Bioterrorism. Clinical recognition and primary management

The recent anthrax attacks in the United States have demonstrated the reality of bioterrorist threats as well as the need for preparedness and planning to mount a successful response to such events. Medical practitioners have a key role in responding to bioterrorist activity because they can contribute to the timely recognition of an event and to the mitigation of morbidity resulting from a bioterrorist attack. The medical community needs to become familiar with how to recognize and manage diseases produced by the biologic agents that might be used by terrorists. This review summarizes the microbiological and clinical aspects of the agents of anthrax, smallpox, plague, and tularemia, which are all considered likely bioterrorist weapons.

Combating high-priority biological agents What to do with drug-allergic patients and those for whom vaccination is contraindicated?

The threat of bioterrorism continues to be a very real one. Regularly, there are news stories on bioterrorism-related topics: What biologic weapons will our enemies likely use to attack the United States? How prepared is our country to successfully counter such attacks? Although these critical questions are being addressed by the leaders of our country, allergists-immunologists, too, will have to grapple with difficult questions during these uncertain and frightening times. We care for a special group of patients with various allergic and immunologic disorders. Some of our patients have immunodeficiency disorders that might preclude them from receiving life-saving vaccines. Our patients with drug allergies are fearful that should they become infected with a biologic agent, they will not be able to receive appropriate treatment. In this article we focus on the various vaccine-related and antibiotic-related adverse effects that the allergist-immunologist might see during treatment of infections caused by Category A agents. Where possible, potential management approaches are outlined.

Prevention and treatment of bacterial diseases caused by bacterial bioterrorism threat agents

There is general consensus that the bacterial agents or products most likely to be used as weapons of mass destruction are Bacillus anthracis, Yersinia pestis, Francisella tularensis and the neurotoxin of Clostridium botulinum. Modern supportive and antimicrobial therapy for inhalational anthrax is associated with a 45% mortality rate, reinforcing the need for better adjunctive therapy and prevention strategies. Pneumonic plague is highly contagious, difficult to recognize and is frequently fatal. Therefore, the development of vaccines against this agent is crucial. Although tularemia is associated with low mortality, the highly infectious nature of aerosolized F. tularensis poses a substantive threat that is best met by vaccine development. Safer antitoxins and a vaccine are required to meet the threat of the use of botulinum toxin as a weapon of mass destruction. In this article, the current status of research in these areas is reviewed.

[Use of monoclonal antibodies to plague microbe antigens at the early stage of infection in white mice for enhancement of the late streptomycin and doxycycline treatment]

It was demonstrated that use for prophylaxy (after 5 h of infection) or for treatment (after 24 h after infection) of the monoclonal antibodies mixture to specific epitops of capsule antigen (fraction 1), lipopolysacharide, murine toxine can prevent development of plague pathogen at 100 of mice infected by approximately 1000 LD50 Yersinia pestis 231. 5-day course of prophylaxy by monoclonal antibodies provided survival of 50 per cent animals. Subsequent use of fraction 1 antigen for 5 days followed by treatment with streptomycin or doxycycline at 6-7-8-9-10 days after infection with Y. pestis 231 prevented infection manifestation at 80 per cent of animals, etiotropic therapy started at the same period was ineffective. When white mice were infected with Y. pestis 231 Fra-, with deleted ability to produce capsule antigen (fraction 1) 80% level of efficacy can be provided by subsequent administration of antibodies to fraction 1 combinated with lipopolysacharide, murine toxine and streptomycin. Use of monoclonal antibodies followed by doxycycline was ineffective.

The usual suspects

Any scientist will think twice before reporting any discrepancy or possible theft of biohazardous material to either his or her institution or to the government.

