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Urinary tract infections (UTIs) and yeast infections are both common conditions that affect millions of people worldwide, particularly women. Although they may share some symptoms, their causes, treatments, and prevention methods are quite different. In this article, we will delve into the critical distinctions between UTIs and yeast infections to help you better understand these conditions and seek appropriate medical attention when necessary.

Urinary Tract Infections: Causes and Treatment
Bacterial Origins of UTIs
UTIs are primarily caused by bacteria, with the most common culprit being Escherichia coli (E. coli). Other bacteria that can lead to UTIs include Staphylococcus epidermidis, Staphylococcus aureus, and Klebsiella pneumoniae. These infections occur when bacteria enter the urinary tract, typically through the urethra, and begin to multiply.

Antibiotic Treatment and Potential Complications
Antibiotic treatment options for urinary tract infections remain standard practice. These antibiotics are designed to kill the bacteria responsible for the infection. However, antibiotic use can lead to some adverse effects and complications, such as:

Allergic reactions
Candida va**nal infections
Nausea and vomiting
Diarrhea
Rashes
Yeast infections
Moreover, excessive or inappropriate use of antibiotics may contribute to the development of antibiotic-resistant strains of bacteria and disrupt the balance of beneficial bacteria that protect against infections.

Home Remedies for UTIs
In addition to medical treatment, some home remedies can help alleviate UTI symptoms and prevent future infections. These remedies include:

Staying hydrated to flush out bacteria
Urinating when the urge arises
Drinking cranberry juice
Taking probiotics
Consuming enough vitamin C
Wiping from front to back after using the toilet
Practicing good s*xual hygiene
It is crucial to remember that complicated UTIs require medical intervention. Seeking prompt medical attention can reduce the risk of developing a severe infection that is more challenging to treat.

Yeast Infections: Causes and Symptoms
Fungal Origins of Yeast Infections
Unlike UTIs, yeast infections are caused by an overgrowth of a fungus called Candida, which is naturally present in the body. These infections are particularly common in women, with three out of every four women experiencing at least one yeast infection in their lifetime.

Symptoms in Women and Men
Yeast infections present with varying symptoms in women and men. In women, symptoms may include:

Extreme itching in and around the va**na
Burning during urination or s*xual in*******se
Swelling and redness around the v***a
Pain and soreness in the va**na
Thick, white, odorless discharge
Men can also develop yeast infections, although less commonly than women. Symptoms in men may include:

Itching, burning, and redness on the p***s
Thick, white substance in the skin folds of the p***s
Shiny, white patches on the p***s
Complicated Infections and Risk Factors
Complicated yeast infections may require a more extended course of treatment or a plan to prevent a recurrence. These infections are more common in pregnant women, individuals with uncontrolled diabetes, and those with weakened immune systems.

It is essential to consult a doctor if:

You have never had a yeast infection before
Symptoms do not improve after treatment
You experience new or unusual pain or discharge in the ge***al area
You have pain during s*xual in*******se
Appropriate medical attention can help relieve symptoms and prevent the spread of potential infections.

Prevention Strategies for UTIs and Yeast Infections
While UTIs and yeast infections have different origins, some general preventive measures can help reduce the risk of both conditions. These strategies include:

Maintaining good personal hygiene
Wearing breathable, cotton underwear
Avoiding harsh soaps and feminine hygiene products
Changing out of wet or damp clothing promptly
Staying well-hydrated
Practicing safe s*x and good s*xual hygiene
Additionally, specific preventative measures for UTIs include urinating after s*xual activity, avoiding irritants such as bubble baths and deodorant sprays, and consuming a diet rich in antioxidants and immune-boosting nutrients. For yeast infections, maintaining balanced blood sugar levels, avoiding douching, and limiting the intake of sugary foods can help prevent the overgrowth of Candida.

When to Seek Medical Help
It is essential to seek medical help for both UTIs and yeast infections, as untreated infections can lead to more severe health complications. For UTIs, potential complications include kidney infections, sepsis, and recurrent infections. Untreated yeast infections can result in chronic pain, the spread of the infection to other parts of the body, and an increased risk of s*xually transmitted infections.

