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People infected during the quarantine will have a higher mortality rate.
Because, staying in confined spaces with other people exposes them to higher viral doses, and the mortality rate is highly dependent on viral dose.
- Medical workers are getting more severly ill than people with otherwise identical risk factors.
- The biggest transmission vector in most countries is between cohabitating family members.
Because, staying in confined spaces with other people exposes them to higher viral doses, and the mortality rate is highly dependent on viral dose.
- Medical workers are getting more severly ill than people with otherwise identical risk factors.
- The biggest transmission vector in most countries is between cohabitating family members.
What is viral load and why are so many health workers getting sick? 'A very large virus army is difficult for our immune system to fight off.'
If I get a higher dose of virus does that mean I will be sicker?
Yes – work on two other coronaviruses: severe acute respiratory syndrome (Sars) and Middle East respiratory syndrome (Mers) has shown this, says Willem van Schaik, professor in Microbiology and Infection at the University of Birmingham, says
“On the basis of previous work on Sars and Mers coronaviruses, we know that exposure to higher doses are associated with a worse outcome and this may be likely in the case of Covid-19 as well,” he says.
Professor Wendy Barclay, head of the department of infectious disease, Imperial College London, says: “In general with respiratory viruses, the outcome of infection – whether you get severely ill or only get a mild cold – can sometimes be determined by how much virus actually got into your body and started the infection off. It’s all about the size of the armies on each side of the battle, a very large virus army is difficult for our immune system’s army to fight off.”
Viral Load Distribution in SARS Outbreak
An unprecedented community outbreak of severe acute respiratory syndrome (SARS) occurred in the Amoy Gardens, a high-rise residential complex in Hong Kong. Droplet, air, contaminated fomites, and rodent pests have been proposed to be mechanisms for transmitting SARS in a short period. We studied nasopharyngeal viral load of SARS patients on admission and their geographic distribution. Higher nasopharyngeal viral load was found in patients living in adjacent units of the same block inhabited by the index patient, while a lower but detectable nasopharyngeal viral load was found in patients living further away from the index patient. This pattern of nasopharyngeal viral load suggested that airborne transmission played an important part in this outbreak in Hong Kong. Contaminated fomites and rodent pests may have also played a role.
High measles mortality in infancy related to intensity of exposure.
In a West African urban community, measles infection in infants was examined over 5 years (1979-1983). In the age group 0 to 11 months, measles mortality was higher among secondary cases (infected in the house) than among index cases (infected outside the house), and the proportion of secondary cases was significantly higher for this age group than for older children. Intensive exposure related to the social pattern of disease transmission may be important in explaining the high infant mortality observed with measles in developing countries. Mortality during the first 12 months of life increased with age, presumably because of the decrease of maternally derived measles antibodies. In children younger than 6 months of age, who are usually considered to be protected by maternal antibody, intensive exposure may lead to infection, as demonstrated by a high level of measles-specific antibodies in some children exposed to an older sibling with measles. The aim of public health policies should be to change conditions of exposure.
Minimum infective dose of animal viruses
The potential for spread of viral and other infectious diseases is a function of the dose required to initiate an infection with either clinical or sub‐clinical sequelae. This is especially important for environmental spread where dilution and natural die‐off are generally assumed to play prominent roles in the control of disease. The use of disinfectants and other methods of pathogen destruction are common in certain instances but often a few survivors will eventually find routes back to their hosts. The importance of the minimum infectious dose is, therefore, evident. This report will review studies on the doses of different viruses required to initiate infection in animals and man.
The dose response of cats to experimental infection with Feline Viral Rhinotracheitis virus
The clinical and virological aspects of the response of cats to intranasal infections with various doses of Feline Viral Rhinotracheitis (FVR) were studied. Cats inoculated with doses of 102, 103, 105, or 107 CCID50 of virus developed a characteristic upper respiratory syndrome whereas a dose of 101 CCID50 failed to establish an infection. Although individual variation in the response was quite marked, it was shown that an increase in the infecting viral dose was correlated with a decrease in the length of the incubation period before onset of pyrexia, other clinical signs and viral excretion. Although increasing viral dose appeared to be directly related to the severity of the clinical signs, this relationship was only found to be statistically significant for dyspnoea. There was some indication of an effect of an increase in infecting viral dose on the duration of the subsequent viral excretion. A significant relationship was found between the duration of viral excretion and the severity of the resultant syndrome. The serological responses of the cats to FVR were generally of low magnitude. The proportion of infected animals with neutralizing antibody titres rose from 6 of 15 (40 per cent) by PID 16 to 20, to 11 of 15 (73 per cent) by PID 30 to 34.
Effect of viral dose on experimental pneumonia caused by aerosol exposure of calves to bovine herpesvirus 1 and Pasteurella haemolytica.
The effect of various aerosol doses of bovine herpesvirus 1, followed four days later by aerosol exposure to a constant level of Pasteurella haemolytica, was studied in 16 crossbred Hereford range calves. A Collision nebulizer was used to generate aerosols from virus suspensions with concentrations of 10(8.2) (high), 10(5.2) (moderate) or 10(2.2) (low) TCID50/mL. The bacterial suspension contained 10(7) colony forming units/mL. Control calves exposed only to P. haemolytica developed no pulmonary lesions. Calves in the low, moderate and high virus exposure groups developed lobular areas of atelectasis; in addition, one calf in the moderate and all four in the high virus exposure group developed fibrinous pneumonia. One of the latter calves died. The 50% effective dose for fibrinous pneumonia under these experimental conditions was 10(6.0) TCID50 bovine herpesvirus 1/mL of suspension in the nebulizer reservoir, and approximately 10(4.0) infectious units inhaled per calf.
Minimum Infective Dose of the Major Human Respiratory and Enteric Viruses Transmitted Through Food and the Environment
Viruses are a significant cause of morbidity and mortality around the world. Determining the minimum dose of virus particles that can initiate infection, termed the minimum infective dose (MID), is important for the development of risk assessment models in the fields of food and water treatment and the implementation of appropriate infection control strategies in healthcare settings. Both respiratory and enteric viruses can be shed at high titers from infected individuals even when the infection is asymptomatic. Presence of pre-existing antibodies has been shown to affect the infectious dose and to be protective against reinfection for many, but not all viruses. Most respiratory viruses appear to be as infective in humans as in tissue culture. Doses of <1 TCID50 of influenza virus, rhinovirus, and adenovirus were reported to infect 50% of the tested population. Similarly, low doses of the enteric viruses, norovirus, rotavirus, echovirus, poliovirus, and hepatitis A virus, caused infection in at least some of the volunteers tested. A number of factors may influence viruses’ infectivity in experimentally infected human volunteers. These include host and pathogen factors as well as the experimental methodology. As a result, the reported infective doses of human viruses have to be interpreted with caution. KeywordsMinimum infectious dose–Respiratory viruses–Enteric viruses–Infection