THE ENHANCING EFFECT OF CONCURRENT INFECTION WITH PNEUMOTROPIC VIRUSES ON PULMONARY TUBERCULOSIS IN MICE

Unmasking the hidden impact of viruses on tuberculosis risk

Tuberculosis (TB) is a leading cause of mortality from an infectious disease. In this opinion article, we focus on accumulating scientific evidence indicating that viral infections may contribute to TB progression, possibly allowing novel preventive interventions. Viruses can remodel the mammalian immune system, potentially modulating the risk of reactivating latent microbes such as Mycobacterium tuberculosis (Mtb). Evidence is mixed regarding the impact of emergent viruses such as SARS-CoV-2 on the risk of TB. Therefore, we posit that important knowledge gaps include elucidating which viral families increase TB risk and whether these provide unique or shared immune mechanisms. We also propose potential future research to define the contribution of viruses to TB pathogenesis.

SARS-CoV-2 coinfection in children with severe airway obstruction due to pulmonary tuberculosis

INTRODUCTION

The severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) pandemic had a significant impact on tuberculosis (TB) control globally, with the number of new TB diagnoses decreasing. Coinfection with some viruses, especially measles, could aggravate TB in children. This is presumably a result of depressed cellular immunity. Reports on children with TB and SARS-CoV-2 coinfection are limited.

METHODS

A retrospective analysis of children up to 13 years old admitted to Tygerberg Hospital, Cape Town, South Africa, from March 2020 to December 2022 with suspected TB-induced airway compression requiring bronchoscopy. Children were included if they presented with severe intrathoracic airway obstruction and/or radiographic evidence of complicated TB. The patients were divided into two groups based on SARS-CoV-2 respiratory polymerase chain reaction results. Demographics, TB exposure, microbiology, SARS-CoV-2 laboratory data, imaging, inflammatory cytokine levels, and bronchoscopy data were collected. Statistical analyses compared SARS-CoV-2 positive and negative groups.

RESULTS

Of the 50 children undergoing bronchoscopy for TB airway obstruction, 7 (14%) were SARS-CoV-2 positive. Cough was more prevalent in the SARS-CoV-2 positive group (p = 0.04). There was no difference in TB culture yield between groups. However, SARS-CoV-2 positive children showed slower radiological improvement at 1 month (p = 0.01), pleural effusions (p < 0.001), and a higher need for endoscopic enucleation (p < 0.001). FDG PET/CT scans indicated an ongoing inflammation in the SARS-CoV-2 positive group.

CONCLUSIONS

Coinfection with SARS-CoV-2 in children with TB airway obstruction appears to complicate the disease course, necessitating more medical interventions and demonstrating a longer duration of the TB inflammatory process. Further research is needed to understand the impact of viral infections on TB progression and outcomes in pediatric patients.

Early cellular mechanisms of type I interferon-driven susceptibility to tuberculosis

Mycobacterium tuberculosis (Mtb) causes 1.6 million deaths annually. Active tuberculosis correlates with a neutrophil-driven type I interferon (IFN) signature, but the cellular mechanisms underlying tuberculosis pathogenesis remain poorly understood. We found that interstitial macrophages (IMs) and plasmacytoid dendritic cells (pDCs) are dominant producers of type I IFN during Mtb infection in mice and non-human primates, and pDCs localize near human Mtb granulomas. Depletion of pDCs reduces Mtb burdens, implicating pDCs in tuberculosis pathogenesis. During IFN-driven disease, we observe abundant DNA-containing neutrophil extracellular traps (NETs) described to activate pDCs. Cell-type-specific disruption of the type I IFN receptor suggests that IFNs act on IMs to inhibit Mtb control. Single-cell RNA sequencing (scRNA-seq) indicates that type I IFN-responsive cells are defective in their response to IFNγ, a cytokine critical for Mtb control. We propose that pDC-derived type I IFNs act on IMs to permit bacterial replication, driving further neutrophil recruitment and active tuberculosis disease.

