Multiple Transmission Routes Research Articles

Air infiltration induced inter-unit dispersion and infectious risk assessment in a high-rise residential building.

Identifying possible airborne transmission routes and assessing the associated infectious risks are essential for implementing effective control measures. This study focuses on the infiltration-induced inter-unit pollutant dispersion in a high-rise residential (HRR) building. The outdoor wind pressure distribution on the building facades was obtained from the wind tunnel experiments. And the inter-household infiltration and tracer gas transmission were simulated using multi-zone model. The risk levels along building height and under different wind directions were examined, and influence of component leakage area was analysed. It is found that, the cross-infection risk can be over 20% because of the low air infiltration rate below 0.7 ACH, which is significantly higher than the risk of 9% obtained in our previous on-site measurement with air change rate over 3 ACH. As the air infiltration rate increases along building height, cross-infection risk is generally higher on the lower floors. The effect of wind direction on inter-unit dispersion level is significant, and the presence of a contaminant source in the windward side results in the highest cross-infection risks in other adjacent units on the same floor. Properly improving internal components tightness and increasing air change via external components are beneficial to the control of internal inter-unit transmission induced by infiltration. However, this approach may increase the cross-infection via the external transmission, and effective control measures should be further explored considering multiple transmission routes.

Conditional persistence and tolerance characterize endoparasite-colonial host interactions.

Colonial hosts offer unique opportunities for exploitation by endoparasites resulting from extensive clonal propagation, but these interactions are poorly understood. The freshwater bryozoan, Fredericella sultana, and the myxozoan, Tetracapsuloides bryosalmonae, present an appropriate model system for examining such interactions. F. sultana propagates mainly asexually, through colony fragmentation and dormant propagules (statoblasts). Our study examines how T. bryosalmonae exploits the multiple transmission routes offered by the propagation of F. sultana, evaluates the effects of such transmission on its bryozoan host, and tests the hypothesis that poor host condition provokes T. bryosalmonae to bail out of a resource that may soon be unsustainable, demonstrating terminal investment. We show that infections are present in substantial proportions of colony fragments and statoblasts over space and time and that moderate infection levels promote statoblast hatching and hence effective fecundity. We also found evidence for terminal investment, with host starvation inducing the development of transmission stages. Our results contribute to a growing picture that interactions of T. bryosalmonae and F. sultana are generally characterized by parasite persistence, facilitated by multiple transmission pathways and host condition-dependent developmental cycling, and host tolerance, promoted by effective fecundity effects and an inherent capacity for renewed growth and clonal replication.

Potential for treatment and a Zika virus vaccine.

Zika virus (ZIKV) has only recently been exposed as a significant public health threat, and much of our limited knowledge of its pathogenesis and triggered immune responses were discovered in only the last few years. There are currently no ZIKV-specific therapeutics or vaccines available. This review seeks to bring the reader up-to-date with the latest developments in finding a way to combat this emerging infectious disease. Current strategies used for developing ZIKV vaccines or treatments follow proven methods used against other flaviviruses. Unfortunately, ZIKV carries many unique challenges, such as the need to target drugs and vaccines towards immunocompromised populations (pregnant mothers and fetuses), the risk of stimulating harmful immune responses (either autoimmune or antibody-dependent enhancement of infection in those with previous flavivirus exposure), frequently silent infection that may delay treatment and increase risk of transmission to others, and multiple routes of transmission (arthropod vector, sexual, bloodborne, and potentially other body fluids). Current medical recommendations are directed towards resolving symptoms and not the actual infection; however, ZIKV treatments and vaccines are in development. Vector control and travel restrictions to endemic areas may remain our only available interventions for some time.

