Bites Of Infected Fleas Research Articles

Distribution and abundance of fleas and rodents of plague importance in the erstwhile endemic states and international seaports of India

Rodents are the reservoirs of the plague bacterium Yersinia pestis, which is transmitted through the bites of infected fleas. In this paper, we studied the distribution and abundance of fleas and rodents in the erstwhile endemic states and seaports of India from 2009 to 2019. The analysis showed that the Rattus rattus (Rr) was the major rodent species found in both Western (66.52 %) and Eastern (48.95 %) seaports of India and the other rodent species recorded were Bandicota indica (Bi) (16.68 % & 34.24 %), Bandicota bengalensis (Bb) (8.88 % & 16.02 %) Rattus norvegicus (Rn) (6.83 % & 0.70 %), Murines hurriane (Mh) (1.08 % & 0 %), Mus musculus (Mm) (0 % & 0.09 %), respectively. Only two flea species namely, Xenopsylla cheopis (X.c) and Xenopsylla astia (X.a) were recorded during the study period in Eastern and Western seaports. Among them, X. astia was found to be the dominant species (55.56 %) and followed by X. cheopis (44.44 %). Further, the female population of X. cheopis and X. astia was higher in both Western and Eastern seaports than the male population. Similarly, Rattus rattus (Rr) (82.43 %,) was the major rodent species found in erstwhile endemic states of India, followed by Tetera indica (Ti) (11.99 %,). Only northern endemic states (HP and UK) reported Rattus rattus terkiminasis (R.rt) (0.01 %). Four flea species namely, Xenopsylla cheopis (64.89 %), Xenopsylla astia (34.89 %), Stivalius ahalae (0.18 %), and Nosopsyllus fasciatus (0.02 %) were recorded from endemic states. The presence of rodents and vector fleas warrants sustained plague surveillance in and around seaports and endemic states.

Assessing the effectiveness of intervention to prevent plague through community and animal-based survey.

Bubonic plague, transmitted by infected flea bites, is the most common form of plague and, left untreated, can progress to the pneumonic form, which is highly contagious. Surveillance focusing on reservoir and vector is considered to be the main approach to prevent plague. Common rodent control methods include the use of rodenticide and snap traps but, in a plague context, the dispersal of fleas from killed animals may pose a serious health threat. Therefore, there is a need for strategies which address reservoir and vector control. The aim of this study was to assess the effects of combination of reservoir and vector control through community-based surveillance. Activities were implemented by local previously trained community agents in two active plague foci in Madagascar. Kartman bait stations containing rodenticide and insecticide were placed indoors while live traps were set outdoors. Small mammals were identified and killed with their fleas. Effectiveness of control measures was evaluated by comparison of plague incidence two years before and after intervention using data on reported human cases of plague from the Central Laboratory of Plague. A total of 4,302 small mammals were captured, with the predominance of the black rat Rattus rattus. Our results found a reduction in plague incidence in the treated site for at least two years after treatment. Community-based interventions played an important role in reducing contact between humans-rodents-fleas. Our study confirms the importance of animal surveillance during the low plague transmission season. The combination of reservoir and vector control with community involvement may be effective at reducing the risks of plague spillover to humans. The strategy of using Kartman bait stations indoors with live traps outdoors can be used to refine proactive plague prevention, however, due to the potential development of resistance to pesticides in flea and rat populations, overuse should be considered.

Plague Prevention and Therapy: Perspectives on Current and Future Strategies.

Plague, caused by the bacterial pathogen Yersinia pestis, is a vector-borne disease that has caused millions of human deaths over several centuries. Presently, human plague infections continue throughout the world. Transmission from one host to another relies mainly on infected flea bites, which can cause enlarged lymph nodes called buboes, followed by septicemic dissemination of the pathogen. Additionally, droplet inhalation after close contact with infected mammals can result in primary pneumonic plague. Here, we review research advances in the areas of vaccines and therapeutics for plague in context of Y. pestis virulence factors and disease pathogenesis. Plague continues to be both a public health threat and a biodefense concern and we highlight research that is important for infection mitigation and disease treatment.

Yersinia pestis: the Natural History of Plague.