Immunosuppression is a conserved driver of tuberculosis susceptibility

Mycobacterium tuberculosis ( Mtb ) causes 1.6 million deaths a year 1 . However, no individual mouse model fully recapitulates the hallmarks of human tuberculosis disease. Here we report that a comparison across three different susceptible mouse models identifies Mtb -induced gene signatures that predict active TB disease in humans significantly better than a signature from the standard C57BL/6 mouse model. An increase in lung myeloid cells, including neutrophils, was conserved across the susceptible mouse models, mimicking the neutrophilic inflammation observed in humans 2,3 . Myeloid cells in the susceptible models and non-human primates exhibited high expression of immunosuppressive molecules including the IL-1 receptor antagonist, which inhibits IL-1 signaling. Prior reports have suggested that excessive IL-1 signaling impairs Mtb control 4-6 . By contrast, we found that enhancement of IL-1 signaling via deletion of IL-1 receptor antagonist promoted bacterial control in all three susceptible mouse models. IL-1 signaling enhanced cytokine production by lymphoid and stromal cells, suggesting a mechanism for IL-1 signaling in promoting Mtb control. Thus, we propose that myeloid cell expression of immunosuppressive molecules is a conserved mechanism exacerbating Mtb disease in mice, non-human primates, and humans.

Co-infection of mice with SARS-CoV-2 and Mycobacterium tuberculosis limits early viral replication but does not affect mycobacterial loads

Viral co-infections have been implicated in worsening tuberculosis (TB) and during the COVID-19 pandemic, the global rate of TB-related deaths has increased for the first time in over a decade. We and others have previously shown that a resolved prior or concurrent influenza A virus infection in Mycobacterium tuberculosis (Mtb)-infected mice resulted in increased pulmonary bacterial burden, partly through type I interferon (IFN-I)-dependent mechanisms. Here we investigated whether SARS-CoV-2 (SCV2) co-infection could also negatively affect bacterial control of Mtb. Importantly, we found that K18-hACE2 transgenic mice infected with SCV2 one month before, or months after aerosol Mtb exposure did not display exacerbated Mtb infection-associated pathology, weight loss, nor did they have increased pulmonary bacterial loads. However, pre-existing Mtb infection at the time of exposure to the ancestral SCV2 strain in infected K18-hACE2 transgenic mice or the beta variant (B.1.351) in WT C57Bl/6 mice significantly limited early SCV2 replication in the lung. Mtb-driven protection against SCV2 increased with higher bacterial doses and did not require IFN-I, TLR2 or TLR9 signaling. These data suggest that SCV2 co-infection does not exacerbate Mtb infection in mice, but rather the inflammatory response generated by Mtb infection in the lungs at the time of SCV2 exposure restricts viral replication.

Burden of influenza A (H1N1)pdm09 infection among tuberculosis patients: a prospective cohort study

BACKGROUND

Influenza and tuberculosis both cause significant morbidity and mortality worldwide. Therefore, this study aimed to estimate the burden of influenza A (H1N1)pdm09 virus infection among human tuberculosis patients and the general population.

METHODS

A prospective cohort study was conducted among a cohort group (TB positive patients) as exposed and a comparison group (general population) as non-exposed. A total of 304 participants were recruited in both groups and followed for a period of 12 weeks. Of the 304 concurrently enrolled individuals, 152 were TB-positive patients (cohort group) and 152 were from the general population (comparison group).To calculate the sample size, the power of study was kept at 80% for detecting a difference at 5% alpha level assuming the 25% prevalence of respiratory viruses in cohort group compared to 12.5% in general population. An oropharyngeal swab was taken from a participant with symptoms of influenza-like illness (ILI). Samples were tested by conventional reverse transcription polymerase chain reaction (RT-PCR) for the detection of influenza A (H1N1)pdm09. All statistical analyses were conducted using R software.