Parasite spreading in spatial ecological multiplex networks

Network ecology is a rising field of quantitative biology representing ecosystems as complex networks. A suitable example is parasite spreading: several parasites may be transmitted among their hosts through different mechanisms, each one giving rise to a network of interactions. Modelling these networked, ecological interactions at the same time is still an open challenge. We present a novel spatially-embedded multiplex network framework for modelling multi-host infection spreading through multiple routes of transmission. Our model is inspired by T. cruzi, a parasite transmitted by trophic and vectorial mechanisms. Our ecological network model is represented by a multiplex in which nodes represent species populations interacting through a food web and a parasite contaminative layer at the same time. We modelled an SI dynamics in two different scenarios: a simple theoretical food web and an empirical one. Our simulations in both scenarios show that the infection is more widespread when both the trophic and the contaminative interactions are considered with equal rates. This indicates that trophic and contaminative transmission may have additive effects in real ecosystems. We also find that the ratio of vectors-to-host in the community (i) crucially influences the infection spread, (ii) regulates a percolating phase transition in the rate of parasite transmission and (iii) increases the infection rate in hosts. By immunising the same fractions of predator and prey populations, we show that the multiplex topology is fundamental in outlining the role that each host species plays in parasite transmission in a given ecosystem. We also show that the multiplex models provide a richer phenomenology in terms of parasite spreading dynamics compared to mono-layer models. Our work opens new challenges and provides new quantitative tools for modelling multi-channel spreading in networked systems.

Predicting bat colony survival under controls targeting multiple transmission routes of white-nose syndrome

White-nose syndrome (WNS) is a lethal infection of bats caused by the psychrophilic fungus Pseudogymnoascus destructans (Pd). Since the first cases of WNS were documented in 2006, it is estimated that as many as 5.5million bats have succumbed in the United States—one of the fastest mammalian die-offs due to disease ever observed, and the first known sustained epizootic of bats. WNS is contagious between bats, and mounting evidence suggests that a persistent environmental reservoir of Pd plays a significant role in transmission as well. It is unclear, however, the relative contributions of bat-to-bat and environment-to-bat transmission to disease propagation within a colony. We analyze a mathematical model to investigate the consequences of both avenues of transmission on colony survival in addition to the efficacy of disease control strategies. Our model shows that selection of the most effective control strategies is highly dependent on the primary route of WNS transmission. Under all scenarios, however, generalized culling is ineffective and while targeted culling of infected bats may be effective under idealized conditions, it primarily has negative consequences. Thus, understanding the significance of environment-to-bat transmission is paramount to designing effective management plans.

Shift in HIV/AIDS Epidemic in Southeastern China: A Longitudinal Study from 1987 to 2015.

Objective: The aim of this study was to investigate the shift in the epidemiological features of HIV/AIDS during the last three decades in Fujian Province, southeastern China, so as to provide evidence for the development of novel HIV/AIDS control strategies. Methods: Data pertaining to the conventional surveillance, sentinel surveillance and epidemiological survey in Fujian Province during the period from 1987 to 2015 were collected. The epidemiological trends were described, and the subtypes of HIV strain were genotyped. In addition, the response to antiretroviral therapy was evaluated, and HIV genotypic resistance was assayed. Results: There was an increasing trend observed in the reported cases of HIV/AIDS in Fujian Province. From 1987 to the end of 2015, a total of 8651 HIV/AIDS cases were reported across the province, with totally 1557 deaths found. Among the total cases, the ratio of male/female cases was 3.7:1, which appeared to be an increasing trend; 77.1% cases were detected in young and middle-aged populations aged 19 to 50 years, however, the new HIV infections recently tended to occur in young people aged 15 to 18 years and in populations aged 50 years and older. Among all infected individuals, 49.3% were married, however, the percentage of unmarried cases increased from 6.67% before 1994 to 40.1% in 2015; 64.8% had junior high school education or lower, however, the proportion of HIV/AIDS cases with junior college education or above gradually increased from 6.5% in 2009 to 21.4% in 2015. The reported HIV/AIDS cases were predominantly found in coastal regions; however, a rapidly increasing trend was seen in the number of HIV/AIDS cases in inland regions, and the geographical variation of the cases gradually reduced. There were multiple routes of HIV transmission found in Fujian Province, and 94.2% infections were sexually transmitted, with a large increase in the percentage of male homosexual transmission. A variety of HIV-1 subtypes were genotyped in the province during the study period, and CRF01-AE and CRF07-BC intersubtype recombinant forms were predominant; however, a declining trend in the proportion of HIV-1 CRF01-AE recombinant virus and a significant rise in the proportion of HIV-1 CRF07-BC recombinant virus were observed. Over 90% HIV inhibition was found in all cases receiving antiretroviral therapy during the period from 2011 to 2015, indicating a low prevalence of HIV drug resistance. Conclusions: An increasing trend is still observed in the HIV/AIDS epidemics in Fujian Province, southeastern China. However, the epidemiological pattern of HIV/AIDS has recently changed in the province, and effective control interventions targeting the shift in the epidemiological features of HIV/AIDS should therefore be implemented to control the spread of the epidemic.

