Deaths Associated with Pneumonic Plague, 1946-2017

From History Books to Headlines: Plague in Modern Times

Although often considered a historical disease, plague remains a modern-day public health concern with global relevance. Caused by the bacterium Yersinia pestis and transmitted to humans primarily through infected flea bites or contact with infected animals, plague persists worldwide, including parts of the southwestern United States. The disease presents in three main forms: bubonic, septicemic, and pneumonic. Bubonic plague, the most common form, is characterized by painful swollen lymph nodes known as buboes. Septicemic plague occurs when the infection enters the blood stream, while pneumonic plague, the most virulent and transmissible form, poses a serious bioterrorism threat due to its ability to spread via respiratory droplets and high fatality rate. Though rare today, with an average of seven cases annually in the U.S., plague still demands awareness and preparedness by emergency nurse practitioners and other clinicians. Early diagnosis, timely antibiotic treatment, and vigilant public health measures are critical to reducing its morbidity and mortality.

Human genetic variation reveals FCRL3 is a lymphocyte receptor for Yersinia pestis

Yersinia pestis is the gram-negative bacterium responsible for plague, one of the deadliest and most feared diseases in human history. This bacterium is known to infect phagocytic cells, such as dendritic cells and macrophages, but interactions with non-phagocytic cells of the adaptive immune system are frequently overlooked despite the importance they likely hold for human infection. To discover human genetic determinants of Y. pestis infection, we utilized nearly a thousand genetically diverse lymphoblastoid cell lines in a cellular genome-wide association study method called Hi-HOST (High-throughput Human in-vitrO Susceptibility Testing). We identified a nonsynonymous SNP, rs2282284, in Fc receptor like 3 (FCRL3) associated with bacterial invasion of host cells (p=9×10-8). FCRL3 belongs to the immunoglobulin superfamily and is primarily expressed in lymphocytes. rs2282284 is within a tyrosine-based signaling motif, causing an asparagine-to-serine mutation (N721S) in the most common FCRL3 isoform. Overexpression of FCRL3 facilitated attachment and invasion of non-opsonized Y. pestis. Additionally, FCRL3 colocalized with Y. pestis at sites of cellular attachment, suggesting FCRL3 is a receptor for Y. pestis. These properties were variably conserved across the FCRL family, revealing molecular requirements of attachment and invasion, including an Ig-like C2 domain and a SYK interaction motif. Direct binding was confirmed with purified FCRL5 extracellular domain. Following attachment, invasion of Y. pestis was dependent on SYK and decreased with the N721S mutation. Unexpectedly, this same variant is associated with risk of chronic hepatitis C virus infection in BioBank Japan. Thus, Y. pestis hijacks FCRL proteins, possibly taking advantage of an immune receptor to create a lymphocyte niche during infection.

Yersinia pestis and pneumonic plague: Insight into how a lethal pathogen interfaces with innate immune populations in the lung to cause severe disease

Yersinia pestis is the causative agent of bubonic, septicemic and pneumonic plague. The historical importance and potential of plague to re-emerge as a threat worldwide are indisputable. The most severe manifestion of plague is pneumonic plague, which results in disease that is 100% lethal without treatment. Y. pestis suppresses host immune responses early in the lung to establish infection. The later stages of infection see the rapid onset of hyperinflammatory responses that prove lethal. The study of Y. pestis host/pathogen interactions have largely been investigated during bubonic plague and with attenuated strains in cell culture models. There remains a somewhat limited understanding of the interactions between virulent Y. pestis and immune populations in the lung that drive severe disease. In this review we give a broad overview of the progression of pneumonic plague and highlighting how Y. pestis interfaces with host innate immune populations in the lung to cause lethal disease.

Analytical framework to evaluate and optimize the use of imperfect diagnostics to inform outbreak response: Application to the 2017 plague epidemic in Madagascar

During outbreaks, the lack of diagnostic "gold standard" can mask the true burden of infection in the population and hamper the allocation of resources required for control. Here, we present an analytical framework to evaluate and optimize the use of diagnostics when multiple yet imperfect diagnostic tests are available. We apply it to laboratory results of 2,136 samples, analyzed with 3 diagnostic tests (based on up to 7 diagnostic outcomes), collected during the 2017 pneumonic (PP) and bubonic plague (BP) outbreak in Madagascar, which was unprecedented both in the number of notified cases, clinical presentation, and spatial distribution. The extent of these outbreaks has however remained unclear due to nonoptimal assays. Using latent class methods, we estimate that 7% to 15% of notified cases were Yersinia pestis-infected. Overreporting was highest during the peak of the outbreak and lowest in the rural settings endemic to Y. pestis. Molecular biology methods offered the best compromise between sensitivity and specificity. The specificity of the rapid diagnostic test was relatively low (PP: 82%, BP: 85%), particularly for use in contexts with large quantities of misclassified cases. Comparison with data from a subsequent seasonal Y. pestis outbreak in 2018 reveal better test performance (BP: specificity 99%, sensitivity: 91%), indicating that factors related to the response to a large, explosive outbreak may well have affected test performance. We used our framework to optimize the case classification and derive consolidated epidemic trends. Our approach may help reduce uncertainties in other outbreaks where diagnostics are imperfect.

The impact of COVID-19 on clinical research for Neglected Tropical Diseases (NTDs): A case study of bubonic plague

BACKGROUND

Among the many collaterals of the COVID-19 pandemic is the disruption of health services and vital clinical research. COVID-19 has magnified the challenges faced in research and threatens to slow research for urgently needed therapeutics for Neglected Tropical Diseases (NTDs) and diseases affecting the most vulnerable populations. Here we explore the impact of the pandemic on a clinical trial for plague therapeutics and strategies that have been considered to ensure research efforts continue.