The Gram-negative bacterium Yersinia pestis is responsible for deadly plague, a zoonotic disease established in stable foci in the Americas, Africa, and Eurasia. Its persistence in the environment relies on the subtle balance between Y. pestis-contaminated soils, burrowing and nonburrowing mammals exhibiting variable degrees of plague susceptibility, and their associated fleas. Transmission from one host to another relies mainly on infected flea bites, inducing typical painful, enlarged lymph nodes referred to as buboes, followed by septicemic dissemination of the pathogen. In contrast, droplet inhalation after close contact with infected mammals induces primary pneumonic plague. Finally, the rarely reported consumption of contaminated raw meat causes pharyngeal and gastrointestinal plague. Point-of-care diagnosis, early antibiotic treatment, and confinement measures contribute to outbreak control despite residual mortality. Mandatory primary prevention relies on the active surveillance of established plague foci and ectoparasite control. Plague is acknowledged to have infected human populations for at least 5,000 years in Eurasia. Y. pestis genomes recovered from affected archaeological sites have suggested clonal evolution from a common ancestor shared with the closely related enteric pathogen Yersinia pseudotuberculosis and have indicated that ymt gene acquisition during the Bronze Age conferred Y. pestis with ectoparasite transmissibility while maintaining its enteric transmissibility. Three historic pandemics, starting in 541 AD and continuing until today, have been described. At present, the third pandemic has become largely quiescent, with hundreds of human cases being reported mainly in a few impoverished African countries, where zoonotic plague is mostly transmitted to people by rodent-associated flea bites.

SUCCESSFUL USE OF EXTRACORPOREAL MEMBRANE OXYGENATION IN MURINE TYPHUS COMPLICATED BY ARDS

SESSION TITLE: Wednesday Medical Student/Resident Case Report Posters SESSION TYPE: Med Student/Res Case Rep Postr PRESENTED ON: 10/23/2019 09:45 AM - 10:45 AM INTRODUCTION: Murine typhus is a flea-borne disease caused by the bacteria Rickettsia typhi. Presentations are widely variable. Critical illness occurs rarely and mortality occurs in less than 1% of patients who receive treatment. We present a case of a patient with acute respiratory distress syndrome (ARDS) secondary to murine typhus successfully temporized with extracorporeal membrane oxygenation (ECMO). CASE PRESENTATION: A 37 year-old man with no past medical history presented with fever (40◦c), headache, weakness, dizziness, and septic physiology. Initial chest imaging was unremarkable. Labs revealed leukopenia, thrombocytopenia, and elevation in liver associated enzymes. Broad spectrum antibiotics were initiated. The following day, he developed shortness of breath and cough which progressed to frank hemoptysis. He was intubated for hypoxic respiratory failure and serial imaging revealed rapidly progressive ARDS. Doxycycline was added. Within 24 hours, hypoxemia and acidosis were refractory to lung protective ventilation strategies and he was cannulated for veno-venous ECMO. His course was complicated by acute renal insufficiency, septic shock, septic cardiomyopathy, and delirium. An exhaustive work-up revealed a high R. typhi IgM titer (1:1024), consistent with acute infection. His work-up was otherwise unremarkable. He rapidly improved, was weaned from pressor support, decannulated from ECMO, and liberated from the ventilator. After extubation, the patient reported regularly feeding stray cats. He completed a 10 day course of doxycycline 100mg twice daily and was discharged home to make a full recovery. DISCUSSION: In the United States, Murine Typhus is endemic to Texas, California, and Hawaii(1). Sporadic cases occur worldwide. Rat fleas (Xenopsylla cheopis) are the classic vector. In the United States, the flea (Ctenocephalides felis) from cats and opossums are also responsible. Disease occurs when an infected flea bites and then stools in the wound(1). Incidence in Texas is 59.5 cases per 100,000(2), but may be more common and misdiagnosed(3). The classic triad of fever, headache, and rash only occurs in a third of patients(3). Flea exposure, elevated liver associated enzymes and thrombocytopenia offer diagnostic clues(3). Once suspected, empiric doxycycline is recommended; however, care is often supportive(1). While mostly indolent, critical illness occurs rarely. Risk factors for severe disease include immunosuppressed state, advanced age, and glucose-6-phosphate dehydrogenase deficiency(3). Without any risk factors, it is unclear why our patient experienced such a complicated course and ultimately required ECMO for respiratory support. CONCLUSIONS: To our knowledge, this case represents the first reported use of ECMO to support a patient with ARDS secondary to Murine typhus and demonstrates the use of ECMO for supportive care in a limiting illness. Reference #1: Civen R, Ngo V. Murine Typhus: An Unrecognized Suburban Vectorborne Disease, Clinical Infectious Diseases, Volume 46, Issue 6, 15 March 2008, Pages 913–918, https://doi.org/10.1086/527443 Reference #2: Murray KO, Evert N, Mayes B, et al. Typhus Group Rickettsiosis, Texas, USA, 2003-2013. Emerg Infect Dis. 2017;23(4):645-648. Reference #3: Tsioutis C, Zafeiri M, Avramopoulos A, et al. Clinical and Laboratory Characteristics, Epidemiology, and Outcomes of Murine Typhus: A Systematic Review, Acta Tropica, Volume 166, 7 February 2017, Pages 16-24, https://doi.org/10.1016/j.actatropica.2016.10.018 DISCLOSURES: No relevant relationships by Daniel Foster, source=Web Response No relevant relationships by Michael Gonzales, source=Web Response No relevant relationships by Chungting Kou, source=Web Response No relevant relationships by Justin Reis, source=Web Response

