[Differences between two populations of Citellophilus tesquorum altaicus from the Tuva natural focus of plague]

Citellophilus tesquorum altaicus fleas from two natural (Karginsky and Barlyksky) populations have been studied. There are differences between the fleas of these populations in susceptibility to plague microbe. The adaptability and abundance of the causative organism in the body are higher in the fleas of the Barlyksky population. The sizes of the head are significantly higher in the females of the Karginsky population. There are no differences in this index between males. According to all 5 studies signs of chaetotaxia, the chaeta abundance is greater in both females and males of the Karginsky population. The fluctuating asymmetry is higher in the Barlyksky fleas that are more susceptible to the studied type of the causative agent of plague.

Plague and contagionism in eighteenth-century England: the role of Richard Mead

An epidemic of plague in Marseilles in 1720 and the fear that it would spread to England led to the passing of a new quarantine act. First, however, the government sought medical advice from Dr. Richard Mead (1673-1754), which took the form of A Short Discourse Concerning Pestilential Contagion, and the Methods to Be Used to Prevent It. This tract was a contribution to the contagion concept of disease at a time when it had not yet become part of the medical mainstream as an explanation for certain epidemic diseases. Critical works appeared almost immediately attacking Mead's ideas. The Short Discourse went through nine editions, the last in 1744. In the last two editions there are further elaborations of his earlier views and references to Newton's Optics and the ether theory. Some of Mead's practical recommendations for dealing with the plague, should it enter the country, were relatively new. References to his plague tract appeared in a number of medical and nonmedical works well beyond his lifetime.

[Influence of a temperature factor on the vector capacity of the flea Citellophilus tesquorum altaicus]

The impact of temperatures (2-3 to 23-25 degrees C) of flea keeping on their vector capacity was studied in the experiment. In hibernated fleas, the relationship of their vector capacity to the temperature of their keeping, estimated by the level of plague block in species and by the case rates of animals was insignificant, i.e. there is a trend for these indices to increase with elevated temperatures. In the fleas of current years breeding, the rate of block significantly increased with a rise of temperatures from 5-6 to 23-25 degrees C. There were also increases in the number of transmissions of a plague pathogen to susliks and in the number of animals with generalized infection with a rise in temperature up to 16-18 degrees C. The findings and constructed regression equations may predict the pattern of changes in the vector capacity of the flea C. tesquorum altaicus in the study range of temperatures in the enzootic area of a Tuva natural focus of plague.

[Study on vector ability of Nosopsyllus wualis leizhouensis in the transmission of plague]

OBJECTIVE

To find out the vector ability and function of Nosopsyllus wualis leizhouensis in the transmitting plague.

METHODS

In T: 19 degrees C +/- 1 degrees C, RH: 85% +/- 5%, data regarding the vector ability as cluster spreading, single flea spreading, single flea transmitting plague to single animal, formative bacterial embolus and infection fleas life-span through experiments was gathered.

RESULTS

The rate of infection on fleas was 94.64%, with 100% transmission rate of colony to spread, and 30% from single flea spreading to single animal. In the experiment of single flea transmission, all of the 388 rattus loseas were bitten by the fleas with bacterial, but only 9 animals were characteristically infected with the transmission potential, vector efficiency, survival potential of embolus, vector index as 0.360, 0.257, 0.868 and 0.223 respectively. The mean survive days of infected flea feed with blood were 17.58 (1 - 58), and the mean survive days of hunger infected flea were 7.25 (1 - 16). Formative bacterial embolus days were 8.80 (2 - 16) and the rate of embolus flea was 78.12%.

CONCLUSION

Nosopsyllus wualis leizhouensis could serve as vector and important in the mode of plague transmittion.

