Lack of Knowledge on “Viral" Modes of Transmission - Mike Rock

Steven Avery

Administrator
Mike Rock - posted on Facebook

The Infectious Myth 2.0 - Private Group
https://www.facebook.com/groups/1816658931849533/posts/2062055673976523/

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LACK OF KNOWLEDGE ON "VIRAL" MODES OF TRANSMISSION:

Much has been made about the lack of evidence for human-to-human transmission of "viruses," especially in regards to the failed transmission experiments during the 1918 Spanish Flu. There were also many failed transmission experiments for Chickenpox, Scarlet Fever, Measles, etc. So it should come as no surprise that given the failure to actually transmit "viruses" from human to human, very little is known about how these "viruses" actually spread. The transmission studies are actually a hodgepodge of conflicting indirect experiments that lead to contradictory results, hence the non-conclusive terms/phrases such as "the evidence suggests," "it is believed/thought," "most probably caused by," etc. Two different studies highlight the lack of knowledge and contradictory information regarding inter-human modes of transmission:

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Transmissibility and transmission of respiratory viruses (March, 2021)
Nancy H. L. Leung
https://www.nature.com/articles/s41579-021-00535-6


From 2021:

TRANSMISSIBILITY AND TRANSMISSION OF RESPIRATORY VIRUSES

"WE KNOW LITTLE ABOUT THE RELATIVE CONTRIBUTION OF EACH MODEL TO THE TRANSMISSION OF A PARTICULAR VIRUS IN DIFFERENT SETTINGS, AND HOW ITS VARIATION AFFECTS TRANSMISSIBILITY AND TRANSMISSION DYNAMICS. Discussion on the particle size threshold between droplets and aerosols and the importance of aerosol transmission for severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) and influenza virus is ongoing."

"RESPIRATORY VIRUS INFECTIONS OFTEN CANNOT BE DIFFERENTIATED CLINICALLY. Respiratory viruses belong to diverse virus families that differ in viral and genomic structures, populations susceptible to infection, disease severity, seasonality of circulation, transmissibility and modes of transmission."

"Alternatively, volunteer transmission studies, where transmission is observed in susceptible volunteers who are exposed to other volunteers who are either experimentally or naturally infected8, may be used to provide important information on the effectiveness of interventions and the importance of presymptomatic or asymptomatic transmission in a controlled setting25. HOWEVER, THESE STUDIES CAN BE CHALLENGING AND EXPENSIVE TO CONDUCT, AND MAY BE CRITICIZED AS TOO ARTIFICIAL."

"MATHEMATICAL OR STATISTICAL MODELS ARE OFTEN USED TO ESTIMATE TRANSMISSIBILITY OF A RESPIRATORY VIRUS IN THE POPULATION, especially during pandemics to assess the extent of transmission. With use of data from surveillance, observational and interventional epidemiological studies, or simulation from modelling studies, TRANSMISSIBILITY IS USUALLY ASSESSED BY THE ESTIMATION OF THE BASIC REPRODUCTION NUMBER (R0) OR SECONDARY ATTACK RATE (SAR)."

"Respiratory viruses are transmitted between individuals when the virus is released from the respiratory tract of an infected person and is transferred through the environment, leading to infection of the respiratory tract of an exposed and susceptible person. There are a number of different routes (or modes) through which transmission could occur, the chance of which is modified by viral, host and environmental factors. ALTHOUGH THERE IS EVIDENCE IN SUPPORT OF INDIVIDUAL MODES OF TRANSMISSION, THE RELATIVE CONTRIBUTION OF DIFFERENT MODES TO A SUCCESSFUL TRANSMISSION EVENT, AND THE RELATIVE EFFECT OF EACH FACTOR ON EACH MODE OR MULTIPLE MODES SIMULTANEOUSLY, IS OFTEN UNKNOWN."

"TRADITIONALLY, IT IS BELIEVED that respiratory viruses are transmitted directly via physical contact between an infected individual (infector) and a susceptible individual (infectee), indirectly via contact with contaminated surfaces or objects (fomites) or directly through the air from one respiratory tract to another via large respiratory droplets or via fine respiratory aerosols."

