Therapeutic monoclonal antibody treatment protects nonhuman primates from severe Venezuelan equine encephalitis virus disease after aerosol exposure.

There are no FDA licensed vaccines or therapeutics for Venezuelan equine encephalitis virus (VEEV) which causes a debilitating acute febrile illness in humans that can progress to encephalitis. Previous studies demonstrated that murine and macaque monoclonal antibodies (mAbs) provide prophylactic and therapeutic efficacy against VEEV peripheral and aerosol challenge in mice. Additionally, humanized versions of two neutralizing mAbs specific for the E2 glycoprotein, 1A3B-7 and 1A4A-1, administered singly protected mice against aerosolized VEEV. However, no studies have demonstrated protection in nonhuman primate (NHP) models of VEEV infection. Here, we evaluated a chimeric antibody 1A3B-7 (c1A3B-7) containing mouse variable regions on a human IgG framework and a humanized antibody 1A4A-1 containing a serum half-life extension modification (Hu-1A4A-1-YTE) for their post-exposure efficacy in NHPs exposed to aerosolized VEEV. Approximately 24 hours after exposure, NHPs were administered a single bolus intravenous mAb. Control NHPs had typical biomarkers of VEEV infection including measurable viremia, fever, and lymphopenia. In contrast, c1A3B-7 treated NHPs had significant reductions in viremia and lymphopenia and on average approximately 50% reduction in fever. Although not statistically significant, Hu-1A4A-1-YTE administration did result in reductions in viremia and fever duration. Delay of treatment with c1A3B-7 to 48 hours post-exposure still provided NHPs protection from severe VEE disease through reductions in viremia and fever. These results demonstrate that post-exposure administration of c1A3B-7 protected macaques from development of severe VEE disease even when administered 48 hours following aerosol exposure and describe the first evaluations of VEEV-specific mAbs for post-exposure prophylactic use in NHPs. Viral mutations were identified in one NHP after c1A3B-7 treatment administered 24 hrs after virus exposure. This suggests that a cocktail-based therapy, or an alternative mAb against an epitope that cannot mutate without resulting in loss of viral fitness may be necessary for a highly effective therapeutic.

High Infection Rates for Adult Macaques after Intravaginal or Intrarectal Inoculation with Zika Virus.

Unprotected sexual intercourse between persons residing in or traveling from regions with Zika virus transmission is a risk factor for infection. To model risk for infection after sexual intercourse, we inoculated rhesus and cynomolgus macaques with Zika virus by intravaginal or intrarectal routes. In macaques inoculated intravaginally, we detected viremia and virus RNA in 50% of macaques, followed by seroconversion. In macaques inoculated intrarectally, we detected viremia, virus RNA, or both, in 100% of both species, followed by seroconversion. The magnitude and duration of infectious virus in the blood of macaques suggest humans infected with Zika virus through sexual transmission will likely generate viremias sufficient to infect competent mosquito vectors. Our results indicate that transmission of Zika virus by sexual intercourse might serve as a virus maintenance mechanism in the absence of mosquito-to-human transmission and could increase the probability of establishment and spread of Zika virus in regions where this virus is not present.

African Green Monkeys Maintain Zika Virus Neutralizing Antibodies for at Least 1,427 Days Postinfection.

We report strong Zika virus (ZIKV) neutralizing antibody responses in African green monkeys (Chlorocebus sabaeus) up to 1,427 days after ZIKV exposure via the subcutaneous, intravaginal, or intrarectal routes. Our results suggest that immunocompetent African green monkeys previously infected with ZIKV are likely protected from reinfection for years, possibly life, and would not contribute to virus amplification during ZIKV epizootics.

Natural history of inhalation melioidosis in rhesus macaques (Macaca mulatta) and African green monkeys (Chlorocebus aethiops).

