Fomite-mediated transmission as a sufficient pathway: a comparative analysis across three viral pathogens

Abstract Background Fomite mediated transmission can be an important pathway causing significant disease transmission in number of settings such as schools, daycare centers, and long-term care facilities. The importance of these pathways relative to other transmission pathways such as direct person-person or airborne will depend on the characteristics of the particular pathogen and the venue in which transmission occurs. Here we analyze fomite mediated transmission through a comparative analysis across multiple pathogens and venues. Methods We developed and analyzed a compartmental model that explicitly accounts for fomite transmission by including pathogen transfer between hands and surfaces. We consider two sub-types of fomite-mediated transmission: direct fomite (e.g., shedding onto fomites) and hand-fomite (e.g., shedding onto hands and then contacting fomites). We use this model to examine three pathogens with distinct environmental characteristics (influenza, rhinovirus, and norovirus) in four venue types. To parameterize the model for each pathogen we conducted a thorough literature search. Results Based on parameter estimates from the literature the reproductive number ( R 0 $\mathcal {R}_{0}$ ) for the fomite route for rhinovirus and norovirus is greater than 1 in nearly all venues considered, suggesting that this route can sustain transmission. For influenza, on the other hand, R 0 $\mathcal {R}_{0}$ for the fomite route is smaller suggesting many conditions in which the pathway may not sustain transmission. Additionally, the direct fomite route is more relevant than the hand-fomite route for influenza and rhinovirus, compared to norovirus. The relative importance of the hand-fomite vs. direct fomite route for norovirus is strongly dependent on the fraction of pathogens initially shed to hands. Sensitivity analysis stresses the need for accurate measurements of environmental inactivation rates, transfer efficiencies, and pathogen shedding. Conclusions Fomite-mediated transmission is an important pathway for the three pathogens examined. The effectiveness of environmental interventions differs significantly both by pathogen and venue. While fomite-based interventions may be able to lower R 0 $\mathcal {R}_{0}$ for fomites below 1 and interrupt transmission, rhinovirus and norovirus are so infectious ( R 0 > > 1 $\mathcal {R}_{0}>>1$ ) that single environmental interventions are unlikely to interrupt fomite transmission for these pathogens.https://deepblue.lib.umich.edu/bitstream/2027.42/146145/1/12879_2018_Article_3425.pd

Environmentally Mediated Transmission Models for Influenza and the Relationships with Meteorological Indices.

High public health concerns for future influenza pandemics and ongoing avian influenza emerging outbreaks need extended studies on influenza. In this dissertation, the impact of environmental factors on human influenza transmission was explored by using multiple modeling approaches. An environmental infection transmission system compartmental model that describes the dynamics of human interaction with pathogens in the environment was developed. Its environmental parameters include: the pathogen elimination rate; and the rate humans pick up pathogens, and deposit them. The environmental persistant ratio indicates whether transmission is density dependent or frequency dependent or in between. The environmental contamination ratio reflects total agent deposition per infection and outbreak probability. The temporal dynamics of the relative importance of different influenza transmission modes over the course of epidemics were further studied in an EITS agent-based model. The temporal variation of the relative importance of different influenza transmission modes is primarily attributable to the environmental dissemination and persistence effects of influenza virus particles in air and on surfaces. Some model parameters, including movement rate, virus die off rate and surface touching rate, significantly alter the temporal dynamics of the relative importance of different influenza transmission modes. A second smaller or equal-sized summer epidemic was identified in 9 of 11 years of study period in Hong Kong, China. We found that a new dominant subtype strain is commonly associated with this second peak. Multiple local weather variables and global climatic indices are statistically significantly associated with the influenza virus positive proportion of virus isolates, and the proportion of Influenza-like illness case among all patients who visit influenza surveillance clinics. We found that the correlations between influenza morbidity and absolute humidity are the strongest among all weather variables. The significant negative absolute humidity anomaly two weeks prior to the onset of influenza epidemics was identified. These findings will provide theoretical contexts to examine the role of the environment in influenza transmission and scientific suggestions for improving public health surveillance.Ph.D.Epidemiological ScienceUniversity of Michigan, Horace H. Rackham School of Graduate Studieshttp://deepblue.lib.umich.edu/bitstream/2027.42/86365/1/shengli_1.pd

