SARS and common viral infections

Serological response to COVID-19 pneumonia and increasing severity over 18 months in a prospective cohort of hospitalized patients

In this study, we present an 18-month serological follow-up of 294 patients with COVID-19 pneumonia. The aim was to assess the dynamics of serological response and its correlation with clinical worsening, as well as to describe clinical worsening determinants. Results of the study showed an early immunoglobulin M response, which clearly diminished starting at 4 months, but nonetheless, a small group of patients remained positive. As for immunoglobulin G, levels were higher up to 6 months in patients who presented clinical worsening during hospitalization. High titers of the immunoglobulin were maintained in all patients during follow-up, which would indicate that humoral immunity due to infection is long-lasting. Male sex, presence of myalgias and extensive radiological affectation were significantly correlated with clinical worsening.

Advanced Molecular and Immunological Diagnostic Methods to Detect SARS-CoV-2 Infection

COVID-19 emerged in late 2019 in China and quickly spread across the globe, causing over 521 million cases of infection and 6.26 million deaths to date. After 2 years, numerous advances have been made. First of all, the preventive vaccine, which has been implemented in record time, is effective in more than 95% of cases. Additionally, in the diagnostic field, there are numerous molecular and antigenic diagnostic kits that are equipped with high sensitivity and specificity. Real Time-PCR-based assays for the detection of viral RNA are currently considered the gold-standard method for SARS-CoV-2 diagnosis and can be used efficiently on pooled nasopharyngeal, or oropharyngeal samples for widespread screening. Moreover, additional, and more advanced molecular methods such as droplet-digital PCR (ddPCR), clustered regularly interspaced short palindromic repeats (CRISPR) and next-generation sequencing (NGS), are currently under development to detect the SARS-CoV-2 RNA. However, as the number of subjects infected with SARS-CoV-2 continuously increases globally, health care systems are being placed under increased stress. Thus, the clinical laboratory plays an important role, helping to select especially asymptomatic individuals who are actively carrying the live replicating virus, with fast and non-invasive molecular technologies. Recent diagnostic strategies, other than molecular methods, have been adopted to either detect viral antigens, i.e., antigen-based immunoassays, or human anti-SARS-CoV-2 antibodies, i.e., antibody-based immunoassays, in nasal or oropharyngeal swabs, as well as in blood or saliva samples. However, the role of mucosal sIgAs, which are essential in the control of viruses entering the body through mucosal surfaces, remains to be elucidated, and in particular the role of the immune response in counteracting SARS-CoV-2 infection, primarily at the site(s) of virus entry that appears to be promising.

RespiCoV: Simultaneous identification of Severe Acute Respiratory Syndrome Coronavirus 2 (SARS-CoV-2) and 46 respiratory tract viruses and bacteria by amplicon-based Oxford-Nanopore MinION sequencing

Since December 2019 the world has been facing the outbreak of the Severe Acute Respiratory Syndrome Coronavirus 2 (SARS-CoV-2). Identification of infected patients and discrimination from other respiratory infections have so far been accomplished by using highly specific real-time PCRs. Here we present a rapid multiplex approach (RespiCoV), combining highly multiplexed PCRs and MinION sequencing suitable for the simultaneous screening for 41 viral and five bacterial agents related to respiratory tract infections, including the human coronaviruses NL63, HKU1, OC43, 229E, Middle East respiratory syndrome coronavirus, SARS-CoV, and SARS-CoV-2. RespiCoV was applied to 150 patient samples with suspected SARS-CoV-2 infection and compared with specific real-time PCR. Additionally, several respiratory tract pathogens were identified in samples tested positive or negative for SARS-CoV-2. Finally, RespiCoV was experimentally compared to the commercial RespiFinder 2SMART multiplex screening assay (PathoFinder, The Netherlands).

