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.     

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.     

Block formation capacity in fleas infected with a plague agent after their feeding with blood substitutes

By feeding plague infected Xenopsylla cheopis fleas with blood substitutes free of blood formed elements blocked fleas were obtained. These fleas are able to transmit plague agent to white mice and cause their mortality.     

Level of parasitic contact in colonies of the little suslik in the semideserts of western Kazakhstan

Field experiments were conducted during the settling of young animals of Citellus pygmaeus in four areas 4 to 13.6 hectares in size. From 3 to 6 animals were caught in each area and labeled by administering radioactive substance (0.5 micrograms of glycine 14C or methionine 35S) and colouring hair on the head. In a day or two labeled sousliks were caught again and in 6-7 days a total catching of animals and collection of ectoparasites from their hair and burrows done. In al, 942 sousliks were caught in the experimental areas and 2624 specimens of fleas of different species and 2305 ticks of R. schulzei collected. The average number of fleas which were labeled on one little souslik for a day was 0.1 to 2.3. The number of labeled fleas in the above areas coincided with the number of fleas infected with plague in the areas of epizootia. The level of parasitic contact in settlements of little souslik cannot provide the development of plague epizootia by transmission of the agent through fleas.     

Efficiency of Neopsylla abagaitui fleas as plague vectors in Transbaikalia

Experiments have shown that the block of proventriculus develops in 1.1 to 1.5% of individuals of the flea Neopsylla abagaitui infected with plague microbe. These insects transmit the agent during bloodsucking to different plague carriers (Citellus dauricus, C. undulatus, Meriones unguiculatus, Microtus gregalis). The plague microbe is preserved in fleas for 65 days (the observation period).     

锡林郭勒草原布氏田鼠体蚤和巢蚤数量动态及蚤类群落演替

1989～1998年对内蒙古阿巴嘎旗那仁宝力格苏木布氏田鼠Microtus brandti体蚤和巢蚤的数量进行了调查和分析,所得体蚤包括3科7属9种, 其中优势种有: 原双蚤田野亚种Amphipsylla primaris mitis占41.84%, 近代新蚤东方亚种Neopsylla pleskei orientalis占41.18%, 光亮额蚤Frontopsylla luculenta占13.18%。所得巢蚤包括2科6属9种, 其中优势种近代新蚤占74.94%; 光亮额蚤占10.04%, 原双蚤占8.20%, 宽圆纤蚤Rhadinopsylla rothschildi占6.44%, 是常见种。田鼠体的原双蚤、近代新蚤、光亮额蚤和体蚤指数间呈正相关(P<0.05)。田鼠巢的近代新蚤、光亮额蚤、宽圆纤蚤和巢蚤指数间正相关显著(P<0.01)。春季巢蚤指数∶春季体蚤指数≈5∶1, 秋季巢蚤指数∶秋季体蚤指数≈75∶1。近代新蚤既是体型蚤又是巢型蚤, 为田鼠的优势蚤种; 原双蚤数量占体蚤的 41.84%, 是体型蚤; 光亮额蚤为体蚤和巢蚤中的常见种。     

A case of experimental transmission of the causative agent of plague from Ornithodoros tartakovskyi ticks to fleas of the great gerbil

Biological interrelations between ectoparasites from the colonies of great gerbil were studied experimentally. Hungry fleas Coptopsylla lamellifer are able to feed on the ticks Ornithodoros tartakovskyi infected with plague and in so doing be infected with plague agent. Such feeding is identified as "heterovampirism".     

