Demographic patterns of human antibody levels to Simulium damnosum s.l. saliva in onchocerciasis-endemic areas: An indicator of exposure to vector bites

Background In onchocerciasis endemic areas in Africa, heterogenous biting rates by blackfly vectors on humans are assumed to partially explain age- and sex-dependent infection patterns with Onchocerca volvulus. To underpin these assumptions and further improve predictions made by onchocerciasis transmission models, demographic patterns in antibody responses to salivary antigens of Simulium damnosum s.l. are evaluated as a measure of blackfly exposure. Methodology/Principal findings Recently developed IgG and IgM anti-saliva immunoassays for S. damnosum s.l. were applied to blood samples collected from residents in four onchocerciasis endemic villages in Ghana. Demographic patterns in antibody levels according to village, sex and age were explored by fitting generalized linear models. Antibody levels varied between villages but showed consistent patterns with age and sex. Both IgG and IgM responses declined with increasing age. IgG responses were generally lower in males than in females and exhibited a steeper decline in adult males than in adult females. No sex-specific difference was observed in IgM responses. Conclusions/Significance The decline in age-specific antibody patterns suggested development of immunotolerance or desensitization to blackfly saliva antigen in response to persistent exposure. The variation between sexes, and between adults and youngsters may reflect differences in behaviour influencing cumulative exposure. These measures of antibody acquisition and decay could be incorporated into onchocerciasis transmission models towards informing onchocerciasis control, elimination, and surveillance.

When and why direct transmission models can be used for environmentally persistent pathogens

Variants of the susceptible-infected-removed (SIR) model of Kermack & McKendrick (1927) enjoy wide application in epidemiology, offering simple yet powerful inferential and predictive tools in the study of diverse infectious diseases across human, animal and plant populations. Direct transmission models (DTM) are a subset of these that treat the processes of disease transmission as comprising a series of discrete instantaneous events. Infections transmitted indirectly by persistent environmental pathogens, however, are examples where a DTM description might fail and are perhaps better described by models that comprise explicit environmental transmission routes, so-called environmental transmission models (ETM). In this paper we discuss the stochastic susceptible-exposed-infected-removed (SEIR) DTM and susceptible-exposed-infected-removed-pathogen (SEIR-P) ETM and we show that the former is the timescale separation limit of the latter, with ETM host-disease dynamics increasingly resembling those of a DTM when the pathogen’s characteristic timescale is shortened, relative to that of the host population. Using graphical posterior predictive checks (GPPC), we investigate the validity of the SEIR model when fitted to simulated SEIR-P host infection and removal times. Such analyses demonstrate how, in many cases, the SEIR model is robust to departure from direct transmission. Finally, we present a case study of white spot disease (WSD) in penaeid shrimp with rates of environmental transmission and pathogen decay (SEIR-P model parameters) estimated using published results of experiments. Using SEIR and SEIR-P simulations of a hypothetical WSD outbreak management scenario, we demonstrate how relative shortening of the pathogen timescale comes about in practice. With atttempts to remove diseased shrimp from the population every 24h, we see SEIR and SEIR-P model outputs closely conincide. However, when removals are 6-hourly, the two models’ mean outputs diverge, with distinct predictions of outbreak size and duration.

Using high-resolution contact networks to evaluate SARS-CoV-2 transmission and control in large-scale multi-day events

The emergence of the highly transmissible SARS-CoV-2 Delta variant has created a need to reassess the risk posed by increasing social contacts as countries resume pre-pandemic activities, particularly in the context of resuming large-scale events over multiple days. To examine how social contacts formed in different activity settings influences interventions required to control outbreaks, we combined high-resolution data on contacts among passengers and crew on cruise ships with network transmission models. We found passengers had a median of 20 (IQR 10-36) unique close contacts per day, and over 60% of their contact episodes were made in dining or sports areas where mask wearing is typically limited. In simulated outbreaks, we found that vaccination coverage and rapid antigen tests had a larger effect than mask mandates alone, indicating the importance of combined interventions against Delta to reduce event risk in the vaccine era.

Transmission of SARS-CoV-2 associated with cruise ship travel: protocol for a systematic review (Version 1)

Background: Maritime and river travel, including cruise ships, have been implicated with spreading viruses through infected passengers and crew. Given the novelty of the SARS-CoV-2 infection, early cruise ship travel transmission models of spread are based on what is known of the dynamics of other respiratory viral infections. Our objective is to provide a rapid summary and evaluation of relevant data on SARS-CoV-2 transmission aboard cruise ships, report policy implications, and highlight research gaps requiring attention. Methods: We will search LitCovid, medRxiv, Google Scholar, and the WHO Covid-19 database using COVID-19, SARS-CoV-2, transmission, and cruise ship appropriate synonyms. We will also search the reference lists of included studies for additional relevant studies. We will include studies reporting onboard SARS-CoV-2 transmission from passengers and/or crew to passengers and/or crew. We will consider any potential transmission mode. We will assess study quality based on five criteria and report important findings. The outcome will consist of the onboard cruise ships transmission of SARS-CoV-2. We will provide a narrative summary of the data and report the outcomes, including quantitative estimates where feasible and relevant. Where possible, compatible datasets may be pooled for meta-analysis. Expected results: We will present the evidence in three distinct packages: study description, methodological quality assessment and data extracted. We will summarize the evidence and will draw conclusions as to the quality of the evidence.