Pneumonic plague

Pneumonic plague, a disease caused by the bacterium Yersinia pestis, is a rare disease in the United States and carries a high mortality. Health care professionals in the United States are not familiar with the clinical presentation and diagnosis of plague pneumonia. The wide prevalence of the bacterium in different parts of the world, its high virulence, and its ability to spread by aerosolization makes it a potential agent of biological warfare in the hands of terrorists. This review focuses on the prevalence, pathogenesis immunity, clinical manifestations, diagnosis, treatment, and prevention of plague pneumonia, with particular emphasis on the plague bacillus as an agent of biological warfare. Based on available information, we discuss measures that need to be undertaken by health care personnel, public health personnel, and epidemiologists in the event of such an attack.

[The plague, possible bioterrorist act]

PLAGUE AND BIOWARFARE: Plague is an infection caused by Yersinia pestis. This is a major agent that might be used as a biological weapon. If the bacteria is sprayed, the most frequent clinical form would be pneumonia. If contaminated fleas were used, the bubonic and septicaemic forms would be those observed. Suspicious context A biowarfare act by spraying Y pestis must be suspected when a patient without any risk factors presents with a primary pulmonary form of the disease in a non endemic area.

PRACTICAL MANAGEMENT

All the patients presenting with a pulmonary form of plague must be hospitalised and isolated in de-pressurised room, at least for the first three days of antibiotherapy. For the other clinical forms, patients must isolated during the first 48 hours of treatment. Treatment must be initiated as rapidly as possible. Strains of Y. pestis are usually sensitive to many antibiotics (streptomycin, gentamicin, doxycycline, ciprofloxacin, chloramphenicol, sulfadiazin, trimethoprime-sulfamethoxazole...).

PREVENTION

In the case of contact with a spray suspected of containing the plague bacilla, doxycycline or ciprofloxacin can be prescribed. A dead cell vaccine exists, but its efficacy in terms of protection from primary pneumonia appears inadequate.

Recognition and management of bioterrorism infections

Recent events have demonstrated that bioterrorists have the ability to disseminate biologic agents in the United States and cause widespread social panic. Family physicians would play a key role in the initial recognition of a potential bioterrorism attack. Familiarity with the infectious agents of highest priority can expedite diagnosis and initial management, and lead to a successful public health response to such an attack. High-priority infectious agents include anthrax, smallpox, plague, tularemia, botulism, and viral hemorrhagic fever. Anthrax and smallpox must be distinguished from such common infections as influenza and varicella. Anthrax treatment is stratified into postexposure prophylaxis and treatment of confirmed cutaneous, intestinal, or inhalation anthrax. Disease prevention by vaccination and isolation of affected persons is key in preventing widespread smallpox infection. Many resources are available to physicians when a bioterrorism attack is suspected, including local public health agencies and the Centers for Disease Control and Prevention.

Bioterrorism and critical care

A bioterrorist attack of any kind has the potential to overwhelm a community and, indeed, in the case of smallpox, an entire nation. During such an attack the number of patients requiring hospitalization and specifically critical care is likely to be enormous. Intensivists will be at the forefront of this war and will play an important role in dealing with mass casualties in an attempt to heal the community. A high degree of suspicion and prompt recognition of an event will be required to contain it. Specific knowledge of the possible agents that can be used will be key in managing patients and in estimating the needs of a health care facility and community to deal with the future course of events. Intensivists play various roles aside from the delivery of critical care to the patient in the ICU. These roles include making triage decisions regarding the appropriate use of critical care beds (which automatically dictates how other non-ICU beds are used and managed) and serving as a team member of ethics committees (on such issues as dying, futility, and withdrawal of care). Indeed, intensivists are no strangers to disaster management and have served on the forefront of many. A biologic weapons attack, however, is likely to push this multidimensional nature of the intensivist to the maximum, because such an attack is likely to result in a more homogeneous critically ill population where the number of critical care staff and supplies to treat the victims may be limited. One hopes that such an event will not occur. Sadly, however the events of September 11, 2001, have only heightened the awareness of such a possibility.