"Various approaches, including environmental sampling, experimental animal and volunteer transmission studies, and epidemiological observations (mostly from outbreak investigations), have been used to provide evidence in support of each individual mode of transmission for different respiratory viruses, ALTHOUGH FOR EACH, SOME MAY CRITICIZE THEIR RELEVANCE6,7. Furthermore, although attempts have been made to classify each mode as ‘obligate’, ‘preferential’ or ‘opportunistic’15,50, LIMITED RESEARCH WAS DONE TO QUANTIFY THE RELATIVE IMPORTANCE OF EACH MODEL TO TRANSMISSION9."

Transmissibility and transmission of respiratory viruses (Aug, 2021)
Nature Reviews - Microbiology
https://www.nature.com/articles/s41579-021-00535-6#ref-CR8


In Summary (Part 1):
-they admit WE KNOW LITTLE about the relative contribution of each mode to the transmission of a particular "virus" in different settings, and how its variation affects transmissibility and transmission dynamics

-respiratory "virus" infections often CANNOT BE DIFFERENTIATED CLINICALLY

-human transmission studies are said to be CHALLENGING (?) and expensive to conduct, and may be CRITICIZED AS TOO ARTIFICIAL (?)

-mathematical or statistical models are often used to ESTIMATE transmissibility of a respiratory "virus" in the population

-transmissibility is usually assessed by the ESTIMATION of the basic reproduction number (R0) or secondary attack rate (SAR)

-although there is evidence in support of individual modes of transmission, the relative contribution of different modes to a successful transmission event, and the relative effect of each factor on each mode or multiple modes simultaneously, IS OFTEN UNKNOWN

-traditionally, IT IS BELIEVED that respiratory "viruses" are transmitted directly via physical contact between an infected individual (infector) and a susceptible individual (infectee), indirectly via contact with contaminated surfaces or objects (fomites) or directly through the air from one respiratory tract to another via large respiratory droplets or via fine respiratory aerosols (in other words: "it is believed" = THEY DON'T KNOW)

-VARIOUS APPROACHES, including environmental sampling, experimental animal and volunteer transmission studies, and epidemiological observations (mostly from outbreak investigations), have been used to provide evidence in support of each individual mode of transmission for different respiratory "viruses," ALTHOUGH FOR EACH, SOME MAY CRITICIZE THEIR RELEVANCE

-although attempts have been made to classify each mode as ‘obligate’, ‘preferential’ or ‘opportunistic’ LIMITED RESEARCH WAS DONE TO QUANTIFY THE RELATIVE IMPORTANCE OF EACH MODE TO TRANSMISSION

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Transmission routes of respiratory viruses among humans (2018)
Jasmin S Kutter - Monique I Spronken - Pieter L Fraaij - Ron AM Fouchier - Sander Herfst
https://www.sciencedirect.com/science/article/pii/S1879625717301773


From 2018:

TRANSMISSION ROUTES OF RESPIRATORY VIRUSES AMONG HUMANS

"Most studies on inter-human transmission routes are INCONCLUSIVE.

The relative importance of respiratory virus transmission routes is NOT KNOWN."

"Many outbreaks have been investigated retrospectively to study the possible routes of inter-human virus transmission. THE RESULTS OF THESE STUDIES ARE OFTEN INCONCLUSIVE and at the same time DATA FROM CONTROLLED EXPERIMENTS IS SPARSE. Therefore, FUNDAMENTAL KNOWLEDGE ON TRANSMISSION ROUTES that could be used to improve intervention strategies IS STILL MISSING."

"Transmission via each of these three routes is complex and depends on many variables such as environmental factors (e.g. humidity and temperature), crowding of people, but also on host factors such as receptor distribution throughout the respiratory tract. THE FACT THAT ALL THESE VARIABLES AFFECT THE DIFFERENT TRANSMISSION ROUTES OF THE DIFFERENT RESPIRATORY VIRUSES IN A DISSIMILAR WAY, MAKES IT VERY DIFFICULT TO INVESTIGATE THEM EXPERIMENTALLY."

