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Non-viraemic transmission of Thogoto virus: vector efficiency of Rhipicephalus appendiculatus and Amblyomma variegatum.

Previous studies have demonstrated that Thogoto virus is transmitted from infected to uninfected ticks when co-feeding on uninfected guinea-pigs, even though the guinea-pigs do not develop a detectable viraemia. Furthermore, tick to tick transmission is potentiated by factors associated with the salivary glands of ticks (saliva activated transmission). The vector efficiency of 2 ixodid tick species, Rhipicephalus appendiculatus and Amblyomma variegatum, for Thogoto virus was assessed using this model. The number of uninfected recipient ticks that acquired Thogoto virus when co-feeding with virus-infected ticks (donors) on uninfected guinea-pigs was determined. When nymphs of either tick species were employed as donors, there was no significant difference in the number of infected recipient nymphs. In contrast, a significant difference in the vector efficiency of adults ticks was observed: 77.0% of recipient ticks which co-fed with R. appendiculatus donor adults acquired Thogoto virus compared to 44.7% of recipient ticks which co-fed with A. variegatum donors. No significant difference in susceptibility to Thogoto virus infection was observed between recipient ticks of the 2 species. Thus, adults of R. appendiculatus are more efficient than A. variegatum in mediating non-viraemic transmission.

Animals↗
PubMed1988

Studies on the host/parasite interface during the development of a pentastomid arthropod parasite in rodent intermediate hosts, with observations on protective surface membranes.

The changing structure of the cuticle of the arthropod pentastomid parasite Porocephalus crotali, during growth to the infective stage in mouse and rattlesnake hosts, is described. The outermost cuticulin layer of the cuticle in instars II-VI is elevated to form a dense mat of epicuticular hairs. Since the VI larval cuticle is retained by the infective (VII) nymph as a protective sheath, effectively all stages in mice present a hairy surface to the host and this may constitute a physical barrier to inflammatory cells. The entire surface is overlain by a triple-track 'unit' membrane whose biophysical properties resemble those of a conventional plasma membrane, and there is evidence to suggest that this membrane is susceptible to immune attack. Under natural circumstances, epicuticular hairs entrap secretion, delivered to the cuticle via innumerable minute ducts which communicate with tegumental secretory cells termed subparietal cells (SPC). SPC synthesize lamellate droplets which unfold on the cuticle to constitute a layer of protective polymorphic vesicles. By contrast, infective nymphs in snakes possess a smooth cuticle and SPC membranous secretion is stacked over the entire surface, in sheets up to 20 deep. The function of the lipid and protein components of SPC secretion is discussed.

Animals↗
PubMed1985

Ontogeny of the invertebrate humoral immune response: studies on various developmental stages of the American cockroach (Periplaneta americana).

Earlier studies revealed that a specific adaptive humoral immune response can be induced in the American cockroach (Periplaneta americana) to the soluble protein complex, Honeybee venom (HBT). We have undertaken a series of ontogenetic studies to determine if there are differences between the protective responses of roaches representing different developmental stages. Our results indicated that the response to HBT in the immature cockroach (nymphs weighing 200-500 mg) was characterized by a significant lag period before immune protection began to develop. However, by the second week of the response, reactivity was comparable to that of the adult. Old adult male roaches (animals 5 months into adulthood) displayed a significant decline in reactivity during the early phases of the response in comparison to younger adults, and in general, appeared to be less vigorous in generating protection. Both the nymph and old adult roaches demonstrated good secondary responsiveness. The results from these experiments indicated that the developmental stage of the roach could be directly correlated to the degree of immunocompetency possessed by the animal. This is similar to the ontogenetic sequence typically found for immune reactivity in vertebrates.

Age Factors↗
PubMed1981

Hyalomma anatolicum anatolicum (Koch, 1844) as a possible vector for transmission of Trypanosoma theileri, Laveran, 1902 in cattle.

Amastigotes, sphaeromastigotes, epimastigotes and trypomastigotes of Trypanosoma theileri, Laveran, 1902 have been observed in the nymphs and adults of Hyalomma anatolicum anatolicum (Koch, 1844). There ticks were obtained from engorged larvae and nymphs collected from a cross-bred bull with detectable parasitaemia. Infection with T. theileri was established in two 6-8-month old cross-bred calves by subcutaneous inoculation of Trypanosomatid flagellates collected from ticks and by feeding of the infected ticks on the ears of these calves.