If you suspect you have a UTI or yeast infection, it is crucial to consult a healthcare professional for an accurate diagnosis and appropriate treatment. Early intervention can help alleviate symptoms, prevent complications, and reduce the risk of recurrence.

Conclusion
Understanding the differences between UTIs and yeast infections is vital for seeking appropriate medical care and implementing effective prevention strategies. While both conditions share some similarities, their causes, symptoms, and treatments are distinct. Remember to maintain good hygiene practices, follow a healthy lifestyle, and consult a healthcare professional if you experience any symptoms of a UTI or yeast infection. By staying informed and proactive, you can reduce your risk of these common but potentially serious infections.

A calorie is a unit of measurement for energy, precisely the amount of energy required to raise the temperature of one gram of water by one degree Celsius. Regarding nutrition, a calorie is the amount of energy provided by a specific food or beverage.

Calories are essential for the human body to function correctly. They provide the energy needed for everyday activities like breathing, walking, and thinking. However, when you consume more calories than your body needs, the excess calories are stored in the body as fat. Over time, this can lead to weight gain and other health issues like high blood pressure, diabetes, and heart disease.

On the other hand, consuming fewer calories than your body needs can lead to weight loss. By creating a calorie deficit through diet and exercise, your body will start to use stored fat for energy, resulting in weight loss.

salad weights measuring tape
Image from Adobe Stock
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This custom-tailored tool will help you better understand your current status and provide valuable insights and advice as you embark on your weight loss mission. So why wait? Give it a try today and take your first step toward a healthier lifestyle!

The Short- and Long-Term Effects of Eating Too Few Calories
Eating too few calories, also known as calorie restriction, can have short- and long-term effects on the body.

Short-term effects of eating too few calories
01Hunger and food cravings: When you’re not consuming enough calories, your body will send hunger signals, and you may experience intense food cravings.
02Fatigue and weakness: Consuming too few calories can lead to feelings of fatigue and weakness, as your body doesn’t have enough energy to function correctly.
03Reduced mental clarity: Your brain needs glucose to function correctly, and consuming too few calories can lead to decreased mental clarity and difficulty concentrating.
04Mood changes: Eating too few calories can also lead to changes in mood, including irritability, anxiety, and depression.
Long-term effects of eating too few calories
01Slower metabolism: When you consume too few calories consistently, your body will slow down its metabolism to conserve energy, making it harder to lose weight.
02Nutrient deficiencies: Consuming too few calories can lead to poverty, as you may need more vitamins, minerals, and other essential nutrients.
03Muscle loss: If you’re not consuming enough calories and protein, your body may break down muscle tissue for energy, leading to muscle loss.
04Increased risk of disease: Chronic calorie restriction can increase the risk of certain conditions, including osteoporosis, weakened immune system, and heart disease.
In summary, while short-term calorie restriction can lead to weight loss, consuming too few calories over the long term can adversely affect your health and well-being. Therefore, balancing and ensuring you drink enough calories to fuel your body and meet your nutrient needs is crucial.

The Role of Metabolism in Low-Calorie Eating
Metabolism is how your body converts food and drinks into energy. It’s a complex process that involves various chemical reactions and bodily functions. Your metabolism rate is affected by multiple factors, including age, gender, genetics, body composition, and physical activity level.

When you’re consuming a low-calorie diet, your metabolism can be affected by a decrease in metabolic rate. When consuming fewer calories than your body needs, your metabolism can slow down to conserve energy. This can make it harder to lose weight and make it easier to gain weight.

Another effect of low-calorie eating on metabolism is the loss of muscle mass. Your body may break down muscle tissue for energy when you’re not consuming enough calories. This can result in a decrease in muscle mass, which can also slow down your metabolism.

Additionally, consuming a low-calorie diet can lead to nutrient deficiencies, affecting various bodily functions, including metabolism. For example, insufficient nutrients like iron or vitamin B12 can lead to anemia, affecting your metabolism and energy levels.

