Immunotherapy for tularemia

A Rare Occurrence of Tularemia in New Jersey

Tularemia has been well described clinically in the United States since the early 1900s. Worldwide, the infection has manifested in a variety of forms through various vectors with geography and local prevalence often considered in the diagnostic work-up. We present a case of a 57-year-old patient who lived in an area with low tularemia infection rates and presented with fever and a tender, swollen elbow. Though initially diagnosed with cellulitis, she was eventually found to have tularemia after further interviewing and questioning, followed by successful treatment with doxycycline. A thorough history including exposures and daily activities should always be considered in an effort to rule out rare infections, even in areas of low disease prevalence.

Aerosol prime-boost vaccination provides strong protection in outbred rabbits against virulent type A Francisella tularensis

Tularemia, also known as rabbit fever, is a severe zoonotic disease in humans caused by the gram-negative bacterium Francisella tularensis (Ft). While there have been a number of attempts to develop a vaccine for Ft, few candidates have advanced beyond experiments in inbred mice. We report here that a prime-boost strategy with aerosol delivery of recombinant live attenuated candidate Ft S4ΔaroD offers significant protection (83% survival) in an outbred animal model, New Zealand White rabbits, against aerosol challenge with 248 cfu (11 LD₅₀) of virulent type A Ft SCHU S4. Surviving rabbits given two doses of the attenuated strains by aerosol did not exhibit substantial post-challenge fevers, changes in erythrocyte sedimentation rate or in complete blood counts. At a higher challenge dose (3,186 cfu; 139 LD₅₀), protection was still good with 66% of S4ΔaroD-vaccinated rabbits surviving while 50% of S4ΔguaBA vaccinated rabbits also survived challenge. Pre-challenge plasma IgG titers against Ft SCHU S4 corresponded with survival time after challenge. Western blot analysis found that plasma antibody shifted from predominantly targeting Ft O-antigen after the prime vaccination to other antigens after the boost. These results demonstrate the superior protection conferred by a live attenuated derivative of virulent F. tularensis, particularly when given in an aerosol prime-boost regimen.

Therapeutic Antibodies for Biodefense

Diseases can be caused naturally by biological agents such as bacteria, viruses and toxins (natural risk). However, such biological agents can be intentionally disseminated in the environment by a State (military context) or terrorists to cause diseases in a population or livestock, to destabilize a nation by creating a climate of terror, destabilizing the economy and undermining institutions. Biological agents can be classified according to the severity of illness they cause, its mortality and how easily the agent can be spread. The Centers for Diseases Control and Prevention (CDC) classify biological agents in three categories (A, B and C); Category A consists of the six pathogens most suitable for use as bioweapons (Bacillus anthracis, Yersinia pestis, Francisella tularensis, botulinum neurotoxins, smallpox and viral hemorrhagic fevers). Antibodies represent a perfect biomedical countermeasure as they present both prophylactic and therapeutic properties, act fast and are highly specific to the target. This review focuses on the main biological agents that could be used as bioweapons, the history of biowarfare and antibodies that have been developed to neutralize these agents.

Dermatological aspects of tularaemia: a study of 168 cases

BACKGROUND

Tularaemia is a zoonotic infectious disease caused by Francisella tularensis, an aerobic, uncapsulated, gram-negative coccobacillus. Several case reports have appeared on the dermatological manifestations of tularaemia, but relatively few longer-term studies are available.

AIM

To identify skin features of tularaemia that aid in its diagnosis.

METHODS

In total, 168 patients (68 male, 100 female) diagnosed with tularaemia were retrospectively examined. All dermatological data for these patients were evaluated.