Vaccines against norovirus: state of the art trials in children and adults

Noroviruses (NoVs), a group of nonenveloped, single-stranded RNA viruses belonging to the Caliciviridae family, are the leading cause worldwide of acute infectious gastroenteritis. Serious and eventual fatal outcomes may be observed in at-risk populations such as the very young or older adults, especially in those with underlying diseases. NoVs are highly infectious, with a low number of virus particles causing infection, and they are highly resistant to environmental conditions. NoVs have multiple routes of transmission including faecal–oral, aerosolized vomitus, person to person and via contaminated surfaces or food and water. NoVs can cause frequent and dramatic outbreaks where people congregate in close quarters such as hospitals, long-term care facilities, cruise liners and military barracks and ships. Of the seven NoV genogroups, human disease is most frequently caused by genogroups I and II, although genogroup IV has also been associated with illness. The absence of reliable, high-yield cell culture systems or animal models has steered the development of vaccines towards nonreplicating recombinant capsid proteins including viruslike particles and the sub-virus-sized P particles. Takeda Vaccines is developing a candidate NoV vaccine formulation based on adjuvanted viruslike particles from the GI.1 genotype and a consensus GII.4 sequence derived from three natural GII.4 variants. Early clinical trial results show good tolerability and robust immune responses to both components. This approach is designed to induce broad protective immune responses in adults and children.

Analysis of the transmission of Trypanosoma cruzi infection through hosts and vectors

Calculating epidemiological measures of infection by Trypanosoma cruzi, the causative agent of Chagas disease, is complex, because it involves several species, different stages of infection in humans and multiple transmission routes. Using the next-generation matrix method, we analysed a model which considers the three stages of human infection, triatomines and dogs (the main domestic reservoirs of T. cruzi when triatomines are present) and the main transmission routes. We derived R 0 and type-reproduction numbers T. We deduced formulas for the number of new infections generated through each transmission route by each infected individual. We applied our findings in Argentine Gran Chaco. The expressions achieved allowed quantifying the high infectivity of dogs and emphasizing the epidemiological importance of the long and asymptomatic chronic indeterminate stage in humans in the spread of the infection. According to the model, it is expected that one infected human infects 21 triatomines, that 100 infected triatomines are necessary to infect one human and 34 to infect a dog, and that each dog infects on average one triatomine per day. Our results may allow quantifying the effect of control measures on infected humans, triatomines and dogs (or other highly infected vertebrate) or on a specific route of transmission, in other scenarios.

Impact of the shedding level on transmission of persistent infections in Mycobacterium avium subspecies paratuberculosis (MAP).

Super-shedders are infectious individuals that contribute a disproportionate amount of infectious pathogen load to the environment. A super-shedder host may produce up to 10 000 times more pathogens than other infectious hosts. Super-shedders have been reported for multiple human and animal diseases. If their contribution to infection dynamics was linear to the pathogen load, they would dominate infection dynamics. We here focus on quantifying the effect of super-shedders on the spread of infection in natural environments to test if such an effect actually occurs in Mycobacteriumavium subspecies paratuberculosis (MAP). We study a case where the infection dynamics and the bacterial load shed by each host at every point in time are known. Using a maximum likelihood approach, we estimate the parameters of a model with multiple transmission routes, including direct contact, indirect contact and a background infection risk. We use longitudinal data from persistent infections (MAP), where infectious individuals have a wide distribution of infectious loads, ranging upward of three orders of magnitude. We show based on these parameters that the effect of super-shedders for MAP is limited and that the effect of the individual bacterial load is limited and the relationship between bacterial load and the infectiousness is highly concave. A 1000-fold increase in the bacterial contribution is equivalent to up to a 2–3 fold increase in infectiousness.Electronic supplementary materialThe online version of this article (doi:10.1186/s13567-016-0323-3) contains supplementary material, which is available to authorized users.