"OUR OBSERVATIONS UNDERSCORE THE URGENT NEED FOR NEW KNOWLEDGE ON RESPIRATORY VIRUS TRANSMISSION ROUTES and the implementation of this knowledge in infection control guidelines to advance intervention strategies for currently circulating and newly emerging viruses and to improve public health."

"Measles virus (MV)

Measles is one of the most contagious viral diseases in humans that has been associated with aerosol transmission for a long time [12, 13, 14••, 15, 16, 17, 18••]. However, it should be noted that MV also replicates systemically, and that there is a role for dead cell debris-associated virus spread via fomites. In the late 1970s and early 1980s, data from RETROSPECTIVE OBSERVATIONAL STUDIES obtained during outbreaks in pediatric practices, a school, and a sporting event SUGGESTED TRANSMISSION THROUGH AEROSOLS [14••, 15, 16, 17, 18••]. Indeed, THOSE STUDIES SHOWED THAT MOST SECONDARY CASES NEVER CAME IN DIRECT CONTACT WITH THE INDEX PATIENT AND SOME WERE NEVER EVEN SIMULTANEOUSLY PRESENT IN THE SAME AREA AS THE INDEX CASE [14••, 18••] Examination of airflow in the pediatricians’ offices showed that aerosols were not only dispersed over the entire examination room but also accumulated in the hallway and other areas [14••, 18••]. Furthermore, based on the investigation of air circulation in a sport stadium, in which a MV outbreak occurred, AUTHORS SUGGESTED that MV had been dispersed through the ventilation system [16]. THUS IT WAS CONCLUDED THAT MV CAN BE TRANSMITTED VIA AEROSOLS. Although coughing is a common symptom associated with measles disease, index patients were described to cough frequently and vigorously in the outbreak reports of pediatric practices. REMINGTON et al. CALCULATED THE INFECTIOUS DOSE OF MV PRODUCED BY THE INDEX CASE THROUGH COUGHING, USING A MATHEMATICAL MODEL BASED ON AIRBORNE TRANSMISSION. They found that the index case produced a very high infectious dose compared to cases from other outbreaks and mentioned a phenomenon called superspreading [18••]."

"Parainfluenza (PIV) and human metapneumovirus (HMPV)

THERE IS A SUBSTANTIAL LACK OF (EXPERIMENTAL) EVIDENCE ON THE TRANSMISSION ROUTES OF PIV (types 1–4) AND HMPV. For both viruses, contact and droplet transmission are commonly accepted transmission routes [23, 24, 25]. However, only virus stability on various surfaces has been investigated so far and it has been shown that PIV and HMPV are stable on non-absorptive surfaces and can barely be recovered from absorptive surfaces [26, 27, 28, 29, 30]."

"Respiratory syncytial virus (RSV)

TRANSMISSION OF RSV AMONG HUMANS IS THOUGHT TO OCCUR VIA DROPLETS AND FOMITES [1, 7]. In the 1980s three potential transmission routes of RSV were studied in humans by dividing infected infants and healthy volunteers into three groups, representing: Firstly, all transmission routes, secondly, transmission via fomites and finally, airborne transmission by allowing the volunteers to have either, firstly, direct contact with infants (cuddlers), secondly, touching potential fomites (touchers) or finally, sitting next to the infant (sitters). Volunteers in the group of the cuddlers and touchers but not the sitters became infected, SUGGESTING THAT DIRECT CONTACT AND DROPLET TRANSMISSION WERE THE PROBABLE ROUTES FOR EFFICIENT INFECTION OF THE VOLUNTEERS AND THAT TRANSMISSION VIA AEROSOLS WAS LESS LIKELY [31]. Another study on the transmission via fomites showed that RSV could be recovered from countertops for several hours, but only for several minutes from absorptive surfaces such as paper tissue and skin [32••]. Later on, in the late 1990s, Aintablian et al. detected RSV RNA in the air up to 7 m away from a patient's head [33]. In spite of that, SINCE VIRUS INFECTIVITY COULD NOT BE DEMONSTRATED, POTENTIAL AIRBORNE TRANSMISSION OF RSV HAS BEEN CONSIDERED NEGLIGIBLE AND TRANSMISSION OF RSV WAS THOUGHT TO OCCUR MAINLY THROUGH CONTACT AND DROPLET TRANSMISSION. However, in a recent study authors were able to collect aerosols that contained viable virus from the air around RSV infected children [34••]. ALTHOUGH THE DETECTION OF VIABLE VIRUS IN THE AIR IS BY ITSELF NOT ENOUGH TO CONFIRM AEROSOL TRANSMISSION, the general PRESUMPTION that RSV exclusively transmits via droplets should be reconsidered and explored further."