Analysis of seroprevalence of antibodies to Rickettsia typhi in the population of the southern region of Kazakhstan

Rickettsia typhi (R. typhi) belongs to the typhus group rickettsiae and causes endemic typhus. Human infection can occur alimentary (consumption of food contaminated with rat feces), through rat fleas (infected flea bites, inhalation of dried flea feces), as well as through ticks that parasitize on rats (infection occurs when a person is bitten by an infected tick). Cases of endemic typhus and seropositivity to R. typhi have been reported in the neighboring China and Russia, nevertheless little is known of the endemic typhus in Kazakhstan. The purpose of this study was to evaluate the prevalence of specific antibodies to R. typhi in the population of the southern region of Kazakhstan. A total of 253 individuals (142 women, 111 men) aged from 1 to 71 years were recruited into the study. Detection of serum IgG antibodies against R. typhi was performed by ELISA. IgG antibodies to R. typhi were detected in 34.4% of the analyzed population. High prevalence was detected in the Turkistan oblast (91.8% on average in the oblast) and in the village of Zhalandy, Almaty oblast (31.9% of all individuals). The seroprevalence was identical in both sexes. Seropositivity was not significantly associated with age, but positive results were not detected in the age group of children under 14 years. The obtained results confirm active circulation of R. typhi in the Turkistan and Almaty oblast of Kazakhstan, which in turn indicates an urgent need for further study of the role of endemic typhus in the structure of fever of unknown origin in the southern region of Kazakhstan. Key words: Rickettsia typhi, Southers region of Kazakhstan, class G immunoglobulins.

Current Perspectives on Plague Vector Control in Madagascar: Susceptibility Status of Xenopsylla cheopis to 12 Insecticides.

Plague is a rodent disease transmissible to humans by infected flea bites, and Madagascar is one of the countries with the highest plague incidence in the world. This study reports the susceptibility of the main plague vector Xenopsylla cheopis to 12 different insecticides belonging to 4 insecticide families (carbamates, organophosphates, pyrethroids and organochlorines). Eight populations from different geographical regions of Madagascar previously resistant to deltamethrin were tested with a World Health Organization standard bioassay. Insecticide susceptibility varied amongst populations, but all of them were resistant to six insecticides belonging to pyrethroid and carbamate insecticides (alphacypermethrin, lambdacyhalothrin, etofenprox, deltamethrin, bendiocarb and propoxur). Only one insecticide (dieldrin) was an efficient pulicide for all flea populations. Cross resistances were suspected. This study proposes at least three alternative insecticides (malathion, fenitrothion and cyfluthrin) to replace deltamethrin during plague epidemic responses, but the most efficient insecticide may be different for each population studied. We highlight the importance of continuous insecticide susceptibility surveillance in the areas of high plague risk in Madagascar.