[The plague]

The word plague evokes associations with old times, but plague actually does still occur all over the world. The survival chances are at the moment much better (antibiotics) than formerly, when half of the patients died; now this figure is 15%. The causal organism is Yersinia pestis, a bacterium in fleas on rodents. This bug is a plausible candidate for attacks by bioterrosists. So, in this time, there is good reason to pay attention to it, as well as to to smallpox and anthrax and their causal organisms.

Bioterrorism: pivotal clinical issues. Consensus review of the Society of Infectious Diseases Pharmacists

OBJECTIVES

To discuss specific facts regarding use as a bioweapon, epidemiology, microbiology, clinical manifestations, diagnosis, antimicrobial therapy, immunization, and isolation precautions for five most likely agents of bioterrorism; to review and provide recommendations for health care clinicians on the management of these bioterrorism agents; and to share information on the pharmacist's role in preparedness and response.

PARTICIPANTS

The manuscript was drafted by the three authors, reviewed by a group of selected members of the Society of Infectious Diseases Pharmacists, and approved by its Board of Directors.

EVIDENCE

The primary focus was to review and summarize recent and key articles on bioterrorism. Preference was given to peer-reviewed journal information and government-sponsored journals, such as the MMWR, Morbidity and Mortality Weekly Report.

CONSENSUS PROCESS

Written comments were requested from each reviewer. Comments were incorporated into the final draft.

CONCLUSION

Pharmacists play an integral role in disaster preparedness and response and should be involved in planning committees. As drug information specialists, pharmacists can assist other health care providers and emergency personnel, as well as provide counseling to calm, comfort, and empower the public.

[Formation of virulent antigen-modified mutants (Fra-, Fra-Tox-) of plague bacteria resistant to rifampicin and quinolones]

Experiments were performed with two strains of plague bacteria--231 (isolated from marmot) and 358 (isolated from human) and their isogenic variants with Fra- and Fra-Tox- phenotype. Mutants resistant to rifampicin (Rifr) and nalidixic acid (Nalr) appeared independently of pathogen phenotype and genotype with frequency n.10(-8)-n.10(-9), subsequently. Rifr mutation influenced on virulence manifestation at albino mice and antigendeficient variants with Fra- and Fra-Tox- phenotype. In every group of strains highly virulent subcultures were registered. Resistance to nalidixic acid mainly was not associated with virulence loss. Nalr mutants of parent and antigenmodified mutants were cross resistant to fluoroqinolones (ciprofloxacin, ofloxacin, pefloxacin, lomefloxacin). LD50 for untreated albino mice did not differ from LD50, for mice treated with rifampicin (when mice were infected with strain resistant to rifampicin) or with nalidixic acid and fluoroquinolones (when animals were infected with Nalr mutants). Antigenmodified strains of plague bacteria and their Rifr, Nalr mutants were able to overcome specific immune reaction. The drugs should be used in synergic combinations (with aminoglycosides or cephalosporines of III generation) to prevent appearance of virulent strains resistant to rifampicin and fluroquinolones.

Therapeutic challenges posed by bacterial bioterrorism threats

The events of the autumn of 2001 in the United States made it clear that the spectre of the use of microorganisms to intentionally harm humans is a reality. The current strategy to control disease outbreaks caused by the intentional release of bacteria is to use antimicrobial agents, both therapeutically and prophylactically. However, multidrug-resistant strains of bacterial bioterrorism agents occur naturally or have been bio-engineered, indicating how vulnerable this strategy is.

Anthrax, tularemia, plague, ebola or smallpox as agents of bioterrorism: recognition in the emergency room

Bioterrorism has become a potential diagnostic consideration in infectious diseases. This article reviews the clinical presentation and differential diagnosis of potential bioterrorist agents when first presenting to the hospital in the emergency room setting. The characteristic clinical features of inhalation anthrax, tularemic pneumonia, plague pneumonia, including laboratory and radiographic finding, are discussed. Ebola vieus and smallpox are also discussed as potential bioterrorist-transmitted infections from the clinical and epidemiologic standpoint. In addition to the clinical features of the infectious diseases mentioned, the article discusses the infectious disease control and epidemiologic implications of these agents when employed as bioterrorist agents. The review concludes with suggestions for postexposure prophylaxis and therapy.