"Rhinovirus

EXTENSIVE HUMAN RHINOVIRUS TRANSMISSION EXPERIMENTS HAVE NOT LED TO A WIDELY-ACCEPTED VIEW ON THE TRANSMISSION ROUTE [35, 36, 37, 38••, 39••, 40]. Inhalation of aerosols (0.2–3 μm) resulted in efficient rhinovirus infection [41], but LITTLE TO NO INFECTIOUS RHINOVIRUS COULD BE DEMONSTRATED IN SNEEZES AND COUGHS as detected by virus titration."

"Influenza A virus

Due to the severity of the yearly influenza epidemics and the potential of zoonotic influenza A viruses to cause severe outbreaks, there have been many studies on influenza A virus transmission among humans. Different kinds of studies, such as air sampling and intervention studies, as well as human challenge studies have been conducted. In addition, transmission events have been described extensively after outbreaks in aircrafts, households and hospital settings. HOWEVER, UNTIL TODAY, RESULTS ON THE RELATIVE IMPORTANCE OF DROPLET AND AEROSOL TRANSMISSION OF INFLUENZA VIRUSES STAY INCONCLUSIVE AND HENCE, THERE ARE MANY REVIEWS INTENSIVELY DISCUSSING THIS ISSUE.

"The presence of virus in aerosols COULD INDICATE POTENTIAL AIRBORNE TRANSMISSION, although many studies only quantified the amount of viral RNA [55, 57•, 61]. A few studies quantified viable virus, ALTHOUGH THIS WAS ONLY RECOVERED FROM A MINORITY OF SAMPLES."

"Coronavirus

In humans, alpha (229E and NL63) and beta coronaviruses (OC43, HKU1, SARS and MERS) ARE ASSOCIATED with respiratory disease [62, 63]. Alpha coronaviruses have a high attack rate early in life and spread rapidly during outbreaks, indicating efficient human to human transmission [63]. Furthermore, samples obtained from staff and patients of a neonatal and pediatric intensive care unit showed a high incidence of human coronaviruses HCoV-229E and HCoV-OC43, SUGGESTING staff-to-patient and patient-to-staff transmission [64]. Unfortunately, THERE IS VERY LITTLE DATA TO CORROBORATE ON THE HCoV-229E, HCoV-NL63 AND HCoV-OC43 TRANSMISSION ROUTES."

"The SARS outbreak was primarily linked to healthcare settings, with ≥49% of the cases linked to hospitals [71], MOST PROBABLY CAUSED BY AEROSOL-GENERATING PROCEDURES ON SEVERELY ILL PATIENTS [72, 73]. Aerosol-generating procedures like intubation, the use of continuous positive-pressure ventilation and drug delivery via nebulizers ARE LIKELY TO PRODUCE ‘fine infectious droplets’, which travel further than droplets from coughs [74]. Additionally, superspreading events contributed to the dispersion of the SARS outbreak [73, 75, 76, 77], particularly in the Hotel Metropole and the Prince of Wales Hospital in Hong Kong [76]. Moreover, a link with transmission to healthcare workers was observed when they were in close proximity (<1 m) to an index patient, SUGGESTING DIRECT CONTACT OR DROPLET TRANSMISSION [73, 78•, 79•]. Air samples and swabs from frequently touched surfaces in a room occupied by a SARS patient tested positive by PCR, ALTHOUGH NO VIRUS COULD BE CULTURED FROM THESE SAMPLES [80]. In the Amoy gardens outbreak fecal droplet transmission was SUGGESTED [81, 82]."