Calories counting and food control concept
Image from Adobe Stock
Nutritional Deficiencies Associated With Not Eating Enough Calories
Consuming enough calories can lead to various nutritional deficiencies, as you may need to be getting enough of specific vitamins, minerals, and other essential nutrients. Here are some of the nutritional deficiencies associated with not eating enough calories:

Protein deficiency
Consuming too few calories and protein can lead to a defect in this critical macronutrient. Protein is necessary for building and repairing tissues in the body, and not getting enough can lead to muscle loss, a weakened immune system, and slow wound healing.

Iron deficiency
Iron is necessary for producing hemoglobin, a protein in red blood cells that carries oxygen throughout the body. Not getting enough iron can lead to anemia, which can cause fatigue, weakness, and shortness of breath.

Vitamin D deficiency
Vitamin D is essential for maintaining healthy bones and teeth and immune function. Not getting enough vitamin D can lead to bone disorders such as osteoporosis and a weakened immune system.

Vitamin B12 deficiency
Vitamin B12 is vital for producing red blood cells and proper nerve function. Not getting enough vitamin B12 can lead to anemia, fatigue, and nerve damage.

Calcium deficiency
Calcium is necessary for strong bones and teeth and muscle and nerve function. Not getting enough calcium can lead to osteoporosis, weakened muscles, and numbness or tingling in the fingers and toes.

Zinc deficiency
Zinc is essential for immune function, wound healing, and protein synthesis. Not enough zinc can weaken immune systems, slow wound healing, and cause hair loss.

What is bacterial vaginosis? Symptoms and causes
Symptoms
Causes
Home remedies
Treatment
Vs. yeast infection
Diagnosis
Prevention tips
FAQs
Summary
Bacterial vaginosis (BV) results from an imbalance in beneficial and harmful bacteria in the va**na. It can cause va**nal itchiness, unusual discharge, and a characteristic odor, among other symptoms.

The body may be able to clear bacterial vaginosis (BV) on its own. Without treatment, however, it increases the risk of other health issues. Seeking medical advice can help a person avoid discomfort and prevent complications.

This article describes what BV feels like, as well as its causes, possible complications, and home remedies and treatments. It also looks at how to prevent BV, and how to distinguish BV from a yeast infection.

Symptoms
Oleksandra Stets/Stocksy
BV is the most commonTrusted Source va**nal condition among females of childbearing age.

Many people with BV have no symptomsTrusted Source. If symptoms occur, they typically involve:

changes to va**nal discharge
a burning, itching, and irritation in the va**nal area
a burning sensation when urinating
The person’s va**nal discharge may have:

a watery, thin consistency
a gray or white color
a strong, unpleasant smell, often described as fishy
There may also be a burning sensation during urination and itching around the outside of the va**na. However, this is less common.

Complications
BV itself is not harmful, but it can increase the riskTrusted Source of other health issues.

General health complications
s*xually transmitted infections (STIs), such as:
herpes
human papillomavirus, better known as HPV
chlamydia
gonorrhea
HIV, as having BV increases a person’s susceptibility to the virus
a postsurgical infection, for example after a hysterectomy
Pregnancy complications
Possible complications of BV during pregnancy include:

early or preterm delivery
loss of pregnancy
the amniotic sac breaking open too early
postpartum endometritis, which is irritation or inflammation of the lining of the uterus after delivery
chorioamnionitis, which is inflammation of the membranes around the fetus
Chorioamnionitis significantly increases the chance of an early delivery. If the newborn lives, they have a higher risk of cerebral palsy.

Fertility complications
BV may directly increase the likelihood of difficulty conceiving. And it may increase the risk of health complications that can affect fertility.

Possible complications include:

Tubal factor infertility: This is infertility caused by damage to the fallopian tubes, which connect the ovaries to the uterus.
Pelvic inflammatory disease: This involves an infection and inflammation of the upper female ge***al tract. Pelvic inflammatory disease can have serious effects, including infertility.
Unsuccessful in vitro fertilization (IVF): If a person has BV, any IVF treatments may be less likely to work.
Causes
BV results from an imbalance in the populations of beneficial and harmful bacteria that naturally live in the va**na.