Animals↗
PubMed1988

The effect of the brown ear-tick Rhipicephalus appendiculatus on the growth of Sanga and European breed cattle.

The effects of larvae, nymphs and adults of the brown ear-tick Rhipicephalus appendiculatus on the growth of Bos indicus X B. taurus (Sanga) steers and on B. taurus steers and heifers was measured by exposing groups, maintained in the same pastures, to different levels of tick challenge. Larvae and nymphs had no significant effect on liveweight gains, but adults had a large effect. Each engorging female tick counted was associated with a loss of 4 g. Their effect on the Sanga cattle was minimised by host resistance which severely limited the number of ticks feeding on them. The B. taurus animals were severely affected and suffered extensive ear damage. Both breeds were subjected to screw-worm fly (Chrysomya bezziana) strike in the lesions caused by heavy tick infestations, but the B. taurus animals were much more prone to attack. The results provide a basis for calculating losses in production caused by this species of tick which is widespread in Africa.

Analysis of Variance↗
PubMed1989

The effect of the bont tick (Amblyomma hebraeum) on the weight gain of Africander steers.

The effects of the bont tick Amblyomma hebraeum on the productivity of cattle need to be quantified in order to design economically optimal control programs. Liveweight gains (LWGs) of three groups of Africander steers, maintained in the same pasture and exposed to zero, medium or high numbers of larvae, nymphs and adults of the tick, were measured. Larvae and nymphs had no significant effect on LWG but adults had a large, statistically significant effect (P less than 0.05). The tick-free group had an average LWG of 20 kg more than the heavily infested group after 3.5 months. No mortality was recorded from ticks or tick-borne diseases during the experiment. There was no relationship between the number of engorging adult female ticks counted and loss of LWG of individual animals. The latter suggests that exposure to ticks as well as engorgement by female ticks causes losses. The loss per adult female that completed engorgement was estimated, by relating the LWGs of individual animals to their tick infestations, to be 4 +/- 2 g per adult female tick. An alternative estimate, made by comparing the average LWG and tick infestations of each treatment group, was equal to 10 +/- 4 g. This latter estimate includes the effect of challenge (and rejection) as well as tick feeding and so was accepted as giving the best estimate. Screw-worm fly (Chrysomya bezziana) struck an average of 7.5% of the cattle infested with ticks in any week but the effects on the productivity of the cattle were minimized by immediate treatment. There was a significant, positive correlation between the incidence of screw-worm fly strike and the numbers of adult ticks counted on the experimental animals. The results provide data for calculating losses caused by A. hebraeum in different parts of its geographical range.

Animals↗
PubMed1990

The effects of bovine tick resistance on the susceptibility of Hyalomma anatolicum anatolicum to infection with Theileria annulata (Ankara).

Two Bos taurus calves were made resistant to tick infestation by exposing them to approximately 500 rabbit-reared nymphs of Hyalomma anatolicum anatolicum twice at a 2-week interval. These two calves, together with a tick-susceptible control calf, were inoculated with a stabilate of Theileria annulata (Ankara). Patent infection resulted in all three calves. Seven-hundred and fifty gerbil-reared nymphs were then applied on each of these calves as well as another tick-susceptible calf that was Theileria free. This infestation was carried out on Day 8 post-inoculation. Ticks that dropped on Day 13 post-inoculation were examined to note the development of T. annulata in them and the histological changes that occurred in the gut and salivary glands. During the second phase of feeding, the gut epithelia of the ticks from the tick-resistant calves were less active. There were no notable differences in the characteristics of the developmental stages of T. annulata between the ticks from the tick-resistant calves and those from the susceptible calf. However, ticks from one calf that acquired a higher level of tick resistance were significantly less susceptible to infection by T. annulata. Bovine tick resistance therefore compromises the vector capacity of H. a. anatolicum and this may be of epidemiological significance in the endemic areas of tropical theileriosis.

Animals↗
PubMed1991

Effect of temperature on transtadial transmission of Theileria annulata in Hyalomma anatolicum anatolicum ticks.

The effect of temperature on the transtadial transmission of Theileria annulata in Hyalomma anatolicum anatolicum was studied. Variation in temperature (4-40 degrees C) had a significant effect on moulting rate of the ticks and transmission of theilerial parasites from nymphs to resultant adults. The temperatures above 40 degrees C and below 12 degrees C prevented moulting. Maximum infection levels were obtained in salivary glands of adult ticks when the infected engorged nymphs were incubated at 24-28 degrees C. The infection rate in salivary glands was assessed using a methyl green pyronin technique.