Evidence of household transfer of ESBL-/pAmpC-producing Enterobacteriaceae between humans and dogs – a pilot study

BackgroundExtended-spectrum cephalosporin-resistant Enterobacteriaceae (ESCRE) are an increasing healthcare problem in both human and veterinary medicine. The spread of ESCRE is complex with multiple reservoirs and different transmission routes. The aim of this study was to investigate if ESCRE carriage in dogs is more prevalent in households with a known human carrier, compared to households where humans are known to be negative for ESCRE. Identical ESCRE strains in humans and dogs of the same household would suggest a possible spread between humans and dogs.MethodsTwenty-two dog owners with a positive rectal culture for ESCRE each collected a rectal sample from their dog. In addition, a control group of 29 healthy dog owners with a documented negative rectal culture for ESCRE each sampled their household dog. Samples were cultivated for ESCRE using selective methods. In households where both humans and dogs carried ESCRE, isolates were further analysed for antimicrobial susceptibility by disc diffusion or microdilution and for genotype and genetic relatedness using molecular methods.ResultsIn 2 of 22 households studied, identical ESCRE strains with respect to bacterial species, antibiogram, genotype, and MLVA type were found in humans and dogs. The ESCRE found in the two households were ESBL-producing E. coli with the resistance gene blaCTX-M-27 and AmpC-producing E. coli with blaCMY-2, blaTEM-1. ESCRE were not found in dogs in the control group.ConclusionsIn households where humans are carrying ESCRE, identical strains were to a limited extent found also in household dogs, indicating a transfer between humans and dogs. In contrast, ESCRE were not found in dogs in households without human carriers.

Knowledge gaps in the epidemiology of Toxocara: the enigma remains.

Toxocara species infect a wide range of companion, domestic and wild animals as definitive and paratenic hosts, via multiple routes of transmission, producing long-lived tissue-inhabiting larvae and resistant eggs that can survive in the external environment. Therefore Toxocara and the disease it causes in humans, toxocariasis, represents an ideal aetiological agent for the development of the one health approach. However, despite increasing awareness of the public health significance of toxocariasis, gaps in our understanding of certain key aspects of the parasite's biology and epidemiology remain. These gaps hinder our ability to integrate research effort within the veterinary, medical and environmental disciplines. This review will highlight key deficits in our understanding of nine dimensions of Toxocara epidemiology and discuss a potential scenario to develop a more integrated, one health approach to improve our understanding of the prevention and control of this complex and cryptic zoonosis.

Determinants of the Final Size and Case Rate of Nosocomial Outbreaks.

Different nosocomial pathogen species have varying infectivity and durations of infectiousness, while the transmission route determines the contact rate between pathogens and susceptible patients. To determine if the pathogen species and transmission route affects the size and spread of outbreaks, we perform a meta-analysis that examines data from 933 outbreaks of hospital-acquired infection representing 14 pathogen species and 8 transmission routes. We find that the mean number of cases in an outbreak is best predicted by the pathogen species and the mean number of cases per day is best predicted by the species-transmission route combination. Our fitted model predicts the largest mean number of cases for Salmonella outbreaks (22.3) and the smallest mean number of cases for Streptococci outbreaks (8.5). The largest mean number of cases per day occurs during Salmonella outbreaks spread via the environment (0.33) and the smallest occurs for Legionella outbreaks spread by multiple transmission routes (0.005). When combined with information on the frequency of outbreaks these findings could inform the design of infection control policies in hospitals.

Impact of biodiversity and seasonality on Lyme-pathogen transmission.

Lyme disease imposes increasing global public health challenges. To better understand the joint effects of seasonal temperature variation and host community composition on the pathogen transmission, a stage-structured periodic model is proposed by integrating seasonal tick development and activity, multiple host species and complex pathogen transmission routes between ticks and reservoirs. Two thresholds, one for tick population dynamics and the other for Lyme-pathogen transmission dynamics, are identified and shown to fully classify the long-term outcomes of the tick invasion and disease persistence. Seeding with the realistic parameters, the tick reproduction threshold and Lyme disease spread threshold are estimated to illustrate the joint effects of the climate change and host community diversity on the pattern of Lyme disease risk. It is shown that climate warming can amplify the disease risk and slightly change the seasonality of disease risk. Both the “dilution effect” and “amplification effect” are observed by feeding the model with different possible alternative hosts. Therefore, the relationship between the host community biodiversity and disease risk varies, calling for more accurate measurements on the local environment, both biotic and abiotic such as the temperature and the host community composition.

