Biology ofRhipicephalus appendiculatus andR. zambeziensis and production of a fertile hybrid under laboratory conditions

In some areas of Eastern and Southern provinces of ZambiaRhipicephalus appendiculatus andR. zambeziensis are sympatric, and numerous intermediate forms as well as typicalR. appendiculatus andR. zambeziensis are found. Experiments were carried out in order to clarify the taxonomic status of the intermediate forms. Biology and hybridization capacities of two strains ofR. appendiculatus (A and D) and one strain ofR. zambeziensis (H) were studied. Infestations on rabbits and calves were performed at the beginning and at the end of the Zambian rainy season. The adults of both species showed preference for the bovine host and performed better at the end of the rainy season. A recently isolated strain ofR. appendiculatus had notably higher larval production per unit engorgement weight than the strain that had been maintained for prolonged periods under laboratory conditions.R. zambeziensis produces fewer larvae and had longer development periods thanR. appendiculatus.The two species cross-breed under laboratory conditions. A fertile hybrid is produced byR. zambeziensis females andR. appendiculatus males, whereas a sterile hybrid is a result of a reciprocal cross. Morphology of adults of the fertile hybrid (H/A) is indistinguishable from the maternal species, whereas adults of the sterile hybrid (A/H) are of maternal, paternal and intermediate forms.Larval production indices (LPI) vary from 0.4 to 3.7 for the H () x A () cross, approximately three-fold less than in the maternal species. For the reciprocal cross, LPI ranges from 0.1 to 2.7, five- to thirty-fold less than in the maternal species. The fertile hybrid has a higher LPI than both first crosses, and under the most favourable climatic conditions LPI is even higher than for the maternal species.Adults of the sterile hybrid rarely formed pairs. Only partially engorged female ticks detached, which produced no viable eggs. Both hybrids may occur in areas where the two species are sympatric. However, detailed field studies will have to be performed in order to gain knowledge on population dynamics, interbreeding and the vector role of the two species and their hybrids under field conditions.     

The effects of nutritional status of rabbits and sheep on their resistance to the ticksRhipicephalus evertsi evertsi andR. appendiculatus

Rabbits and sheep were exposed to low-and high-protein diets and subsequently infested three times with adults ofRhipicephalus appendiculatus andRhipicephalus evertsi evertsi. The mean weight ofR.e. evertsi females which dropped from rabbits maintained on a high-protein diet decreased from 515.0±24.9 mg (naive) to 381.5±25.0 (second infestation) to 340.3±23.3 mg (third infestation) while the weight of ticks fed on animals which were exposed to a low-protein diet did not change significantly (2.7%). The mean weight of engorged females ofR. appendiculatus which completed their blood meal on rabbits (high protein) decreased from 520.9±31.8 (naive) to 369.3±39 mg (3rd infestation), a significant decrease of 29.1% compared to a 12.3% decrease in weight between the 1 st and 3rd infestation of females fed on animals on a low-protein diet.Rhipicephalus e. evertsi fed on sheep exhibited the same phenomenon. The mean decrease in weight of 4rd-infestation ticks which dropped from sheep fed lucerne was 26.2% compared to 16.6% for ticks from sheep which were fed on grass.Hosts maintained on a low-protein diet failed to acquire resistance to ticks, lost weight and developed anaemia while those on a high-protein diet developed resistance, maintained weight and did not develop anaemia.The nutritional stress of the hosts and its application in South Africa are 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.     