The Importance of Environmental Interventions in Eliminating Trachoma Infection in Africa: The Case of Gashoho Health District, Burundi

Gashoho Health District, Burundi, has not achieved the World Health Organisation (WHO) target of elimination of the blinding infectious disease, trachoma, by 2020. The work in this thesis addresses this problem using three different approaches. Firstly, a cross-sectional study was undertaken to establish the current trachoma prevalence in Gashoho and whether poor sanitation was a risk factor for infection. 468 individuals from 117 households across four villages were clinically examined for signs of trachoma infection, and completed a questionnaire about environmental risk factors. The current prevalence of trachoma in Gashoho was 7.9% (95 % CI 5.0 - 10.6%). Children under 9 years old had an overall prevalence of 19.5% (95% CI 13.7-26.4%). Household access to a sanitary toilet almost halved the odds of trachoma infection (OR 0.437, 95 % CI 0.256 - 0.743). Then, mathematical models based on the SIS framework, but incorporating environmentally mediated transmission, were utilised to explore whether improved sanitation might eliminate trachoma in Gashoho. Stability analysis showed the existence of two basic reproductive numbers, R0H and R0E, governing human-to-human and environmentally mediated transmission. Persistence of trachoma was shown to depend on the sum of these quantities exceeding one. Numerical simulations suggested that the elimination of trachoma was possible in Gashoho, given environmental interventions that increased pathogen clearance from the environment. To complete the work in the thesis and allow rapid translation of the results into policy and practice, a new method of monitoring and evaluation of environmental interventions was proposed. Using computational and algebraic methods, Stratified Truncated Sequential Sampling was developed to link monitoring in individual villages to policy decisions at the Health District level. In conclusion, this thesis generates new knowledge and methods for improving trachoma control efforts in Gashoho Health District, Burundi

Center of Excellence Annual Report, July 1996-June 1997

The center was created in 1984 to promote interdisciplinary activities designed to improve the quality of human life through better animal health; expand livestock disease research capabilities in the College of Veterinary Medicine (UTCVM) and the Institute of Agriculture; identify and characterize animal diseases that are similar to human disease; and develop new strategies for the diagnosis, treatment, and prevention of disease. Since 1984, the center has developed successful programs that affect the understanding, treatment, and prevention of livestock and human diseases. These programs predominately focus on molecular and cellular approaches to research in infectious diseases, toxicology, host defense, molecular genetics, and carcinogenesis

Pursuing effective vaccines against cattle diseases caused by apicomplexan protozoa

Apicomplexan parasites are responsible for important livestock diseases that affect the production of much needed protein resources, and those transmissible to humans pose a public health risk. Vaccines, recognized as a cost-effective and environmentally friendly method for the prevention of infectious diseases in livestock, can avert losses in food production and decrease the exposure of humans to zoonotic pathogens. This review focuses on the need for and advances in vaccine development against the apicomplexan parasites Theileria spp., Babesia spp., Toxoplasma gondii, Neospora caninum, Eimeria spp., Besnoitia spp., Sarcocystis spp., and Cryptosporidium parvum. Together, the effect of these parasites on the cattle industry worldwide causes an enormous burden, yet they remain poorly controlled and very few effective and practical vaccines against them are available.Vaccine development is hampered by our scarce and limited knowledge of the biology and mechanisms of pathogenesis of these microorganisms, and the absence of correlates of host immune protection. More studies focused on these aspects as well as on the identification of parasite vulnerabilities that can be exploited for vaccine design are needed. Novel “omics” and gene editing approaches in understanding complex parasite biology together with advances in vaccinology will facilitate the development of effective, sustainable, and practical vaccines against cattle diseases caused by apicomplexan parasites. Such vaccines will help prevent animal and human diseases and allow production of enough animal protein to feed the growing human population in the twenty-first century and beyond