СAPSULAR ANTIGEN OF YERSINIA PESTIS

Plague is a zoonosis caused by gram-negative bacteria Yersinia pestis, which, as a rule, is transmitted to humans from septicemic rodents by the bites of infected fleas. This microbe killed more people than all of the wars in the human history. Y. pestis circulation in the natural plague foci is ensured by the whole number of pathogenicity factors with differing functional orientation. This review is devoted to one of them, Y. pestis capsular antigen (F1 or Caf1). The history of its discovery and studying of its genetic control, biosynthesis, isolation and purification, and physicochemical properties are reviewed. Its roles in plague pathogenesis and its application as a main component of plague vaccines are also discussed. Y. pestis capsule under light microscopy is visually amorphous, while high-resolution electron microscopy displays the structure formed from separate fimbria-like cords up to 200 nm long, diverging from the bacterial surface in different directions. At 37°C Y. pestis produce 800–1000 times more capsular antigen than at 28°C. Genes coding for 17.6-kD Caf1 protein, which contains 170 amino acids, are located in caf1 operon of pFra plasmid. Analysis of caf1 operon nucleotide sequence testified its close phylogenetic relationship with the gene clusters coding for pilus adhesins that were secreted with the help of chaperone/usher systems in enterobacteria including six additional adhesins in Y. pestis. Y. pestis multiplication within macrophages is the obligatory stage of plague pathogenesis, and the plague pathogen virulence correlates not with resistance to phagocyte ingesting but with bacterial ability to survive and multiply within phagolysosomes of phagocytes due to neutralization of antibacterial functions of eukaryotic cells. The capsule formed out of the Caf1 aggregates protects Y. pestis from ingestion by naïve host’s phagocytes and prevents from initiation of the alternative pathway of the complement system. Molecular usher Caf1A responsible for capsular antigen anchoring on the surface of bacterial cell has a high affinity to human interleukin 1β. Caf1 can compete with interleukins 1α, 1β, and 1ra in binding to receptors on lymphoid cells preventing development of adequate immune response. Immunodiagnosis of plague is based on detection of Caf1 or anti-Caf1 antibodies since this Y. pestis antigen is species specific. Covering bacterial surfaces capsular antigen is also the paramount component of all modern plague vaccines. Its leading role in induction of intense immunity in mice, rats, monkeys, and men was shown clearly. However, non-capsulated (Caf1–) variants of Y. pestis keeping their virulence at the level of the wild-type strains might be selected and accumulated in immune animals. This indicates inadmissibility of application of monoantigen plague vaccines and necessity for design of immunoprophylactic preparations aimed at two or three molecular targets.

PLASMINOGEN ACTIVATOR OF YERSINIA PESTIS

Plague has been the cause of three pandemics and has led to the death of millions of people. Plague is a typical zoonosis caused by Yersinia pestis that circulates in populations of wild rodents inhabiting natural plague foci on all continents except for Australia. Transmission of plague is provided by flea bites. Circulation of Y. pestis in natural plague foci is supported by a numerous of pathogenicity factors. This review explores one of them, plasminogen activator Pla. This protein is one of representatives of omptins, a family of enterobacterial outer membrane proteases that are responsible for colonization of specific organs or even infection generalization as a result of successful overcoming of the host innate immunity. The review reflects the history of its discovery and studying of its genetic control, biosynthesis, isolation and purification, physicochemical properties. Highly purified preparations of plasminogen activator are deficient in enzymatic activities but renaturation in the presence of Y. pestis lipooligosaccharide restores enzymatic properties of Pla. This pathogenicity factor is absent in representatives of the most ancient phylogenetic group of the plague pathogen, bv. caucasica, while the ancestor of other groups of Y. pestis subsp. microtus obtained in result of horizontal transfer Pla isoform with characteristics similar to properties of omptins from the less virulent enterobacteria. After that in the course of microevolution the “classic” isoform of Pla with increased protease activity was selected that is typical of all highly virulent for humans strains of Y. pestis subsp. pestis. The “classic” isoform of Pla Y. pestis is functionally similar to mammalian plasminogen activators transforming plasminogen into plasmin with the help of limited proteolysis. Pla protease activating plasminogen and also degrading the main plasmin inhibitor — α2-antiplasmin and, respectively, determining Y. pestis ability to lyse fibrin clots preventing bacteria dissemination after bites of infected fleas or subcutaneous challenge is believed to be the main Y. pestis factor responsible for generalization of infectious process. Pla-mediated ability of Y. pestis for selective binding with extracellular matrix and basal membranes may promote further hydrolysis of these structures by the host’s plasmin and overcoming tissue barriers by the pathogen. Y. pestis plasminogen activator also hydrolyses C3 complement component, human antimicrobial peptide — cathelicidin LL-37 and such cytokines as tumor necrosis factor α, interferon γ, interleukin 8 and protein 1 of monocyte chemotaxis. The main endogenic TFPI tissue factor pathway inhibitor also highly susceptible to proteolytic action of Pla, and efficiency of TFPI inactivation is much higher than efficacy of plasminogen activation. The review also debates the possibility of using Pla as a molecular target for prophylaxis and treatment of plague.

