Passive transfer of resistance in rabbits infested with adult Ixodes ricinus L: humoral factors influence feeding and egg laying.

Parital immunity against the bites of female I. ricinus was transferred to normal rabbits by inoculating immune serum from resistant animals. Transferred humoral factors diminished the weight of the ticks' blood meal by 29% and increased the feeding period by about 1 day in comparison with ectoparasites engorged on controls. They provoked also the failure of egg laying by female I. ricinus. Only 55% of ticks fed on treated rabbits laid eggs (94% on controls). The immunological state of immune serum donors or recipients was studied and the IgG and homocytotropic specific anti-I. ricinus antibodies were identified. The immediate hypersensitivity of rabbits' skin was also controlled.     

Rabbits infested with adultIxodes ricinus L.: Effects of mepyramine on acquired resistance

Summary The results of this work demonstrate that histamine seems to be involved in the expression of the resistance acquired by rabbits to I. ricunus. Daily treatment of animals with the H₁-antihistaminic mepyramine inhibited the effects of immunity. This observation applies to the effect of resistance on the weight of engorged ticks, the duration of the blood meal and the success of egg laying and hatching.The present work was supported by the Swiss National Fund for Research, grant No. 3.303-78. We are grateful to Dr L. Julou (Rhône-Poulenc) for a gift of mepyramine.     

Comparison of cutaneous hyperemia in cattle elicited by larvae ofBoophilus microplus and by prostaglandins and other mediators

Summary Blood flow has been measured in bovine skin following the injection of tick antigens and a number of pharmacological mediators; including histamine, prostaglandins and slow reacting substance of anaphylaxis. The greates increase in blood flow (20 times normal) was recorded with tick antigens and with prostaglandin F2. This mediator may therefore influence blood flow during immune reactions to ticks and during the rapid ingestion of blood by the ticks.Acknowledgments. This work was supported by the Australian Meat Research Committee. We would like to thank J. M. Gough for her technical assistance.     

Passive transfer of resistance in rabbits infested with adultIxodes ricinus L.: Humoral factors influence feeding and egg laying

Summary Partial immunity against the bites of I. ricinus was transferred to normal rabbits by inoculating immune serum from resistant animals. Transferred humoral factors diminished the weight f the ticks' blood meal by 29% and increased the feeding period by about 1 day in comparison with ectoparasites engorged on controls. They provoked also the failure of egg laying by I. ricinus. Only 55% of ticks fed on treated rabbits laid eggs (94% on controls). The immunological state of immune serum donors or recipients was studied and the IgG and homocytotropic specific anti-I. ricinus antibodies were identified. The immediate hypersensitivity of rabbits' skin was also controlled.The present work was supported by the Swiss National Fund for Scientific Research, grant No. 3.558.75.     

Effects and duration of resistance acquired by rabbits on feeding and egg laying in Ixodes ricinus L.

Summary Rabbits gradually developed a resistance against Ixodes ricinus ticks as a result of sequential experimental infestations. The resistance was characterized by an increased duration of feeding, by ticks engorging to a smaller extent and by reduced egg production. Once established, the immunity persisted for at least 9 months. Changes in the titre of circulating anti-I. ricinus antibodies was measured by indirect immunofluorescence.The present work was supported by the Swiss National Fund for Scientific Research, grant No. 3.558-0.75.     

Effect of host age on the expression of acquired resistance to ticks

Summary Young guinea-pigs (350 g) expressed significantly greater levels of acquired resistance to challenge by larvalAmblyomma americanum ticks than older guinea-pigs (520–800 g). This finding suggests that younger guinea-pigs are immunologically more responsive to tick infestation than older mature individuals. Therefore, host age is an important variable in evaluating acquired resistance to ticks.Supported in part by grants from the United States Public Health Service, National Institutes of Health No. AI 17555, AI 19657, RR 05443 and from the Rockefeller Foundation.     

The relationship of phosphodiesterase and cyclic AMP to the process of fluid secretion in the salivary glands of the ixodid tick Amblyomma americanum.

