Relationship of the flea Citellophilus tesquorum altaicus (Siphonaptera: Ceratophyllidae) with the plague agent

Some aspects of relationships of the flea Citellophilus tesquorum altaicus and bacterium Yersinia pestis of two strains isolated from different parts of the Tuva natural plague focus were studied. Peculiarities of elimination and blood meal activity of fleas infected with two strains of the plague agent were not revealed. Differences in mortality and alimentary activity are considerably determined by the sex of insects. The ability of examined strains to form a proventriculus block was not identical in the strains examined. This ability was expressed higher in the strain I-3428, which originated from the same part of the natural focus as the insectarium flea culture, than in the strain I-3327. During the spring and first half of summer, the proventriculus block appeared more frequently in females. The increasing of the fraction of blocked individuals was observed in both sexes from spring to summer. As for the ability to transmit the plague agent, similar seasonal increasing was noted in males, but in females, the ability to inoculate the plague microbe was always maintained at the same level.     

Experimental study of the infecting ability of the flea Coptopsylla lamellifer rostrata in the Kyzylkum natural focus of plague

Experimental infecting of the fleas Coptopsylla lamellifer rostrata by plague was carried out. The fleas were infected by feeding through biomembrane (skin of a white mouse) with a mixture of defibrinated blood of guinea-pig and plague microbes. Under concentration 2-3 milliard of the microbes in 1 millilitre, from 60 to 100% of the fleas were infected. Forming of the block of proventriculus was observed in 9-13 day. Mean percent of blocking for all experiments was less than 1%. Maximal rate of blocking (2.8%) was observed in the experiment under everyday 3-hour feeding. After planting of the fleas with blocks on great gerbil (2 fleas on one gerbil) 20% of the gerbils were infected. The conclusion had been made that C. lamellifer rostrata has only insignificant effectiveness as a vector of plague agent in Kyzylkum. Probably it is caused by some specific features of this subspecies.     

The epizootiological significance of flea accumulation in aggregations of the female long-tailed suslik in the Tuva plague focus

The formation of aggregations of related females is a peculiarity of the intrapopulational organization of long-tailed suslik that results in the accumulation of Citellophilus tesquorum, the main vector and keeper of the plague microbe in the Tuva plague nidus. The plague agent is adapted to the existence on the territory occupied by aggregations of females that manifests itself in the delay of the beginning and prolixity of block-formation periods in fleas. The transfer of the agent from one place to another takes place only at the high abundance of long-tailed suslik. When the number of the suslik is low the plague microbe circulates in the ranges of one or several neighbouring aggregations of females having no possibility for successful transfer to a new place.     

Host influence on the frequency of block formation in males and females of Citellophilus tesquorum altaicus Ioff, 1936 (Siphonaptera: Ceratophyllidae) and transmission the plague pathogen by these fleas

Data obtained during feeding of Citellophilus tesquorum aitaicus Ioff, 1936 infested females and males (Siphonaptera: Ceratophyllidae), the main vectors of plague in Tuva natural plague locus, on the natural host and laboratory animal was analyzed. It was found that sexual differences in fleas depended on the type of the host. Females fed more actively on the longtailed ground Citellus undulatus than on white mouse. Alimentary activity of males on these animals was similar. Higher mortality of fed females and males was noted during feeding on mice. Frequency of formation of the "block" and transmission of the pathogen in males was higher during bloodsucking on the ground squirrel; in females, during feeding on mice. Thus, differences in the transmission of the plague pathogen, revealed in laboratory on white mice, can be quite different in nature. So, extrapolation of experimental data on natural processes of interrelations between plague pathogen and ectoparasites must be performed taking into account revealed peculiarities.     

The influence of the host on the frequency of block formation in males and females of Citellophilus tesquorum altaicus Ioff, 1936 (Siphonaptera: Ceratophyllidae) and transmission of the plague pathogen by these fleas

Data obtained during feeding of infested females and males of Citellophilus tesquorum altaicus Ioff, 1936 (Siphonaptera: Ceratophyllidae), the main vector of plague in Tuva natural plague focus, on the natural hosts and on laboratory animals were analyzed. Sexual differences in fleas were found to depend on the host. Females fed more actively on longtailed ground squirrels Spermophilus undulatus than on white mice. The feeding activity of males on the two hosts did not differ. A higher mortality of infested females and males was observed during feeding on mice. The frequency of block formation and pathogen transmission in males was higher during bloodsucking on the ground squirrel; in females, during feeding on mice. Thus, sex-related differences in the plague pathogen transmission revealed in laboratory white mice may be not the same in nature. This should be taken into account when extrapolating the experimental data on the natural relations between the plague pathogen and ectoparasites.     

