Lifelong Residents

This chapter assesses some of the more intransigent persistent virus infections. Persistent viruses tend to strike up stable relationships with their respective hosts as they skilfully evade immune response and exploit the host to ensure their own long-term survival. This is an incredibly successful lifestyle for a virus, and generally causes little harm to the host. However, there can still be problems. The most obvious of these is seen with immunosuppression of the host leading to virus reactivation and disease, but there are also more subtle, long-term effects. The chapter then considers herpesviruses, such as varicella zoster virus (VZV) and herpes simplex virus (HSV); human papilloma virus (HPV) and cytomegalovirus (CMV); retroviruses; human immunodeficiency virus-1 (HIV-1); and hepatitis viruses.

Dose-dependent response to infection with Ebola virus in the ferret model and evidence of viral evolution in the eye.

Filoviruses are high consequence infections with limited approved medical countermeasures (MCMs). MCM development is dependent upon well-characterised animal models for the assessment of anti-viral agents and vaccines. Following large scale Ebola virus disease outbreaks in Africa, some survivors are left with long-term sequelae and persistent virus in immune-privileged sites for many years. We report the characterisation of the ferret as a model for Ebola virus (EBOV) infection, reproducing disease and lethality observed in humans. The onset of clinical signs is rapid, and EBOV is detected in the blood, oral and rectal swabs, and all tissues studied. We identify viral RNA in the eye (a site of immune privilege) and report on specific genomic changes in EBOV present in this structure. Thus, the ferret model has utility in testing MCMs that prevent or treat long term EBOV persistence in immune-privileged sites. Importance Recent re-emergence of Ebola in Guinea that caused over 28000 cases between 2013-2016 has been linked to the original virus from that region. It appears the virus has remained in the region for at least 5 years and is likely to have been maintained in humans. Persistence of Ebola in areas of the body for extended periods of time has been observed such as in the eye and semen. Despite the importance of re-introduction of Ebola from this route, such events are rare in the population which makes studying medical interventions to clear persistent virus difficult. We studied various doses of Ebola in ferrets and detected virus in the eyes of most ferrets. We believe this model will enable the study of medical interventions that promote clearance of Ebola virus from sites that promote persistence.

EBV-Driven Lymphoproliferative Disorders and Lymphomas of the Gastrointestinal Tract: A Spectrum of Entities with a Common Denominator (Part 1)

EBV is the most common persistent virus in humans. The interaction of EBV with B lymphocytes, which are considered the virus reservoir, is at the base of the life-long latent infection. Under circumstances of immunosuppression, the balance between virus and host immune system is altered and hence, EBV-associated lymphoid proliferations may originate. These disorders encompass several entities, ranging from self-limited diseases with indolent behavior to aggressive lymphomas. The virus may infect not only B-cells, but even T- and NK-cells. The occurrence of different types of lymphoid disorders depends on both the type of infected cells and the state of host immunity. EBV-driven lymphoproliferative lesions can rarely occur in the gastrointestinal tract and may be missed even by expert pathologists due to both the uncommon site of presentation and the frequent overlapping morphology and immunophenotypic features shared by different entities. The aim of this review is to provide a comprehensive overview of the current knowledge of EBV-associated lymphoproliferative disorders, arising within the gastrointestinal tract. The review is divided in three parts. In this part, the available data on EBV biology, EBV-positive mucocutaneous ulcer, EBV-positive diffuse large B-cell lymphoma, not otherwise specified and classic Hodgkin lymphoma are discussed.

Persistent Southern Tomato Virus (STV) Interacts with Cucumber Mosaic and/or Pepino Mosaic Virus in Mixed-Infections Modifying Plant Symptoms, Viral Titer and Small RNA Accumulation

Southern tomato virus (STV) is a persistent virus that was, at the beginning, associated with some tomato fruit disorders. Subsequent studies showed that the virus did not induce apparent symptoms in single infections. Accordingly, the reported symptoms could be induced by the interaction of STV with other viruses, which frequently infect tomato. Here, we studied the effect of STV in co- and triple-infections with Cucumber mosaic virus (CMV) and Pepino mosaic virus (PepMV). Our results showed complex interactions among these viruses. Co-infections leaded to a synergism between STV and CMV or PepMV: STV increased CMV titer and plant symptoms at early infection stages, whereas PepMV only exacerbated the plant symptoms. CMV and PepMV co-infection showed an antagonistic interaction with a strong decrease of CMV titer and a modification of the plant symptoms with respect to the single infections. However, the presence of STV in a triple-infection abolished this antagonism, restoring the CMV titer and plant symptoms. The siRNAs analysis showed a total of 78 miRNAs, with 47 corresponding to novel miRNAs in tomato, which were expressed differentially in the plants that were infected with these viruses with respect to the control mock-inoculated plants. These miRNAs were involved in the regulation of important functions and their number and expression level varied, depending on the virus combination. The number of vsiRNAs in STV single-infected tomato plants was very small, but STV vsiRNAs increased with the presence of CMV and PepMV. Additionally, the rates of CMV and PepMV vsiRNAs varied depending on the virus combination. The frequencies of vsiRNAs in the viral genomes were not uniform, but they were not influenced by other viruses.