An imbalance can occur for many reasonsTrusted Source, including:

having s*x with a new partner
having s*x with multiple partners
douching
not using a barrier method, such as a condom, during s*x
being pregnant
recently using antibioticsTrusted Source
BV oftenTrusted Source develops after s*x with a new partner. BV is not an STI, but it can increase the risk of developing an STI.

The role of bacteria
All parts of the body have bacteria, and only some are harmful. Health problems can arise when there are more harmful bacteria than helpful bacteria in a given area.

Most bacteria in the va**na are helpful, and BV occurs when the harmful bacteria grow in number.

The va**na should contain bacteria called Lactobacilli. They produce lactic acid, making the va**na slightly acidic. This prevents some harmful bacteria from growing there.

Having lower levels of Lactobacilli can cause the va**na to become less acidic. If the va**na is not acidic enough, harmful bacteria can grow and thrive.

Experts still do not understandTrusted Source exactly how these harmful bacteria are linked with BV.

Risk factors
Anyone with a va**na can develop BV. These factors can increase the likelihood of having it:

using certain feminine hygiene products, such as va**nal deodorants and douches
using a perfumed bubble bath
using some scented soaps
bathing in water that contains antiseptic liquids
washing underwear with a strong detergent
having s*x with a new partner
having multiple s*x partners
smoking
A person cannot acquire BV from:

toilet seats
bedding
swimming pools
Home remedies
One home remedy that may help treat BV is probiotics. These are live bacteria that are beneficial. The term “probiotics” also describes some beneficial yeasts.

As a 2021 review notes, multiple studies have demonstrated that probiotics may help treat and prevent BV.

Certain probiotics can increase the number of va**nal Lactobacilli, helping to restore the natural balance of bacteria in the va**na.

Vaginal pH balance: Symptoms, remedies, and tests
Typical va**nal pH level
What causes unbalanced va**nal pH??
How to maintain va**nal pH balance
Summary
Maintaining the pH balance of the va**na is essential to keeping it healthy. The normal pH level of the va**na is between 3.8 and 5. Infections, douching, and the presence of menstrual blood are some of the factors that can change the balance.

Doctors can take a va**nal pH measurement to determine how acidic the va**nal environment is. It is also possible to test this at home.

In the va**na, a high pH may cause infections as it can allow bacteria and yeast to thrive.

In this article, learn more about normal va**nal pH levels, how to test them at home, and what to do to restore va**nal pH balance.

Typical va**nal pH level
Clique Images/Stocksy
A normal va**nal pH is between 3.8 and 5Trusted Source. A pH level within this range can help to keep bacterial and fungal infections at bay.

This range is moderately acidic.

What is considered a “normal” va**nal pH level varies by age. A woman of reproductive age would have a normal va**nal pH between 4.0 to 4.5Trusted Source, while women who have yet to begin menstruating or who are postmenopausal may have a normal va**nal pH higher than 4.5Trusted Source

Lactobacilli bacteria live in the va**na and secrete lactic acid and hydrogen peroxide, which give the va**na its acidic pH level.

Vaginal pH is usually less than 4.5 during a woman’s reproductive years unless a condition or infection raises it.

What causes unbalanced va**nal pH?
Several conditions and infections can affect the va**nal pH balance, usually by increasing pH levels.

Causes of changes in va**nal pH include the following:

Bacterial vaginosis
Bacterial vaginosis is a medical condition that occurs when too much bacteria is present in the va**na. This can cause an increase in va**nal pH levels.

A person with bacterial vaginosis may experience itching, burning, or pain in the va**na. They may also feel a burning sensation when urinating and notice a white or gray discharge.

Douching
Douching refers to washing or cleaning the va**na using particular solutions, such as those containing vinegar or baking soda.

