stages of the two-host tick Rhipicephalus evertsi evertsi Neumann was demonstrated. Repeated infestations of both hosts with larvae resulted in a significant reduction in the weight of later engorged nymphs. A sharp decline in the numbers of nymphs which successfully fed on both hosts was also observed. This study provides evidence for a gradual decrease in the mean weight of engorged nymphs towards the end of the detachment period suggesting that, in two-host ticks, the onset of nymphal feeding acts as an immune booster in a host already primed by the larval feed and that this results in a reduced feeding performance.
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Resistance of Brahman and Hereford cattle to African ticks with reference to serum gamma globulin levels and blood composition.
Field collections of ticks from two breeds of cattle showed that the common species of ticks were Amblyomma hebraeum, Rhipicephalus appendiculatus and Rhipicephalus evertsi evertsi. The density of these species was higher on Hereford than on Brahman cattle. The results also indicated that the density of immature stages of the above-mentioned ticks is higher on Hereford than on Brahman cattle. A positive correlation was found between the number of ticks on the cattle and the serum gamma globulin levels, an indication of an increase in the production of antibodies. An inverse relationship was found between tick burden and red blood cell count and hemoglobin concentration. Other blood components, such as basophils, eosinophils and lymphocytes were not affected by the changes in the density of the tick populations. It appears that resistance may have been acquired by the hosts and that Brahman cattle may acquire resistance to a higher degree than Herefords.
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