RESULTS

Of the 168 patients, 149 (88.69%) had tularaemia of the oropharyngeal type, 12 (7.73%) had the ulceroglandular type, 5 (2.9%) had the oculoglandular type and 2 (0.59%) had the pulmonary type. Secondary skin manifestations were found in 26 patients (15.47%). Sweet syndrome (SS) was found in 11 patients (6.54%), most of whom presented with the oropharyngeal form, while erythema nodosum (EN) was found in 7 patients (4.16%), dermatitis in 2 (1.19%), urticaria in 2 (1.19%), acneiform eruptions in 1 (0.59%), vasculitis-like eruptions in 1 (0.59%) and SS + EN in 1 (0.59%). Patients with the oropharyngeal form had a statistically significant (P < 0.001) higher number of skin findings than patients with the other forms.

CONCLUSIONS

In clinical practice, tularaemia may present with various cutaneous manifestations, and dermatologists who work in endemic regions must be aware of the possibility of this disease.

Hematopoietic MyD88 and IL-18 are essential for IFN-γ-dependent restriction of type A Francisella tularensis infection

Francisella tularensis is a highly infectious intracellular bacterium that causes the potentially fatal disease tularemia. We used mice with conditional MyD88 deficiencies to investigate cellular and molecular mechanisms by which MyD88 restricts type A F. tularensis infection. F. tularensis-induced weight loss was predominately dependent on MyD88 signaling in nonhematopoietic cells. In contrast, MyD88 signaling in hematopoietic cells, but not in myeloid and dendritic cells, was essential for control of F. tularensis infection in tissue. Myeloid and dendritic cell MyD88 deficiency also did not markedly impair cytokine production during infection. Although the production of IL-12 or -18 was not significantly reduced in hematopoietic MyD88-deficient mice, IFN-γ production was abolished in these animals. In addition, neutralization studies revealed that control of F. tularensis infection mediated by hematopoietic MyD88 was entirely dependent on IFN-γ. Although IL-18 production was not significantly affected by MyD88 deficiency, IL-18 was essential for IFN-γ production and restricted bacterial replication in an IFN-γ-dependent manner. Caspase-1 was also found to be partially necessary for the production of IL-18 and IFN-γ and for control of F. tularensis replication. Our collective data show that the response of leukocytes to caspase-1-dependent IL-18 via MyD88 is critical, whereas MyD88 signaling in myeloid and dendritic cells is dispensable for IFN-γ-dependent control of type A F. tularensis infection.

Sensitive Detection of Francisella tularensis Directly from Whole Blood by Use of the GeneXpert System

Francisella tularensis is a potential bioterrorism agent that is highly infectious at very low doses. Diagnosis of tularemia by blood culture and nucleic acid-based diagnostic tests is insufficiently sensitive. Here, we demonstrate a highly sensitive F. tularensis assay that incorporates sample processing and detection into a single cartridge suitable for point-of-care detection. The assay limit of detection (LOD) and dynamic range were determined in a filter-based cartridge run on the GeneXpert system. F. tularensis DNA in buffer or CFU of F. tularensis was spiked into human or macaque blood. To simulate detection in human disease, the assay was tested on blood drawn from macaques infected with F. tularensis Schu S4 at daily intervals. Assay detection was compared to that with a conventional quantitative PCR (qPCR) assay and blood culture. The assay LOD was 0.1 genome equivalents (GE) per reaction and 10 CFU/ml F. tularensis in both human and macaque blood. In infected macaques, the assay detected F. tularensis on days 1 to 4 postinfection in 21%, 17%, 60%, and 83% of macaques, respectively, compared to conventional qPCR positivity rates of 0%, 0%, 30%, and 100% and CFU detection of blood culture at 0%, 0%, 0%, and 10% positive, respectively. Assay specificity was 100%. The new cartridge-based assay can rapidly detect F. tularensis in bloodstream infections directly in whole blood at the early stages of infection with a sensitivity that is superior to that of other methods. The simplicity of the automated testing procedures may make this test suitable for rapid point-of-care detection.

