Feeding patterns of immature stages of Hyalomma truncatum and Hyalomma marginatum rufipes on different hosts.

In this study we examine the feeding patterns of immature stages of Hyalomma truncatum and Hyalomma marginatum rufipes ticks on different hosts. Larvae of H. truncatum developed through a three-host pattern on two species of field mice, Rhabdomys pumilio and Lemniscomys rosalia. On guinea-pigs, both Hyalomma species followed a mixed two-host and three-host pattern, with the latter route being preferred, since more than 70% of the fully fed larvae dropped off from their hosts. H. truncatum was a two-host tick on rabbits. Larvae of H. marginatum rufipes did not prefer R. pumilio and L. rosalia as hosts. On guinea-pigs, H. marginatum rufipes immatures showed a mixed two-host and three-host pattern with a bias towards the three-host life cycle, since approximately 58% of the fully fed larvae dropped off. On rabbits, H. marginatum rufipes was exclusively a two-host tick. Mean engorgement weights and blood quantities ingested by H. truncatum nymphs that developed through a three-host pattern on mice were significantly higher (p < 0.0001) than for those that developed through a two-host pattern on guinea-pigs and rabbits. For H. marginatum rufipes, there were no significant differences (p > 0.05) between engorgement weights of nymphs that developed through two-host and three-host patterns. However, there were significant differences (p < 0.0001) in blood quantities ingested by nymphs of this tick species following feeding on different hosts.

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.

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.

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.

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.

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.

Ovarian morphology of the springbok, Antidorcas marsupialis.

The ovarian morphology of the springbok is described, using material of 1 290 ewes collected at the De Beers farm, Benfontein. A deep longitudinal recess in foetal ovaries. The right ovary was slightly larger than the left ovary according to its linear and mass measurements. Considerable distortion of the amygdaloidal ovarian shape occurred in the presence of a protruding corpus luteum. Ovaries were much flattened during advanced pregnancy. A description of the appearance of intra-ovarian corpora observed in macroscopical sections is given. No predilection for the site of ovulation was observed.

The anatomy of the female reproductive tract of the springbok (Antidorcas marsupialis).

The anatomy of the female reproductive tract of the springbok is described, using material of 25 ewes collected at the S.A. Lombard Nature Reserve and 300 ewes collected at the De Beers farm Benfontein. No difference in the length of left and right fallopian tubes (104 +/- 24 mm) was observed, and from the funnel to the isthmus it narrows considerably from 15 mm to 1,25 mm. A distinct flexure is formed by the utero-tubal juncture. A complete ovarian bursa with a ventral orifice occurs. The reproductive tract increases in mass from 9.2 g in infants to 38,0 g in adults. The right uterine horn of the bicornuate tract is consistently longer. Caruncles are more numerous in the right (60,2 +/- 9,37) than the left (45,8 +/- 10,18) uterine horn. The intricate cervical lumen consisting of four to six valves in non-pregnant ewes becomes a simple S-shaped canal with advanced pregnancy.