Usefulness of ELISA Using Total Antibody against Plant-Expressed Recombinant Nucleocapsid Protein of SARS-CoV-2

Here, we aimed to investigate the diagnostic value of a serological assay using the nucleocapsid protein developed for severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) detection and evaluated its performance using three commercial enzyme-linked immunosorbent assays (ELISAs), namely, Standard E 2019 novel coronavirus disease (COVID-19) total antibody (Ab) ELISA (SD Biosensor), and EDI novel coronavirus COVID-19 IgG and IgM ELISA. A recombinant nucleocapsid protein (rNP) was expressed from plants and Escherichia coli for the detection of serum total Ab. We prospectively collected 141 serum samples from 32 patients with reverse transcription-PCR (RT-PCR)-confirmed COVID-19 and determined the sensitivity and dynamics of their total Ab response. Specificity was evaluated using 158 prepandemic samples. To validate the assays, we evaluated the performance using two different cutoff values. The sensitivity and specificity for each assay were as follows: 92.91% and 94.30% (plant-rNP), 83.69% and 98.73% (SD Biosensor), 75.89% and 98.10% (E. coli-rNP), 76.47% and 100% (EDI-IgG), and 80.39% and 80% (EDI-IgM). The plant-based rNP showed the highest sensitivity and area under the receiver operating characteristic (ROC) curve (0.980) among all the assays (P < 0.05). The seroconversion rate for total Ab increased sequentially with disease progression, with a sensitivity of 100% after 10 to 12 days of post-symptom onset (PSO) for both rNP-plant-based and SD Biosensor ELISAs. After 2 weeks of PSO, the seroconversion rates were >80% and 100% for EDI-IgM and EDI-IgG ELISA, respectively. Seroconversion occurred earlier with rNP plant-based ELISA (5 days PSO) compared with E. coli-based (7 days PSO) and SD Biosensor (8 days PSO) ELISA. We determined that rNP produced in plants enables the robust detection of SARS-CoV-2 total Abs. The assay can be used for serosurvey and complementary diagnosis of COVID-19. IMPORTANCE At present, the principal diagnostic methods for COVID-19 comprise the identification of viral nucleic acid by genetic approaches, including PCR-based techniques or next-generation sequencing. However, there is an urgent need for validated serological assays which are crucial for the understanding of immune responses against SARS-CoV-2. In this study, a highly sensitive and specific serological antibody assay was developed for the detection of SARS-CoV-2 with an overall accuracy of 93.56% using a recombinant nucleoprotein expressed from plants.

An outlook on coronavirus disease 2019 detection methods

Diagnostic testing plays a fundamental role in the mitigation and containment of coronavirus disease 2019 (COVID-19), as it enables immediate quarantine of those who are infected and contagious and is essential for the epidemiological characterization of the virus and estimating the number of infected cases worldwide. Confirmation of viral infections, such as COVID-19, can be achieved through two general approaches: nucleic acid amplification tests (NAATs) or molecular tests, and serological or antibody-based tests. The genetic material of the pathogen is detected in NAAT, and in serological tests, host antibodies produced in response to the pathogen are identified. Other methods of diagnosing COVID-19 include radiological imaging of the lungs and in vitro detection of viral antigens. This review covers different approaches available to diagnosing COVID-19 by outlining their advantages and shortcomings, as well as appropriate indications for more accurate testing.

•

Diagnostic tests to detect coronavirus disease 2019 (COVID-19).

•

Advantages and disadvantages associated with each detection method.

•

Implications for a more accurate and rapid testing of COVID-19 or other similar future emergent viruses.

Evaluation of anti-SARS-CoV-2 antibody levels: two different methods

OBJECTIVE

Severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) disease (COVID-19) is still a major problem worldwide. Antibody response to SARS-CoV-2 has not yet been fully clarified, and clinical benefits of serological tests remain unclear. Despite the presence of numerous systems and methods used to analyze antibody levels, it is difficult to mention about standardization. This study aims to evaluate antibody levels of COVID-19 patients obtained by different methods.

METHODS

Specimens of 55 patients were included in this study. Patients underwent SARS-CoV-2 real-time polymerase chain reaction test, COVID-19 IgM/IgG antibody rapid test (Hotgen), and Roche SARS-CoV-2 antibody test.

RESULTS

In this study, the positive values of COVID-19 IgM/IgG antibody rapid test, Roche SARS-CoV-2 antibody test, and SARS-CoV-2 real-time polymerase chain reaction test were 37, 26, and 31, respectively, whereas the negative values were 18, 29, and 24, respectively. A comparison of the results using χ² test revealed a significant difference among SARS-CoV-2 real-time polymerase chain reaction, COVID-19 IgM/IgG antibody rapid test (Hotgen), and Roche SARS-CoV-2 antibody test.

CONCLUSIONS

We recommend antibody testing in close contact tracing as well as in real-time polymerase chain reaction negative symptomatic subjects. Standardization is important as positive values show significant variations among antibody tests.