Confronting bioterrorism: physicians on the front line

The events surrounding September 11, 2001, and its aftermath have compelled the public health and medical community to face the hitherto unfamiliar reality of bioterrorism. Physicians and public health personnel are frontline soldiers in this new form of warfare. This article provides a general overview of the pathophysiology, clinical presentation, diagnosis, and management of patients infected with the 6 highest priority agents that could potentially be used in bioterrorism. The diseases discussed include anthrax, smallpox, tularemia, plague, botulism, and viral hemorrhagic fevers. Despite the unpredictable nature of bioterrorism, disaster preparedness and knowledge of essential diagnostic and epidemiological principles can contribute substantially toward combating this new threat.

Biological agents as weapons 2: anthrax and plague

Although most naturally occurring infections with anthrax and plague are cutaneous, both organisms are most likely to be deliberately disseminated in aerosolised form, resulting in severe pulmonary illness. Mortality from both would be high and rapid in the absence of early and effective treatment, making swift and effective liaison between alert clinicians and public health authorities crucial to an effective response. Differentiating features include mediastinal widening (anthrax) and haemoptysis (plague). Doxycycline and ciprofloxacin are effective agents for prophylaxis and treatment for both diseases. Medical advocacy for strengthening the Biological Weapons Convention, particularly with an enforceable protocol including verification and compliance provisions, is needed.

[Evaluation of the effectiveness of antibacterial substances in treating an experimental form of bubonic plague in monkeys]

The modelling of glandular plague and selection of the conditions for estimating the efficacy of new antibacterials for the treatment of the infection were performed on hamadryads (baboons). The experiments showed that the average LD50 of the culture of a highly virulent strain of Yersinia pestis on its subcutaneous administration to the animals was 2089 viable microbes. In 18 per cent of the episodes the experimental glandular plague in the animals was complicated by secondary plague pneumonia. Subcutaneous administration of 2 x 10(7) viable microbial cell of the plague pathogen caused acute sepsis and the animal death. The treatment of the experimental glandular plague in the hamadryads demonstrated that new antibacterials such as amikacin, netilmicin, ceftriaxone, cefotaxime, ceftizoxime, doxycycline, rifampicin, ofloxacin and ciprofloxacin were not inferior in their efficacy to streptomycin and tetracycline successfully used in the therapy of patients with plague.

[Ofloxacin efficacy in the prophylaxis and treatment of experimental plague due to antigen complete and defective strains of the pathogen]

Strains of the plague microbe, antigen complete and defective by fraction I and mouse toxin had the same in vitro susceptibility to ofloxacin (MIC 0.08 mg/L). The drug was superior in its activity to pefloxacin and especially nalidixic acid. In the experiments with albino mice (prophylaxis, 5 days) the ofloxacin efficacy was lower when the infection was due to the plague microbe strains deprived of the ability to produce fraction I and mouse toxin, evident from a statistically significant increase of the drug ED50 and a decrease of the animal survival percentage. When used in the doses corresponding to the human average daily doses, ofloxacin provided effective animal protection (80 to 100 per cent survival) after the prophylaxis for 7 days and the treatment of the plague infection irrespective of the strains, complete or antigen changed. However, when the infection is due to the antigen changed strain, ofloxacin should be used in the maximum daily doses at least for 7 days.

Vaccines, biological warfare, and bioterrorism

This article presents a brief history of the use of biological agents in warfare and bioterrorism. Bacillus anthracis, smallpox virus, and Yersinia pestis, historically have been and currently are considered the most likely candidates for potential use under these circumstances. This article discusses the clinical syndromes these agents cause and the role of vaccines in protection against them.