"To date, THERE IS LITTLE DATA ON THE HUMAN-TO-HUMAN MERS-CoV TRANSMISSION ROUTE [83]."

"Adenovirus

This is illustrated by, for example, outbreaks among military recruits for which AIRBORNE SPREAD WAS SUGGESTED [92, 94, 99]. It is difficult to eliminate adenovirus from skin, fomites and environmental surfaces [100]. An outbreak in a mental care facility WAS PROBABLY ENHANCED by spending the day mainly in a crowded room while sharing cigarettes and soda cans, SUGGESTING INDIRECT FOMITE SPREAD [101]."

"During a military training period, increased numbers of adenovirus infections occurred over time, which correlated with an increased detection of PCR-positive air filters. Additionally, a correlation between disease and the extent of ventilation was observed, with more ventilation resulting in fewer disease cases [103•]. In a more recent study in military recruits, positive viral DNA samples were mainly obtained from pillows, lockers and rifles, although adenovirus DNA was also detected in air samples. NO CONSISTENT CORRELATION BETWEEN INCREASED POSITIVE ENVIRONMENTAL SAMPLES AND DISEASE WAS OBSERVED [104]."

"Studies on the transmission routes of respiratory viruses have been performed since the beginning of the 20th century [105]. DESPITE THIS, THE RELATIVE IMPORTANCE OF TRANSMISSION ROUTES OF RESPIRATORY VIRUSES IS STILL UNCLEAR"

"Inter-human transmission has been studied under many different (experimental) conditions. A summary of the advantages and disadvantages of the different study designs (Table 3) HIGHLIGHTS THE DIFFICULTY OF HUMAN TRANSMISSION EXPERIMENTS. As a consequence, CONTRASTING RESULTS HAVE BEEN OBTAINED FOR MANY VIRUSES. This is also reflected in Table 2, summarizing the experimental data on inter-human transmission. Besides the difficulty of performing studies under well-controlled conditions, another key issue is that often (attenuated) laboratory strains are studied in healthy adults, WHICH DOES NOT REFLECT THE NATURAL CIRCUMSTANCES and target group and HENCE INFLUENCE THE OUTCOME OF THE STUDIES."

"Unfortunately, TERMS AND DEFINITIONS OF RESPIRATORY TRANSMISSION ROUTES AND ISOLATION GUIDELINES ARE NOT ALWAYS USED IN A UNIFORM WAY, LEAVING ROOM FOR PERSONAL INTERPRETATION. But more importantly, information on the transmission route does not always reflect the isolation guidelines (e.g. for PIV and rhinovirus, Figure 1). As a proxy for transmission route, virus stability is often referred to in the guidelines, however, this can only imply a role for indirect contact transmission but is by no means conclusive on the transmission route. In hospital settings, prevention of contact transmission is generally implemented in standard infection prevention precautions such as strict hand hygiene and cough etiquette. IT IS IMPORTANT TO NOTE DIFFERENCES IN ISOLATION GUIDELINES BETWEEN DIFFERENT ORGANIZATIONS AND THE LACK OF CORRELATION TO SCIENTIFIC DATA. The variation in described transmission routes and associated isolation guidelines among the different organizations UNDERSCORES THE LACK OF CONVINCING DATA."

"Well-designed human infection studies could be employed to investigate the role of transmission routes of respiratory viruses among humans [112••]. However, SINCE HUMAN TRANSMISSION EXPERIMENTS ARE VERY CHALLENGING, ANIMAL TRANSMISSION MODELS CAN PROVIDE AN ATTRACTIVE ALTERNATIVE AND SHOULD BE EXPLORED AND DEVELOPED FOR ALL RESPIRATORY VIRUSES. In such experiments, the influence of environmental factors on transmission routes can also be investigated [113]. HOWEVER, BEFORE EXTRAPOLATING EXPERIMENTALLY GENERATED DATA TO HUMANS, IT IS IMPORTANT TO UNDERSTAND THE LIMITATIONS OF THESE MODELS, AND APPRECIATE THE HETEROGENEITY OF EXPERIMENTAL SETUPS EMPLOYED IN LABORATORIES [114]. Furthermore, quantitative data such as viral load in the air can be obtained by air sampling methods in various environments, such as hospital settings. Air sampling of viruses is an increasingly used technology in animal and human experiments. HOWEVER, WHEREAS MOST STUDIES RELY ON THE DETECTION OF VIRAL GENOME COPIES, viability assays such as plaque assays or virus titration SHOULD BE INCLUDED TO GAIN INFORMATION ON VIRUS INFECTIVITY.