Redefining snakebite envenoming as a zoonosis: disease incidence is driven by snake ecology, socioeconomics and anthropogenic impacts

Snakebite is the only WHO-listed, not infectious neglected tropical disease (NTD), although its eco-epidemiology is similar to that of zoonotic infections: envenoming occurs after a vertebrate host contacts a human. Accordingly, snakebite risk represents the interaction between snake and human factors, but their quantification has been limited by data availability. Models of infectious disease transmission are instrumental for the mitigation of NTDs and zoonoses. Here, we represented snake-human interactions with disease transmission models to approximate geospatial estimates of snakebite incidence in Sri Lanka, a global hotspot. Snakebites and envenomings are described by the product of snake and human abundance, mirroring directly transmitted zoonoses. We found that human-snake contact rates vary according to land cover (surrogate of occupation and socioeconomic status), the impacts of humans and climate on snake abundance, and by snake species. Our findings show that redefining snakebite as zoonosis provides a mechanistic eco-epidemiological basis to understand snakebites, and the possible implications of global environmental and demographic change for the burden of snakebite.

Adaptive data-driven age and patch mixing in contact networks with recurrent mobility

Infectious disease transmission models often stratify populations by age and geographic patches. Contact patterns between age groups and patches are key parameters in such models. Arenas et al. (2020) develop an approach to simulate contact patterns associated with recurrent mobility between patches, such as due to work, school, and other regular travel. Using their approach, mixing between patches is greater than mobility data alone would suggest, because individuals from patches A and B can form a contact if they meet in patch C. We build upon their approach to address three potential gaps that remain. First, our approach includes a distribution of contacts by age that is responsive to underlying age distribution of the mixing pool. Second, different age distributions by contact type are also maintained in our approach, such that changes to the numbers of different types of contacts are appropriately reflected in changes to the overall age mixing patterns. Finally, we introduce and distinguish between two mixing pools associated with each patch, with possible implications for the overall connectivity of the population: the home pool, in which contacts can only be formed with other individuals residing in the same patch; and the travel pool, in which contacts can be formed with some residents of, and any other visitors to the patch. We describe in detail the steps required to implement our approach, and present results of an example application.Graphical Abstract

SOCRATES-CoMix: a platform for timely and open-source contact mixing data during and in between COVID-19 surges and interventions in over 20 European countries

Background SARS-CoV-2 dynamics are driven by human behaviour. Social contact data are of utmost importance in the context of transmission models of close-contact infections. Methods Using online representative panels of adults reporting on their own behaviour as well as parents reporting on the behaviour of one of their children, we collect contact mixing (CoMix) behaviour in various phases of the COVID-19 pandemic in over 20 European countries. We provide these timely, repeated observations using an online platform: SOCRATES-CoMix. In addition to providing cleaned datasets to researchers, the platform allows users to extract contact matrices that can be stratified by age, type of day, intensity of the contact and gender. These observations provide insights on the relative impact of recommended or imposed social distance measures on contacts and can inform mathematical models on epidemic spread. Conclusion These data provide essential information for policymakers to balance non-pharmaceutical interventions, economic activity, mental health and wellbeing, during vaccine rollout.

1483A meta-analysis of the serial interval and generation time of COVID-19 transmission

Background Variation of the estimated serial interval and generation time introduces heterogeneity in COVID-19 transmission models. We conducted a systematic review and meta-analysis to estimate more precise serial intervals and generation times of COVID-19. Methods A literature search was conducted using the WHO Global COVID-19 Literature database from 1 January 2020 to 30 April 2021. A single reviewer performed the data extraction. A random-effects model was used to pool the estimates. Subgroup analysis was performed to check the estimates for heterogeneity by geographical region and the presence of lockdown measures. Results A total of 222 articles were retrieved of which 73 articles were included based on the selection criteria. Serial intervals were reported in 65 articles that provided 75 unique estimates from 16,805 transmission pairs. Generation intervals were reported in 9 articles that provided 9 unique estimates from 1,150 transmission pairs. The pooled serial interval was 5.00 days (95% CI: 4.68, 5.33). The pooled generation time was 4.37 days (95% CI: 3.58, 5.16). The serial interval estimates did not vary by either geographical region (P > 0.05) or the presence of lockdown measures (P > 0.05). Conclusions This analysis provides more precise pooled serial and generation intervals that may decrease misspecifications of future transmission models. Key messages Epidemiological parameters are crucial components in estimating the dynamics of COVID-19 transmission. Periodically updating serial and generation time intervals are important to reduce model misspecification for a new disease such as COVID-19.

Estudo comparativo entre transmissões automotivas automáticas e manuais

O mercado automobilístico vem intensificando a criação e a aplicação de novas tecnologias veiculares. Nesse sentindo, entre os elementos que sofreram notável evolução, destacam-se as transmissões automotivas, que são objetos fundamentais na dinâmica veicular, pois contribuem para o deslocamento do automóvel e, além disso, são ofertadas no mercado nas mais diversas variações. O objetivo deste trabalho foi elaborar uma análise técnica comparativa entre os principais modelos de transmissões presentes no mercado: automática e manual. Primeiramente, foi realizada uma comparação em relação à parte mecânica estudando os principais cálculos associados ao desempenho de modelos equipados com esses mecanismos e foi realizada uma análise econômica. Os resultados mostram um relacionamento de aspectos que englobam desempenho, manutenção e consumo entre esses componentes com bons resultados. The automobile market has been intensifying the creation and application of new vehicle technologies. In this sense, among the elements that have undergone notable evolution, automotive transmissions stand out, which are fundamental objects in vehicle dynamics, as they contribute to the displacement of the automobile and, in addition, are offered in the market in the most diverse variations. The objective of this work was to elaborate a comparative technical analysis between the main transmission models present in the market: automatic and manual. First, a comparison in relation to the mechanical part was carried out, studying the main calculations associated with the performance of models equipped with these mechanisms, and an economic analysis was carried out. The results show a relationship of aspects that encompass performance, maintenance and consumption between these components with good results.