Detection of novel Bartonella strains and Yersinia pestis in prairie dogs and their fleas (Siphonaptera: Ceratophyllidae and Pulicidae) using multiplex polymerase chain reaction

We developed a multiplex polymerase chain reaction (PCR) assay that simultaneously detects three types of flea-associated microorganisms. Targets for the assay were sequences encoding portions of the gltA, a 17-kDa antigen, and pla genes of Bartonella spp. Strong et al., Rickettsia spp. da Rocha-Lima, and Yersinia pestis Yersin, respectively. A total of 260 flea samples containing bloodmeal remnants were analyzed from fleas collected from abandoned prairie dog (Cynomys ludovicianus) burrows at the site of an active plague epizootic in Jefferson County, CO. Results indicated that 34 (13.1%) fleas were positive for Bartonella spp., 0 (0%) were positive for Rickettsia spp., and 120 (46.2%) were positive for Y. pestis. Twenty-three (8.8%) of these fleas were coinfected with Bartonella spp. and Y. pestis. A second group of 295 bloodmeal-containing fleas was collected and analyzed from abandoned burrows in Logan County, CO, where a prairie dog die-off had occurred 2-4 mo before the time of sampling. Of these 295 fleas, 7 (2.4%) were positive for Bartonella spp., 0 (0%) were positive for Rickettsia spp., and 46 (15.6%) were positive for Y. pestis. Coinfections were not observed in fleas from the Logan County epizootic site. The multiplex PCR also was used to identify Y. pestis and Bartonella in prairie dog blood and tissues. This report represents the first identification of Bartonella from prairie dogs and their fleas. Prairie dog fleas were tested with PCR, and the Bartonella PCR amplicons produced were sequenced and found to be closely related to similar sequences amplified from Bartonella that had been isolated from prairie dog blood samples. Phylogenetic analyses indicate that the sequences of bartonellae from prairie dogs and prairie dog fleas cluster tightly within a clade that is distinct from those containing other known Bartonella genotypes.

[Factors of Yersinia pestis providing circulation and persistence of plague pathogen in ecosystems of natural foci. Communication 2]

To maintain continuous circulation of plague pathogen in natural foci, the pathogen should be capable of invading host organism, resisting the bactericide protective systems of rodent, and reproducing itself to maintain the content of bacteria at a level sufficient for further transmission by fleas to a new host. Each of these stages of the Yersinia pestis circulation is determined by a variety of factors of plague pathogen, which may act either individually or in combination. Each of the factors itself may be involved in the pathological process at different stages of its development or in pathogen transmission. However, it is only the aggregate of the factors (regardless of significant or insignificant individual contribution to the sum effect) that provides persistence of plague pathogen in natural foci. The plague pathogen factors providing its transmission from one host organism to the next as well as correlation of individual factors of pathogensis and expression of various household genes with plague pathogensis virulence are considered in the second communication. This review was compiled on the basis of not only well-known works but also some sources of limited availability, particularly, for English-speaking audience.

The highly rearranged mitochondrial genome of the plague thrips, Thrips imaginis (Insecta: Thysanoptera): convergence of two novel gene boundaries and an extraordinary arrangement of rRNA genes

To help understand the mechanisms of gene rearrangement in the mitochondrial (mt) genomes of hemipteroid insects, we sequenced the mt genome of the plague thrips, Thrips imaginis (Thysanoptera). This genome is circular, 15,407 bp long, and has many unusual features, including (1) rRNA genes inverted and distant from one another, (2) an extra gene for tRNA-Ser, (3) a tRNA-Val lacking a D-arm, (4) two pseudo-tRNA genes, (5) duplicate control regions, and (6) translocations and/or inversions of 24 of the 37 genes. The mechanism of rRNA gene transcription in T. imaginis may be different from that of other arthropods since the two rRNA genes have inverted and are distant from one another. Further, the rRNA genes are not adjacent or even close to either of the two control regions. Tandem duplication and deletion is a plausible model for the evolution of duplicate control regions and for the gene translocations, but intramitochondrial recombination may account for the gene inversions in T. imaginis. All the 18 genes between control regions #1 and #2 have translocated and/or inverted, whereas only six of the 20 genes outside this region have translocated and/or inverted. Moreover, the extra tRNA gene and the two pseudo-tRNA genes are either in this region or immediately adjacent to one of the control regions. These observations suggest that tandem duplication and deletion may be facilitated by the duplicate control regions and may have occurred a number of times in the lineage leading to T. imaginis. T. imaginis shares two novel gene boundaries with a lepidopsocid species from another order of hemipteroid insects, the Psocoptera. The evidence available suggests that these shared gene boundaries evolved by convergence and thus are not informative for the interordinal phylogeny of hemipteroid insects. We discuss the potential of hemipteroid insects as a model system for studies of the evolution of animal mt genomes and outline some fundamental questions that may be addressed with this system.