Paradoxopsyllus scorodumovi (Aphaniptera) flea, an effective vector of plague in a Gorno-Altai natural focus

A study was conducted on the fleas of P. scorodumovi and five local strains of the plague microbe, one of which is typical of the strains of the Altai subspecies and four are non-typical of this nidus. The fleas of this species are capable to transmit not only the plague agent of the strains typical of this nidus but also non-typical ones which differ in some biological properties and are avirulent for most carriers but Pallas's pika. Biological peculiarities of fleas of P. scorodumovi in addition to their high efficiency as vectors of the plague microbe enable us to associate the more active autumn epizooty with fleas of this species.     

The epizootiological role of the population organization of the stock of fleas on the long-tailed suslik in a natural focus of plague in Tuva

Spatial location of epizootic events in the Tuva plague focus is determined at a considerable degree by the population structure of the flea Citellophilus tesquorum--the main plague microbe vector. Within the enzootic territory occupied by five populations of the long-tailed ground squirrel (Citellus undulatus) there are six populations of C. tesquorum. Each population of fleas has a corresponding autonomic plague focus. Various conditions for the microbe life activity in these populations are recovered. The circulation of the microbe is closely connected with certain intrapopulation groupings of fleas--the nuclei of populations.     

Seasonal dynamics of epizootic process of the plague agent <Emphasis Type="Italic">Yersinia pestis</Emphasis> transmission to the long-tailed suslik <Emphasis Type="Italic">Citellus undulatus</Emphasis> by the flea <Emphasis Type="Italic">Citellophilus tesquorum</Emphasis> in Tuva

Transmission of Yersinia pestis to the long-tailed suslik (Citellus undulatus) by fleas (Citellophilus tesquorum) in the Tuva natural plague focus in different seasons (spring, summer, and autumn) was studied experimentally. Between feeding periods, insects were kept in an artificial nest under temperature and humidity closely corresponding to seasonal ones. The character of the agent transmission was estimated according to the fraction of fleas with the agent in the aggregated state (bacterial lumps, partial blocks of proventriculus), the fraction of blocked individuals, and the fraction of infected susliks and of those with the generalized form of infection. Seasonal dynamics of epizootic process of the Y. pestis transmission corresponded to the results obtained in the epizootic examination of the Tuva natural plague focus and reflected the dynamics of the epizootic process (increase-peak-decline). The activity of the formation of a proventriculus block in C. t. altaicus, the infection ability of the fleas, and the sensitivity of long-tailed Siberian susliks to Y. pestis were the highest in mid-summer (July-first ten days of August), during the period of epizooty activation in the focus. The maximal number of C. t. altaicus with the plague agent at the aggregated state was observed in the cold period, before wintering of insects and after their hibernation.     

Epizootological role of fleas in the Gorno-Altai natural plague focus (a review)

Epizootological role of fleas in the Gorno-Altai natural plague focus (Sailugemsk focus) and numerous data on the flea viability are analyzed and generalized. Information concerning the flea natural infectivity with Yersinia pestis altaica is represented. Ecological peculiarities of some flea species parasitizing the main host, Mongolian pika Ochotona pallasi, and nature of their interrelations with Y. pestis are investigated. It is shown that the flea taxocenosis provides the permanent all year-round circulation of Y. pestis in the Gorno-Altai natural focus. Certain combinations of structural elements of the flea taxocenosis have a dominant significance in determination the circulation process at different phases of the annual epizootic cycle.     

The population variability of Yersinia pestis in soil samples from the natural focus of plague

Three Y. pestis strains were found to exist in the experimental soil ecosystem at a temperature of 4 degrees - 8 degrees C for a longer period (10 months, the term of observation) than at room temperature (3.5 months). Y. pestis population structure was characterized by relative stability in strains of the subspecies altaica and heterogeneity in the strain of the main subspecies, manifested by the loss of the pgm locus by vegetative cells and the preservation of pgm+ variants in the latent (uncultivable) form (LF). In the populations of all strains uniformity in calcium dependence, the tendency towards a decrease in the synthesis of factor 1, nutritional requirements in amino acids was observed. An important factor of the preservation of Y. pestis in the soil was LF formation. At room temperature this process quickly resulted in the death of the population. At 4 degrees - 8 degrees C A. pestis altaica avirulent strain could be inoculated onto solid nutrient media for a two-fold longer period (for 4 month) than the strain with selective virulence and for 5.5 months longer than Y. pestis pestis highly virulent strain.     