Zoonotic and Reverse Zoonotic Transmissibility of SARS-CoV-2

The Coronavirus Disease 2019 (COVID-19) is the first known pandemic caused by a coronavirus. Its causative agent, severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2), appears to be capable of infecting different mammalian species. Recent detections of this virus in pet, zoo, wild, and farm animals have compelled inquiry regarding the zoonotic (animal-to-human) and reverse zoonotic (human-to-animal) transmissibility of SARS-CoV-2 with the potential of COVID-19 pandemic evolving into a panzootic.

It is important to monitor the global spread of disease and to assess the significance of genomic changes to support prevention and control efforts during a pandemic. An understanding of the SARS-CoV-2 epidemiology provides opportunities to prevent the risk of repeated re-infection of humans and requires a robust One Health-based investigation. This review paper describes the known properties and the existing gaps in scientific knowledge about the zoonotic and reverse zoonotic transmissibility of the novel virus SARS-CoV-2 and the COVID-19 disease it causes.

Antibody Detection and Dynamic Characteristics in Patients With Coronavirus Disease 2019

Background

The corona virus disease 2019 (COVID-19) caused by the corona virus 2 (SARS-CoV-2) has been rapidly spreading nationwide and abroad. A serologic test to identify antibody dynamics and response to SARS-CoV-2 was developed.

Methods

The antibodies against SARS-CoV-2 were detected by an enzyme-linked immunosorbent assay (ELISA) based on the recombinant nucleocapsid protein of SARS-CoV-2 in patients with confirmed or suspected COVID-19 at 3-40 days after symptom onset. The gold standard for COVID-19 diagnosis was nucleic acid testing for SARS-CoV-2 by RT-PCR. The serodiagnostic power of the specific IgM and IgG antibodies against SARS-CoV-2 was investigated in terms of sensitivity, specificity, positive predictive value (PPV), negative predictive value (NPV) and consistency rate.

Results

The seroconversion of specific IgM and IgG antibodies were observed as early as the 4^th day after symptom onset. In the confirmed patients with COVID-19, sensitivity, specificity, PPV, NPV, and consistency rate of IgM were 77.3% (51/66), 100%, 100%, 80.0%, and 88.1%, and those of IgG were 83.3.3% (55/66), 95.0%, 94.8%, 83.8%, and 88.9 %. In patients with suspected COVID-19, sensitivity, specificity, PPV, NPV, and consistency rate of IgM were 87.5% (21/24), 100%, 100%, 95.2%, and 96.4%, and those of IgG were 70.8% (17/24), 96.6%, 85.0%, 89.1%, and 88.1%. Both antibodies performed well in serodiagnosis for COVID-19 rely on great specificity.

Conclusions

The antibodies against SARS-CoV-2 can be detected in the middle and later stage of the illness. Antibody detection may play an important role in the diagnosis of COVID-19 as complement approach for viral nucleid acid assays.

Rapid Antibody-Based COVID-19 Mass Surveillance: Relevance, Challenges, and Prospects in a Pandemic and Post-Pandemic World

The aggressive outbreak of the severe acute respiratory syndrome coronavirus-2 (SARS-CoV-2) as COVID-19 (coronavirus disease-2019) pandemic demands rapid and simplified testing tools for its effective management. Increased mass testing and surveillance are crucial for controlling the disease spread, obtaining better pandemic statistics, and developing realistic epidemiological models. Despite the advantages of nucleic acid- and antigen-based tests such as accuracy, specificity, and non-invasive approaches of sample collection, they can only detect active infections. Antibodies (immunoglobulins) are produced by the host immune system within a few days after infection and persist in the blood for at least several weeks after infection resolution. Antibody-based tests have provided a substitute and effective method of ultra-rapid detection for multiple contagious disease outbreaks in the past, including viral diseases such as SARS (severe acute respiratory syndrome) and MERS (Middle East respiratory syndrome). Thus, although not highly suitable for early diagnosis, antibody-based methods can be utilized to detect past infections hidden in the population, including asymptomatic ones. In an active community spread scenario of a disease that can provide a bigger window for mass detections and a practical approach for continuous surveillance. These factors encouraged researchers to investigate means of improving antibody-based rapid tests and employ them as reliable, reproducible, sensitive, specific, and economic tools for COVID-19 mass testing and surveillance. The development and integration of such immunoglobulin-based tests can transform the pandemic diagnosis by moving the same out of the clinics and laboratories into community testing sites and homes. This review discusses the principle, technology, and strategies being used in antibody-based testing at present. It also underlines the immense prospect of immunoglobulin-based testing and the efficacy of repeated planned deployment in pandemic management and post-pandemic sustainable screenings globally.

