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Trends in Parasitology Nov 2020Plasmodium falciparum infections in low-transmission settings are often asymptomatic with low parasite densities despite low herd immunity. Based on studies in Zanzibar,... (Review)
Review
Plasmodium falciparum infections in low-transmission settings are often asymptomatic with low parasite densities despite low herd immunity. Based on studies in Zanzibar, this may be due to parasitic (nonvirulence) rather than host (immunity) factors. In high-transmission settings, high replication rate and virulence represents a competitive advantage, whereas in low-transmission settings nonvirulent parasites escape both competition and treatment. Such parasites also survive longer in low-transmission settings due to lower host immunity response and less frequent indirect drug exposure. This has major implications for optimal malaria control and elimination strategies.
Topics: Animals; Asymptomatic Infections; Humans; Malaria, Falciparum; Plasmodium falciparum; Prevalence; Selection, Genetic
PubMed: 32855077
DOI: 10.1016/j.pt.2020.07.008 -
Veterinary Parasitology Dec 2020Toxoplasma gondii infections are common in humans and animals worldwide. T. gondii causes mortality in several species of marine mammals, including threatened Southern... (Review)
Review
Toxoplasma gondii infections are common in humans and animals worldwide. T. gondii causes mortality in several species of marine mammals, including threatened Southern sea otters (Enhydra lutris) and endangered Hawaiian monk seals (Monachus schauinslandi). Marine mammals are now considered sentinels for environmental exposure to protozoan agents contaminating marine waters, including T. gondii oocysts. Marine mammals also serve as food for humans and can result in foodborne T. gondii infections in humans. The present review summarizes worldwide information on the prevalence of clinical and subclinical infections, epidemiology, and genetic diversity of T. gondii infecting marine mammals in the past decade. The role of genetic types of T. gondii and clinical disease is discussed.
Topics: Animals; Asymptomatic Infections; Caniformia; Cetacea; Genetic Variation; Otters; Prevalence; Toxoplasma; Toxoplasmosis, Animal; Trichechus
PubMed: 33271425
DOI: 10.1016/j.vetpar.2020.109296 -
The Lancet. Infectious Diseases Jun 2021People with persistently asymptomatic severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) infection experience no symptoms throughout the course of infection,... (Review)
Review
People with persistently asymptomatic severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) infection experience no symptoms throughout the course of infection, and pre-symptomatic individuals become infectious days before they report symptoms. Transmission of SARS-CoV-2 from individuals without symptoms contributes to pandemic spread, but the extent of transmission from persistently asymptomatic individuals remains unknown. We describe three methodological issues that hinder attempts to estimate this proportion. First, incomplete symptom assessment probably overestimates the asymptomatic fraction. Second, studies with inadequate follow-up misclassify pre-symptomatic individuals. Third, serological studies might identify people with previously unrecognised infection, but reliance on poorly defined antibody responses and retrospective symptom assessment might result in misclassification. We provide recommendations regarding definitions, detection, documentation, and follow-up to improve the identification and evaluation of people with persistently asymptomatic SARS-CoV-2 infection and their contacts. Accurate characterisation of the persistently asymptomatic fraction of infected individuals might shed light on COVID-19 pathogenesis and transmission dynamics, and inform public health responses.
Topics: Asymptomatic Infections; COVID-19; Humans; Pandemics; Retrospective Studies; SARS-CoV-2; Serologic Tests
PubMed: 33301725
DOI: 10.1016/S1473-3099(20)30837-9 -
Mathematical Biosciences and... Nov 2023The aim of this paper is to investigate the spread of the HIV/AIDS epidemic in China during 2008-2021. A new mathematical model is proposed to study the dynamics of HIV...
The aim of this paper is to investigate the spread of the HIV/AIDS epidemic in China during 2008-2021. A new mathematical model is proposed to study the dynamics of HIV transmission with acute infection, fast asymptomatic infections, and slow asymptomatic infections. The basic reproduction number is obtained by the next-generation matrix method. A quantitative analysis of the model, including the local behavior, global behavior, and permanence, is performed. Numerical simulations are presented to enhance the results of these analyses. The behavior or the model's parameters are estimated from real data. A sensitivity analysis shows that the proportion of asymptomatic infections co-infected with other diseases significantly affects the basic reproduction number. We further analyze the impact of implementing single and multiple measure(s) in parallel with the epidemic. The study results conclude that multiple measures are more effective in controlling the spread of AIDS compared to just one. The HIV epidemic can be effectively curbed by reducing the contact rate between fast asymptomatic infected individuals and susceptible populations, increasing the early diagnosis and screening of HIV-infected individuals co-infected with other diseases, and treating co-infected patients promptly.
Topics: Humans; Acquired Immunodeficiency Syndrome; Asymptomatic Infections; China; HIV Infections
PubMed: 38124575
DOI: 10.3934/mbe.2023919 -
Medical Decision Making : An... May 2023It has been reported that a substantial number of COVID-19 infections are asymptomatic, with both symptomatic and asymptomatic infections contributing to transmission...