Animals↗
PubMed1992

Studies on naturally acquired immunity to African ticks. II. Observations on cattle exposed to Rhipicephalus appendiculatus under varying periods of repeated infestations.

Groups of Friesian cattle were infested repeatedly with Rhipicephalus appendiculatus at weekly intervals (eight infestations) and at intervals of 3 weeks (seven infestations) and 6 weeks (seven infestations). The engorgement weight of adults, nymphs and larvae decreased significantly initially, from the second infestation, but rose significantly at later infestations. This rise was more dramatic with larval instars than with any other. A new method for quantifying the resistance status of animals was introduced; this method showed that the resistance acquired by cattle during 6-weekly reinfestations was more stable than that acquired by cattle during weekly and 3-weekly reinfestations. The criteria for assessing natural resistance to ticks was reappraised. These are classified into those serving long- and short-term purposes, and those which have direct and indirect effects. Criteria which could serve long- and short-term purposes include a reduced number of engorged ticks, an increased number of dead male and female ticks, a decreased number of ticks which fed above the critical engorgement weight and an increased number which fed within the pre-mating weight and decreased the number of copulations. The criterion of reduced engorgement weight can serve the short-term purpose only. A new manifestation of resistance to ticks, i.e. decreased moulting weights of nymphs and adults, together with the criterion of decreased egg hatchability, were classified as indirect effects because they were manifested after the ticks had dropped off the resistant cattle.

Animals↗
PubMed1992

Laboratory and field observations on anti-tick properties of the plant Gynandropsis gynandra (L.) Brig.

A shrubby plant, abundant in east Kenya, Gynandropsis gynandra (L.) Brig., was shown to exhibit repellent and acaricidal properties to larvae, nymphs and adult Rhipicephalus appendiculatus and Amblyomma variegatum ticks. All stages of ticks avoided the leaves of the plant and a high percentage of the ticks which were continuously exposed to its leaves died; surviving ticks were weak and inactive but regained activity when exposed to fresh air. The effectiveness of the plant's leaves as a repellent and acaricide was most pronounced on nymphs and least pronounced on adults. Field investigations indicated that ticks were not found up to 2-5 m from the plant in areas where the plant was predominant. The potential of using the plant for tick control within an integrated tick management system in the resource-poor farming context in Africa was highlighted.

Animals↗
PubMed1993

Characterisation of salivary gland antigens of Triatoma infestans and antigen-specific serum antibody response in mice exposed to bites of T. infestans.

In mice, the antigen-specific serum antibody response following exposure to bites of Triatoma infestans nymphs and adults was determined using enzyme-linked immunosorbent assay (ELISA). The second and the third exposure to T. infestans bites resulted in higher antibody levels than during the primary exposure. Antigen-specific antibody development was faster in mice exposed to bites of nymphs than in mice exposed to adults; however, a higher antibody level was found in mice bitten by adult bugs. Protein components of T. infestans saliva were characterised using electrophoretic and blotting techniques. The immunoblotting patterns were similar in mice exposed to insect bites of various developmental stages. Antigen-specific serum antibodies reacted only with high molecular mass components (two double bands of 100 and 120 kDa, and the 80 kDa antigen). The 80 kDa component was glycosylated. Affinity to lectin derived from Pisum sativum revealed the presence of a bi- or triantennary complex type of glycan. There were similar glycan structures in the main glycoprotein components of T. infestans saliva at 18-35 kDa; however, the components did not react with antibodies of mice exposed to insect bites.

Animals↗
PubMed1993

Experimental transmission of Dipetalonema dracunculoides (Cobbold 1870) by Rhipicephalus sanguineus (Latreille 1806).

A dog naturally infected with Dipetalonema dracunculoides and having a microfilaremia of 6050 microfilariae per mm3 of blood was used as source of infection. Experimentally cultivated nymphs of Rhipicephalus sanguineus were fed on the donor dog. Once engorged, ninety-three nymphs were removed and kept at 30 degrees C and RH 90% until they moulted to the adult stage. To study the development of microfilariae in the vector, ten ticks were dissected at Day 37 post-infection. Adult infected ticks were fed on two uninfected dogs. The observed pre-patent periods were 69 and 76 days. Trans-stadial transmission of Dipetalonema dracunculoides by Rhipicephalus sanguineus was demonstrated.