Epizootiological importance of Frontopsylla hetera (Siphonaptera) fleas in the Gorno-Altai natural plague focus

Experiments conducted during all seasons have established that F. hetera, one of the mass species of fleas in Mountain Altai, can be infected both by the strain of selective virulence typical to this nidus and by the non-typical non-virulent mountain-altai strain of plague agent. The non-virulent strain does not form in fleas the block of proventriculus and within 1.5-2 months they become free from the microbe. At the infection with the typical strain of the altai subspecies rare transmissions of the agent to Pallas' pika can take place as well as its long preservation in fleas.     

Enhanced blocking capacity of the plague microbe in the body of the flea

During the stay of plague microbe in the organism of flea, under the effect of bactericidal factor increases its ability to form the block of proventriculus in these insects. Thus, in fleas infected on white mice, which were infected in a natural way through blocked individuals, the block of proventriculus appears 2 to 3 times as often (59.5 and 34.0%) as in insects (15.02%) infected on animals, which were infected artificially.     

Analysis of complete sequence of cryptic plasmid pTP33 from <Emphasis Type="Italic">Yersinia pestis</Emphasis> isolated in Tuva natural focus of plague

This paper studies a full nucleotide sequence of cryptic plasmid pTP33, which was isolated from the typical plague strain of the Tuvinian natural focus, Yersinia pestis I-2638. Sequencing was carried out using the 454 GS Junior platform (Roche). In analysis using the software package GS De Novo Assembler v. 2.7 (Roche) and the algorithm Newbler v. 2.7, 1855 nucleotide reads, which contained 1101246 nucleotides, were assembled to a contig of 33 978 bp. The GC content of the obtained nucleotide sequence was 50.25%. During annotation, we found 56 open reading frames. Homologs of the predicted reading frames were sought in the BLAST databases. We detected 22 reading frames coding hypothetical proteins, 23 frames coding phagerelated proteins, and 11 frames coding proteins with known functions, including toxin–antitoxin system YefM-YoeB, nucleic acids and polysaccharides metabolism proteins (exopolysaccharide production protein ExoZ, exodeoxyribonuclease VIII), and replication proteins (ParA). Some predicted pTP33 proteins were found to be homologs (from 45 to 75%) with sequences of phage-related proteins of certain microorganisms—endosymbionts of insects (Sodalis glossinidius) and endosymbionts of entomopathogenic nematodes (Photorhabdus luminescens, P. asymbiotica, Xenorhabdus bovienii).     

The ability of flea species on the common vole from mountainous Dagestan to transmit and preserve the causative agent of plague

The infection ability and terms of preservation of plague microbe in fleas of common vole from Dagestan high-mountain plague focus (Frontopsylla causasica, Megabothris turbidus, Ctenophthalmus intermedius and Amphipsylla rossica) was studied experimentally. Block formation and transmission of the infection by F. caucasica and M. turbidus was observed. The transmission of plague microbe by Ct. intermedius fleas was first carried out. These species of fleas preserve the infection for a long time. Experiments with fleas of A. rossica yielded negative results.     

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.     

The Ability of the Fleas Citellophilus tesquorum and Frontopsylla luculenta luculenta (Siphonaptera,Ceratophyllidae) to Survive Below-Zero Temperatures during Winter

Entomological Review - This comparative study addresses survivorship of the fleas Citellophilus tesquorum and Frontopsylla luculenta from five natural populations in Siberia at below-zero...     

Several principles for epidemiologic evaluation of individual regions of the Trans-Caucasian plains-piedmont natural focus of plague]

The authors analyse many-year data concerning the epizootological study of seven landscape-geographical regions of the Eastern Transcaucasus differing by natural conditions and the enzootic intensity. Quantitative assessment of natural nidality determined by the level (norm) of many-year indices calculated for the years of 1955--1974 are presented for each region. Flea vectors were more numerous in localities of stable enzootic manifestation; also the numbers of Meriones erythrourus (carrier rodent) was more stable than in the regions of temporary occurrence of the causative agent and those free of plague. Many-year level of the flea (X. conformis) abundance index equal to one served as the threshold value determining the territory enzooticity.     

Dispersal of the flea Ctenophyllus hirticrus and spreading of plague epizooties in Gorny Altai

Gradual dispersion of an abundant flea species Ctenophyllus hirticrus specific to the Pallas's pika (the main plague carrier), is revealed in the Gorno-Altai natural plague focus on the territory, occupied by two populations of this lagomorph. Spreading of Yersinia pestis in these areas took place a short time later the rise of this ectoparasite's abundance. It is supposed that the colonization of these areas by C. hirticrus was one of the factors determined epizooties spreading within the focus and formation of new sites of stable Y. pestis preservation.