Transmission of Yersinia pestis cultures with different plasmid content from Xenopsylla cheopis to Calomys callosus

Most Brazilian Yersinia pestis isolates display a typical plasmid profile composed of the three classical plasmids: pYV, pPst and pFra. However, some cultures lack at least one of these plasmids, while a few of them harbour atypical DNA bands of molecular weight ranging from 147 to 11.5 kb. To investigate whether Y. pestis displaying atypical plasmid content could be propagated among rodents in nature through flea bites, we carried out studies with fleas ( Xenopsylla cheopis) and rodents ( Calomys callosus) reared in the laboratory and five Y. pestis cultures differing in plasmid content. The results suggest that: (1) the single presence of pYV is not sufficient for the transmission of Y. pestis by fleas, (2) pPst is not essential for transmission, (3) two atypical DNA bands of molecular weight of 30 kb and >90 kb have no biological role, and (4) pFra is required for the transmission of Y. pestis by flea bites. Other studies are needed to determine whether this plasmid alone is sufficient for transmission.

[Yersinia pestis as a dangerous biological weapon]

Plague is an infectious disease caused by the Yersinia pestis microorganism, which is transmitted to the human host from a natural reservoir (different rodent species) by a flea bite. Plague is still encountered in humans in the areas of its enzootic prevalence in local rodent populations. Infection by flea bite results in a bubonic or septicemic plague, possibly complicated by secondary pneumonia. The person with pneumonic symptoms may be a source of a droplet-borne inhalatory infection for other people who consequently develop primary pneumonic plague. Despite a clinical form, plague is a severe infection characterized by a short incubation period, rapid onset and quick progress with mortality exceeding 50% if not treated properly. The pneumonic plague is associated with a particularly rapid progress and the mortality rate of almost 100% if not treated properly. As Yersinia pestis can be easily obtained and cultured and is highly pathogenic for humans, it poses a serious threat of being used for bioterrorism purposes. Artificially created aerosol containing plague bacilli can cause numerous and almost simultaneous cases of primary pulmonic plague in an exposed population. Persons exposed would most likely develop severe pneumonia with rapidly progressing respiratory and circulatory failure. The use of the Yersinia pestis strains resistant to antibiotics typically applied cannot be excluded.

[Plague control in Madagascar: evaluation of the efficacy of Kartman baitboxes in urban areas]

A method associating an anticoagulant rodenticide and an insecticide called Kartman bait-box aimed both at fighting reservoir and vectors of plague. It was evaluated in two neighbourhoods of Antananarivo (Madagascar) from October 2002 to May 2003. It involved the local community in the control. The study was carried out in Ambodirano-Ampefiloha refered as treated neighbourhood in which the Kartman bait box were laid out with an anticoagulant rodenticide and an insecticide with a rapid action versus a "pilot neighbourhood", Ankorondrano-Andranomahery in which the boxes were provided with non poisoning bait and non insecticidal white powder. The rodenticide used was Baraki (difethialone 25 ppm) and the insecticide was a powder of Propoxur 3%. The evaluation of effectiveness of this method was based on the four following parameters: (1) the number of dead rats collected daily inside and in the vicinity of the houses, (2) the daily number of baits non consumed in the Kartman bait box, (3) the cheopis index of the rats trapped using the BTS trap, and (4) the flea carrier index of the rats captured monthly with BTS trap. The cheopis index and the flea carrier index of the rats were calculated monthly. The number of rats that died in the treated neighbourhood was of 968 versus 3 in the pilot neighbourhood. The other parameters reached a stable level after 3 months. Between days 120 and 180, the mean number of unconsumed baits was 2.79 in the treated neighbourhood versus 0.14 in the pilot neighbourhood, the flea carriage (percentage of parasitized hosts) was 0% versus 61% in the pilot neighbourhood, and the cheopis index was 0.0 versus 5.0 in the pilot neighbourhood. This study demonstrates that Kartman bait-boxes reached the rat borne and the vectors of plague found in urban area. We propose to use this method extensively both during epidemic and inter-epidemic contexts.