Uniquely insidious: Yersinia pestis biofilms

Bubonic plague, one of history's deadliest infections, is transmitted by fleas infected with Yersinia pestis. The bacteria can starve fleas by blocking their digestive tracts, which stimulates the insects to bite repeatedly and thereby infect new hosts. Direct examination of infected fleas, aided by in vitro studies and experiments with the nematode Caenorhabditis elegans, have established that Y. pestis forms a biofilm in the insect. The extracellular matrix of the biofilm seems to contain a homopolymer of N-acetyl-d-glucosamine, which is a constituent of many bacterial biofilms. A regulatory mechanism involved in Y. pestis biofilm formation, cyclic-di-GMP signaling, is also widespread in bacteria; yet only Y. pestis forms biofilms in fleas. Here, the historical background of bubonic plague is briefly described and recent studies investigating the mechanisms by which these unique and deadly biofilms are formed are discussed.     

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.     

The experimental action of lindane on the vector capacity of plague-infected fleas]

Being fed on white mice, intoxicated with subtoxic doses of lindane, blocked fleas sharply decreased in number. The inhibition of the vector ability of fleas, infected with plague, under the systemic effect of lindane is shown.     

Pathogenic action of the plague microbe on the flea Xenopsylla cheopis and the ultrastructure of the causative agent at various times of its stay in the vector

Pathology of gastro-intestinal tract of Xenopsylla cheopis fleas infected with plague microbe was determined by means of electron microscopy. Ultrastructure of plague microbe during different periods of its stay in the vector was studied.     

Horizontal transmission of Rickettsia felis between cat fleas, Ctenocephalides felis

Rickettsia felis is a rickettsial pathogen primarily associated with the cat flea, Ctenocephalides felis. Although laboratory studies have confirmed that R. felis is maintained by transstadial and transovarial transmission in C. felis, distinct mechanisms of horizontal transmission of R. felis among cat fleas are undefined. Based on the inefficient vertical transmission of R. felis by cat fleas and the detection of R. felis in a variety of haematophagous arthropods, we hypothesize that R. felis is horizontally transmitted between cat fleas. Towards testing this hypothesis, flea transmission of R. felis via a bloodmeal was assessed weekly for 4 weeks. Rhodamine B was used to distinguish uninfected recipient and R. felis-infected donor fleas in a rickettsial horizontal transmission bioassay, and quantitative real-time PCR assay was used to measure transmission frequency; immunofluorescence assay also confirmed transmission. Female fleas acquired R. felis infection more readily than male fleas after feeding on a R. felis-infected bloodmeal for 24 h (69.3% and 43.3%, respectively) and both Rickettsia-uninfected recipient male and female fleas became infected with R. felis after cofeeding with R. felis-infected donor fleas (3.3-40.0%). Distinct bioassays were developed to further determine that R. felis was transmitted from R. felis-infected to uninfected fleas during cofeeding and copulation. Vertical transmission of R. felis by infected fleas was not demonstrated in this study. The demonstration of horizontal transmission of R. felis between cat fleas has broad implications for the ecology of R. felis rickettsiosis.     

Changes in Flea (Siphonaptera) Vector Activity in the Siberian Natural Plague Foci

Comparative analysis of vector activity of fleas in the Siberian natural plague foci was carried out during two long-term periods of experimental studies: 1967–1980 and 1983–2007. The data on block formation frequency in adult fleas infected with Yersinia pestis were analyzed for 127 experiments with 15 flea species and subspecies. The vector activity of fleas in all the Siberian plague foci (Altai, Tuva, and Transbaikalia) has increased over a rather short time period of 30–40 years. The frequencies of flea blocking were significantly different (P < 0.001) between the analyzed periods in all the three plague foci.

     

中国云南部分人间鼠疫流行区蚤类区系调查(英文)