Preparing for bioterrorism: category A agents

September 11, 2001, brought the possibility of biologic acts of terrorism against the United States into the national consciousness. As the American people brace themselves for this new threat to the national well-being, clinicians must understand how to prevent, recognize, and treat the biologic agents that could be used in terrorist attacks. This article discusses the most likely biologic agents, including diagnostic laboratory procedures, treatment options, psychological effects, special populations, and reporting requirements.

[Effect of antibacterial therapy on the epidemic threat of experimental pneumonic plague in monkeys]

High therapeutic efficacy of aminoglycosides, quinolones, cephalosporins and rifampicins was demonstrated in experiments performed on monkeys, infected aerogenically by Yersinia pestis 1300. Antibacterials inhibited Y. pestis cells reproduction in the infected animals organisms evaluated by dynamics of bacterial cells isolated from the blood and fauces of the animals. It was shown that antibacterial therapy prevented infection transmission from the infected animals. The time of respiratory tract sanitation was in the range from 12 to 48 hours after the treatment and depended on drug efficacy.

[The experimental validation of the advantages of combined emergency (fluoroquinolones) and specific (EV Nalr) prevention of plague versus their sequential use]

Mice immunization with reference vaccine at the early stage of plague infection provided animals survival and prolonged mean survival period up to 2-5 days. Ciprofloxacin, ofloxacin and pefloxacin prevents development of post vaccine immunity at white mice, immunized by reference vaccine strain EV. Nalidixic acid and norfloxacin effect on post vaccine immunity was lower. Use of immunogenic strain EV Nafr (resistant to nalidixic acid and fluoroquinolones) provided antiplague immunity formation at the background of fluoroquinolones prophylaxis. Ciprofloxacin, ofloxacin and pefloxacin used for plague prophylaxis at white mice infected with Yersinia pestis (about 1000 LD50) inhibited postinfective immunity development. Nalidixic acid and norfloxacin didn't demonstrate such effect. Urgent (fluoroquinolones) and specific (EV Nalr) combined prophylaxis was evaluated as more effective for a 5-day period and provided the development of antiplague immunity.

Failure of oily chloramphenicol depot injection to treat plague in a murine model

Effective low-cost single-dose therapy would be invaluable in treating human plague. The efficacy of single- or two-dose injections of oily chloramphenicol (OCm) was compared with that of standard multiple injections of reference drugs (streptomycin or chloramphenicol) in a murine plague model. A single injection of OCm was ineffective. Two doses cleared bacteraemia and limited bacterial growth in the mouse spleen but were less effective in reducing mortality than standard therapy. However, because of the marked pharmacokinetic differences between mice and humans, the failure of depot injection of OCm in murine plague treatment is not indicative of its ineffectiveness in human plague.

The threat of biological terrorism: a public health and infection control reality

Bioterrorism is an emerging public health and infection control threat. Potential biological agents include smallpox, anthrax, plague, tularemia, botulinum toxin, brucellosis, Q fever, viral encephalitis, hemorrhagic fever, and staphylococcal enterotoxin B. An understanding of the epidemiology, clinical manifestations, and management of the more likely candidate agents is critical to limiting morbidity and mortality from a biological event. Effective response requires an increased index of suspicion for unusual diseases or syndromes, with prompt reporting to health authorities to facilitate recognition of an outbreak and subsequent intervention. Hospital epidemiology programs will play a crucial role in this effort.

[Comparative study of the medicines used in the fight against plague on the basis of the plague treatises of the Medical Faculty of Paris (1348-1349), of Joannes de Vesalia (after 1454) and of Thomas Montanus (1669)]

The remedies proposed for the prevention and treatment of the plague by the Medical Faculty of Paris and by Joannes de Vesalia are mainly derived from plants and animals apart from some minerals used in medieval medicine. Alchemical preparations, absent in the Compendium, are rarely mentioned by Joannes de Vesalia. About 90% of the simples preconized by the Faculty of Paris are still used as remedies in the tractates of Joannes de Vesalia and Montanus. The development of chemistry in the 16th and 17th centuries is responsible for the introduction of 'chemical' medicines in therapy. Montanus accepts these remedies with some reserve but favours also amulets and magic drugs. The plethora of medicines proposed demonstrates the inefficacy of therapeutics.

