Change in phagocytic activity toward the agent of tularemia in highly sensitive animals with mixed infections]

An increase of the ingestive and digestive capacity of neutrophils to the homologous causative agent and tularemia microbe was revealed by the opsonophagocytic test in Microtus arvalis, albino mice and guinea pigs infected with sublethal Yersinia pseudotuberculosis and Salmonella typhimurium doses. In subsequent tularemia infection some of the animals displayed a reduction of the septicemia intensity, prolongation of the disease and elevation of the susceptibility threshold. Period of manifestation of the inhibitory action on tularemia coincided with that of the increase in phagocytic activity     

Comparative study of the effectiveness of amikacin and streptomycin in experimental tularemia

In vitro study on antibacterial activity of amikacin in comparison to that of streptomycin revealed a high sensitivity of tularemia microbes of three geographical races to it. Amikacin showed a high therapeutic activity in treatment of albino mice infected with tularemia. The prospects of amikacin use in prophylaxis and treatment of tularemia are defined by its antibiotic activity against streptomycin-resistant forms of the tularemia causative agent.     

Detection of the tularemia zoonosis in the territory of the Kartlian Plain

The natural focus of tularemia was found to cover the whole territory of the Kartlian plain. Epizooty occurred mainly among common voles with the involvement of insectivorous voles. Hard ticks, gamasids and fleas infected with Francisella tularensis were detected. Rodents highly sensitive to tularemia can be affected by this infection. Water rats were not involved into the enzootic process. Further studies are necessary for the final solution of this problem.     

Lysozyme concentration in the loose connective tissue of animals with different species sensitivity to brucellosis]

Lysozyme content was determined in the subcutaneous cellular tissue of guinea pigs and albino rats differing by species resistance to brucella infection. Experiments were conducted on intact animals and those inoculated subcutaneously with live Br. abortus 19-BA vaccine. Connective tissue was taken from the site of the vaccine administration and from the contralateral side (control). Observations showed connective tissue of the animals highly sensitive to brucella infection to be exceedingly poor in this enzyme; as to connective tissue of albino rats with low sensitivity--it contained high amount of this enzyme. Lysozyme content increased considerably in the animals belonging to both species in the inflammatory focus developing at the site of the vaccine inoculation.     

A rapid method of evaluation of the effectiveness of antibacterial drugs]

Efficacy of antibiotics in the treatment of experimental tularemia was studied comparatively on various biological models. It was shown that the antibiotics which proved active against the tularemia microbe in albino mice when studied by the rapid and routine methods were highly efficient in the treatment and prevention of experimental tularemia in rabbits and baboons (hamadryas). The experiments showed basic possibilities to perform rapid estimation (for at least 2 days) of drug efficacy in experimental glanders and melioidosis in golden hamsters. The rapid method developed by the authors was recommended for the use in primary estimation of the efficacy of new drugs in the treatment of tularemia, glanders and melioidosis.     

Isolation of the causative agent of tularemia from Siberian lemmings in Eastern Taymyr]

The authors present the results of bacteriological and serological study for tularemia of 498 lemmings caught in Taimyr. Positive results were revealed in 4 out of 98 sera examined in the indirect hemagglutination test. In carrying out 67 biological tests on albino mice there were isolated for the first time in the Soviet Union 6 cultures of the causative agent of tularemia from the spleen of lemmings. By morphological, cultural and virulent properties the cultures obtained failed to differ from those isolated in other regions of the Soviet Union, and, consequently, we referred to the holoarctic race. Thus, it was established by the authors (both serologically and bacteriologically) that there existed tundra foci of tularemia.     

Determination of natural foci of tularemia in the Tuva ASSR]

Eleven strains of tularemia causative agents were isolated in 1974 in bacteriological study of ixodes ticks Dermacentor nuttalli (13088 in all) by biotests on albino mice. Tularemia was confirmed retrospectively in two humans who contracted the disease from ondatra cadavers. Skin allergic test with tularin was used to examine 1733 residents of seven populated localities; a positive result was obtained in 2 persons. Finally, in examination of 240 sera of cattle agglutination reaction proved to be positive in 6 cases in titres of from 1:20 to 1:80. Thus, natural nidality of tularemia in Tuva was established for the first time.     