归纳了中国云南 13个人间鼠疫流行区的调查资料 ,对调查疫区的蚤类区系进行了研究。总计捕获12 0 77只小兽 ,隶属啮齿目、食虫目及攀目 3个目中的 9科、2 9属、4 7种。从小兽体表共采获 9369只蚤 ,经分类鉴定 ,隶属 5科、18属、33种。 33种蚤及 4 7种小兽宿主均按其分类阶元详细列于文末。结果表明 ,山区蚤及小兽宿主的种数明显多于坝区。坝区农耕地的优势种相对简单 ,优势种地位突出 ,黄胸鼠及印鼠客蚤分别是最重要的宿主及蚤种 (构成比分别为 83 2 7%和 75 32 % )。山区的优势种相对较复杂 ,优势种的种类较多 ,但其构成比较低 ( 10 96%～ 4 7 95% )。黄胸鼠及绒鼠为山区地带的两种优势宿主 ,缓慢细蚤、端凹栉眼蚤、印鼠客蚤、偏远古蚤及短突栉眼蚤为山区地带的 5种优势蚤种。多数蚤种可寄生两种以上的小兽宿主 ,但其所寄生的主要宿主并不多。结果提示 ,作为疫区主要媒介的印鼠客蚤及其所对应的主要寄生宿主 (黄胸鼠 )在坝区突出的优势种地位 ,似可解释近年疫区的鼠疫病人主要出现在坝区的原因     

The plague

The plague has been one of the most devastating diseases of human history. Despite major advances in diagnosis, prevention, and treatment, it has not been possible to eradicate this infection. Plague is still active in Africa, in Asia and in the Americas, and is classified as a currently re-emerging disease. The plague is mainly a disease of rodents, which is transmitted by fleabites. Humans develop two main clinical forms: bubonic plague (following bites of infected fleas, lethal in 50-70% of the cases in less than a week if an appropriate treatment is not started rapidly), and pneumonic plague (after inhalation of infected droplets, lethal in less than three days in 100% of cases without immediate treatment). Y. pestis, the causative agent of plague, is usually sensitive to most antibiotics, but the first multi-resistant strain was recently described. No efficient and safe vaccines are currently available. The plague bacillus is one of the few organisms that could be used for biological warfare.     

中国云南人间鼠疫流行区蚤类宿主特异性及宿主选择(英文)

应用生态学中的生态位宽度及生态位重叠研究方法,对中国云南人间鼠疫流行区１１种蚤的宿主特异性及宿主选择进行了研究。宿主特异性用Ｌｅｖｉｎｓ生态位宽度进行测定。宿主选择用夹角余弦生态位重叠进行测定。结果表明：长形病蚤普洱亚种及印鼠客蚤的生态位宽度最窄、宿主特异性最高,近端远棒蚤二刺亚种及斯氏新蚤滇川亚种的生态位最宽、宿主特异性最低。印鼠客蚤（云南人间鼠疫流行区的主要鼠疫媒介）的优势宿主是黄胸鼠。印鼠客蚤较高的宿主特异性意味着该蚤可能主要在其优势宿主的不同个体间保存或传播鼠疫病原体。短突栉眼蚤及端凹栉眼蚤在宿主选择上较接近,而其它蚤种在宿主选择上差异较大。     

Characteristics of the multiplication of a virulent strain of the plague microbe in Xenopsylla cheopis fleas infected parenterally

Xenopsylla cheopis fleas infected parenterally with the virulent strain of plague microbe of gerbil variant preserved the agent to the end of their lives. In the body cavity the microbes retained their ability for reproduction which was, however, limited. During the first seven days after the infection the number of microbes slightly increased and later became stabilized. Its mean indices (mean g) varied within the limits of 500 to 2000 microbe cells per 1 individual, maximum index rarely exceeded 30 000 microbe cells. Parenteral infection with plague agent did not affect essentially the longevity of fleas.     

Possible vector dissemination by swift foxes following a plague epizootic in black-tailed prairie dogs in northwestern Texas