Global dynamics of a network epidemic model for waterborne diseases spread

A network epidemic model for waterborne diseases spread is formulated, which incorporates both indirect environment-to-human and direct human-to-human transmission routes. We consider direct human contacts as a heterogeneous network and assume homogeneous mixing between the environment and human population. The basic reproduction number R0 is derived through the local stability of disease-free equilibrium and established as a sharp threshold that governs the disease dynamics. In particular, we have shown that the disease-free equilibrium is globally asymptotically stable if R0<1; while if R0>1, in case of permanent immunity the endemic equilibrium is globally asymptotically stable based on Kirchhoff’s matrix tree theorem, and in case of temporal immunity sufficient conditions are given to guarantee global stability of the endemic equilibrium. Moreover, various immunization strategies are investigated and compared. The results obtained are informative for us to further understand the disease propagation in multiple transmission routes and devise some effective intervening measures to fight against the diseases spread.

Modelling American Trypanosomiasis in an Endemic Zone: Application to the Initial Spread of Household Infection in the Argentine Chaco

The complex dynamics of Trypanosoma cruzi infection (Chagas disease) involves different actors and multiple transmission routes. Based on the information currently available, here, we propose a new and more comprehensive model to better understand the dynamics of the infection. This mathematical deterministic model was formulated considering: (i) the three clinical forms in humans: acute, chronic indeterminate and chronic with determinate pathology, (ii) the three main modes of transmission in the human population: vector-borne, congenital and transfusional, (iii) populations of triatomines and dogs as the main domestic reservoirs of T. cruzi and (iv) open populations. A numerical simulation was also performed to estimate the initial spread of the infection in a typical rural household in the endemic zone of the Argentine Gran Chaco. We also analysed the incidence of infected individuals corresponding to each of the three species (humans/triatomines/dogs) over times until the appearance of the first case in the other species. The model predicts that, in the absence of control measures, a few infected individuals are sufficient for the establishment and dispersion of the infection in all the inhabitants of the household. The model proposed and the results obtained allow describing the consequences of the presence of infected individuals in any of the three species considered in the dynamics and the output of the infection.

A metapopulation model for sylvatic &lt;em&gt; T. cruzi&lt;/em&gt; transmission with vector migration

This study presents a metapopulation model for the sylvatic transmission of Trypanosoma cruzi, the etiological agent of Chagas' disease, across multiple geographical regions and multiple overlapping host-vector transmission cycles. Classical qualitative analysis of the model and several submodels focuses on the parasite's basic reproductive number, illustrating how vector migration across patches and multiple transmission routes to hosts (including vertical transmission) determine the infection's persistence in each cycle. Numerical results focus on trends in endemic [equilibrium] persistence levels as functions of vector migration rates, and highlight the significance of the different epidemiological characteristics of transmission in each of the three regions.

Determination of the Prevalence of &lt;i&gt;Helicobacter heilmannii&lt;/i&gt;-Like Organisms Type 2 (HHLO-2) Infection in Humans and Dogs Using Non-Invasive Genus/Species-Specific PCR in Korea