An experimental study of mixed tularemia and Omsk hemorrhagic fever infection in muskrats]

Musk-rats were infected simultaneously and at three-day interval with tularemia and Omsk hemorrhagic fever (OHF); the course of this mixed infection under the mentioned conditions were studied. Virological, microbiological and morphological data indicated that infection of musk-rats with OHF and tularemia caused development of mixed infection in them. A more severe course of mixed infection was associated with enhanced vascular affections caused by the action of the OHF virus. An inhibition of tularemia caused by the OHF development was noted in the course of mixed infection.     

Rapid evaluation of the effectiveness of antibacterial drugs in experimental tularemia

Rapid estimation of the protective effect of antibacterial drugs on Fransiella tularensis for not more than 2 days was shown possible in experiments on albino mice infected with tularemia. High efficacy of aminoglycosides (kanamycin, gentamicin, streptomycin, amikacin, netilmicin, tobramycin, sagamycin, ribostamycin and sisomicin), tetracyclines (tetracycline, doxycycline, minocycline and methacycline), rifampicin, phosphomycin and oxolinic acid was determined with the recommended rapid method. Amoxycillin, ampicillin, piperacillin, carbenicillin, erythromycin, levomycetin, cefradine, cefmetazole, cefatrizine, cefoxitin, cefsulodin and bactrim (biseptol) proved to be inefficient against the tularemia causative agent.     

Cytopathic effect of the tularemia microbe on a culture of peritoneal macrophages

Morphological analysis of the process of interaction of tularemia microbe strains differing by virulence with macrophages demonstrated that all these strains produced a lethal effect on macrophages obtained from the animales sensitive to the infection. The macrophages obtained from the animals were but little sensitive to tularemia and were resistant to the action of the causative agent of this infection. The data obtained led to a supposition on the presence in the tularemia causative agent of a factor responsible for its lethal action on the macrophages.     

Information value of the indices of the nonspecific resistance of the body

A number of nonspecific resistance characteristics in mice, such as the total number of peritoneal exudate cells, the percentage and absolute number of macrophages, their cytochemical activity in the spontaneous tetrazolium test and cytochemical capacity, have been studied by comparison with the resistance of the animals to tularemia infection induced by Francisella tularensis, Ga?ski?'s vaccinal strain 15. Of these characteristics, the cytochemical capacity of peritoneal exudate macrophages, i.e. the total cytochemical activity of macrophages contained in a unit of volume, has been the most informative as regards the level of nonspecific resistance to this infection. Other characteristics under study cannot serve as criteria for the evaluation of the nonspecific resistance of the body to F. tularensis.     

Susceptibility of the common hamster (Cricetus cricetus) to Francisella tularensis and its effect on the epizootiology of tularemia in an area where both are endemic

Francisella tularensis is a highly infectious zoonotic agent causing the disease tularemia. The common hamster (Cricetus cricetus) is considered a pest in eastern Europe, and believed to be a source of human tularemia infections. We examined the role of the common hamster in the natural cycle of tularemia using serologic methods on 900 hamsters and real-time polymerase chain reaction (PCR) on 100 hamsters in an endemic agricultural area. We collected 374 Ixodes acuminatus ticks from the hamsters and tested them by real-time PCR. All tests were negative. To examine clinical signs, pathology, and histopathology of acute tularemia infection similar to the natural infection, two hamsters were infected with a large dose of a wild strain of F. tularensis ssp. holarctica. After a short period of apathy, the animals died on the eighth and ninth days postinfection. The pathologic, histopathologic, and immunohistochemical examination contributed to the diagnosis of septicemia in both cases. Our results confirmed previous findings that common hamsters are highly sensitive to F. tularensis. We conclude that although septicemic hamsters may pose substantial risk to humans during tularemia outbreaks, hamsters in interepizootic periods do not act as a main reservoir of F. tularensis.     

