[A trial at using the systemic action of ivermectin for suppressing the vector capacity of ticks (Ixodidae) infected with the tick-borne encephalitis virus]. / Popytka ispol'zovaniia sistemnogo deistviia ivermektina dlia podavleniia vektornoi sposobnosti kleshchei (Ixodidae), zarazhennykh virusom kleshchevogo éntsefalita.

Adult Dermacentor marginatus hatched from nymphs infected with TBE virus and poisoned with ivermectin retain their vector abilities. Even small individuals with a 1.5-2 times lesser mass as against the reference mass contain the virus in the body in the same titers and the virions in salivary gland alveoli. Administration of an oil solution of ivermectin into the stomach of white mice, nymph feeders, in a dose surpassing threefold the dose recommended for intramuscular injection of this agent completely suppressed shedding of intact nymphs but did not suppress it in those infected. The nymph mass, size and mass of adult ticks hatched from them dropped under the effect of ivermectin dosage build-up in both intact and infected ticks, but these processes were slower in ticks infected with TBE virus. The authors suggest that the ticks infected with TBE virus are much more resistant to the process of gamma-aminobutyric acid depression, the mechanism of ivermectin action. They emphasize the necessity of bearing in mind the possible differences in the reactions to systemic poisons of intact and infected ticks when organizing vector control measures.

[The possible role of the salivary gland substrate in ixodid ticks as an adjuvant enhancing arbovirus transmission]. / Vozmozhnaia rol' substrata sliunnykh zhelez iksodid v kachestve ad''iuvanta, usilivaiushchego peredachu arbovirusov.

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.

Peculiarities of tick-borne encephalitis virus reproduction in Haemaphysalis inermis ticks and their explants.

Virological, electron microscopic and immunomorphological investigation on the reproduction of tick-borne encephalitis (TBE) virus in Haemaphysalis inermis ticks and in tissue explants from nymphs during their metamorphosis revealed that the virus reproduced in the cells of different tissues and organs of ticks which were in different phases and stages of life cycle. During the eclipse phase of TBE virus persistence in ticks, when no virus could be demonstrated by infectivity assay, viral particles were detected by electron microscopy.

Variability of Powassan virus cultured in tissue explants and organism of Hyalomma anatolicum ticks.

The variability of Powassan virus was studied during successive passages in Hyalomma anatolicum ticks or prolonged reproduction in their tissue explants. It had been shown that in the course of tick passages and during reproduction in the explants, pathogenicity of the virus in respect to causing acute disease in mice after peripheral inoculation was decreased, while virus ability to cause death after intracerebral (i.c.) inoculation remained unchanged. In mice infected with the original strain P-40 of Powassan virus damaging effect of the immune response prevailed, while in mice infected with the strains passaged for a long time in ticks (strain P-40Hat) or in tick tissue explants (strain P-40Haex), the protective effect of the immune response was prominent.

[Mono- and mixed infection by the tick-borne encephalitis and Powassan viruses of tissue explants from ticks of the genus Hyalomma]. / Mono- i smeshannaia infektsiia virusami kleshchevogo éntsefalita i Povassan éksplantatov tkanei kleshchei roda Hyalomma.

The paper presents results of virusological and electron microscope studies of the reproduction of viruses of tick-borne encephalitis and Povassan at mono- and mixed persistent infection of explants of imaginal tissues of Hyalomma anatolicum and H. dromedarii with these viruses. The virus reproduction in explants was observed within 208 to 217 days after the infection. Joint reproduction of two model viruses within 1-2 months after the infection can take place and after that the inhibition of the reproduction of one of the viruses. This inhibition can be of cyclic character.