Burkholderia pseudomallei, the causative agent of melioidosis, is recognized as a serious health threat due to its involvement in septic and pulmonary infections in areas of endemicity and is recognized by the Centers for Disease Control and Prevention as a category B biothreat agent. An animal model is desirable to evaluate the pathogenesis of melioidosis and medical countermeasures. A model system that represents human melioidosis infections is essential in this process. A group of 10 rhesus macaques (RMs) and 10 African green monkeys (AGMs) was exposed to aerosolized B. pseudomallei 1026b. The first clinical signs were fever developing 24 to 40 h postexposure followed by leukocytosis resulting from a high percentage of neutrophils. Dyspnea manifested 2 to 4 days postexposure. In the AGMs, an increase in interleukin 1ß (IL-1ß), IL-6, IL-8, gamma interferon (IFN-γ), and tumor necrosis factor alpha (TNF-α) was observed. In the RMs, IL-1ß, IL-6, and TNF-α increased. All the RMs and AGMs had various degrees of bronchopneumonia, with inflammation consisting of numerous neutrophils and a moderate number of macrophages. Both the RMs and the AGMs appear to develop a melioidosis infection that closely resembles that seen in acute human melioidosis. However, for an evaluation of medical countermeasures, AGMs appear to be a more appropriate model.

No Evidence of rVSV-Ebola Virus Vaccine Replication or Dissemination in the Sand Fly Phlebotomus papatasi.

Following vaccination with the live attenuated, recombinant vesicular stomatitis virus Indiana serotype Ebola virus (rVSV-EBOV) vaccine, persons may exhibit a transient vaccine-associated viremia. To investigate the potential for Old World sand flies to transmit this vaccine following feeding on a viremic person, we fed laboratory-reared Phlebotomus papatasi an artificial blood meal containing 7.2 log10 plaque-forming units of rVSV-EBOV. Replication or dissemination was not detected in the body or legs of any P. papatasi collected at seven (n = 75) or 15 (n = 75) days post-feed. These results indicate a low potential for rVSV-EBOV to replicate and disseminate in P. papatasi, a species whose geographic distribution ranges from Morocco to southwest Asia and as far north as southern Europe.

ACTIVating Resources for the COVID-19 Pandemic: In Vivo Models for Vaccines and Therapeutics.

The Preclinical Working Group of Accelerating COVID-19 Therapeutic Interventions and Vaccines (ACTIV), a public-private partnership spearheaded by the National Institutes of Health, has been charged with identifying, prioritizing, and communicating SARS-CoV-2 preclinical resources. Reviewing SARS-CoV-2 animal model data facilitates standardization and harmonization and informs knowledge gaps and prioritization of limited resources. To date, mouse, hamster, ferret, guinea pig, and non-human primates have been investigated. Several species are permissive for SARS-CoV-2 replication, often exhibiting mild disease with resolution, reflecting most human COVID-19 cases. More severe disease develops in a few models, some associated with advanced age, a risk factor for human disease. This review provides a snapshot that recommends the suitability of models for testing vaccines and therapeutics, which may evolve as our understanding of COVID-19 disease biology improves. COVID-19 is a complex disease, and individual models recapitulate certain aspects of disease; therefore, the coordination and assessment of animal models is imperative.

Modeling mosquito-borne and sexual transmission of Zika virus in an enzootic host, the African green monkey.

Mosquito-borne and sexual transmission of Zika virus (ZIKV), a TORCH pathogen, recently initiated a series of large epidemics throughout the Tropics. Animal models are necessary to determine transmission risk and study pathogenesis, as well screen antivirals and vaccine candidates. In this study, we modeled mosquito and sexual transmission of ZIKV in the African green monkey (AGM). Following subcutaneous, intravaginal or intrarectal inoculation of AGMs with ZIKV, we determined the transmission potential and infection dynamics of the virus. AGMs inoculated by all three transmission routes exhibited viremia and viral shedding followed by strong virus neutralizing antibody responses, in the absence of clinical illness. All four of the subcutaneously inoculated AGMs became infected (mean peak viremia: 2.9 log10 PFU/mL, mean duration: 4.3 days) and vRNA was detected in their oral swabs, with infectious virus being detected in a subset of these specimens. Although all four of the intravaginally inoculated AGMs developed virus neutralizing antibody responses, only three had detectable viremia (mean peak viremia: 4.0 log10 PFU/mL, mean duration: 3.0 days). These three AGMs also had vRNA and infectious virus detected in both oral and vaginal swabs. Two of the four intrarectally inoculated AGMs became infected (mean peak viremia: 3.8 log10 PFU/mL, mean duration: 3.5 days). vRNA was detected in oral swabs collected from both of these infected AGMs, and infectious virus was detected in an oral swab from one of these AGMs. Notably, vRNA and infectious virus were detected in vaginal swabs collected from the infected female AGM (peak viral load: 7.5 log10 copies/mL, peak titer: 3.8 log10 PFU/mL, range of detection: 5-21 days post infection). Abnormal clinical chemistry and hematology results were detected and acute lymphadenopathy was observed in some AGMs. Infection dynamics in all three AGM ZIKV models are similar to those reported in the majority of human ZIKV infections. Our results indicate that the AGM can be used as a surrogate to model mosquito or sexual ZIKV transmission and infection. Furthermore, our results suggest that AGMs are likely involved in the enzootic maintenance and amplification cycle of ZIKV.