Activation of natural tularemia foci of the field-meadow and steppe types on the territory of Tula Province 1977-1978

Natural tularemia foci of the meadow and steppe type are extremely stable and become active in those years when the most favourable living conditions for rodents appear. For the first time during the last 30 years a great increase in the number of common voles, accompanied by widely spread epizooty covering the whole territory of the Tula region, was observed. House mice, common field mice, harvest mice and black rats were also involved in this epizooty and 235 tularemia patients with all clinical forms of the disease were registered, the pulmonary form of the disease being prevalent. The cases of the disease were observed among both urban and rural population. In spite of a high morbidity rate, no cases of group infection were registered in domestic conditions and among agricultural workers due to the existence of the numerous immune layer among the population. The formation of this layer resulted from planned vaccinal prophylaxis covering, on the average, 86.3% of the rural population of the region.     

Phase variations of Francisella tularensis lipopolysaccharide in human infection and immunization

The comparative study of the specificity of antibodies in human sera after tularemia infection and immunization with live tularemia infection was carried out with the use of passive hemagglutination and immunoblotting techniques. The sera of tularemia patients contained two different types of immunoglobulins: strictly specific to the antigenic epitopes of F. tularensis Iipopolysaccharide (LPS) and strictly specific to F. tularensis subsp. novicida LPS. Such phenomenon may be due to phase variations of the antigenic structure of F. tularensis LPS in the body of a slightly susceptible host. The immune sera of vaccinated were found to contain antibodies, strictly specific only to F. tularensis LPS. At the same time in one vaccinee by the presence of pronounced postvaccinal reactions was found sharply defined interaction between serum imunoglobulins and F. tularensis subsp. novicida LPS. As the result, the data on the possibility of the antigenic modification of F. tularensis in tularemia infection in humans were obtained. At the same time antigenic epitopes, characteristic of faintly pathogenic and closely related F. tularensis novicida LPS, appeared in the structure of F. tularensis LPS.     

Effect of land reclamation on the transformation of the types of natural tularemia foci

Land reclamation measures carried out on the territory of a flood-plain-paludal focus of tularemia change the ecological and biocenotic links, which leads to the formation of a meadow-field focus with other-than-before sources and vectors of tularemia infection.     

Administration of a synthetic TLR4 agonist protects mice from pneumonic tularemia

Francisella tularensis is a Gram-negative intracellular pathogen that causes the zoonosis tularemia. Because F. tularensis LPS causes weak TLR4 activation, we hypothesized that administration of a synthetic TLR4 agonist, aminoalkyl glucosaminide phosphate (AGP), would boost the innate immune system and compensate for reduced TLR4 stimulation. Intranasal administration of AGPs induced intrapulmonary production of proinflammatory cytokines and chemokines. Mice treated with AGPs before and after inhalation of Francisella novicida exhibited augmented cytokine and inflammatory responses to infection; reduced bacterial replication in lung, liver, and spleen; and increased survival, whereas all PBS-treated control mice died within 4 days of infection, all AGP-treated mice showed prolonged time-to-death, and 30-60% of AGP-treated mice survived. The protective effect of AGP was lost in mice lacking IFN-gamma. Long-term survivors developed specific Th1 splenocyte responses and specific Abs dominated by IgG2 isotypes. Survivors were fully protected from rechallenge with aerosolized F. novicida. Thus, preventive administration of AGP successfully modulated innate immune responses to aerosolized F. novicida, leading to protective immunity to pneumonic tularemia. This is the first report of the protective effect of a TLR ligand on resistance to F. novicida-induced pneumonic tularemia.     

Occurrence of natural tularemia foci in Kamchatka

The focus of tularemia in the Ust-Kamchatsky region belongs probably to the flood-plain and swamp type with muskrats and tundra voles being the main carriers. In autumn 1980 for the first time three cultures were isolated in this region: 1 from a tundra vole and 2 from muskrats. The presence of antibodies to tularemia antigen in Norway rats was revealed in the passive hemagglutination test.     