Solve the case: Infected flea bites in an older patient

Age-related changes lead to an increase in skin problems and around 70% of older people have a treatable skin condition ( Jordan, 2002 ). Skin conditions may be caused by the older person having difficulty caring for their ageing skin. Sometimes other conditions, such as flea bites, scabies and bed bugs may be mistakenly diagnosed as eczema. This article, one of a series, uses a case study approach to outline how an 86-year-old lady with infected flea bites benefited from a holistic approach to treatment. It explains how what initially appeared to be treatment failure was a mixture of healthcare beliefs and memory difficulties, and outlines how these were addressed and how her home and pet were treated to eliminate a flea infestation.

Plague Epidemics and Lice, Democratic Republic of the Congo

To the Editor: Plague, a zoonotic disease caused by the gram-negative bacterium Yersinia pestis, is transmitted to humans by the bites of infected fleas (such as Xenopsylla cheopis), scratches from infected animals, and inhalation of aerosols or consumption of food contaminated with Y. pestis (1). Decades ago, Blanc and Baltazard proposed that human-to-human transmission of Y. pestis could be mediated by human ectoparasites, such as the human body louse (2). This hypothesis was further supported by experimental data from animal models (3). To further test this hypothesis among humans, we conducted a field assessment in April 2010, in which we collected body and head lice from persons living in a highly plague-endemic area near the Rethy Health District, Province Orientale, Democratic Republic of the Congo. This health district has 157,000 inhabitants, and during 2004–2009 it had more suspected plague cases (1,624 cases of suspected plague, 39 deaths) than any other health district in the Democratic Republic of the Congo. In April 2010, we visited the dwellings of 10 patients for whom suspected cases of plague had been diagnosed during January–April 2010. All patients had symptoms typical of bubonic plague, and their illnesses were reported as suspected bubonic plague. However, because of the lack of laboratory facilities in Rethy, none of these diagnoses could be microbiologically confirmed. A total of 154 body lice and 35 head lice were collected from clothes and hair of persons living in or near the patients’ dwellings. Body lice were preserved in ethanol before being sent to the laboratory. Total DNA was extracted by using an EZ1 automated extractor (QIAGEN, Courtaboeuf, France) and subjected to parallel real-time PCRs selective for the Y. pestis pla gene, the Rickettsia prowazekii ompB gene, a Borrelia recurrentis noncoding genomic fragment, and the Bartonella quintana internal transcribed spacer. B. quintana PCR primers and probe have been shown to be specific for B. quintana (4). Primers and probe sequences and experimental conditions have been reported (4). Negative controls contained PCR buffer without DNA, as described (4). Any amplification with a cycle threshold (Ct) <40 was regarded as positive. Negative controls remained negative in all PCR-based experiments, which were not prone to in-laboratory contamination, and all samples were negative for R. prowazekii and B. recurrentis. Conversely, B. quintana was detected in 50 (32.5%) of the 154 body lice (Ct 18.62–38.45) and 6 (17.1%) of the 35 head lice (Ct 29.48–38.68). The Y. pestis pla gene was detected in 1 head louse (Ct 38), which was negative for the other pathogens, and in 2 body lice (Ct 37.36 and 36.97, respectively), which were positive for B. quintana. B. quintana has been detected in head louse specimens collected in Ethiopia and Senegal (5–7) and in body louse specimens collected in Burundi, Rwanda, Zimbabwe (8), and Ethiopia (5); we add Democratic Republic of the Congo to the list. Body lice are acknowledged vectors for human-to-human transmission of B. quintana (9). Detection of Y. pestis in head and body lice has been reported (2). Detailed observations in south Morocco showed that body lice collected from blood culture–negative bubonic plague patients were negative for Y. pestis, whereas body lice collected from septicemic patients were positive according to guinea pig inoculation results (2). Further experiments in a rabbit experimental model demonstrated the possibility of direct louse-bite transmission of Y. pestis (3). A recent search for Y. pestis in head lice in Ethiopia found none (5). Our detection of B. quintana and the plague agent Y. pestis in modern head and body lice is similar to findings of a paleomicrobiological investigation at a medieval plague site near Paris (10). There, high-throughput real-time PCR investigation of dental pulp collected from 14 teeth from 5 skeletons detected B. quintana DNA in teeth from 3 skeletons and Y. pestis DNA in teeth from 2, including 1 with co-infection. Altogether, these data suggest that transmission of B. quintana and Y. pestis has been ongoing for centuries in populations in which louse infestation is prevalent. This finding indicates that lice might play a role in transmission of Y. pestis and that preventing and controlling louse infestations might help limit the extension of plague epidemics in louse-infested populations.