RESULTS

A total of 95 participants developed influenza-like illness (ILI) symptoms. Among these, 64 tested positive for influenza A(H1N1)pdm09, of which 39 were from the exposed group and 25 were from the non-exposed group. During the 12-week period of follow-up, the influenza A (H1N1)pdm09 incidence rate was 20 per 1000 people. The risk of testing positive for influenza A (H1N1)pdm09 was 1.66 times higher in the exposed group compared to the non-exposed group. The cumulative incidence indicated that 25% of the TB cohort and 16% of the comparison group were at risk of getting influenza A (H1N1)pdm09 during the 12 weeks of follow-up.

CONCLUSION

Participants from the TB cohort had a higher incidence of influenza A (H1N1)pdm09 than the general population suggesting that they should be prioritized for influenza vaccination.

René Dubos, the Autochthonous Flora, and the Discovery of the Microbiome

Now characterised by high-throughput sequencing methods that enable the study of microbes without lab culture, the human "microbiome" (the microbial flora of the body) is said to have revolutionary implications for biology and medicine. According to many experts, we must now understand ourselves as "holobionts" like lichen or coral, multispecies superorganisms that consist of animal and symbiotic microbes in combination, because normal physiological function depends on them. Here I explore the 1960s research of biologist René Dubos, a forerunner figure mentioned in some historical accounts of the microbiome, and argue that he arrived at the superorganism concept 40 years before the Human Microbiome Project. This raises the question of why his contribution was not hailed as revolutionary at the time and why Dubos is not remembered for it.

Coronavirus Activates an Altruistic Stem Cell-Mediated Defense Mechanism that Reactivates Dormant Tuberculosis: Implications in Coronavirus Disease 2019 Pandemic

We postulate that similar to bacteria, adult stem cells may also exhibit an altruistic defense mechanism to protect their niche against external threat. Herein, we report mesenchymal stem cell (MSC)–based altruistic defense against a mouse model of coronavirus, murine hepatitis virus-1 (MHV-1) infection of lung. MHV-1 infection led to reprogramming of CD271⁺ MSCs in the lung to an enhanced stemness phenotype that exhibits altruistic behavior, as per previous work in human embryonic stem cells. The reprogrammed MSCs exhibited transient expansion for 2 weeks, followed by apoptosis and expression of stemness genes. The conditioned media of the reprogrammed MSCs exhibited direct antiviral activity in an in vitro model of MHV-1–induced toxicity to type II alveolar epithelial cells by increasing their survival/proliferation and decreasing viral load. Thus, the reprogrammed MSCs can be identified as altruistic stem cells (ASCs), which exert a unique altruistic defense against MHV-1. In a mouse model of MSC-mediated Mycobacterium tuberculosis (MTB) dormancy, MHV-1 infection in the lung exhibited 20-fold lower viral loads than the MTB-free control mice on the third week of viral infection, and exhibited six-fold increase of ASCs, thereby enhancing the altruistic defense. Notably, these ASCs exhibited intracellular replication of MTB, and their extracellular release. Animals showed tuberculosis reactivation, suggesting that dormant MTB may exploit ASCs for disease reactivation.

Influenza and tuberculosis co-infection: A systematic review

Introduction

There are limited data on risk of severe disease or outcomes in patients with influenza and pulmonary tuberculosis (PTB) co‐infection compared to those with single infection.

Methods

We conducted a systematic review of published literature on the interaction of influenza viruses and PTB. Studies were eligible for inclusion if they presented data on prevalence, disease association, presentation or severity of laboratory‐confirmed influenza among clinically diagnosed or laboratory‐confirmed PTB cases. We searched eight databases from inception until December 2018. Summary characteristics of each study were extracted, and a narrative summary was presented. Cohort or case‐control studies were assessed for potential bias using the Newcastle‐Ottawa scale.

Results

We assessed 5154 abstracts, reviewed 146 manuscripts and included 19 studies fulfilling selection criteria (13 human and six animal). Of seven studies reporting on the possible effect of the underlying PTB disease in patients with influenza, three of four analytical studies reported no association with disease severity of influenza infection in those with PTB, whilst one study reported PTB as a risk factor for influenza‐associated hospitalization.