Persistence of Francisella tularensis McCoy et Chapin tularemia agent in the organism of highly sensitive rodents after oral infection

In the literature there are no data on the possibility of obtaining in experiment non-fatal tularemia infection (persistence) in rodents highly sensitive to it (Group I) when using highly virulent strains circulating in nature for infection by natural routes. Our detailed experiments on 1483 adult voles Microtus rossiaemeridionalis Ogn. (syn. M. subarvalis Meyer et al.) of laboratory origin using virulent strains of Francisella tularensis holarctica Ols. et Meshch. and natural alimentary infection by feeding on bodies of died animals or forced dosed administration of a mixture of dead and living bacteria to the voles through the oesophagus demonstrated the possibility of the animals to survive tularemia with subsequent long-term chronic carrier state of the infectious agent. They also confirmed the ability of voles to eat readily cadavers of their kin (cannibalism, necrophagia). Experiments with the fully virulent strain 503 and feeding on cadavers were carried out on 439 voles. 203 animals died from acute tularemia, 43 from side effects and 193 survived. Two of the latter (0.5%) exhibited chronic bacterial carrier state, and agglutinins to tularemia microbe (1:320) were found in their blood. From 309 voles subjected to dosed feeding, 153 died from acute tularemia, 27 from side effects and 129 survived. Two of them were bacterial carriers and 6 (1.9%) showed agglutinins (1:160-1:1280). In experiments with strain 165, spontaneously less virulent for guinea pigs, 433 voles were fed on cadavers. 170 of them died from acute tularemia, 53 from side effects, and 210 animals survived. Among the latter, 14 animals (3.2%) were found immune to 100 LD50 of the highly virulent strain 1298. In dosed feeding of 302 voles with the strain 165, 90 animals died from acute tularemia, 59 from side effects, and 153 survived, including 63 animals (20.7%) immune to 100 LD50. The surviving immune voles exhibited seroconversion and long-term persistence of the infectious agent in the internal organs (up to day 257-313--period of observation), accompanied bacteriuria in some cases. Histological examination of the kidney revealed, for the first time, important pathological changes of glomerulonephritis type with elements of pyelonephritis. Protracted stay of the agent in the organism of the vole does not affect its virulence. Persistence of tularemia agent in the organism of voles highly sensitive to tularemia in alimentary administration to them of living and dead bacteria is achieved as a result of anticipatory development of immunological reactions in response to a massive dose of killed antigen, against the background of which the accumulation of simultaneously administered     

Results of the study of bird droppings collected in the Lithuanian SSR for the purpose of searching out tularemia epizootics

There are practically no records of cases of tularemia among humans in the Lithuanian SSR. Nevertheless, the mass sero-allergic survey of the population for tularemia, carried out 10-12 years ago, showed that 2.3% of the adult population in the Republic had had contacts with the causative agent of this infection. The work was aimed at the determination of the present activity of the foci of tularemia. During 6 years in 22 rural districts 2582 samples of avian excrements, containing bones and wool of small animals, were collected and studied by means of the antibody neutralization test (ANT). In 132 (5.1 +/- 0.4%) excrement samples collected on the territory of 12 districts Francisella tularensis antigen was detected. The average ANT titer was 45.2, the maximum titer (10 excrement samples) reached 1: 160. The study revealed the existence of the natural foci of tularemia in Lithuania at present, but their activity proved to be low. The most unfavorable situation was found to exist in western districts of the Republic.     

Schistosoma mansoni: passive transfer of resistance by serum in the vector snail, Biomphalaria glabrata

Passive transfer of natural resistance to Schistosoma mansoni (PR-1 strain) has been successfully accomplished in the snail intermediate host, Biomphalaria glabrata (PR albino, M-line strain). Injection of serum (cell-free hemolymph) from a naturally schistosome-resistant strain of B. glabrata (10-R2) into PR albino snails induced a complete protection from a primary infection with the parasite in 29 of 48 snails (60.4%). In comparison, inoculation of homologous PR albino serum or heterologous proteins (fetal calf serum) had no effect. Moreover, this protection could be induced 24 hr prior to, or 24 hr after, exposure to the parasite, although heating of 10-R2 serum to 70 C for 30 min destroyed its protective ability. When in vitro transformed sporocysts were preincubated in 10-R2 or PR albino serum and then were injected into susceptible snails, a high level of infection (88.5 and 83.3%, respectively) was produced in both groups. Thus, the 10-R2 serum factor does not appear to be mediating specific parasite recognition by host hemocytes. Alternatively, our results suggest that 10-R2 serum possesses a heat-labile factor which specifically activate B. glabrata hemocytes to encapsulate and destroy sporocysts whereas PR albino serum lacks this factor.