Global problems of imported disease.
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Eight dogs, given imidocarb dipropionate subcutaneously at a dose of 6 mg/kg, were challenged with a sporozoite stabilate of a French strain of Babesia canis, prepared from infected Dermacentor reticulatus ticks, 2, 3, 4 or 5 weeks after treatment. Three control dogs were similarly infected but not preventively treated. One of the controls and one of the dogs treated 5 weeks prior to challenge died of babesiosis. Prepatent and incubation periods were similar in treated and control dogs, and all dogs showed important reductions in the packed cell volume. Relapses were commonly seen after recovery from the initial reaction. Although further work is needed before a final conclusion can be drawn to whether imidocarb is suitable as a chemoprophylactic against B. canis infection, it can be used as a curative drug.
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Ixodes ticks are infected by Borrelia burgdorferi when larvae feed on spirochete-infected mice. We studied the acquisition of B. burgdorferi by larval ticks, characterized the production of outer surface protein A (OspA) by spirochetes entering larvae, and examined the effects of OspA antibodies on the establishment of B. burgdorferi infections in ticks. Most larvae were infected by spirochetes 24 to 48 h after placement on mice. OspA antibodies stained the first spirochetes observed in larvae, suggesting that OspA is synthesized early during the colonization of the vector. When OspA antibodies were administered to B. burgdorferi-infected mice and larvae were then placed on the animals, the severity of larval infection and the number of infected ticks (7 of 16) were decreased compared with that of controls (15 of 16). The inhibitory effects of OspA antibodies were observed with passive antibody transfer as well as active host-generated immunity. The lower larval infection rate observed in the presence of OspA antibodies was exacerbated after the larval molt since only 1 of 12 nymphs was infected, and none of the mice that were fed upon by these nymphs became infected with B. burgdorferi. Therefore, an OspA antibody response in mice altered the reservoir competence of the vertebrate host by inhibiting the movement of B. burgdorferi from the host to the vector.
The suckling mouse cataract agent (SMCA) is a filtrable (<220 nm), noncultivable agent isolated from ticks in Georgia in 1961. It grows to high titer in the eyes and brains of intracerebrally inoculated mice in which it induces cataract, uveitis, and chronic brain infection. SMCA in high titer may also be recovered from the tissues of embryonated hen eggs in which the infection is lethal within 4 to 9 days. Fine-structural studies of ultrathin sections of pellets obtained by ultracentrifugation of SMCA-infected egg allantoic fluids have revealed pleomorphic structures with morphological characteristics typical of mycoplasma. Similar organisms have been observed in egg allantoic fluids infected with an SMCA-related tick isolate, GT-48, but not in fluids from uninoculated control eggs. Mycoplasma-like entities were also observed in high concentration within retinal tissues of rats and mice studied at the time of maximal retinitis and uveitis after SMCA inoculation. Comparable tissues from normal mouse eyes were free of microorganisms. These fine-structural observations are in agreement with those reported by other investigators and suggest that SMCA-induced pathology is associated with an agent that resembles mycoplasma in size and morphology but differs from typical mycoplasma in its apparent non-cultivability on artificial media and its resistance to inactivation by broad-spectrum antibiotics.
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Lyme borreliosis is an infectious illness caused by the spirochete Borrelia burgdorferi and is transmitted by tick vectors. A prospective study was performed from January 1990, to investigate whether Lyme arthritis might have been undetected among patients with (unclassified arthritis) oligoarthritis of "unknown" aetiology. 210 patients were tested for antibodies to Borrelia burgdorferi: 82 patients with oligoarthritis of "unknown" aetiology; 52 patients with Reiter's syndrome; 20 patients with seronegative, B-27 positive oligoarthritis and 56 controls. Serological testing for Borrelia burgdorferi was performed by indirect immunofluorescence assay. The occurrence of positive antibodies (1:80) in 11 (13.4%) patients with arthritis of "unknown" aetiology was significantly different from the combined control group (1.6%) (p < 0.05). Four out of 11 patients remembered a tick bite, two out of 11 patients developed erythema migrans after 3 to 10 days. Six weeks later 2 patients developed oligoarthritis and one patient after a month. In the remaining 8 patients arthritis was the first sign of the disease. Knees were most commonly affected (90%). Radiographic abnormalities (osteoporosis, soft tissue swelling) were noted in 3 patients. The synovial fluid findings were typical for inflammatory arthritides in 6 patients. The diagnosis of Lyme borreliosis was made according to following data: origin from an area endemic for Lyme borreliosis, tick bite, erythema migrans, significant levels of the antibodies to the Borrelia burgdorferi and oligoarthritis. It can be concluded that arthritis may be the main manifestation of Borrelia burgdorferi infection.
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This article offers a personal perspective on the efforts to model the habitat suitability for ticks. A serious effort is being made to provide maps at an adequate resolution that can plot the probability of the presence and even the abundance of tick parasites of humans and that can be used to develop control programs for species with economic interest. Some of the methods being currently evaluated are described together with a summary of the techniques using remotely sensed information to capture the abiotic features of the habitat. Some examples, developed using different methods, are provided for the Mediterranean region and part of the U.S., together with an overview of the performance of these models.
Since its immigration in the Pacific island of New Caledonia in 1942 (i.e. about 240 tick-generations ago), the cattle tick Boophilus microplus has experienced a remarkable adaptive diversification there. In order to better understand the population factors involved, we have investigated the B. microplus population structure on that main host-species, Bos taurus. This study was based microsatellite loci and confirmed that the island colonization came along with a significant bottleneck. Knowledge on B. microplus biology led us to expect B. microplus populations to be composed of highly inbred lineages irregularly dispatched among the individual hosts belonging to the same herds. Instead, this study evidenced a weak inbreeding level and an absence of genetic differentiation within herds. Complementarily, a significant signal of isolation by distance exhibited that human-traffic of cattle does not promote high tick dispersal within the island. Finally, the tick density was found to be about a few hundreds of reproducing adults per squared kilometre, for a gene dispersal range of about a few hundred metres per tick generation. Results are discussed with regard to the evolution of new adaptive changes.
The ratio of variance to mean (s2/means) of numbers of Ixodes rubicundus (males and females) per sheep was used as a measure of the dispersion pattern of this tick within a naturally infested population of sheep. Sheep were divided into two groups, one with previous contact with I. rubicundus and the other with no previous contact. Samples of 10 sheep from each group were searched for ticks on a weekly basis for 19 weeks during the winter of 1986. In each group, both male and female ticks had an s2/means ratio greater than 1 for the majority of observation periods indicating an aggregated dispersion pattern. The degree of aggregation was greater with increasing density of the ticks. The implications of these results are discussed both in relation to sampling procedures and potential control strategies.
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Using a model: salivary glands of Dermacentor ticks--tick-borne encephalitis virus--guinea pig--D. marginatus ticks, it became possible to confirm the data of Jones et al. (1989) on the role of a substrate of Rhipicephalus appendiculatus glands as a strong enhancer of orthomyxovirus Togoto transmission during subcutaneous administration of a moderate virus dose to virus-resistant guinea pig. A tendency was only noticed towards better infectivity of ticks with the administration of sub- or supraoptimal virus doses together with the adjuvant (salivary gland substrate), as well as enhanced sensitivity of male individuals to a combination of virus with adjuvant. The latter fact can be explained by a transptyal way of infection typical for male individuals, which was noted earlier during joint nutrition with infected female individuals. A lower level of virus reproducibility in ticks who got it together with the adjuvant, as compared to the control, has been established. Low titer in female individuals after nutrition reduces the likelihood of transovarial transmission of virus with adjuvant.