These solutions claim to reduce va**nal odor, but, in fact, they may worsen the smell. This is because they wash out good bacteria, which affects the va**nal pH balance and can make someone more prone to infections.

Menopause
Vaginal pH levels can be an indication of menopausal statusTrusted Source. Women who are postmenopausal may have a slightly higher va**nal pH than women of reproductive age.

Reduced estrogen levels during menopause may affect a person’s va**nal pH.

Other va**nal infections
The presence of infections other than bacterial vaginosis may also increase the va**nal pH.

Examples include Trichomonas va**nalis and group B Streptococcus (GBS).

Presence of menstrual blood
Blood has a higher pH than the va**nal environment. When a person is menstruating, the presence of menstrual blood can increase va**nal pH levels.

Presence of semen
Semen is basic, which is the opposite of the va**na’s acidic environment. When semen enters the va**na, it may temporarily increase the pH.

Taking antibiotics
People use antibiotics to kill harmful bacteria, but these medications can kill good bacteria as well. This will include bacteria in the va**na. If a person is taking antibiotics, their va**nal pH may be out of balance.

Urinary tract infections (UTIs)
UTIs do not cause a higher va**nal pH, but having a high pH can increase a person’s risk of developing a UTI.

Reduced estrogen levels during perimenopause and menopause can put a person at risk of developing more frequent UTIs, as lower estrogen allows the va**nal pH to rise.

Doctors may prescribe estrogen treatments to lower the va**nal pH and to prevent further UTIs.

Other conditions
Researchers have also linked higher va**nal pH with several other conditions, including infertility, premature birth, and increased risks for s*xually transmitted infections (STIs).

How to maintain va**nal pH balance
People can purchase home-testing kits that measure the pH balance of the va**na. These kits are available in some pharmacies and online.

At-home testing can reveal elevated pH levels, which could indicate the presence of an infection.

The test involves placing a strip of paper that measures pH against the wall of the va**na for a designated amount of time.

After removing the paper, a person can compare the resulting color to those on a chart in the kit. Each color corresponds to a pH value.

People should read all of the information that the test kit includes. This will include recommendations on the timing of the test, including not performing the test while menstruating or too soon after s*x.

If a person’s va**nal pH levels are routinely high without any symptoms of an infection, they can take several steps at home to reduce their pH levels. These include:

Avoiding harsh soaps and douching. Soaps typically have a high pH, and using them to clean the va**nal area may increase va**nal pH. It is best to use warm water and a gentle cleanser to clean the v***a but to refrain from using soap inside the va**na. This will help to maintain the va**nal pH balance.
Changing tampons regularly. Tampons should be changed every four to eight hours. This also helps reduces the risk of bacterial infections, including toxic shock syndrome (TSS).
Using barrier protection during s*x. Using barrier protection, such as condoms or dental dams, not only helps to prevent pregnancy and STIs but can prevent semen and other fluids from affecting pH levels in the va**na.
Avoiding scented feminine hygiene products. Sprays, bubble baths and scented pads or tampons can increase the risk of yeast infections which can impact the pH of the va**na.
Doctors can also prescribe creams, such as estrogen cream, which may help to reduce the va**na’s pH levels.

Summary
Keeping va**nal pH levels in balance can help to reduce infections and prevent complications.

Doctors rarely rely just on measurements of va**nal pH to diagnose medical conditions, such as yeast infections, or to determine whether or not someone is approaching menopause. However, va**nal pH tests can help to confirm a suspected diagnosis.

People can take steps, such as using probiotic supplements and not douching, to help keep their va**nal pH levels balanced.

How to naturally lose weight fast
Intermittent fasting
Tracking diet and exercise
Mindful eating
Protein for breakfast
Avoid sugar
Fiber
Gut bacteria balance
Sleep
Managing stress
Takeaway
Many diets, supplements, and meal replacement plans claim to ensure rapid weight loss, but lack any scientific evidence. However, there are some strategies backed by science that have an impact on weight management.

These strategies include exercising, keeping track of calorie intake, intermittent fasting, and reducing the number of carbohydrates in the diet.