Real-time PCR for the early detection and quantification of Coxiella burnetii as an alternative to the murine bioassay.

Real-time PCR was used to analyze archived blood from non-human primates (NHP) and fluid samples originating from a well-controlled Q fever vaccine efficacy trial. The PCR targets were the IS1111 element and the com1 gene of Coxiella burnetii. Data from that previous study were used to evaluate real-time PCR as an alternative to the use of sero-conversion by mouse bioassay for both quantification and early detection of C. burnetii bacteria. Real-time PCR and the mouse bioassay exhibited no statistical difference in quantifying the number of microorganisms delivered in the aerosol challenge dose. The presence of C. burnetii in peripheral blood of non-human primates was detected by real-time PCR as early after exposure as the mouse bioassay with results available within hours instead of weeks. This study demonstrates that real-time PCR has the ability to replace the mouse bioassay to measure dosage and monitor infection of C. burnetii in a non-human primate model.

The aerosol rabbit model of TB latency, reactivation and immune reconstitution inflammatory syndrome.

The large reservoir of human latent tuberculosis (TB) contributes to the global success of the pathogen, Mycobacterium tuberculosis (Mtb). We sought to test whether aerosol infection of rabbits with Mtb H37Rv could model paucibacillary human latent TB. The lung burden of infection peaked at 5 weeks after aerosol infection followed by host containment of infection that was achieved in all rabbits. One-third of rabbits had at least one caseous granuloma with culturable bacilli at 36 weeks after infection suggesting persistent paucibacillary infection. Corticosteroid-induced immunosuppression initiated after disease containment resulted in reactivation of disease. Seventy-two percent of rabbits had culturable bacilli in the right upper lung lobe homogenates compared to none of the untreated controls. Discontinuation of dexamethasone led to predictable lymphoid recovery, with a proportion of rabbits developing multicentric large caseous granuloma. The development and severity of the immune reconstitution inflammatory syndrome (IRIS) was dependent on the antigen load at the time of immunosuppression and subsequent bacillary replication during corticosteroid-induced immunosuppression. Clinically, many aspects were similar to IRIS in severely immunosuppressed HIV-infected patients who have functional restoration of T cells in response to effective (highly active) antiretroviral therapy. This corticosteroid model is the only animal model of the IRIS. Further study of the rabbit model of TB latency, reactivation and IRIS may be important in understanding the immunopathogenesis of these poorly modeled states as well as for improved diagnostics for specific stages of disease.

Susceptibility to tuberculosis: composition of tuberculous granulomas in Thorbecke and outbred New Zealand White rabbits.

We sought to characterize the lung cellular immune responses to inhaled Mycobacterium tuberculosis (Mtb) of the susceptible inbred Thorbecke rabbit (the genomically sequenced strain, now unavailable) and compare it to outbred, Mtb-resistant, New Zealand White rabbits. Using Mtb CDC1551, we confirmed that the inbred rabbits allowed establishment of infection with this low virulence strain, compared to poor establishment in outbred rabbits. With a more virulent strain, Mtb Erdman, that establishes infection well in both rabbit strains, we analyzed granulomas from rabbit lungs 5 weeks after aerosol infection. The lung granulomas of inbred rabbits had significantly higher frequencies of cells expressing MHC Class II and CD11b, and lower frequencies of CD8+ T cells than the outbred controls. Macrophage-sized cells expressing MHC Class II in inbred rabbit granulomas showed significantly decreased intensity of expression, suggesting impaired maturation. Although the inbred dermal tuberculin reactions were decreased, the in vitro IFN-gamma mRNA responses of hilar node lymphocytes to tuberculin were higher than those of outbred rabbits. Further delineation of the outbred rabbit's resistant immune response to Mtb infection is warranted.

Virus-encoded miRNAs in Ebola virus disease.