An association between influenza infection and PTB disease was found in three of five analytical studies; whereas the two other studies reported a high frequency of PTB disease progression and complications among patients with seasonal influenza co‐infection.

Conclusion

Human analytical studies of an association between co‐infection and severe influenza‐ or PTB‐associated disease or increased prevalence of influenza co‐infection in individuals' hospitalized for PTB were not conclusive. Data are limited from large, high‐quality, analytical epidemiological studies with laboratory‐confirmed endpoints.

Examining the Complex Relationship Between Tuberculosis and Other Infectious Diseases in Children

Millions of children are exposed to tuberculosis (TB) each year, many of which become infected with Mycobacterium tuberculosis. Most children can immunologically contain or eradicate the organism without pathology developing. However, in a minority, the organism overcomes the immunological constraints, proliferates and causes TB disease. Each year a million children develop TB disease, with a quarter dying. While it is known that young children and those with immunodeficiencies are at increased risk of progression from TB infection to TB disease, our understanding of risk factors for this transition is limited. The most immunologically disruptive process that can happen during childhood is infection with another pathogen and yet the impact of co-infections on TB risk is poorly investigated. Many diseases have overlapping geographical distributions to TB and affect similar patient populations. It is therefore likely that infection with viruses, bacteria, fungi and protozoa may impact on the risk of developing TB disease following exposure and infection, although disentangling correlation and causation is challenging. As vaccinations also disrupt immunological pathways, these may also impact on TB risk. In this article we describe the pediatric immune response to M. tuberculosis and then review the existing evidence of the impact of co-infection with other pathogens, as well as vaccination, on the host response to M. tuberculosis. We focus on the impact of other organisms on the risk of TB disease in children, in particularly evaluating if co-infections drive host immune responses in an age-dependent way. We finally propose priorities for future research in this field. An improved understanding of the impact of co-infections on TB could assist in TB control strategies, vaccine development (for TB vaccines or vaccines for other organisms), TB treatment approaches and TB diagnostics.

The Impact of Influenza and Tuberculosis Interaction on Mortality Among Individuals Aged ≥15 Years Hospitalized With Severe Respiratory Illness in South Africa, 2010-2016

Background

Data on the prevalence and impact of influenza–tuberculosis coinfection on clinical outcomes from high–HIV and –tuberculosis burden settings are limited. We explored the impact of influenza and tuberculosis coinfection on mortality among hospitalized adults with lower respiratory tract infection (LRTI).

Methods

We enrolled patients aged ≥15 years admitted with physician-diagnosed LRTI or suspected tuberculosis at 2 hospitals in South Africa from 2010 to 2016. Combined nasopharyngeal and oropharyngeal swabs were tested for influenza and 8 other respiratory viruses. Tuberculosis testing of sputum included smear microscopy, culture, and/or Xpert MTB/Rif.

Results

Among 6228 enrolled individuals, 4253 (68%) were tested for both influenza and tuberculosis. Of these, the detection rate was 6% (239/4253) for influenza, 26% (1092/4253) for tuberculosis, and 77% (3113/4053) for HIV. One percent (42/4253) tested positive for both influenza and tuberculosis. On multivariable analysis, among tuberculosis-positive patients, factors independently associated with death were age group ≥65 years compared with 15–24 years (adjusted odds ratio [aOR], 3.6; 95% confidence interval [CI], 1.2–11.0) and influenza coinfection (aOR, 2.3; 95% CI, 1.02–5.2). Among influenza-positive patients, laboratory-confirmed tuberculosis was associated with an increased risk of death (aOR, 4.5; 95% CI, 1.5–13.3). Coinfection with other respiratory viruses was not associated with increased mortality in patients positive for tuberculosis (OR, 0.7; 95% CI, 0.4–1.1) or influenza (OR, 1.6; 95% CI, 0.4–5.6).