Animals↗
PubMed2006

Chagas disease parasite induces behavioural changes in the kissing bug Mepraia spinolai.

Parasites have been shown to manipulate the feeding behaviour of their invertebrate vectors, which results in an increased probability of transmission to definitive hosts. Most evidence for this hypothesis comes from protozoan species with salivary transmission but evidence for stercorarian parasite transmission is lacking. We present experimental evidence that infection of the kissing bug Mepraia spinolai (Hemiptera; Reduviidae) with the protozoan Trypanosoma cruzi reduced the time to detect potential hosts in comparison to control insects. Infected bugs bit about twice more often than uninfected nymphs and defecated 8 min after the last blood meal whereas uninfected bugs needed 11 min. The behaviour of male and female nymphs did not differ significantly. Since all of these traits relate to parasite transmission, we suggest that parasite-mediated changes in the foraging and defecation behaviour of M. spinolai may promote the spread of T. cruzi toward definitive hosts.

Animals↗
PubMed2006

The toxic effects of neem extract and azadirachtin on the brown planthopper, Nilaparvata lugens (Stål) (BPH) (Homoptera: Delphacidae).

Extracts of neem (Azadirachta indica A. Juss) are used in the developing world for many purposes including management of agricultural insect pests. The effects of different neem extracts (aqueous (NSKEaq), ethanol (NSKEeth) and hexane (NSKEhex)) on mortality, survival and weight of the brown planthopper, Nilaparvata lugens (Stål) (BPH) (Homoptera: Delphacidae) third and fourth nymphal instars were investigated. When fed rice plants treated with neem derivatives in bioassays, the survival of BPH nymphs is affected. Comparisons were made with the pure neem limonoid, azadirachtin (AZA) to ascertain its role as a compound responsible for these effects. AZA was most potent in all experiments and produced almost 100% nymphal mortality at 0.5 ppm and higher concentrations. When higher concentrations were applied, the effects appeared shortly after treatment and mortality was higher. Many insects died after remaining inactive for several days or during prolonged moulting. At lower concentrations, if moulting was achieved, disturbed growth and abnormalities were then likely to occur in the moulting process. Nymphs that were chronically exposed to neem extract showed a reduction in weight (45-60%). The results clearly indicate the simple NSKE (aqueous, ethanolic or both), containing low concentrations of AZA, can be used effectively to inhibit the growth and survival of BPH.

Animals↗
PubMed2006

RNAi studies reveal a conserved role for RXR in molting in the cockroach Blattella germanica.

Ecdysteroids play a major role during developmental growth in insects. The more active form of these hormones, 20-hydroxyecdysone (20E), acts upon binding to its heterodimeric receptor, formed by the two nuclear receptors, EcR and RXR/USP. Functional characterization of USP has been exclusively conducted on the holometabolous insect Drosophila melanogaster. However, it has been impossible to extend such analysis to primitive-hemimetabolous insects since species of this group are not amenable to genetic analysis. The development of methodologies based on gene silencing using RNA interference (RNAi) after treatment with double-stranded RNA (dsRNA) in vivo has resolved such limitations. In this paper, we show that injection of dsRNA into the haemocoel of nymphs and adults of the cockroach Blattella germanica can be used to silence gene function in vivo. In our initial attempt to test RNAi techniques, we halted the expression of the adult-specific vitellogenin gene. We then used the same technique to silence the expression of the B. germanica RXR/USP (BgRXR) gene in vivo during the last nymphal instar. BgRXR knockdown nymphs progressed through the instar correctly but they arrested development at the end of the stage and were unable to molt into adults. The results described herein suggest that RXR/USP function, in relation to molting, is conserved across the insect Class.

Animals↗
PubMed2006

Infection of Ixodes scapularis ticks with Rickettsia monacensis expressing green fluorescent protein: a model system.