Ebola virus (EBOV) is a negative-strand RNA virus that replicates in the cytoplasm and causes an often-fatal hemorrhagic fever. EBOV, like other viruses, can reportedly encode its own microRNAs (miRNAs) to subvert host immune defenses. miRNAs are short noncoding RNAs that can regulate gene expression by hybridizing to multiple mRNAs, and viral miRNAs can enhance viral replication and infectivity by regulating host or viral genes. To date, only one EBOV miRNA has been examined in human infection. Here, we assayed mouse, rhesus macaque, cynomolgus macaque, and human samples infected with three EBOV variants for twelve computationally predicted viral miRNAs using RT-qPCR. Ten miRNAs aligned to EBOV variants and were detectable in the four species during disease with several viral miRNAs showing presymptomatic amplification in animal models. miRNA abundances in both the mouse and nonhuman primate models mirrored the human cohort, with miR-1-5p, miR-1-3p, and miR-T3-3p consistently at the highest levels. These striking similarities in the most abundant miRNAs during infection with different EBOV variants and hosts indicate that these miRNAs are potential valuable diagnostic markers and key effectors of EBOV pathogenesis.

Zika Virus Infection in Syrian Golden Hamsters and Strain 13 Guinea Pigs.

To evaluate potential immunocompetent small animal models of Zika virus (ZIKV) infection, we inoculated Syrian golden hamsters (subcutaneously or intraperitoneally) and strain 13 guinea pigs (intraperitoneally) with Senegalese ZIKV strain ArD 41525 or Philippines ZIKV strain CPC-0740. We did not detect viremia in hamsters inoculated subcutaneously with either virus strain, although some hamsters developed virus neutralizing antibodies. However, we detected statistically significant higher viremias (P = 0.0285) and a higher median neutralization titer (P = 0.0163) in hamsters inoculated intraperitoneally with strain ArD 41525 compared with strain CPC-0740. Furthermore, some hamsters inoculated with strain ArD 41525 displayed mild signs of disease. By contrast, strain 13 guinea pigs inoculated intraperitoneally with either strain did not have detectable viremias and less than half developed virus neutralizing antibodies. Our results support the use of the Syrian golden hamster intraperitoneal model to explore phenotypic variation between ZIKV strains.

Low potential for mechanical transmission of Ebola virus via house flies (Musca domestica).

BACKGROUND: Ebola virus (EBOV) infection results in high morbidity and mortality and is primarily transmitted in communities by contact with infectious bodily fluids. While clinical and experimental evidence indicates that EBOV is transmitted via mucosal exposure, the ability of non-biting muscid flies to mechanically transmit EBOV following exposure to the face had not been assessed. RESULTS: To investigate this transmission route, house flies (Musca domestica Linnaeus) were used to deliver an EBOV/blood mixture to the ocular/nasal/oral facial mucosa of four cynomolgus macaques (Macaca fascicularis Raffles). Following exposure, macaques were monitored for evidence of infection through the conclusion of the study, days 57 and 58. We found no evidence of systemic infection in any of the exposed macaques. CONCLUSIONS: The results of this study indicate that there is a low potential for the mechanical transmission of EBOV via house flies - the conditions in this study were not sufficient to initiate infection.

Recombinant C fragment of botulinum neurotoxin B serotype (rBoNTB (HC)) immune response and protection in the rhesus monkey.

Botulinum neurotoxin B (BoNTB) is a distinct protein subtype of a family of neurotoxins with the potential for use in biological warfare or terrorist attacks. This study is one in a series evaluating the immunogenicity and protective effects of recombinant vaccines against the different subtypes of botulinum toxin. The recombinant subunit vaccines encoding the C fragment portion ( approximately 50 kDa) of the toxins are produced in the yeast, Pichia pastoris. In this study, groups of rhesus monkeys were vaccinated with three doses (1 and 5microg per dose) of rBoNTB(H(c)) vaccine. Total and neutralizing antibody titers were determined at various times during and postvaccination. Two groups of vaccinated monkeys plus non-vaccinated controls were actively challenged with B toxin by aerosol exposure. All monkeys receiving vaccine were protected from the toxin and no clinical signs of disease were observed, while controls displaying classic signs of botulism succumbed to the toxin challenge. Two additional groups of monkeys receiving the same vaccine regiment as the first two groups had significant levels of circulating neutralizing antibody titers up to 24 months postvaccination. This non-human primate study demonstrated the short- and long-term immunity afforded by the rBoNTB(H(c)) vaccine.