Plague in Kazakhstan at the present time

Since 1990 to 2002, 19 human plague cases and 2 bacteria-carriers cases were registered in natural plague foci on the territory of the republic. For last 12 years plague in forms of bubonic and bubonic-septic was diagnosed in Kazakhstan. Out of 19 patients (14 men--73.6% and 5 women--26.3%), 13 persons recovered (8.4%), 6 persons died (31.6%). Employment of the treatment in the new scheme sharply lowered lethality from plague. Live attenuated Y. pestis EV vaccine available for human and camel use is applied as a basic preventive measure in plague natural foci. Epidemiological importance of ill camels remains high. At the analyzed period, in 5 cases infection was a result of forced camel slaughter. 11 people (57.8%) were infected through flea bites. Central Asian desert plague focus is still the most active and its potential to start epidemic increases in connection with rising of anthropogenic influence. All these changes occur on the background of epidemiological survey decreasing in natural plague foci.

Animals, disease, and man: making connections

The intricate causal relationships between disease in man and disease in animals first began to be elucidated in the mid-19th century. Although the connections between animal and human disease are now generally understood, individuals as well as societies remain slow to act on this knowledge. This paper examines the gradual recognition of these disease connections and explores the parallel theme of man's reluctance to appreciate the implications of these connections. It identifies factors that have inhibited the realization of the links between disease in man and animals, and discusses several milestones in the scientific elucidation of these links. Beginning with emerging concerns over the relationship between bovine and human tuberculosis in the 1860s, it follows the discovery of insect vectors, animal reservoirs, and the links between animals, influenza, and man. Despite warnings of the potential significance for human disease of patterns of changes in the relationship with animals and the natural world, scientists have continued to treat human and animal health as largely independent disciplines, while historians too have neglected this important aspect of human disease.

[Xenopsylla cheopis (Siphonaptera: Xenopsyllinae), fleas in rural plague areas of high altitude Madagascar: level of sensitivity to DDT, pyrethroids and carbamates after 50 years of chemical vector control]

The resistance of Xenopsylla cheopis from urban area to pyrethroids, to DDT, and their susceptibility to carbamate are known. We have evaluated the susceptibility of X. cheopis collected from three rural localities: Ambodisiarivo (district of Antananarivo Avaradrano), Mandoto (district of Betafo), Analaroa (district of Anjozorobe) in the province of Antananarivo and in Besoa (district of Ambalavao) in the province of Fianarantsoa. The standard WHO protocol was used and four insecticides were tested: deltamethrin 0.025%, cyfluthrin 0.15% (pyrethroids), DDT 4% (organochlorine), propoxur 1% and bendiocarb 0.1% (carbamate). X. cheopis has been shown resistance to DDT 4%, to deltamethrin 0.025% but was susceptible in the rural area around Antananarivo City. They were tolerant to deltamethrin 0.025% and cyfluthrin 0.15% but susceptible to propoxur 0.1% and bendiocarbe 1% in the districts of Betafo and Anjozorobe. In Besoa, X. cheopis was resistant to DDT 4%, tolerant to deltamethrin 0.025% and cyfluthrin 0.15% but susceptible to propoxur 0.1% and bendiocarbe 1%. These results indicate that DDT and pyrethroids can not be recommended any more for the vector control in the rural area around the capital. The use of pyrethroids in the other districts of the central highland must be joined with a X. cheopis susceptibility control. In case of resistance to pyrethroids, carbamates would be proposed to control plague vector in the rural area. The high level of resistance to DDT and pyrethroid in the rural area around the capital confirms the importance of studying the flea population in different area of Madagascar and the possibility of the gene resistance propagation.

[The plague at the Tsenabe Isotry market in Antananarivo: a complex epidemiologic situation]

The transmission of Yersinia pestis is intense among rats in the wholesale market Tsenabe Isotry in the capital Antananarivo (anti-F1 sero-prevalence 80%, flea index 8.4 for a cut-off risk index of > 1). However, the number of plague-suspected (not laboratory confirmed) human cases has only been 3 in this district during a four years period from 1995 to 1999. A seroepidemiological survey among the market vendors was undertaken in June 1999 to test the hypothesis that the low incidence of human plague is due to acquired immunity. In addition, surveillance of the rat and the flea populations in the market was carried out. Only 3 (3.2%) of 95 screened vendors were anti-F1 IgG positive, whereas the markers of plague transmission among rodents and fleas were still high. This result suggests that the low incidence of human plague was not due to acquired immunity but to other factors such as the limited contact between humans and the rat fleas because of the abundance of rats, the absence of epizootic due to the resistance of rats in the capital and a particular behaviour of the predominant rat Rattus norvegicus.