Immune response to Yersinia outer proteins and other Yersinia pestis antigens after experimental plague infection in mice

There is limited information concerning the nature and extent of the immune response to the virulence determinants of Yersinia pestis during the course of plague infection. In this study, we evaluated the humoral immune response of mice that survived lethal Y. pestis aerosol challenge after antibiotic treatment. Such a model may replicate the clinical situation in humans and indicate which virulence determinants are expressed in vivo. Immunoglobulin G enzyme-linked immunosorbent assay and immunoblotting were performed by using purified, recombinant antigens including F1, V antigen, YpkA, YopH, YopM, YopB, YopD, YopN, YopE, YopK, plasminogen activator protease (Pla), and pH 6 antigen as well as purified lipopolysaccharide. The major antigens recognized by murine convalescent sera were F1, V antigen, YopH, YopM, YopD, and Pla. Early treatment with antibiotics tended to reduce the immune response and differences between antibiotic treatment regimens were noted. These results may indicate that only some virulence factors are expressed and/or immunogenic during infection. This information may prove useful for selecting potential vaccine candidates and for developing improved serologic diagnostic assays.

[Experimental evaluation of prospects for the use of beta-lactams in plague infection caused by pathogens with plasmid resistance to penicillins]

High therapeutic efficacies of ceftriaxone, ceftazidime, cefotaxime and azthreonam in the treatment of experimental plague induced by beta-lactamase-producing strains of the plague microbe containing R plasmids RP-1, R57b and R40a were shown to correlate with their in vitro antibacterial activities. The therapeutic efficacy of sulbactam/ampicillin was recorded in the treatment of plague induced by the strain containing R plasmids R57b and R40a (the treatment course of 7 days). However, it was lower when the infection was due to the strain containing plasmid RP-1 (beta-lactamase TEM-2). Cefoperazone was not active in the treatment of experimental plague induced by the strains containing plasmids RP-1 and R57b (beta-lactamases TEM-2 and OXA-3). Ceftriaxone versus the antibiotics tested was considered to be the drug of choice for the etiotropic therapy of plague induced not only by the type strains of the plague microbe but also by its variants with the plasmid pattern resistance to penicillins.

[Pulmonic plague]

One hundred years after Yersin discovered Yersinia pestis during the plague epidemic in Hong Kong in 1894, human plague still has not been eliminated. The epidemic in 1994 in India, a country where no cases had been observed since 1996, raised great concern. Plague is an epizootic bacterial infection caused by a Gram negative coccobacillus, Y. pestis, transmitted by the bite of infected fleas. Bubonic plague is the most common form. Other clinical presentations include asymptomatic plague, abortive plague, pharyngeal plague, septicemic plague, meningeal plague, and primary or secondary pneumonic plague which is observed in 5 to 20% of cases. Plague is a highly communicable disease between humans despite antibiotic therapy which has reduced mortality by 80%. The prognosis depends on early diagnosis. Streptomycin and cyclines are the gold standard treatment.

[Pathomorphological changes in albino mice infected with plague and treated with cefotaxime]

Pathomorphological and bacteriological changes in albino mice infected with plague and treated with cefotaxime were investigated. The control animals which died within 3 days had structural changes characteristic of generalized plague with lesions in the infection site, regional lymph nodes, spleen, liver and lungs. The plague microbe was isolated from the tissues of all the organs and blood. The animals treated with cefotaxime (200 mg/kg for 7 days) survived. The histological examination conclusively demonstrated the absence of the changes characteristic of generalized plague in their internal organs. The infection process was mainly restricted by the primary complex and was strictly localized. The tissue reaction around the focus in the second part of the experiment developed in accordance with the productive type inflammation followed by the organization and cicatrization. In the bacteriological investigation the plague causative agent was detectable during the first days of the treatment in the site of the infection. During the subsequent days the plague microbe was not detected.