Circulating microRNA profiles of Ebola virus infection.

Early detection of Ebola virus (EBOV) infection is essential to halting transmission and adjudicating appropriate treatment. However, current methods rely on viral identification, and this approach can misdiagnose presymptomatic and asymptomatic individuals. In contrast, disease-driven alterations in the host transcriptome can be exploited for pathogen-specific diagnostic biomarkers. Here, we present for the first time EBOV-induced changes in circulating miRNA populations of nonhuman primates (NHPs) and humans. We retrospectively profiled longitudinally-collected plasma samples from rhesus macaques challenged via intramuscular and aerosol routes and found 36 miRNAs differentially present in both groups. Comparison of miRNA abundances to viral loads uncovered 15 highly correlated miRNAs common to EBOV-infected NHPs and humans. As proof of principle, we developed an eight-miRNA classifier that correctly categorized infection status in 64/74 (86%) human and NHP samples. The classifier identified acute infections in 27/29 (93.1%) samples and in 6/12 (50%) presymptomatic NHPs. These findings showed applicability of NHP-derived miRNAs to a human cohort, and with additional research the resulting classifiers could impact the current capability to diagnose presymptomatic and asymptomatic EBOV infections.

Ebola Virus Infections in Nonhuman Primates Are Temporally Influenced by Glycoprotein Poly-U Editing Site Populations in the Exposure Material.

Recent experimentation with the variants of the Ebola virus that differ in the glycoprotein's poly-uridine site, which dictates the form of glycoprotein produced through a transcriptional stutter, has resulted in questions regarding the pathogenicity and lethality of the stocks used to develop products currently undergoing human clinical trials to combat the disease. In order to address these concerns and prevent the delay of these critical research programs, we designed an experiment that permitted us to intramuscularly challenge statistically significant numbers of naïve and vaccinated cynomolgus macaques with either a 7U or 8U variant of the Ebola virus, Kikwit isolate. In naïve animals, no difference in survivorship was observed; however, there was a significant delay in the disease course between the two groups. Significant differences were also observed in time-of-fever, serum chemistry, and hematology. In vaccinated animals, there was no statistical difference in survivorship between either challenge groups, with two succumbing in the 7U group compared to 1 in the 8U challenge group. In summary, survivorship was not affected, but the Ebola virus disease course in nonhuman primates is temporally influenced by glycoprotein poly-U editing site populations.

Pulmonary gene expression profiling of inhaled ricin.

Aerosol exposure to ricin causes irreversible pathological changes of the respiratory tract resulting in epithelial necrosis, pulmonary edema and ultimately death. The pulmonary genomic profile of BALB/c mice inhalationally exposed to a lethal dose of ricin was examined using cDNA arrays. The expression profile of 1178 mRNA species was determined for ricin-exposed lung tissue, in which 34 genes had statistically significant changes in gene expression. Transcripts identified by the assay included those that facilitate tissue healing (early growth response gene (egr)-1), regulate inflammation (interleukin (IL)-6, tristetraproline (ttp)), cell growth (c-myc, cytokine-inducible SH2-containing protein (cish)- 3), apoptosis (T-cell death associated protein (tdag)51, pim-1) and DNA repair (ephrin type A receptor 2 (ephA2)). Manipulation of these gene products may provide a means of limiting the severe lung damage occurring at the cellular level. Transcriptional activation of egr-1, cish-3, c-myc and thrombospondin (tsp)-1 was already apparent when pathological and physiological changes were observed in the lungs at 12 h postexposure. These genes may well serve as markers for ricin-induced pulmonary toxicity. Ongoing studies are evaluating this aspect of the array data and the potential of several genes for clinical intervention.

Pathologic changes associated with brucellosis experimentally induced by aerosol exposure in rhesus macaques (Macaca mulatta).