IFNAR1 signaling in NK cells promotes persistent virus infection

Inhibition of type 1 interferon (IFN-I) signaling promotes the control of persistent virus infection, but the underlying mechanisms remain poorly understood. Here, we report that genetic ablation of Ifnar1 specifically in natural killer (NK) cells led to elevated numbers of T follicular helper cells, germinal center B cells, and plasma cells and improved antiviral T cell function, resulting in hastened virus clearance that was comparable to IFNAR1 neutralizing antibody treatment. Antigen-specific B cells and antiviral antibodies were essential for the accelerated control of LCMV Cl13 infection following IFNAR1 blockade. IFNAR1 signaling in NK cells promoted NK cell function and general killing of antigen-specific CD4 and CD8 T cells. Therefore, inhibition of IFN-I signaling in NK cells enhances CD4 and CD8 T cell responses, promotes humoral immune responses, and thereby facilitates the control of persistent virus infection.

In combat against viruses

The late 20th century and the early 21st century have been marked by the explosive development of virology due to activation of viral infections. New mutations of the influenza virus, high incidence of persistent virus infections in humans, as well as respiratory viral diseases that have not yet been eradicated has boosted further development of this direction [1].

COVID-19 Vaccines May Not Prevent Nasal SARS-CoV-2 Infection and Asymptomatic Transmission

Current COVID-19 vaccine candidates are administered by injection and designed to produce an IgG response, preventing viremia and the COVID-19 syndrome. However, systemic respiratory vaccines generally provide limited protection against viral replication and shedding within the airway, as this requires a local mucosal secretory IgA response. Indeed, preclinical studies of adenovirus and mRNA candidate vaccines demonstrated persistent virus in nasal swabs despite preventing COVID-19. This suggests that systemically vaccinated patients, while asymptomatic, may still be become infected and transmit live virus from the upper airway. COVID-19 is known to spread through respiratory droplets and aerosols. Furthermore, significant evidence has shown that many clinic and surgical endonasal procedures are aerosol generating. Until further knowledge is acquired regarding mucosal immunity following systemic vaccination, otolaryngology providers should maintain precautions against viral transmission to protect the proportion of persistently vulnerable patients who exhibit subtotal vaccine efficacy or waning immunity or who defer vaccination.

Equine herpetic infection: features of pathogenesis and diagnosis

Equine alphaherpesviruses ― causative agents of rhinopneumonitis−viral abortion (EHV-1) and rhinopneumonitis (EHV-4) ― represent the subfamily Alphaherpesvirinae, genus Varicellovirus. EHV-1 causes abortion, respiratory pathology, and neurological disorders in horses of different ages. EHV-4 causes predominantly respiratory disease in foals and sporadic abortions in mares. In the etiopathogenesis of herpesvirus infections EHV-1 and EHV-4, the determining factors are pronounced tropism to epithelial cells, persistence in a non-replicative form, and unpredictable reactivation of a persistent virus with its release into the environment. EHV-1 and EHV-4 have similar antigenic determinants and cross-react in serological reactions. The high level of antigenic relationship between EHV-1 and EHV-4 can make it difficult to interpret serologic results in natural infections. The EHV-1 and EHV-4 strains in active circulation are genetically rather conservative. The exception is the new EHV-1 strains with a mutation in the gene encoding viral DNA polymerase, which caused outbreaks of neuroparalytic disease in some European countries and the United States. In several cases, the neurological syndrome has been reported due to use of some commercial vaccines

A Novel Anphevirus in Aedes albopictus Mosquitoes Is Distributed Worldwide and Interacts with the Host RNA Interference Pathway

The Asian tiger mosquito Aedes albopictus is a competent vector for several human arboviruses including dengue, chikungunya and Zika viruses. Mosquitoes also harbor insect-specific viruses (ISVs) that may modulate host physiology and potentially affect the transmission of viruses that are pathogenic to vertebrates, thus representing a potential tool for vector control strategies. In Ae. albopictus we identified a novel anphevirus (family Xinmoviridae; order Mononegavirales) provisionally designated here as Aedes albopictus anphevirus (AealbAV). AealbAV contains a ~12.4 kb genome that is highly divergent from currently known viruses but displays gene content and genomic organization typical of known anpheviruses. We identified AealbAV in several publicly available RNA-Seq datasets from different geographical regions both in laboratory colonies and field collected mosquitoes. Coding-complete genomes of AealbAV strains are highly similar worldwide (>96% nucleotide identity) and cluster according to the geographical origin of their hosts. AealbAV appears to be present in various body compartments and mosquito life stages, including eggs. We further detected AealbAV-derived vsiRNAs and vpiRNAs in publicly available miRNA-Seq libraries of Ae. albopictus and in samples experimentally coinfected with chikungunya virus. This suggests that AealbAV is targeted by the host RNA interference (RNAi) response, consistent with persistent virus replication. The discovery and characterization of AealbAV in Ae. albopictus will now allow us to identify its infection in mosquito populations and laboratory strains, and to assess its potential impact on Ae. albopictus physiology and ability to transmit arboviruses.

Asymptomatic reinfection in two healthcare workers from India with genetically distinct SARS-CoV-2

Reinfection of SARS-CoV-2 is an apparently rare entity and only a few cases have been reported from across the world with the genetic characterization of the virus, differentiating reinfection from persistent virus shedding. These cases, therefore, provide unique insights into the long term protective immunity to SARS-CoV-2. The earlier reports suggest that patients were symptomatic in either one or both the episodes of infection. Here we report a unique case of asymptomatic SARS-CoV-2 reinfection in two healthcare workers from India identified in routine surveillance. Genome sequencing of the virus suggests that genetically distinct SARS-CoV-2 caused the infections. Our analysis demonstrates that asymptomatic reinfection could potentially be an under-reported entity with implications in long term surveillance of SARS-CoV-2 infections. This report also highlights the need for genomic surveillance of healthcare workers who are potentially not only at higher risk for primary infections but also for reinfections.