Antibiotic treatment of experimental pneumonic plague in mice

A mouse model was developed to evaluate the efficacy of antibiotic treatment of pneumonic plague; streptomycin was compared to antibiotics with which there is little or no clinical experience. Infection was induced by inhalation of aerosolized Yersinia pestis organisms. Antibiotics were administered by intraperitoneal injection every 6 hours for 5 days, at doses that produced levels of drug in serum comparable to those observed in humans treated for other serious infections. These studies compared in vitro to in vivo activity and evaluated the efficacy of antibiotics started at different times after exposure. Early treatment (started 24 h after challenge, when 0 of 10 mice tested had positive blood cultures) with netilmicin, ciprofloxacin, ofloxacin, ceftriaxone, ceftazidime, aztreonam, ampicillin, and rifampin (but not cefazolin, cefotetan, or ceftizoxime) demonstrated efficacy comparable to streptomycin. Late treatment (started 42 h after exposure, when five of five mice tested had positive blood cultures) with netilmicin, ciprofloxacin, ofloxacin, and a high dose (20 mg/kg of body weight every 6 h) of gentamicin produced survival rates comparable to that with streptomycin, while all of the beta-lactam antibiotics (cefazolin, cefotetan, ceftriaxone, ceftazidime, aztreonam, and ampicillin) and rifampin were significantly inferior to streptomycin. In fact, all groups of mice treated late with beta-lactam antibiotics experienced accelerated mortality rates compared to normal-saline-treated control mice. These studies indicate that netilmicin, gentamicin, ciprofloxacin, and ofloxacin may be alternatives for the treatment of pneumonic plague in humans. However, the beta-lactam antibiotics are not recommended, based upon poor efficacy in this mouse model of pneumonic plague, particularly when pneumonic plague may be associated with bacteremia.

[In vitro influence of biologically active factors of microorganisms on antibiotic susceptibility of Yersinia pestis]

To estimate the in vitro susceptibility of the plague microbe to chemotherapeutics, various experimental models with the maximum closeness to the host conditions were tested. The tests included the assay of the drug antibacterial activity against the plague microbe by the method of two-fold dilutions in biological fluids i.e. human normal (nonimmune) serum (HNS) and guinea pig heparinized blood. Hottinger broth was used as the control. It was shown that any system used for estimation of the drug MIC influenced the plague microbe susceptibility. Thus, the serum complement increased the antibacterial activity of cefotaxime, rifampicin, doxycycline, erythromycin and polymyxin B. In the blood of a susceptible host (guinea pigs) the activity of quinoxydine and dioxydine against the plague microbe markedly increased while the effect of benzylpenicillin, cefotaxime and furazolidone decreased. The data on the in vitro activity of the antibiotics in blood were comparable with those on their in vivo therapeutic efficacy.

Efficacy of doxycycline and ciprofloxacin against experimental Yersinia pestis infection

The efficacies of ciprofloxacin and doxycycline prophylaxis and therapy were assessed against experimental pneumonic plague infections induced by two strains of Yersinia pestis in a mouse model. When exposed to an aerosol of Y. pestis strain GB, containing 8.39 x 10(5) +/- 4.17 x 10(4) cfu, the retained dose was 7.3 x 10(3) +/- 2.3 x 10(3) cfu. When exposed to an aerosol of Y. pestis strain CO-92, containing 1.86 x 10(5) +/- 7.4 x 10(3) cfu, the retained dose was 3.4 x 10(4) +/- 2.6 x 10(3) cfu. Both strains resulted in a respiratory and systemic infection closely resembling human pneumonic plague. Ciprofloxacin prophylaxis and therapy was successful against both strains for up to 24 h after challenge, but not after 48 h. Both doxycycline prophylaxis and therapy regimens were ineffective against both strains, although strain CO-92 was more susceptible in vitro to doxycycline than strain GB and supra-MIC levels were achieved in the serum and lungs of the animal.