Ultimately, THE KNOWLEDGE GAP ON INTER-HUMAN TRANSMISSION SHOULD BE FILLED BY DEVELOPING AND PERFORMING STATE-OF-THE ART EXPERIMENTS IN A NATURAL SETTING. Combined with animal transmission models and air sampling in different (health care and experimental) settings, THESE DATA SHOULD RESULT IN A THOROUGH SCIENTIFIC UNDERSTANDING OF THE INTER-HUMAN TRANSMISSION ROUTES OF RESPIRATORY VIRUSES."

https://www.sciencedirect.com/science/article/pii/S1879625717301773#bib0795

In Summary (Part 2):

-most studies on inter-human transmission routes are INCONCLUSIVE

-the relative importance of respiratory "virus" transmission routes is NOT KNOWN

-the results of these studies are often INCONCLUSIVE and at the same time data from controlled experiments is SPARSE

-fundamental knowledge on transmission routes that could be used to improve intervention strategies IS STILL MISSING

-the fact that all these variables affect the different transmission routes of the different respiratory "viruses" in a dissimilar way, MAKES IT VERY DIFFICULT TO INVESTIGATE THEM EXPERIMENTALLY

-their observations underscore the URGENT NEED FOR NEW KNOWLEDGE on respiratory "virus" transmission routes

-for Measles (MV), data from RETROSPECTIVE OBSERVATIONAL STUDIES from the 1970's and 80's obtained during outbreaks in pediatric practices, a school, and a sporting event SUGGESTED transmission through aerosols

-those studies showed that MOST SECONDARY CASES NEVER CAME IN DIRECT CONTACT WITH THE INDEX PATIENT and some were NEVER EVEN SIMULTANEOUSLY PRESENT IN THE SAME AREA as the index case

-based on the investigation of air circulation in a sport stadium, in which a MV outbreak occurred, AUTHORS SUGGESTED that MV had been dispersed through the ventilation system

-thus it was concluded that MV can be transmitted via aerosols

-Remington et al. calculated the infectious dose of MV produced by the index case through coughing, USING A MATHEMATICAL MODEL based on airborne transmission

-for Parainfluenza (PIV) and human metapneumovirus (HMPV), there is a SUBSTANTIAL LACK OF (EXPERIMENTAL) EVIDENCE on the transmission routes

-for Respiratory syncytial "virus" (RSV), transmission among humans is THOUGHT TO OCCUR via droplets and fomites

-since "virus" infectivity COULD NOT BE DEMONSTRATED, potential airborne transmission of RSV has been considered negligible and transmission of RSV was THOUGHT TO OCCUR mainly through contact and droplet transmission

-the detection of "viable virus" in the air is by itself NOT ENOUGH TO CONFIRM aerosol transmission

-extensive human rhinovirus transmission experiments HAVE NOT LED to a widely-accepted view on the transmission route

-LITTLE TO NO INFECTIOUS RHINOVIRUS could be demonstrated in sneezes and coughs

-until today, results on the relative importance of droplet and aerosol transmission of influenza "viruses" STAY INCONCLUSIVE and hence, there are many reviews intensively discussing this issue

-the presence of "virus" in aerosols COULD INDICATE POTENTIAL AIRBORNE TRANSMISSION, although many studies only quantified the amount of "viral" RNA

-a few studies quantified "viable virus," ALTHOUGH THIS WAS ONLY RECOVERED FROM A MINORITY OF SAMPLES