Ticks (Acari: Ixodidae) are ubiquitous hosts of rickettsiae (Rickettsiaceae: Rickettsia), obligate intracellular bacteria that occur as a continuum from nonpathogenic arthropod endosymbionts to virulent pathogens of both arthropod vectors and vertebrates. Visualization of rickettsiae in hosts has traditionally been limited to techniques utilizing fixed tissues. We report epifluorescence microscopy observations of unfixed tick tissues infected with a spotted fever group endosymbiont, Rickettsia monacensis, transformed to express green fluorescent protein (GFP). Fluorescent rickettsiae were readily visualized in tick tissues. In adult female, but not male, Ixodes scapularis infected by capillary feeding, R. monacensis disseminated from the gut and infected the salivary glands that are crucial to the role of ticks as vectors. The rickettsiae infected the respiratory tracheal system, a potential dissemination pathway and possible infection reservoir during tick molting. R. monacensis disseminated from the gut of capillary fed I. scapularis nymphs and was transstadially transmitted to adults. Larvae, infected by immersion, transstadially transmitted the rickettsiae to nymphs. Infected female I. scapularis did not transovarially transmit R. monacensis to progeny and the rickettsiae were not horizontally transmitted to a rabbit or hamsters. Survival of infected nymphal and adult I. scapularis did not differ from that of uninfected control ticks. R. monacensis did not disseminate from the gut of capillary fed adult female Amblyomma americanum (L.), or adult Dermacentor variabilis (Say) ticks of either sex. Infection of I. scapularis with R. monacensis expressing GFP provides a model system allowing visualization and study of live rickettsiae in unfixed tissues of an arthropod host.

Animals↗
PubMed1989

Prevalence of Borrelia burgdorferi in Ixodes ricinus ticks in Berlin (West).

In 1986, 1711 nymphal and adult Ixodes ricinus orginating from Berlin (West) forests were examined individually or in pools of up to 10 ticks for the presence of Borrelia burgdorferi, the etiologic agent of Lyme borreliosis. Detection of borreliae was carried out by means of a culture method using modified Barbour-Stoenner-Kelly-Medium (BSK II). Tick populations from 14 out of 15 locations contained positive specimens. The calculated minimal infection rate of pooled ticks was 2.5% in nymphs (n = 1365), 10.2% in females (n = 59), and 5.3% in males (n = 114). Among those ticks examined individually, none of the nymphs (n = 49) proved to be positive but B. burgdorferi was isolated from 8.2% of the females (n = 73) and 7.8% of the males (n = 51). Fifty-five out of 56 isolates were identified as B. burgdorferi by means of an indirect immunofluorescence test (IFT) using monoclonal antibody H 5332. From these results B. burgdorferi must be considered as being present in the Berlin area.

Animals↗
PubMed1998

Development, reproductive capacity and survival of Amblyomma variegatum and Boophilus decoloratus in relation to host resistance and climatic factors under field conditions.

To determine the developmental periods, fecundity and survival of Amblyomma variegatum and Boophilus decoloratus and the effect of host resistance, a study was carried out in the field at Abernossa ranch in Ethiopia using three breeds of cattle: Arssi, Boran and Boran x Friesian crossbreed. The investigation took place between October 1991 and September 1992. The developmental periods of both tick species were recorded. The hatching periods of larvae, engorgement, larvo-nymphal and nympho-adult moulting periods during various climatic seasons in shaded and dry areas were also recorded. While the engorgement periods recorded on the animal were relatively constant for each tick species throughout the period of investigation, the pre-hatching and moulting periods were influenced by seasons. Generally, the duration of the life cycle was longest during the peak of rains and shortest during the dry season. In A. variegatum, the duration of the life cycle, irrespective of seasons, was shorter in the open than in the shaded site but this difference was not observed in B. decoloratus. Adults survived longer than nymphs, and nymphs longer than larvae in both tick species and A. variegatum survived much longer than B. decoloratus. All these variations were statistically significant (P < 0.001). A. variegatum and B. decoloratus fed on Boran X Friesian crossbreed cattle survived longer than ticks fed on the indigenous Boran and Arssi breeds, although the survival of both tick species fed on the latter two breeds was not significantly different from each other. The least tick resistant cattle (Boran X Friesian) produced the largest ticks with highest survival periods, whereas the most resistant indigenous cattle (Arssi and Boran) cattle produced the smallest ticks with the lowest survival periods. In all cases, more eggs were laid by A. variegatum than by B. decoloratus. However, in both tick species, the number of eggs laid and their hatchability were higher in those ticks fed on crossbreed than on indigenous cattle. The engorgement weights were positively correlated with the number of eggs laid and their hatchability.

Animals↗