Phosphodiesterase (PDE) activity in the salivary glands of the female. Amblyomma americanum decreased as the tick progressed from a slow to a rapid phase of feeding, while the rate of fluid secretion increased when glands were stimulated with cyclic AMP and theophylline. Dopamine stimulated PDE activity and an 'inhibitory' factor was found in glands obtained from rapidly engorging ticks which decreased PDE activity. These findings are discussed as they relate to the process of fluid secretion by salivary glands of feeding ixodid ticks.     

Non-viraemic transmission of tick-borne encephalitis virus: a mechanism for arbovirus survival in nature

The vectors of arthropod-borne viruses (arboviruses) become infected by feeding on the viraemic blood of an infected animal. This theory is based on transmission studies involving artificial infection of vertebrate hosts by syringe inoculation. To reproduce natural conditions of virus transmission, infected and uninfected vectors (ticks) of tick-borne encephalitis virus, the most important arbovirus in Europe, were allowed to feed together on uninfected wild vertebrate hosts. The greatest numbers of infected ticks were obtained from susceptible host species that had undetectable or very low levels of viraemia. The results suggest that nonviremic transmission is an important mechanism for the survival of certain arboviruses in nature.     

Effect of immunization of male rabbits against androstenedione

Summary After active immunization of male rabbits against androstenedione and with increasing antibody titre the concentration of androstenedione and testosterone in peripheral blood increased more than 1000-fold resp. 20-fold above values of control animals. On histological examination of the testes a marked Leydig's cell hyperplasia was found, though there was no difference in testis weight.     

Effects and duration of resistance acquired by rabbits on feeding and egg laying in Ixodes ricinus L.

Rabbits gradually developed a resistance against Ixodes ricinus ticks as a result of sequential experimental infestations. The resistance was characterized by an increase duration of feeding, by ticks engorging to a smaller extent and by reduced egg production. Once established, the immunity persisted for at least 9 months. Changes in the titre of circulating anti-I. ricinus antibodies was measured by indirect immunofluorescence.     

Cerebral ischemia is the main cause for the onset of heat stroke syndrome in rabbits.

During the onset of heat stroke, rabbits displayed hyperthermia (42.8 degrees C), and decreased cerebral perfusion pressure and decreased cerebral blood flow (as reflected by a prolonged cerebral circulation time) compared to those of normothermic rabbits. On the other hand febrile rabbits, during the fever plateau did not show the above responses, although they had a similar level of hyperthermia (42.4 degrees C). The data support the concept that cerebral ischemia is the main cause for the onset of the heat stroke syndrome.     

Beta-blockade of morphine-induced hyperlactacidemia in rabbits.

In morphinized rabbits blood lactate levels are elevated. Hyperlactacidemia persists after cessation of morphine injections. This morphine-induced lactate accumulation is completely abolished by simultaneous propranolol treatment. Phentolamine does not modify the action of morphine.     

Na,K-ATPase in the salivary gland of the ixodid tickAmblyomma hebraeum (Koch) and its relation to the process of fluid secretion

Summary Total and ouabain-sensitive ATPase activities were determined in the salivary glands of ticks throughout the feeding cycle. Activities were very low in unfed specimens. In the glands of feeding females, the activities rose until a maximum was reached for both ATPase components at approximately 200 mg. The activities remain low in males throughout the feeding period. These findings are discussed in relation to the fluid secretory process of the salivary glands.Generously supported by the Swiss National Fund for Scientific Research, request No. 3.3460.74 We are also very grateful to Mr.H. Bouvard, Ciba-Geigy Ltd., Les Barges, Vouvrey, VS, for supplying us with ticks.     