-in humans, alpha (229E and NL63) and beta coronaviruses (OC43, HKU1, SARS and MERS) are ASSOCIATED with respiratory disease

-there is VERY LITTLE DATA to corroborate on the HCoV-229E, HCoV-NL63 and HCoV-OC43 transmission routes

-"SARS" was MOST PROBABLY CAUSED by aerosol-generating procedures on severely ill patients

-aerosol-generating procedures like intubation, the use of continuous positive-pressure ventilation and drug delivery via nebulizers ARE LIKELY TO PRODUCE ‘FINE INFECTIOUS DROPLETS’

-a link with transmission to healthcare workers was observed when they were in close proximity (<1 m) to an index patient, SUGGESTING direct contact or droplet transmission

-air samples and swabs from frequently touched surfaces in a room occupied by a "SARS" patient tested positive by PCR, ALTHOUGH NO "VIRUS" COULD BE CULTURED FROM THESE SAMPLES (I guess detecting "virus" with PCR doesn't mean "virus" is present... 🤔)

-to date, THERE IS LITTLE DATA ON THE HUMAN-TO-HUMAN MERS-CoV TRANSMISSION ROUTE

-for "adenovirus," airborne spread WAS SUGGESTED among military recruits

-an outbreak in a mental care facility WAS PROBABLY ENHANCED by spending the day mainly in a crowded room while sharing cigarettes and soda cans, SUGGESTING INDIRECT FOMITE SPREAD

-in a more recent study in military recruits, positive "viral" DNA samples were mainly obtained from pillows, lockers and rifles, although "adenovirus" DNA was also detected in air samples yet NO CONSISTENT CORRELATION BETWEEN INCREASED POSITIVE ENVIRONMENTAL SAMPLES AND DISEASE WAS OBSERVED (another strike against PCR results = "virus" 🤔)

-the relative importance of transmission routes of respiratory "viruses" is still UNCLEAR

-a summary of the advantages and disadvantages of the different study designs HIGHLIGHTS THE DIFFICULTY OF HUMAN TRANSMISSION EXPERIMENTS

-as a consequence, CONTRASTING RESULTS HAVE BEEN OBTAINED for many "viruses"

-besides the DIFFICULTY OF PERFORMING STUDIES UNDER WELL-CONTROLLED CONDITIONS, another key issue is that often (attenuated) laboratory strains are studied in healthy adults, WHICH DOES NOT REFLECT THE NATURAL CIRCUMSTANCES and target group and HENCE INFLUENCE THE OUTCOME OF THE STUDIES

-unfortunately, terms and definitions of respiratory transmission routes and isolation guidelines are NOT ALWAYS USED IN A UNIFORM WAY, leaving room for PERSONAL INTERPRETATION

-it is important to note differences in isolation guidelines between different organizations and the LACK OF CORRELATION TO SCIENTIFIC DATA

-the VARIATION IN DESCRIBED TRANSMISSION ROUTES and associated isolation guidelines among the different organizations UNDERSCORES THE LACK OF CONVINCING DATA

-SINCE HUMAN TRANSMISSION EXPERIMENTS ARE VERY CHALLENGING, animal transmission models can provide an attractive alternative and should be explored and developed for all respiratory "viruses"

-however, before extrapolating experimentally generated data to humans, IT IS IMPORTANT TO UNDERSTAND THE LIMITATIONS OF THESE MODELS, and appreciate the heterogeneity of experimental setups employed in laboratories

-however, whereas MOST STUDIES RELY ON THE DETECTION OF "VIRAL" GENOME COPIES, viability assays such as plaque assays or "virus" titration SHOULD BE INCLUDED to gain information on "virus" infectivity

-the KNOWLEDGEABLE GAP on inter-human transmission should be filled by developing and performing state-of-the art experiments IN A NATURAL SETTING

-these data SHOULD RESULT in a thorough scientific understanding of the inter-human transmission routes of respiratory "viruses"

In other words, after over a hundred years and countless studies, we still do not have a thorough understanding of the inter-human transmission routes of respiratory "viruses." Now why would that be...? 🤔
 
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