OBJECTIVE: To develop an aerosol exposure method for induction of brucellosis in rhesus macaques (Macaca mulatta). ANIMALS: 10 adult rhesus macaques. PROCEDURE: 8 rhesus macaques were challenge exposed with 10(2) to 10(5) colony-forming units of Brucella melitensis 16M by use of an aerosol-exposure technique, and 2 served as control animals. All macaques were euthanatized 63 days after challenge exposure. Gross and microscopic lesions, bacterial burden in target organs, and histologic changes in tissues were evaluated. RESULTS: Grossly, spleen weights were increased in exposed macaques, compared with spleen weights in control macaques. Histologically, there was inflammation in the liver, kidneys, spleen, testes, and epididymides in exposed macaques. The spleen and lymph nodes had increased numbers of lymphohistiocytic cells. Morphometrically, the spleen also had an increased ratio of white pulp to red pulp. Areas of hepatitis and amount of splenic white pulp increased with increasing exposure dose. CONCLUSIONS AND CLINICAL RELEVANCE: Pathologic findings in rhesus macaques after aerosol exposure to B melitensis are similar to those observed in humans with brucellosis. IMPACT FOR HUMAN MEDICINE: These results may aid in the development of a vaccine against brucellosis that can be used in humans.

Transient lipopolysaccharide-induced resistance to aerosolized Bacillus anthracis in New Zealand white rabbits.

Previous studies have demonstrated that prior infection by various bacterial pathogens induces nonspecific resistance to subsequent infection by other gram-negative and gram-positive bacterial pathogens. In the present study, we evaluated whether underlying inflammation enhanced host resistance to inhalational Bacillus anthracis infection in New Zealand White rabbits (SPF; Bordetella- and Pasteurella-free). Accordingly, rabbits were pretreated with either the inflammagen bacterial LPS (60,000 EU/kg), a component of the outer membrane of gram-negative bacteria, or saline (vehicle). Administration of LPS resulted in brief pyrexia and a significant increase in the proinflammatory cytokine TNFα, thus confirming LPS-induced inflammation. At 24 h after LPS treatment, rabbits were exposed to aerosolized B. anthracis spores (Ames strain; approximately 300 LD50). Blood samples collected at various times after challenge were cultured. Compared with their saline-pretreated counterparts, LPS-pretreated, B. anthracis challenged rabbits exhibited delays in 2 biomarkers of B. anthracis infection-anthrax-induced pyrexia (25 h versus 66 h after challenge, respectively) and bacteremia (26 h versus 63 h, respectively)-and survived longer (41 h versus 90 h, respectively). Similar to control animals, all LPS-pretreated, B. anthracis-challenged rabbits exhibited pathology consistent with inhalational anthrax. Taken together, these results suggest that prior or underlying stimulation of the innate immune system induces transient host resistance to subsequent B. anthracis infection in SPF New Zealand white rabbits. In particular, our results emphasize the importance of using animals that are free of underlying infections to prevent confounding data in studies for inhalational anthrax characterization and medical countermeasure evaluation.

Aerosolized Bacillus anthracis infection in New Zealand white rabbits: natural history and intravenous levofloxacin treatment.

The natural history for inhalational Bacillus anthracis (Ames strain) exposure in New Zealand white rabbits was investigated to better identify potential, early biomarkers of anthrax. Twelve SPF Bordetella-free rabbits were exposed to 150 LD(50) aerosolized B. anthracis spores, and clinical signs, body temperature, complete blood count, bacteremia, and presence of protective antigen in the blood (that is, antigenemia) were examined. The development of antigenemia and bacteremia coincided and preceded both pyrexia and inversion of the heterophil:lymphocyte ratio, an indicator of infection. Antigenemia was determined within 1 h by electrochemiluminescence immunoassay, compared with the 24-h traditional culture needed for bacteremia determination. Rabbits appeared clinically normal until shortly before succumbing to anthrax approximately 47 h after challenge or approximately 22 h after antigenemia, which suggests a relatively narrow therapeutic window of opportunity. To evaluate the therapeutic rabbit model, B. anthracis-exposed rabbits were treated (after determination of antigenemia and later confirmed to be bacteremic) intravenously with the fluoroquinolone antibiotic levofloxacin for 5 d at a total daily dose of 25 or 12.5 mg/kg, resulting in nearly 90% and 70% survival, respectively, to the study end (28 d after challenge). The peak level for 12.5 mg/kg was equivalent to that observed for a 500-mg daily levofloxacin dose in humans. These results suggest that intravenous levofloxacin is an effective therapeutic against inhalational anthrax. Taken together, our findings indicate that antigenemia is a viable and early biomarker for B. anthracis infection that can be used as a treatment trigger to allow for timely intervention against this highly pathogenic disease.