Plague: The Disease,Yersinia pestisand its Genome

Plague is a highly virulent, vector-borne disease of ancient antecedents, transmitted from members of the family Rodentia, through the bites of infected fleas. The disease, caused by the bacterium Yersinia pestis, presents itself in septicaemic, bubonic and pneumonic forms. The rat flea Xenopsylla cheopis is most often implicated in transmission. The plague remains one of the most dreaded infectious diseases, which has raised its head in western, northern and southern regions in the last few decades, being a category ‘A’ critical agent with a significant threat to public health and national security. Rapid antigen detection or nucleic acid-based molecular tests for plague are not widely available. Modern immunoprophylactic regimes for pre- and postgeneration vaccination are needed. Complete genome sequences unveiled for all four biotypes and other strains/isolates recently will help scientists gain insights into the genomic rearrangement and pathogenicity of the organism.

Peste, uma doença ocupacional

Plague is a zoonosis caused by the bacterium Yersinia pestis, transmitted mainly by the bites of infected fleas. Distributed worldwide, it is a potential threat to human populations due to the persistence of the infection among wild rodents and to its high potential for epidemics. In view of the changes in the epidemiological profiles of infectious diseases and socio-cultural changes in different parts of the world, an accurate perception of the professionals at risk of contamination is essential, in order to protect themselves and to prevent the spread of the disease and subsequent morbidity and mortality among human populations.

Flea bites: diagnosis, treatment and prevention

Flea infestations are increasingly common in today's centrally heated, carpeted homes. The consequences of fleabites vary: sometimes they are a minor nuisance, but on occasion they can cause allergic reactions and infections. This article uses a case study approach to outline how an 86-year-old woman was treated for infected fleabites and how her home and pet were treated to eliminate a flea infestation.

