[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.