To determine whether swift foxes (Vulpes velox) could facilitate transmission of Yersinia pestis to uninfected black-tailed prairie dog (Cynomys ludovicianus) colonies by acquiring infected fleas, ectoparasite and serologic samples were collected from swift foxes living adjacent to prairie dog towns during a 2004 plague epizootic in northwestern Texas, USA. A previous study (1999-2001) indicated that these swift foxes were infested almost exclusively with the flea Pulex irritans. Black-tailed prairie dogs examined from the study area harbored only Pulex simulans and Oropsylla hirsuta. Although P. irritans was most common, P. simulans and O. hirsuta were collected from six swift foxes and a single coyote (Canis latrans) following the plague epizootic. Thus, both of these canids could act as transport hosts (at least temporarily) of prairie dog fleas following the loss of their normal hosts during a plague die-off. All six adult swift foxes tested positive for antibodies to Y. pestis. All 107 fleas from swift foxes tested negative for Y. pestis by mouse inoculation. Although swift foxes could potentially carry Y. pestis to un-infected prairie dog colonies, we believe they play only a minor role in plague epidemiology, considering that they harbored just a few uninfected prairie dog fleas (P. simulans and O. hirsuta).     

Yersinia pestis infection and laboratory conditions alter flea-associated bacterial communities

We collected Oropsylla montana from rock squirrels, Spermophilus varigatus, and infected a subset of collected fleas with Yersinia pestis, the etiological agent of plague. We used bar-tagged DNA pyrosequencing to characterize bacterial communities of wild, uninfected controls and infected fleas. Bacterial communities within Y. pestis-infected fleas were substantially more similar to one another than communities within wild or control fleas, suggesting that infection alters the bacterial community in a directed manner such that specific bacterial lineages are severely reduced in abundance or entirely eliminated from the community. Laboratory conditions also significantly altered flea-associated bacterial communities relative to wild communities, but much less so than Y. pestis infection. The abundance of Firmicutes decreased considerably in infected fleas, and Bacteroidetes were almost completely eliminated from both the control and infected fleas. Bartonella and Wolbachia were unaffected or responded positively to Y. pestis infection.     

云南省玉龙鼠疫疫源地野外鼠形动物寄生蚤丰盛度影响因素分析

【目的】分析云南省玉龙鼠疫疫源地野外鼠形动物寄生蚤丰盛度的影响因素。【方法】选取云南省玉龙鼠疫疫源地3个海拔区域,按4个季节进行野外捕鼠,捕获的鼠形动物用梳检法收集体表寄生蚤并在显微镜下分类鉴定。通过实际测量和实地观察相结合的方式收集潜在影响鼠形动物寄生蚤丰盛度的因素包括鼠形动物特征变量指标(如种类、年龄、性别、体长、体重)、环境和气象因子(如海拔、季节)等数据。采用EpiData 3.02软件建立数据库,在R软件下使用跨栏负二项分布回归分析鼠形动物寄生蚤丰盛度的影响因素。【结果】从捕获的884只鼠形动物中检获寄生蚤9种484头,以特新蚤指名亚种、方叶栉眼蚤、无值大锥蚤、云南栉眼蚤为主(86.16%)。回归分析显示： 2 700-3 000 m和3 000 m以上海拔鼠形动物染蚤概率较2 400-2 700 m分别增加1.27和3.72倍;湿度高于70%时,鼠形动物染蚤概率较湿度≤70%时减少41%;与齐氏姬鼠的染蚤概率相比,中华姬鼠的染蚤概率降低50%,大绒鼠的染蚤概率增加79%;体长超过104 mm的鼠形动物染蚤概率较体长≤104 mm的鼠形动物染蚤概率增加76%;气温高于15℃时,鼠形动物染蚤数量较温度≤15℃时降低67%;成年鼠形动物的染蚤数量较未成年鼠形动物的染蚤数量增加2.25倍;与春季相比,夏季的染蚤数量增加2.00倍,秋季的染蚤概率减少48%,冬季的染蚤概率和染蚤数量分别增加1.44和1.06倍。【结论】玉龙鼠疫疫源地野外鼠形动物寄生蚤以特新蚤指名亚种、方叶栉眼蚤、无值大锥蚤、云南栉眼蚤为优势蚤种。鼠形动物寄生蚤丰盛度与海拔、季节、气温、湿度等环境气象因子及鼠形动物种类、体长、年龄等鼠形动物特征变量密切相关。