Potential Effects of Coronaviruses on the Cardiovascular System: A Review

Importance

Severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2), which causes coronavirus disease 2019 (COVID-19) has reached a pandemic level. Coronaviruses are known to affect the cardiovascular system. We review the basics of coronaviruses, with a focus on COVID-19, along with their effects on the cardiovascular system.

Observations

Coronavirus disease 2019 can cause a viral pneumonia with additional extrapulmonary manifestations and complications. A large proportion of patients have underlying cardiovascular disease and/or cardiac risk factors. Factors associated with mortality include male sex, advanced age, and presence of comorbidities including hypertension, diabetes mellitus, cardiovascular diseases, and cerebrovascular diseases. Acute cardiac injury determined by elevated high-sensitivity troponin levels is commonly observed in severe cases and is strongly associated with mortality. Acute respiratory distress syndrome is also strongly associated with mortality.

Conclusions and Relevance

Coronavirus disease 2019 is associated with a high inflammatory burden that can induce vascular inflammation, myocarditis, and cardiac arrhythmias. Extensive efforts are underway to find specific vaccines and antivirals against SARS-CoV-2. Meanwhile, cardiovascular risk factors and conditions should be judiciously controlled per evidence-based guidelines.

Molecular and Immunological Diagnostic Tests of COVID-19: Current Status and Challenges

Rapid spread of coronavirus disease 2019 (COVID-19) is ravaging the globe. Since its first report in December 2019, COVID-19 cases have exploded to over 14 million as of July 2020, claiming more than 600,000 lives. Implementing fast and widespread diagnostic tests is paramount to contain COVID-19, given the current lack of an effective therapeutic or vaccine. This review focuses on a broad description of currently available diagnostic tests to detect either the virus (SARS-CoV-2) or virus-induced immune responses. We specifically explain the working mechanisms of these tests and compare their analytical performance. These analyses will assist in selecting most effective tests for a given application, for example, epidemiology or global pandemic research, population screening, hospital-based testing, home-based and point-of-care testing, and therapeutic trials. Finally, we lay out the shortcomings of certain tests and future needs.

Clinical characteristics and co-infections of 354 hospitalized patients with COVID-19 in Wuhan, China: a retrospective cohort study

From December 2019, a novel coronavirus, SARS-CoV-2, caused an outbreak of pneumonia in Wuhan city and rapidly spread throughout China and globally. However, the clinical characteristics and co-infection with other respiratory pathogens of patients with COVID-19 and the factors associated with severity of COVID-19 are still limited. In this retrospective cohort study, we included 354 inpatients with COVID-19 admitted to Renmin Hospital of Wuhan University from February 4, 2020 to February 28, 2020. We found levels of interleukin-6, interleukin-10, C-reactive protein, D-dimer, white blood cell count and neutrophil count were clearly elevated in males and critical cases compared with females and severe and mild cases, respectively. However, lymphopenia was more severe in males than females and levels of tumor necrosis factor alpha were reduced significantly in critical cases than severe and mild cases. 23.5% of severe cases and 24.4% of critical cases were co-infected with other respiratory pathogens. Additionally, stepwise multivariable regression analysis suggested that co-infection, lymphocyte count and levels of D-dimer were associated with severity of COVID-19.These findings provide crucial clues for further identification of the mechanisms, characteristics and treatments of patients with COVID-19.

Twenty Years of Active Bacterial Core Surveillance

Active Bacterial Core surveillance (ABCs) was established in 1995 as part of the Centers for Disease Control and Prevention Emerging Infections Program (EIP) network to assess the extent of invasive bacterial infections of public health importance. ABCs is distinctive among surveillance systems because of its large, population-based, geographically diverse catchment area; active laboratory-based identification of cases to ensure complete case capture; detailed collection of epidemiologic information paired with laboratory isolates; infrastructure that allows for more in-depth investigations; and sustained commitment of public health, academic, and clinical partners to maintain the system. ABCs has directly affected public health policies and practices through the development and evaluation of vaccines and other prevention strategies, the monitoring of antimicrobial drug resistance, and the response to public health emergencies and other emerging infections.