Activities of Murine Peripheral Blood Lymphocytes Provide Immune Correlates That Predict Francisella tularensis Vaccine Efficacy

We previously identified potential correlates of vaccine-induced protection against Francisella tularensis using murine splenocytes and further demonstrated that the relative levels of gene expression varied significantly between tissues. In contrast to splenocytes, peripheral blood leukocytes (PBLs) represent a means to bridge vaccine efficacy in animal models to that in humans. Here we take advantage of this easily accessible source of immune cells to investigate cell-mediated immune responses against tularemia, whose sporadic incidence makes clinical trials of vaccines difficult. Using PBLs from mice vaccinated with F. tularensis Live Vaccine Strain (LVS) and related attenuated strains, we combined the control of in vitro Francisella replication within macrophages with gene expression analyses. The in vitro functions of PBLs, particularly the control of intramacrophage LVS replication, reflected the hierarchy of in vivo protection conferred by LVS-derived vaccines. Moreover, several genes previously identified by the evaluation of splenocytes were also found to be differentially expressed in immune PBLs. In addition, more extensive screening identified additional potential correlates of protection. Finally, expression of selected genes in mouse PBLs obtained shortly after vaccination, without ex vivo restimulation, was different among vaccine groups, suggesting a potential tool to monitor efficacious vaccine-induced immune responses against F. tularensis. Our studies demonstrate that murine PBLs can be used productively to identify potential correlates of protection against F. tularensis and to expand and refine a comprehensive set of protective correlates.

Francisella tularensis as a potential agent of bioterrorism?

Francisella tularensis is a category A bioterrorism agent. It is the etiological agent of tularemia, a zoonotic disease found throughout the northern hemisphere. The intentional spread of F. tularensis aerosols would probably lead to severe and often fatal pneumonia cases, but also secondary cases from contaminated animals and environments. We are not ready to face such a situation. No vaccine is currently available. A few antibiotics are active against F. tularensis, but strains resistant to these antibiotics could be used in the context of bioterrorism. We need new therapeutic strategies to fight against category A bioterrorism agents, including development of new drugs inhibiting F. tularensis growth and/or virulence, or enhancing the host response to infection by this pathogen.

New therapeutic approaches for treatment of tularaemia: a review

Antibiotic treatment of tularaemia is based on a few drugs, including the fluoroquinolones (e.g., ciprofloxacin), the tetracyclines (e.g., doxycycline), and the aminoglycosides (streptomycin and gentamicin). Because no effective and safe vaccine is currently available, tularaemia prophylaxis following proven exposure to F. tularensis also relies on administration of antibiotics. A number of reasons make it necessary to search for new therapeutic alternatives: the potential toxicity of first-line drugs, especially in children and pregnant women; a high rate of treatment relapses and failures, especially for severe and/or suppurated forms of the disease; and the possible use of antibiotic-resistant strains in the context of a biological threat. This review presents novel therapeutic approaches that have been explored in recent years to improve tularaemia patients' management and prognosis. These new strategies have been evaluated in vitro, in axenic media and cell culture systems and/or in animal models. First, the activities of newly available antibiotic compounds were evaluated against F. tularensis, including tigecycline (a glycylcycline), ketolides (telithromycin and cethromycin), and fluoroquinolones (moxifloxacin, gatifloxacin, trovafloxacin and grepafloxacin). The liposome delivery of some antibiotics was evaluated. The effect of antimicrobial peptides against F. tularensis was also considered. Other drugs were evaluated for their ability to suppress the intracellular multiplication of F. tularensis. The effects of the modulation of the innate immune response (especially via TLR receptors) on the course of F. tularensis infection was characterized. Another approach was the administration of specific antibodies to induce passive resistance to F. tularensis infection. All of these studies highlight the need to develop new therapeutic strategies to improve the management of patients with tularaemia. Many possibilities exist, some unexplored. Moreover, it is likely that new therapeutic alternatives that are effective against this intracellular pathogen could be, at least partially, extrapolated to other human pathogens.