ABSTRACTHelicobacter spp. may have multiple routes of transmission. It is unclear, however, whether the agent is zoonotic and therefore transmitted from an animal reservoir, including dogs. The aim of this population-based study was to assess the relationship between pet ownership or frequent exposure to dogs and Helicobacter spp. infection, especially focusing on HHLO-2 (Helicobacter heilmannii-like organisms type 2) in saliva and feces samples in Korea, using non-invasive genus/species-specific PCR. One hundred twenty-four eligible human subjects and 39 dogs participated in this study. Relativity of contact with dogs and Helicobacter spp. infection diagnosed by genus-specific PCR showed a statistically significant result (P<0.01), but in the relativity analyses between contact with dogs and H. pylori, H. felis and H. bizzozeronii infections diagnosed using species-specific PCR, only Helicobacter felis showed a statistically significant result. Although H. pylori infection showed a statistically significant relativity, no statistically significant association was found between veterinarian subjects and Helicobacter. spp., H. felis and H. bizzozeronii infections. On performing risk factor analyses of HHLO-2 infection by transmission, using matching species, between HHLO-2-positive dog owners and HHLO-2-positive dogs, Helicobacter felis infection showed an extremely significant relativity (P<0.0001), and Helicobacter bizzozeronii may also be a possible significant risk factor (P<0.01). These results suggest that HHLO-2 infection might be a zoonotic infection, because continuous contact with dogs was proved to be correlated with human H. felis and H. bizzozeronii infections in this study.

Norovirus: a challenging pathogen

Noroviruses account for over 90% of all viral gastroenteritis cases and ~50% of all outbreaks worldwide. Each year in Australia, there are an estimated 1.8 million cases. Casesmaybe sporadic or part of outbreaks, occurring in either the community or healthcare setting. Outbreaks are associated with significant morbidity and some mortality. They incur substantial costs and can be difficult to control in healthcare institutions or other closed settings. Multiple factors (related to virus biological properties, human immune responses or inadequate management modalities) make it a challenging pathogen to control. They include: multiple transmission routes, low infectious dose, environmental survival, spread and persistence, diagnostic difficulty, hand hygiene controversies, imperfect immunity and immune evasion, asymptomatic and prolonged shedding, lack of vaccine and lack of antiviral treatment. The purpose of this article is to promote a better understanding of these factors in order that health professionals may be better equipped to manage the problems posed by noroviruses. Until large-scale effective vaccination and specific treatments become available, the safeguarding of food and water supplies and the rigorous and timely application of outbreak management and infection control measures will remain the key to norovirus disease prevention and control.

Indirect Transmission of Influenza A Virus between Pig Populations under Two Different Biosecurity Settings

Respiratory disease due to influenza virus is common in both human and swine populations around the world with multiple transmission routes capable of transmitting influenza virus, including indirect routes. The objective of this study was to evaluate the role of fomites in influenza A virus (IAV) transmission between pig populations separated by two different biosecurity settings. Thirty-five pigs were divided into four experimental groups: 10 pigs (1 replicate) were assigned to the infected group (I), 10 pigs (2 replicates of 5 pigs) were assigned to the low biosecurity sentinel group (LB), 10 pigs (2 replicates of 5 pigs) were assigned to the medium biosecurity sentinel group (MB), and 5 pigs (1 replicate) were assigned to the negative control group (NC). Eight of 10 pigs in the infected group were inoculated with IAV and 36 hours following inoculation, personnel movement events took place in order to move potentially infectious clothing and personal protective equipment (PPE) to sentinel pig rooms. Following contact with the infected group, personnel moved to the MB group after designated hygiene measures while personnel moved directly to the LB group. Nasal swabs and blood samples were collected from pigs to assess IAV infection status and fomites were sampled and tested via RRT-PCR. All experimentally inoculated pigs were infected with IAV and 11 of the 144 fomite samples collected following contact with infected pigs were low level positive for IAV genome. One replicate of each sentinel groups LB and MB became infected with IAV and all five pigs were infected over time. This study provides evidence that fomites can serve as an IAV transmission route from infected to sentinel pigs and highlights the need to focus on indirect routes as well as direct routes of transmission for IAV.

Global analysis of multiple routes of disease transmission on heterogeneous networks

In this paper, we propose and study an SIS epidemic model with multiple transmission routes on heterogeneous networks. We focus on the dynamical evolution of the prevalence. Through mathematical analysis, we obtain the basic reproduction number R0 by investigating the local stability of the disease-free equilibrium and also investigate the effects of various immunization schemes on disease spread. We further obtain that the disease will die out independent of the initial infections if the basic reproduction number is less than one, otherwise if the basic reproduction number is larger than one, the system converges to a unique endemic equilibrium, which is globally stable and thus the disease persists in the population. Our theoretical results are conformed by a series of numerical simulations and suggest a promising way for the control of infectious diseases with multiple routes.