BACKGROUND
It has been reported that a substantial number of COVID-19 infections are asymptomatic, with both symptomatic and asymptomatic infections contributing to transmission dynamics. Yet, the share of asymptomatic cases varies greatly across studies. One reason for this could be the measurement of symptoms in medical studies and surveys.
DESIGN
In 2 experimental survey studies (total > 3,000) with participants from Germany and the United Kingdom, respectively, we varied the inclusion of a filter question on whether participants who tested positive for COVID-19 had experienced symptoms prior to presenting a checklist of symptoms. We measured the reporting of asymptomatic (versus symptomatic) COVID-19 infections.
RESULTS
The inclusion of a filter question increased the reporting of asymptomatic (versus symptomatic) COVID-19 infections. Particularly mild symptoms were underreported when using a filter question.
CONCLUSIONS AND IMPLICATIONS
Filter questions affect the reporting of (a)symptomatic COVID-19 cases. To account for such differences in the estimation of population infection rates, future studies should transparently report the applied question format.
HIGHLIGHTS
Both symptomatic and asymptomatic infections are important for COVID-19 transmission dynamics.In previous research, symptoms have been assessed either with or without a filter question prior to presenting a symptom list.We show that filter questions reduce the reporting of asymptomatic infections.Particularly mild symptoms are underreported when using a filter question.
Topics: Humans; COVID-19; SARS-CoV-2; Asymptomatic Infections; Symptom Assessment; Prevalence
PubMed: 36846876
DOI: 10.1177/0272989X231158380 -
JAMA Network Open Jul 2021This cohort study investigates asymptomatic and symptomatic COVID-19 case rates before and after the initial vaccine rollout among health care personnel in Orange...
This cohort study investigates asymptomatic and symptomatic COVID-19 case rates before and after the initial vaccine rollout among health care personnel in Orange County, California.
Topics: Adolescent; Adult; Aged; Aged, 80 and over; Asymptomatic Infections; COVID-19; Cohort Studies; Female; Health Personnel; Humans; Male; Middle Aged; Vaccination; Young Adult
PubMed: 34236414
DOI: 10.1001/jamanetworkopen.2021.15980 -
Malaria Journal Dec 2022Mass screening and treatment (MSaT) aims at reducing the spread of malaria in communities by identifying and treating infected persons regardless of the symptoms. This...
BACKGROUND
Mass screening and treatment (MSaT) aims at reducing the spread of malaria in communities by identifying and treating infected persons regardless of the symptoms. This study was conducted to identify and treat asymptomatic cases using MSaT approaches in the community.
METHODS
Three rounds of MSaT using cluster combination approaches were carried out during September 2018 to December 2019 to identify and treat asymptomatic malaria cases in the community. All individuals who were present in the household were screened using RDT irrespective of malaria related symptoms. Simultaneously thick and thin blood smear and blood spot were collected for further analysis using microscopy and diagnostic PCR done in a subset of the samples.
RESULTS
Logistic regression analysis revealed that asymptomatic malaria cases significantly less among the older age groups compared with < 5 years children (OR ranged between 0.52 and 0.61; p < 0.05), lowest in cluster 4 (OR = 0.01; p < 0.0001); during third round of MSaT survey (OR = 0.11; p < 0.0001) and significantly higher in moderate to high endemic areas (OR = 88.30; p < 0.0001).
CONCLUSION
Over the three rounds of MSaT, the number of asymptomatic cases were significantly less in the older age groups, and during third round. Similarly, the asymptomatic cases were significantly less in the low endemic area with API < 1 (cluster four). Therefore, the malaria elimination programme may consider the MSaT strategy to identify asymptomatic cases that would be otherwise missed by routine fever based surveillance. This MSaT strategy would help accomplish the malaria elimination goal in an expedited manner.
Topics: Child; Humans; Aged; Malaria, Falciparum; Plasmodium falciparum; Malaria; Mass Screening; Polymerase Chain Reaction; Asymptomatic Infections; Prevalence
PubMed: 36575544
DOI: 10.1186/s12936-022-04423-z -
The Pediatric Infectious Disease Journal Mar 2023Asymptomatic SARS-CoV-2 infections have raised concerns for public health policies to manage epidemics. This systematic review and meta-analysis aimed to estimate the... (Meta-Analysis)
Meta-Analysis
BACKGROUND
Asymptomatic SARS-CoV-2 infections have raised concerns for public health policies to manage epidemics. This systematic review and meta-analysis aimed to estimate the age-specific proportion of asymptomatic SARS-CoV-2 infected persons globally by year of age.
METHODS
We searched PubMed, Embase, medRxiv and Google Scholar on September 10, 2020, and March 1, 2021. We included studies conducted during January to December 2020, before routine vaccination against COVID-19. Because we expected the relationship between the asymptomatic proportion and age to be nonlinear, multilevel mixed-effects logistic regression (QR decomposition) with a restricted cubic spline was used to model asymptomatic proportions as a function of age.