Development of resistance in calves to nymphs ofRhipicephalus appendiculatus (Acarina: Ixodidae) during test feeds

A test of host resistance to infestation by the tickRhipicephalus appendiculatus was repeated 5 times, at weekly intervals, on 2 initially susceptible calves. One hundred nymphs (NN) were used each time. Pairs of tick-susceptible rabbits served as controls. The engorged NN were weighed, then allowed to moult individually, and the sex of each was noted after emergence of the adult. During the course of the experiment there was a significant reduction in mean engorged weight (especially in the pre-male NN) and also in the length of the feeding period, and a downward trend in the percentage of NN which engorged. There was a significant increase in the percentage of engorged NN that moulted. Pre-male NN were significantly heavier than pre-female NN after feeding on susceptible hosts, but though mean feeding times were the same, they took 1–2 days longer to moult than pre-females at 28°C. It was concluded that the test itself could induce resistance if applied to fully susceptible calves.     

A hybridization model forRhipicephalus appendiculatus andR. zambeziensis (Acarina: Ixodidae) using glucose-6-phosphate-isomerase isoenzymes

In the Eastern Province of Zambia,Rhipicephalus appendiculatus (Neumann) andR. zambeziensis (Walker) are sympatric. Intermediate forms as well as typical specimens are found. No morphological criteria could detect cross-breeding between these species in the field.Hybrids betweenR. appendiculatus andR. zambeziensis were produced and glucose-phosphate-isomerase (EC 5.3.1.9.; GPI) isoenzymes resolved by agarose electrophoresis. Phenotyping hybrids in the F1 and F2 generations was explained by the autosomal transmission of two loci of GPI-genes. Identification of some hybrid phenotypes offers the possibility of showing presently undetected hybridization in the field. A genetic model is proposed to explain the patterns.     

The role of hair in swimming of laboratory mice: implications for behavioural studies in animals with abnormal hair

Animal swimming tests, such as the forced swim test, are extensively used in biomedical research to study rodent behaviour. Hair and skin exposed to water may be an important factor affecting the performance in this test. Since various hair and skin abnormalities are not uncommon in genetically modified or drug-treated laboratory animals, this test may be inappropriate for these animals. Because on occasions it is necessary to screen their swimming behaviour, in the present study we aimed to assess the role of hair in swimming of laboratory rodents in the forced swim test, widely used in behavioural research. For this, we shaved laboratory mice (129S1 strain) and compared their swimming patterns with those of unshaven controls. Overall, shaving mice did not affect their swimming behaviours in the 5 min forced swim test. Our results indicate that hair condition is not an important factor in the forced swim test for this mouse strain, and suggest that this test may have wider utility for behavioural analyses of mice with abnormal hair.     

Observations on successive infestations of the rabbit host by the ticksRhipicephalus appendiculatus andR. zambeziensis (Acari: Ixodidae)

Successive infestation of the rabbit host by instars of the brown ear tickRhipicephalus appendiculatus resulted in a progressive decline in engorgement and egg weights of adult instars and a reduction in percentage recovery of nymphs and larvae. Repetitive infestation with adults and larvae resulted in increased skin hypersensitivity reactions at the attachment site.Successive infestation withR. zambeziensis caused a more significant decline in engorgement and egg weights of adults than forR. appendiculatus. Percentage recoveries of larvae and nymphs were also significantly reduced.A cross-infestation study indicated thatR. appendiculatus andR. zambeziensis share antigenic moieties.     

Polynucleotide vaccines: potential for inducing immunity in animals.

Polynucleotide immunization has been described as the Third Revolution in Vaccinology. Early studies suggest the potential benefits of this form of immunization including: long-lived immunity, a broad-spectrum of immune responses (both cell mediated immunity, and humoral responses) and the simultaneous induction of immunity to a variety of pathogens through the use of multivalent vaccines. Using a murine model, we studied methods to enhance and direct the immune response to polynucleotide vaccines. We demonstrated the ability to modulate the magnitude and direction of the immune response by co-administration of plasmid encoded cytokines and antigen. Also, we clearly demonstrated that the cellular components (cytosolic, membrane-anchored, or extracellular) to which the expressed antigen is delivered determines the types of immune responses induced. Since induction of immunity at mucosal surfaces (route of entry for many pathogens) is critical to prevent infection, various methods of delivering polynucleotide vaccines to mucosal surfaces have been attempted and are described. Expansion of studies in various species, using natural models, should be extremely helpful in demonstrating the universality of this approach to immunization and more importantly, accurately identify parameters that are critical for the development of protective immunity.     