Conclusions

Tuberculosis coinfection is associated with increased mortality in individuals with influenza, and influenza coinfection is associated with increased mortality in individuals with tuberculosis. These data may inform prioritization of influenza vaccines or antivirals for tuberculosis patients and inform tuberculosis testing guidelines for patients with influenza.

Influenza interaction with cocirculating pathogens and its impact on surveillance, pathogenesis, and epidemic profile: A key role for mathematical modelling

Evidence is mounting that influenza virus interacts with other pathogens colonising or infecting the human respiratory tract. Taking into account interactions with other pathogens may be critical to determining the real influenza burden and the full impact of public health policies targeting influenza. This is particularly true for mathematical modelling studies, which have become critical in public health decision-making. Yet models usually focus on influenza virus acquisition and infection alone, thereby making broad oversimplifications of pathogen ecology. Herein, we report evidence of influenza virus interactions with bacteria and viruses and systematically review the modelling studies that have incorporated interactions. Despite the many studies examining possible associations between influenza and Streptococcus pneumoniae, Staphylococcus aureus, Haemophilus influenzae, Neisseria meningitidis, respiratory syncytial virus (RSV), human rhinoviruses, human parainfluenza viruses, etc., very few mathematical models have integrated other pathogens alongside influenza. The notable exception is the pneumococcus-influenza interaction, for which several recent modelling studies demonstrate the power of dynamic modelling as an approach to test biological hypotheses on interaction mechanisms and estimate the strength of those interactions. We explore how different interference mechanisms may lead to unexpected incidence trends and possible misinterpretation, and we illustrate the impact of interactions on public health surveillance using simple transmission models. We demonstrate that the development of multipathogen models is essential to assessing the true public health burden of influenza and that it is needed to help improve planning and evaluation of control measures. Finally, we identify the public health, surveillance, modelling, and biological challenges and propose avenues of research for the coming years.

Temporal association in hospitalizations for tuberculosis, invasive pneumococcal disease and influenza virus illness in South African children

Introduction

The seasonal variability in hospitalization for tuberculosis may in part relate to super-imposed bacterial or predisposing respiratory viral infections. We aimed to study the temporal association between hospitalization for culture-confirmed pulmonary tuberculosis (PTB), invasive pneumococcal disease (IPD) and influenza virus epidemics in South African children.

Methods

We undertook a retrospective analysis which examined seasonal trends, from 2005 to 2008, for hospitalization for culture-confirmed PTB and IPD among children in relation to the influenza epidemics in Soweto, South Africa. Original time-series of the influenza virus epidemics and hospitalization rates for PTB and IPD were decomposed into three components: a trend cycle component, a seasonal component and an irregular component using the X-11 seasonal adjustment method. To compare the seasonality amongst the three series, the trend and irregular components were removed and only seasonal components examined.

Results

Across the study period, the influenza virus epidemics peaked during May to July (winter) months, which was closely followed by an increase in the incidence of hospitalization for IPD (August to October) and PTB (August to November).

Discussion

Within- and between-year temporal changes associated with childhood TB hospitalization may in part be driven by factors which influence temporal changes in pneumococcal disease, including potential variability in the severity of influenza virus epidemics in temperate climates. The dynamics of the interplay between the host and these infectious agents appears to be complex and multifactorial.

Pandemic Influenza (H1N1) and Mycobacterium tuberculosis Co-infection

We hereby observe four co-infection cases of pandemic influenza H1N1 and Mycobacterium tuberculosis with various clinical presentations. It may be prudent to consider M. tuberculosis co-infections when patients with pandemic influenza reveal unusual clinical features that do not improve despite appropriate treatments against the influenza, especially in Korea, in the endemic areas of M. tuberculosis.