AsymptomaticYersinia pestisInfection, China

To the Editor: Plague is one of the oldest identifiable diseases. Modern public health measures and effective antimicrobial treatments have led to a decrease in plague cases worldwide. However, plague remains endemic in many natural foci. Since the early 1990s, the World Health Organization (WHO) has reported a steadily increasing trend in human plague cases, which has resulted in the recognition of plague as a reemerging disease (1). The emergence of antimicrobial drug–resistant strains of Yersinia pestis, along with an increasing number of plague cases, remind us that plague still poses a serious public health threat (2,3). In China, human cases of plague have been reported to WHO nearly every year from 1989 to 2003; these account for 9.5% of cases and 15.5% of deaths from this disease in Asia (1). Human cases of plague in China are usually caused by contact with plague-infected rodents. Here, we report the results of a serologic survey by using 3 methods (passive hemagglutination assay, Western blot, and protein microarray analysis) in marmot hunters in Qinghai Province, China. One hundred twenty serum samples were collected in 2 villages in Huangyuan County, Qinghai Province, from marmot hunters (63 samples) and their family members (57 samples); none had a history of fever in the past 2 years. One hundred nineteen serum samples were collected from persons with no history of marmot hunting in 2 nearby counties in Qinghai Province in which plague was not endemic. Thirty serum samples were collected from persons in Beijing and used as negative controls. All serum samples were initially screened with a passive hemagglutination assay to detect immunoglobulin (Ig) G antibody against F1 antigen of Y. pestis, by using a standard protocol (4). We then used an F1 antigen–based Western blot to analyze all serum samples. The protein microarray analysis was performed with 149 purified recombinant proteins of Y. pestis (5). The results of the serologic survey are summarized in the Table. The passive hemagglutination assay showed 17 positive samples in the marmot hunter population. None of the control serum samples were positive for F1 antigen in this assay. Western blot identified 9 additional positive samples in the marmot hunter population, resulting in a seropositivity rate of 21.7% (26/120). We also found positive samples in 4 (3.4%) of 119 serum samples by using Western blot in persons from areas in which plague was not endemic. Identical results were also obtained by using protein microarray analysis, which validated the results of Western blot. Table Analysis of sera for plague antibody by 3 methods Previous studies have shown that plague antibodies were more prevalent in males in the exposed population, and differences in the age, sex, or ethnic group of plague patients are the result of variations in exposure to the pathogen, not intrinsic factors (6,7). Our study showed that in the marmot hunter population, the plague seropositivity rate was significantly higher in males (36.8%, 25/68) than in females (2.0%, 1/52, p<0.01). Among the marmot hunter population, 63 (92.6%) of 68 males were hunters. Plague antibodies were also more prevalent in marmot hunters (39.7%, 25/63) than in their family members (1.8%, 1/57, p<0.01). This is the first serologic survey of plague in the marmot hunter population. The plague seropositivity rate of 21.7% (26/120) in hunters and their families is much higher than the 3.4% (4/119) in the population from regions in which plague was not endemic (p<0.01). Seroprevalence in marmot hunters was even higher (39.7%), which suggests that marmot hunting is a risk factor for plague infection. The marmot (Marmota himalayana) is the main host of Y. pestis in Qinghai Province. Plague-infected marmots are more easily captured by hunters. When persons hunt and butcher marmots without any effective protection, Y. pestis can be transmitted through tiny wounds in the skin, by bites of infected fleas, or by the respiratory route. Asymptomatic plague infection in marmot hunters might be explained by prophylactic use of antimicrobial drugs. Most hunters usually take sulfamethoxazole or tetracycline as a prophylactic measure. Even if the hunters were infected with Y. pestis, they would likely not develop symptomatic plague. However, if the antimicrobial drugs are not effective or hunters do not use prophylaxis, symptomatic infections will occur. Most reported human cases of plague in Qinghai Province were caused by hunting or butchering marmots, as shown by a recent outbreak of plague in October 2004 in Qinghai, in which 19 cases were reported and 8 persons died (M. Li et al., unpub. data).

La peste

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.

Role of the Yersinia pestis Hemin Storage ( hms ) Locus in the Transmission of Plague by Fleas

Yersinia pestis, the cause of bubonic plague, is transmitted by the bites of infected fleas. Biological transmission of plague depends on blockage of the foregut of the flea by a mass of plague bacilli. Blockage was found to be dependent on the hemin storage (hms) locus. Yersinia pestis hms mutants established long-term infection of the flea's midgut but failed to colonize the proventriculus, the site in the foregut where blockage normally develops. Thus, the hms locus markedly alters the course of Y. pestis infection in its insect vector, leading to a change in blood-feeding behavior and to efficient transmission of plague.

Algorithms in the diagnosis and management of exotic diseases. XXV. Plague.

Plague is an acute bacterial infection of man caused by Yersinia pestis. The natural reservoirs of the organism are predominantly urban and sylvatic rodents, and it is transmitted among animals and occasionally to man by bites of infected fleas. Plague has a cosmopolitan distribution with significant foci of infection in the Americas, Africa, and Asia. Y. pestis has caused devastating pandemics throughout history with high mortality rates, in which pneumonic man-to-man transmission has occurred in addition to the usual flea-to-man spread. Today, in the United States, urban plague carried by rats has been eliminated, but sylvatic plague persists in rodents and other mammals of rural areas in the southwestern states with occasional transmission to man. The most common clinical form is acute regional lymphadenitis, called bubonic plague. Less common forms include septicemic, pneumonic, and meningeal plague. Mortality is high in untreated patients, but antibiotic treatment with streptomycin administered early in the course of disease markedly reduces fatalities.