RESULTS
A total of 38 studies were included in the meta-analysis. In total, 6556 of 14,850 cases were reported as asymptomatic. The overall estimate of the proportion of people who became infected with SARS-CoV-2 and remained asymptomatic throughout infection was 44.1% (6556/14,850, 95% CI: 43.3%-45.0%). The predicted asymptomatic proportion peaked in children (36.2%, 95% CI: 26.0%-46.5%) at 13.5 years, gradually decreased by age and was lowest at 90.5 years of age (8.1%, 95% CI: 3.4%-12.7%).
CONCLUSIONS
Given the high rates of asymptomatic carriage in adolescents and young adults and their active role in virus transmission in the community, heightened vigilance and public health strategies are needed among these individuals to prevent disease transmission.
Topics: Child; Adolescent; Young Adult; Humans; COVID-19; SARS-CoV-2; Epidemics; Public Health; Asymptomatic Infections
PubMed: 36730054
DOI: 10.1097/INF.0000000000003791 -
Journal of Clinical Epidemiology Nov 2021To characterize asymptomatic SARS-CoV-2 infections and develop a symptom-based risk score useful in primary healthcare.
OBJECTIVES
To characterize asymptomatic SARS-CoV-2 infections and develop a symptom-based risk score useful in primary healthcare.
STUDY DESIGN AND SETTING
Sixty-one thousand ninty-two community-dwelling participants in a nationwide population-based serosurvey completed a questionnaire on COVID-19 symptoms and received an immunoassay for SARS-CoV-2 IgG antibodies between April 27 and June 22, 2020. Standardized prevalence ratios for asymptomatic infection were estimated across participant characteristics. We constructed a symptom-based risk score and evaluated its ability to predict SARS-CoV-2 infection.
RESULTS
Of all, 28.7% of infections were asymptomatic (95% CI 26.1-31.4%). Standardized asymptomatic prevalence ratios were 1.19 (1.02-1.40) for men vs. women, 1.82 (1.33-2.50) and 1.45 (0.96-2.18) for individuals <20 and ≥80 years vs. those aged 40-59, 1.27 (1.03-1.55) for smokers vs. nonsmokers, and 1.91 (1.59-2.29) for individuals without vs. with case contact. In symptomatic population, a symptom-based score (weights: severe tiredness = 1; absence of sore throat = 1; fever = 2; anosmia/ageusia = 5) reached standardized seroprevalence ratio of 8.71 (7.37-10.3), discrimination index of 0.79 (0.77-0.81), and sensitivity and specificity of 71.4% (68.1-74.4%) and 74.2% (73.1-75.2%) for a score ≥3.
CONCLUSION
The presence of anosmia/ageusia, fever with severe tiredness, or fever without sore throat should serve to suspect COVID-19 in areas with active viral circulation. The proportion of asymptomatics in children and adolescents challenges infection control.
Topics: Adolescent; Adult; Aged; Aged, 80 and over; Asymptomatic Infections; COVID-19; Child; Child, Preschool; Female; Humans; Infant; Infant, Newborn; Male; Middle Aged; Primary Health Care; Risk Factors; Seroepidemiologic Studies; Spain; Young Adult
PubMed: 34126206
DOI: 10.1016/j.jclinepi.2021.06.005 -
The American Journal of Tropical... Apr 2024Viral gastrointestinal infections are an important public health concern, and the occurrence of asymptomatic enteric virus infections makes it difficult to prevent and...
Viral gastrointestinal infections are an important public health concern, and the occurrence of asymptomatic enteric virus infections makes it difficult to prevent and control their spread. This study aimed to determine the prevalence of and factors associated with asymptomatic enteric virus infection in adults in northern Laos. Fecal samples were collected from apparently healthy participants who did not report diarrhea or high fever at the time of the survey in northern Laos, and enteric viruses were detected using polymerase chain reaction (PCR) and reverse transcription (RT)-PCR. Individual characteristics, including the gut microbiome, were compared between asymptomatic carriers and noncarriers of each enteric virus. Of the participants (N = 255), 12 (4.7%) were positive for norovirus genogroup I (GI), 8 (3.1%) for human adenovirus, and 1 (0.4%) for norovirus GII; prevalence tended to be higher in less-modernized villages. Gut microbial diversity (evaluated by the number of operational taxonomic units) was higher in asymptomatic carriers of norovirus GI or human adenovirus than in their noncarriers. Gut microbiome compositions differed significantly between asymptomatic carriers and noncarriers of norovirus GI or human adenovirus (permutational analysis of variance, P <0.05). These findings imply an association between asymptomatic enteric virus infection and modernization and/or the gut microbiome in northern Laos.
Topics: Adult; Humans; Gastroenteritis; Gastrointestinal Microbiome; Laos; Diarrhea; Norovirus; Virus Diseases; Feces; Asymptomatic Infections; Caliciviridae Infections
PubMed: 38471149
DOI: 10.4269/ajtmh.23-0209