Immunoglobulin-binding proteins in ticks: new target for vaccine development against a blood-feeding parasite

Humans have a long history of trying to control ticks. At first, attempts focused on modifying the habitat, whereas later efforts relied heavily on the use of chemicals. Current research is directed at finding a vaccine against ticks. A strategy of targeting 'concealed antigens' succeeded with the first commercialised vaccine against the cattle tick Boophilus microplus. However, vaccine development against other tick species appears unsatisfactory to date. Vaccination depends on a specific antibody-mediated immunoreaction that damages the parasite. Immunoglobulin molecules of vertebrate hosts can pass through gut barriers into the haemolymph of ectoparasites while retaining antibody activity. Research on the ixodid tick Rhipicephalus appendiculatus revealed that host immunoglobulin-G in the parasite was excreted via salivation, during feeding. Immunoglobulin-binding proteins in tick haemolymph and salivary glands are thought to be responsible for such excretion. The discovery of an immunoglobulin excretion system in ticks indicates that they have a highly developed mechanism to protect themselves from their host's antibody attack. Such a mechanism questions whether immunization strategies will be effective against ticks, unless they circumvent or disable the ticks' immunoglobulin excretion system.     

Alloxan-induced hyperglycemia increases progestin and androgen accumulation by isolated rabbit follicles in vitro

Follicles isolated from Alloxan-treated rabbits and incubated in vitro, accumulated more progesterone and testosterone than those from saline-treated rabbits. LH augmented the accumulation of these 2 steroids. By contrast, the estradiol response to LH stimulation by follicles from Alloxan-induced hyperglycemic rabbits was diminished when compared to follicles from saline-treated rabbits. Ovaries from hyperglycemic rabbits also appeared to have more cystic follicles.     

Action de l'acide folique sur l'hématopoïèse chez l'animal normal

Summary After intravenous injections of 10 or more of folic acid to normal rabbits the following phenomena are observed in the blood: a rapid variation of the colorimetric index: a marked leucocytosis. The figure illustrates these phenomena which are very fugitive, particularly the leucocytosis.     

Cerebral ischemia is the main cause for the onset of heat stroke syndrome in rabbits

During the onset of heat stroke, rabbits displayed hyperthermia (42.8°C), and decreased cerebral perfusion pressure and decreased cerebral blood flow (as reflected by a prolonged cerebral circulation time) compared to those of normothermic rabbits. On the other hand febrile rabbits, during the fever plateau did not show the above responses, although they had a similar level of hyperthermia (42.4°C). The data support the concept that cerebral ischemia is the main cause for the onset of the heat stroke syndrome.The work reported here was supported by grants from the National Science Council (Taipei, Taiwan, Republic of China).     

Aggregation pheromones in 2 Australian hard ticks,Ixodes holocyclus and Aponomma concolor

Summary The presence of an aggregation pheromone has been demonstrated for the first time in indigenous Australian ticks. Filter paper discs exposed to either Australian paralysis ticks Ixodes holocyclus or echidna ticks Aponomma concolor showed inter-sex or intra-sex attraction for ticks of their own species. Nymphal exuviae of Ap. concolor were highly attractive to adult ticks. Discs were significantly attractive to I. holocyclus at distances up to 80 cm.Our thanks to Mr I. J. Lewis, Director, Cattle Tick Research Station, for initiating the study of possible pheromones in I. holocyclus, and for his continued encouragement throughout.     

Action and interaction of two alpha 1-adrenoceptor agonists, methoxamine and St 587, on the rabbit's blood pressure and EEG

In rabbits methoxamine reversed the vasopressor effect of St 587 and abolished the EEG synchronizing action of St 587. The interaction on the blood pressure could be ascribed either to the different chemical structures of St 587 and methoxamine or to partial agonistic properties of St 587. The interaction on the EEG appears to be more complex.     

Action and interaction of two 888-1888-1888-1agonists,methoxamine and St 587, on the rabbit's blood pressure and EEG

Summary In rabbits methoxamine reversed the vasopressor effect of St 587 and abolished the EEG synchronizing action of St 587. The interaction on the blood pressure could be ascribed either to the different chemical structures of St 587 and methoxamine or to partial agonistic properties of St 587. The interaction on the EEG appears to be more complex.