Gastric campylobacter-like organisms: their role in gastric disease of laboratory animals

Campylobacter pylori, first isolated in 1982, is now recognized as a primary cause of acute gastritis in man, and there is substantial data suggesting that this organism also plays an important role in the pathogenesis of duodenal ulcers. More recently, Campylobacter-like organisms and other morphologically distinct spiral bacteria have been isolated from gastric lesions in a variety of laboratory animal species. The zoonotic significance of C. pylori and other gastric spiral bacteria isolated from man as well as laboratory and domestic animals requires further study. An appreciation of the ecological and pathological role of gastric spiral bacteria in domestic and laboratory animals is an essential first step when considering the role and proper selection of animal models in the study of C. pylori gastroduodenal disease.     

Monitoring of antibiotic resistance in bacteria isolated from laboratory animals

The drug resistance of microorganisms isolated from laboratory animals never treated with antibiotics is being reported consistently, while the number of laboratory animals used in medicine, pharmacy, veterinary medicine, agriculture, nutrition, and environmental and health science has increased rapidly in Korea. Therefore, this study examined the development of antimicrobial resistance in bacteria isolated from laboratory animals bred in Korea. A total of 443 isolates (7 species) containing 5 Sphingomonas paucimobilis, 206 Escherichia coli, 60 Staphylococcus aureus, 15 Staphylococcus epidermidis, 77 Enterococcus faecalis, 27 Citrobacter freundii, 35 Acinetobacter baumannii were collected from the nose, intestine, bronchus and reproductive organs of ICR mice and SD rats. Of these species, Acinetobacter baumannii and Enterococcus faecalis showed significant antimicrobial resistance according to the minimum inhibition concentration (MIC) in E-test. In case of Acinetobacter baumannii, several isolates showed MIC values 16-128 μg/mL for cefazolin and cefoxitin, and higher resistance (128-512 μg/mL) to nitrofurantoin than that of standard type. Resistance to cefazolin, cefoxitin and nitrofurantoin was detected in 17.14, 20.00, and 8.57% of the Acinetobacter baumannii isolates, respectively. In addition, 44.1% of the Enterococcus faecalis isolates collected from the laboratory animals were resistant to oxacillin concentration of 16-32 μg/mL range, while MIC value of standard type was below oxacillin concentration of 6 μg/mL. These results suggest that in rodent species of laboratory animals, Acinetobacter baumannii are resistance to cefazolin, cefoxitin and nitrofurantoin, whereas those of Enterococcus faecalis were resistance to oxacillin.     

Environmental enrichment of laboratory animals used in regulatory toxicology studies

There is a wealth of information in the published literature which describes a multitude of approaches to enriching the environment of laboratory animals. This paper attempts to review the various methods of enrichment through social contact, enhancement of the environment and diet, and improvements in husbandry. It attempts to place the various enrichment initiatives within the context of a laboratory which conducts regulatory toxicology, describes some of the experiences in the author's own laboratory and attempts to highlight those ideas which might prove practical to implement in the future. The aim is to demonstrate that a creative approach to environmental enrichment is indeed compatible with regulatory toxicology. It is hoped that this will encourage those responsible for the care and welfare of animals in such a laboratory to challenge historical practices and include environmental enrichment as a fundamental necessity of study design.     

The relief of pain in laboratory animals

The data concerning the types of analgesic drugs available and the experimental evidence for their efficacy in laboratory species are reviewed. The information is then extrapolated to the clinical situation to provide guidance as to methods of achieving effective analgesia in experimental animals. The most generally useful agent at present seems to be buprenorphine which can be used to provide effective, long lasting analgesia in a wide range of species.