Porcine reproductive and respiratory syndrome virus modifies innate immunity and alters disease outcome in pigs subsequently infected with porcine respiratory coronavirus: implications for respiratory viral co-infections

The innate immune response is critical for host defence against respiratory coronaviruses (CoVs). This study demonstrated that an ongoing respiratory virus infection compromises innate immune responses and affects the pathogenesis of a respiratory CoV co-infection. An innate immunosuppressive respiratory virus infection was established by infecting weaned pigs with porcine reproductive and respiratory syndrome virus (PRRSV); 10 days later, the pigs were exposed to porcine respiratory coronavirus (PRCV). The PRRSV/PRCV dual-infected pigs had reduced weight gains, a higher incidence of fever and more severe pneumonia compared with either single infection. Significant suppression of innate immune responses [reduced alpha interferon (IFN-alpha) levels in the lungs and reduced blood natural killer cell cytotoxicity] by the ongoing PRRSV infection was observed in dual-infected pigs, which coincided with exacerbated pneumonia during early PRCV infection. The subsequent PRCV infection led to enhanced PRRSV replication in the lungs and a trend towards increased serum T-helper type 1 (Th1) (IFN-gamma) but decreased Th2 [interleukin (IL)-4] responses, further exacerbating PRRSV pneumonia. Following PRCV infection, more severe PRRSV-related pulmonary alveolar macrophage (PAM) apoptosis occurred, as determined by an in situ terminal deoxynucleotidyl transferase-mediated dUTP nick end labelling assay, suggesting increased PRRSV replication in PAMs. Collectively, these observations suggest interactive effects between PRCV and PRRSV via early innate (IFN-alpha) and later adaptive Th1 (IFN-gamma) and Th2 (IL-4) immune responses. These findings imply that an existing immunomodulating respiratory viral co-infection may be a contributing factor to more severe pneumonia in respiratory CoV disease. This study provides new insights into host-pathogen interactions related to co-infection by CoVs and other respiratory viruses.

Features discriminating SARS from other severe viral respiratory tract infections

This study investigated the discriminatory features of severe acute respiratory syndrome (SARS) and severe non-SARS community-acquired viral respiratory infection (requiring hospitalization) in an emergency department in Hong Kong. In a case-control study, clinical, laboratory and radiological data from 322 patients with laboratory-confirmed SARS from the 2003 SARS outbreak were compared with the data of 253 non-SARS adult patients with confirmed viral respiratory tract infection from 2004 in order to identify discriminatory features. Among the non-SARS patients, 235 (93%) were diagnosed as having influenza infections (primarily H3N2 subtype) and 77 (30%) had radiological evidence of pneumonia. In the early phase of the illness and after adjusting for baseline characteristics, SARS patients were less likely to have lower respiratory symptoms (e.g. sputum production, shortness of breath, chest pain) and more likely to have myalgia (p < 0.001). SARS patients had lower mean leukocyte and neutrophil counts (p < 0.0001) and more commonly had “ground-glass” radiological changes with no pleural effusion. Despite having a younger average age, SARS patients had a more aggressive respiratory course requiring admission to the ICU and a higher mortality rate. The area under the receiver operator characteristic curve for predicting SARS when all variables were considered was 0.983. Using a cutoff score of >99, the sensitivity was 89.1% (95%CI 82.0–94.0) and the specificity was 98.0% (95%CI 95.4–99.3). The area under the receiver operator characteristic curve for predicting SARS when all variables except radiological change were considered was 0.933. Using a cutoff score of >8, the sensitivity was 80.7% (95%CI 72.4–87.3) and the specificity was 94.5% (95%CI 90.9–96.9). Certain clinical manifestations and laboratory changes may help to distinguish SARS from other influenza-like illnesses. Scoring systems may help identify patients who should receive more specific tests for influenza or SARS.