METHODS

To understand the impact of the COVID-19 pandemic on the trial accrual rate, we documented changes in patterns of all-cause consultations that took place before and during the pandemic at health centres in two districts of the Amoron'I Mania region of Madagascar where the trial is underway. We also considered trends in plague reporting and other external factors that may have contributed to slow recruitment.

RESULTS

During the pandemic, we found a 27% decrease in consultations at the referral hospital, compared to an 11% increase at peripheral health centres, as well as an overall drop during the months of lockdown. We also found a nation-wide trend towards reduced number of reported plague cases.

DISCUSSION

COVID-19 outbreaks are unlikely to dissipate in the near future. Declining NTD case numbers recorded during the pandemic period should not be viewed in isolation or taken as a marker of things to come. It is vitally important that researchers are prepared for a rebound in cases and, most importantly, that research continues to avoid NTDs becoming even more neglected.

Reporter-Phage-Based Detection and Antibiotic Susceptibility Testing of Yersinia pestis for a Rapid Plague Outbreak Response

Pneumonic plague is a lethal infectious disease caused by Yersinia pestis, a Tier-1 biothreat agent. Antibiotic treatment can save infected patients; however, therapy should begin within 24 h of symptom onset. As some Y. pestis strains showed an antibiotic resistance phenotype, an antibiotic susceptibility test (AST) must be performed. Performing the Clinical and Laboratory Standards Institute (CLSI)-recommended standard process, which includes bacterial isolation, enumeration and microdilution testing, lasts several days. Thus, rapid AST must be developed. As previously published, the Y. pestis-specific reporter phage ϕA1122::luxAB can serve for rapid identification and AST (ID-AST). Herein, we demonstrate the ability to use ϕA1122::luxAB to determine minimal inhibitory concentration (MIC) values and antibiotic susceptibility categories for various Y. pestis therapeutic antibiotics. We confirmed the assay by testing several nonvirulent Y. pestis isolates with reduced susceptibility to doxycycline or ciprofloxacin. Moreover, the assay can be performed directly on positive human blood cultures. Furthermore, as Y. pestis may naturally or deliberately be spread in the environment, we demonstrate the compatibility of this direct method for this scenario. This direct phage-based ID-AST shortens the time needed for standard AST to less than a day, enabling rapid and correct treatment, which may also prevent the spread of the disease.

Antibiotic Therapy of Plague: A Review

Plague-a deadly disease caused by the bacterium Yersinia pestis-is still an international public health concern. There are three main clinical forms: bubonic plague, septicemic plague, and pulmonary plague. In all three forms, the symptoms appear suddenly and progress very rapidly. Early antibiotic therapy is essential for countering the disease. Several classes of antibiotics (e.g., tetracyclines, fluoroquinolones, aminoglycosides, sulfonamides, chloramphenicol, rifamycin, and β-lactams) are active in vitro against the majority of Y. pestis strains and have demonstrated efficacy in various animal models. However, some discrepancies have been reported. Hence, health authorities have approved and recommended several drugs for prophylactic or curative use. Only monotherapy is currently recommended; combination therapy has not shown any benefits in preclinical studies or case reports. Concerns about the emergence of multidrug-resistant strains of Y. pestis have led to the development of new classes of antibiotics and other therapeutics (e.g., LpxC inhibitors, cationic peptides, antivirulence drugs, predatory bacteria, phages, immunotherapy, host-directed therapy, and nutritional immunity). It is difficult to know which of the currently available treatments or therapeutics in development will be most effective for a given form of plague. This is due to the lack of standardization in preclinical studies, conflicting data from case reports, and the small number of clinical trials performed to date.

Dangerous Pathogens as a Potential Problem for Public Health

Pathogens are various organisms, such as viruses, bacteria, fungi, and protozoa, which can cause severe illnesses to their hosts. Throughout history, pathogens have accompanied human populations and caused various epidemics. One of the most significant outbreaks was the Black Death, which occurred in the 14th century and caused the death of one-third of Europe's population. Pathogens have also been studied for their use as biological warfare agents by the former Soviet Union, Japan, and the USA. Among bacteria and viruses, there are high priority agents that have a significant impact on public health. Bacillus anthracis, Francisella tularensis, Yersinia pestis, Variola virus, Filoviruses (Ebola, Marburg), Arenoviruses (Lassa), and influenza viruses are included in this group of agents. Outbreaks and infections caused by them might result in social disruption and panic, which is why special operations are needed for public health preparedness. Antibiotic-resistant bacteria that significantly impede treatment and recovery of patients are also valid threats. Furthermore, recent events related to the massive spread of Severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) are an example of how virus-induced diseases cannot be ignored. The impact of outbreaks, such as SARS-CoV-2, have had far-reaching consequences beyond public health. The economic losses due to lockdowns are difficult to estimate, but it would take years to restore countries to pre-outbreak status. For countries affected by the 2019 coronavirus disease (COVID-19), their health systems have been overwhelmed, resulting in an increase in the mortality rate caused by diseases or injuries. Furthermore, outbreaks, such as SARS-CoV-2, will induce serious, wide-ranging (and possibly long-lasting) psychological problems among, not only health workers, but ordinary citizens (this is due to isolation, quarantine, etc.). The aim of this paper is to present the most dangerous pathogens, as well as general characterizations, mechanisms of action, and treatments.