Virus World

The COVID-19 pandemic has prompted the search for animal models that recapitulate the pathophysiology observed in humans infected with SARS-CoV-2 and allow rapid and high throughput testing of drugs and vaccines. Exposure of larvae to SARS-CoV-2 Spike (S) receptor binding domain (RBD) recombinant protein was sufficient to elevate larval heart rate and treatment with captopril, an ACE inhibitor, reverted this effect. Intranasal administration of SARS-CoV-2 S RBD in adult zebrafish recombinant protein caused severe olfactory and mild renal histopathology.

Zebrafish intranasally treated with SARS-CoV-2 S RBD became hyposmic within minutes and completely anosmic by 1 day to a broad-spectrum of odorants including bile acids and food. Single cell RNA-Seq of the adult zebrafish olfactory organ indicated widespread loss of expression of olfactory receptors as well as inflammatory responses in sustentacular, endothelial, and myeloid cell clusters. Exposure of wildtype zebrafish larvae to SARS-CoV-2 in water did not support active viral replication but caused a sustained inhibition of ace2 expression, triggered type 1 cytokine responses and inhibited type 2 cytokine responses. Combined, our results establish adult and larval zebrafish as useful models to investigate pathophysiological effects of SARS-CoV-2 and perform pre-clinical drug testing and validation in an inexpensive, high throughput vertebrate model.

Preprint available in bioRxiv (Nov. 8 , 2020):

https://doi.org/10.1101/2020.11.06.368191

About two-thirds of the London NHS staffers surveyed reported diminished ability to taste or smell, a prominent, early Covid symptom, shows new research. A large proportion of U.K. health-care workers may have been infected with coronavirus early in the pandemic, according to a survey suggesting that loss of smell and taste may be a guide to determining its prevalence in populations. About two-thirds of the London National Health Service staffers surveyed reported diminished ability to taste or smell — one of the prominent, early symptoms of Covid-19 — just weeks after the coronavirus arrived in the U.K., according to research published Thursday in The Lancet Microbe journal.

Health-care professionals on the front lines are far more likely to contract the virus compared with individuals in the general community, earlier studies have found. Yet it’s unclear how many NHS staff have contracted the virus as testing has been limited. The high rate of the loss of smell, called anosmia, suggests that a larger proportion may have been infected than previously thought. “Some people get smell loss before other symptoms, or as the only symptom,” of Covid, said Carl Philpott, professor of rhinology at the University of East Anglia’s Norwich Medical School, in an interview. “It has a sudden onset, so people really notice the difference.” 

When Covid-19 patients have smell loss it tends to be sudden and severe. And they usually don't have a blocked, stuffy or runny nose - most people with coronavirus can still breathe freely Another thing that sets them apart is their "true" loss of taste. It's not that their taste is somewhat impaired because their sense of smell is out of action, say the researchers in the journal Rhinology. Coronavirus patients with loss of taste really cannot tell the difference between bitter or sweet 

Experts suspect this is because the pandemic virus affects the nerve cells directly involved with smell and taste sensation.

The main symptoms of coronavirus are:

• high temperature
• new, continuous cough
• loss of smell or taste

Anyone with these symptoms should self-isolate and arrange to have a swab test to check if they have the virus. Members of their household should isolate too to prevent possible spread.

Lead investigator Prof Carl Philpott, from the University of East Anglia, carried out smell and taste tests on 30 volunteers: 10 with Covid-19, 10 with bad colds and 10 healthy people with no cold or flu symptoms.  Smell loss was much more profound in the Covid-19 patents. They were less able to identify smells, and they were not able to discern bitter or sweet tastes at all. Prof Philpott, who works with the charity Fifth Sense, which was set up to help with people with smell and taste disorders, said: "There really do appear to be distinguishing features that set the coronavirus apart from other respiratory viruses. "This is very exciting because it means that smell and taste tests could be used to discriminate between Covid-19 patients and people with a regular cold or flu." He said people could do their own smell and taste tests at home using products like coffee, garlic, oranges or lemons and sugar. He stressed that diagnostic throat and nose swab tests were still essential if someone thought they might have coronavirus. The senses of smell and taste return within a few weeks in most people who recover from coronavirus, he added.

COVID-19 has heterogeneous manifestations, though one of the most common symptoms is a sudden loss of smell (anosmia or hyposmia). We investigated whether olfactory loss is a reliable predictor of COVID-19.

This preregistered, cross-sectional study used a crowdsourced questionnaire in 23 languages to assess symptoms in individuals self-reporting recent respiratory illness. We quantified changes in chemosensory abilities during the course of the respiratory illness using 0-100 visual analog scales (VAS) for participants reporting a positive (C19+; n=4148) or negative (C19-; n=546) COVID-19 laboratory test outcome. Logistic regression models identified singular and cumulative predictors of COVID-19 status and post-COVID-19 olfactory recovery.

Both C19+ and C19- groups exhibited smell loss, but it was significantly larger in C19+ participants (mean±SD, C19+: -82.5±27.2 points; C19-: -59.8±37.7). Smell loss during illness was the best predictor of COVID-19 in both single and cumulative feature models (ROC AUC=0.72), with additional features providing no significant model improvement. VAS ratings of smell loss were more predictive than binary chemosensory yes/no-questions or other cardinal symptoms, such as fever or cough. Olfactory recovery within 40 days was reported for ~50% of participants and was best predicted by time since illness onset.

Conclusions: As smell loss is the best predictor of COVID-19, we developed the ODoR-19 tool, a 0-10 scale to screen for recent olfactory loss. Numeric ratings ≤2 indicate high odds of symptomatic COVID-19 (10<OR<4), especially when viral lab tests are impractical or unavailable.

Preprint available at medRxiv (July 26, 2020):

https://doi.org/10.1101/2020.07.22.20157263