Influenza A virus impairs control of Mycobacterium tuberculosis coinfection through a type I interferon receptor-dependent pathway

Influenza followed by severe acute bacterial pneumonia is a major cause of mortality worldwide. Several mechanisms account for this enhanced susceptibility, including increased production of type I interferon (IFN). In individuals infected with Mycobacterium tuberculosis, the influence of acute viral infections on tuberculosis progression is unclear. We show that prior exposure of mice to influenza A virus, followed by M. tuberculosis infection, leads to enhanced mycobacterial growth and decreased survival. Following M. tuberculosis/influenza virus coinfection, mycobacterial growth is enhanced by a type I IFN signaling pathway. Our findings highlight the detrimental influence influenza virus infection can have before or during M. tuberculosis infection.

Effect of the lesion due to influenza virus on the resistance of mice to inhaled pneumococci

1. The normal lung of the mouse possesses the power of reducing markedly its content of Type I pneumococci within 3 hours after inhalation of the organisms in the form of fine droplets. 2. Lungs with fully developed influenza viral pneumonia not only fail to reduce the pulmonary content of pneumococci administered in this manner but, on the contrary, support their growth. 3. After intrabronchial inoculation into mice, influenza virus multiplies rapidly in the lung within 24 hours. 4. Criteria have been established for distinction between true viral lesions of the lung and changes due to the inoculation of diluents as vehicles for the virus. 5. 24 hours after inoculation of virus, there are no macroscopic lesions in the lung and the microscopic changes are due to the diluent. 6. Presence and multiplication of the virus in the lung 24 hours after inoculation have no apparent effect on the power of the lung to reduce rapidly its content of inhaled pneumococci. 7. The effect of the virus in lowering resistance to secondary bacterial infection appears to be due to the presence of the lesion produced by the virus.

A GENETIC STUDY OF SUSCEPTIBILITY TO EXPERIMENTAL TUBERCULOSIS IN MICE INFECTED WITH MAMMALIAN TUBERCLE BACILLI

A study has been made of the genetic aspects of the difference between two inbred strains of mice (C57B1/6 and Swiss) in response to experimental infection with mammalian tubercle bacilli. Males and females, 4 to 6 weeks of age were inoculated intravenously with 0.2 ml of a 1/50 culture dilution of Mycobacterium tuberculosis var. bovis (Vallée strain) grown in tween albumin medium. Mean survival time for C57B1 animals was 28.1 ± 0.6 days and for Swiss, 55.3 ± 0.6 days postinfection. The characteristic survival time of the two strains was reversed in mice receiving a smaller infective dose. The age of mice at the time of inoculation also affected the results of infection: both C57B1 and Swiss, inoculated at 12 months of age, died at the same rate, but when inoculated at older ages, C57B1 survived slightly longer. Bacteriologic studies demonstrated that there was no significant difference between the two mouse strains with regard to the numbers of viable units of tubercle bacilli recovered from various organs during the 2 week period following infection with a 10^–3 culture dilution of Vallée. Moreover, the standard infective inoculum (1/50 culture dilution) did not activate corynebacterial pseudotuberculosis in C57B1 mice, a strain known to be latently infected with Corynebacterium kutscheri, rapid multiplication of tubercle bacilli occurred, but no corynebacteria were recovered. When C57B1 and Swiss strains were crossed, survival tests after infection with the standard inoculum demonstrated that mice of the F₁ generation were more resistant than either parent. Whether the overdominance was due to a new combination of parental genes for resistance or to heterosis was not determined. The increased litter size of the F₁ mice, an evidence of increased vigor, supports the view that heterosis was involved. In backcrosses to the resistant strain (Swiss), survival time gradually became stabilized at approximately the parental level. In the 1st backcross to the susceptible strain (C57B1), survival times fell into two classes indicating segregation of genes, with perhaps dominance of genes from the Swiss. After repeated backcrosses to C57B1, mice of the 4th backcross generation had a survival time essentially the same as that of the original parental strain. On the basis of having obtained progeny characterized by the original parental susceptibilities after genetic tendencies had been intermingled by crossbreeding, it was concluded that hereditary factors influenced the response of mice to experimental infection with M. tuberculosis. The number of genes was not determined.