Role of laboratory variables in differentiating SARS-coronavirus from other causes of community-acquired pneumonia within the first 72 h of hospitalization

The Centers for Disease Control and Prevention (CDC) recommend that SARS-coronavirus (SARS-CoV) testing be considered in epidemiologically high-risk patients hospitalized with community-acquired pneumonia (CAP) if no alternative diagnosis is identified after 72 h. The aim of this study was to identify routine laboratory variables that might indicate the need for SARS-CoV testing. Routine hematological/biochemical variables in patients with laboratory-confirmed SARS (2003) were compared with those in consecutive patients hospitalized June–December 2004 with radiologically confirmed CAP. Stepwise logistic regression analyses were performed to identify discriminating variables at baseline and by day 3 of hospitalization. Nasopharyngeal aspiration and antigen detection for influenza virus and respiratory syncytial virus using an immunofluorescence assay (IFA) were routinely performed in patients with CAP. Altogether, 181 patients with CAP (who remained undiagnosed by IFA) and 303 patients with SARS were studied. The mean intervals from symptom onset to admission were 3.1 and 2.8 days, respectively (p > 0.05). The etiological agent of CAP was identified retrospectively in only 39% of cases, the majority being bacterial pathogens. At baseline, age and absolute neutrophil count (ANC) were the only independent discriminating variables (p < 0.0001). Using a value of <4.4 × 10⁹/l as the cutoff for ANC, the sensitivity and specificity of ANC for discriminating SARS were 64 and 95%, respectively (AUC 0.90). By day 3 of hospitalization, age (p < 0.0001), change in ANC (p = 0.0003), and change in bilirubin (p = 0.0065) were discriminating variables. A model combining age <65 years, a change in ANC of >−3 × 10⁹/l, and a change in bilirubin of ≥0 mmol/l had a sensitivity of 43% and a specificity of 95% for SARS (AUC 0.90). There are only a few laboratory features (including lymphopenia) that clearly discriminate SARS from other causes of CAP. Nevertheless, when evaluating epidemiologically high-risk patients with CAP and no immediate alternative diagnosis, a low ANC on presentation along with poor clinical and laboratory responses after 72 h of antibiotic treatment may raise the index of suspicion for SARS and indicate a need to perform SARS-CoV testing.

Characterization of viral agents causing acute respiratory infection in a San Francisco University Medical Center Clinic during the influenza season

Background. With use of polymerase chain reaction (PCR) and a centrifugation-enhanced viral culture method, we characterized the viruses causing acute respiratory infection in adults during an influenza season.

Methods. During January-March 2002, nasopharyngeal wash specimens from previously healthy adults presenting with respiratory symptoms were evaluated for viral pathogens with centrifugation-enhanced viral culture and PCR.

Results The diagnoses in 266 cases included unspecified upper respiratory infection (in 142 [54%] of the cases), acute bronchitis (42 [16%]), sinusitis (23 [9%]), pharyngitis (22 [8%]), and pneumonia (17 [6%]). The use of a shell vial assay and PCR identified a pathogen in 103 (39%) of the patients, including influenza A or B in 54, picornavirus in 28 (including rhinovirus in 24), respiratory syncytial virus (RSV) in 12, human metapneumovirus in 4, human coronavirus OC43 in 2, adenovirus in 2, parainfluenza virus type 1 in 1, and coinfection with influenza and parainfluenza virus type 1 in 2.

Conclusion. Our findings demonstrate that, even during the influenza season, rhinovirus and RSV are prevalent and must be considered in the differential diagnosis of adult acute respiratory infection before prescribing antiviral medication. Human coronavirus and human metapneumovirus did not play a substantial role. PCR was an especially useful tool in the identification of influenza and other viral pathogens not easily detected by traditional testing methods.

Human metapneumovirus as a major cause of human respiratory tract disease

BACKGROUND

Human metapneumovirus (hMPV) is a newly identified paramyxovirus that appears to be one of the most significant and common viral infections in humans. The virus, first isolated in 2001, is a clear cause of lower respiratory tract disease in both the very young and the frail elderly. The virus causes acute wheezing in children or, less commonly, croup or pneumonia.

METHODS/RESULTS

Molecular epidemiology studies have shown that field strains exhibit sufficient sequence diversity to designate 2 subgroups of circulating viruses. Small animal and nonhuman primate models of infection have been described, which will allow studies of pathogenesis and immunity. Recombinant viruses have already been generated by several groups using reverse genetics, which facilitates the study of the biology of the virus and the generation of live attenuated vaccine candidates.

CONCLUSIONS

Ongoing research promises to elucidate the molecular basis for pathogenesis and immunity of human metapneumovirus infections and to pave the way for rapid vaccine development.