In this article, we consider nine effective methods of weight loss.

Science-backed ways to lose weight
Victoria Gardner/EyeEm
Methods of weight loss that scientific research supports include the following:

1. Trying intermittent fasting
Intermittent fasting (IF) is a pattern of eating that involves regular short-term fasts and consuming meals within a shorter time period during the day.

Several studiesTrusted Source have indicated that short-term intermittent fasting, which is up to 24 weeks in duration, leads to weight loss in overweight individuals.

The most common intermittent fasting methods include the following:

Alternate day fastingTrusted Source (ADF): Fast every other day and eat a typical diet on non-fasting days. The modified versionTrusted Source involves eating just 25–30% of the body’s energy needs on fasting days.
The 5:2 Diet: Fast on 2 out of every 7 days. On fasting days eat 500–600 calories.
The 16/8 method: Fast for 16 hours and eat only during an 8-hour window. For most people, the 8-hour window would be around noon to 8 p.m. A study on this method found that eating during a restricted period resulted in the participants consuming fewer calories and losing weight.
It is best to adopt a healthy eating patternTrusted Source on non-fasting days and to avoid overeating.

2. Tracking your diet and exercise
If someone wants to lose weight, they should be aware of what they eat and drink each day. The most effective way to do this is to log these items in either a journal or an online food tracker.

Researchers estimated in 2017 that there would be 3.7 billion health app downloads by the end of the year. ResearchTrusted Source suggests that tracking diet, physical activity, and weight loss progress on the go can be an effective way of managing weight.

One studyTrusted Source found that consistent tracking of physical activity helped with weight loss. Meanwhile, a review studyTrusted Source found a positive correlation between weight loss and the frequency of monitoring food intake and exercise. Even a device as simple as a pedometer can be a useful weight-loss tool.

3. Eating mindfully
Mindful eating is a practice where people pay attention to how and where they eat food. This practice can enable people to enjoy the food they eat and maintain a healthy weightTrusted Source.

As most people lead busy lives, they often tend to eat quickly on the run, in the car, working at their desks, and watching TV. As a result, many people are barely aware of the food they are eating.

Techniques for mindful eating include:

Sitting down to eat, preferably at a table: Pay attention to the food and enjoy the experience.
Avoiding distractions while eating: Do not turn on the TV, or a laptop or phone.
Eating slowly: Take time to chew and savor the food. This technique helps with weight loss, as it gives a person’s brain enough time to recognize the signals that they are full, which can help to prevent over-eating.
Making considered food choices: Choose foods that are full of nourishing nutrients and those that will satisfy for hours rather than minutes.
4. Eating protein for breakfast
Protein can regulate appetite hormones to help people feel full. This is mostly due to a decrease in the hunger hormone ghrelin and a rise in the satiety hormones peptide YY, GLP-1, and cholecystokininTrusted Source.

ResearchTrusted Source on young adults has also demonstrated that the hormonal effects of eating a high protein breakfast can last for several hours.

Good choices for a high protein breakfast include eggs, oats, nut and seed butters, quinoa porridge, sardines, and chia seed pudding.

5. Cutting back on sugar and refined carbohydrates
The Western diet is increasingly high in added sugars, which has definite links to obesityTrusted Source, even when the sugar occurs in beveragesTrusted Source rather than food.

Refined carbohydrates are heavily processed foods that no longer contain fiber and other nutrients. These include white rice, bread, and pasta.

These foods are quick to digest, and they convert to glucose rapidly.

Excess glucose enters the blood and provokes the hormone insulin, which promotes fat storage in the adipose tissue. This contributes to weight gain.

Where possible, people should swap processed and sugary foods for more healthful options. Good food swaps include:

whole-grain rice, bread, and pasta instead of the white versions
fruit, nuts, and seeds instead of high sugar snacks
herb teas and fruit-infused water instead of high sugar sodas
smoothies with water or milk instead of fruit juice
6. Eating plenty of fiber

How does the Mediterranean diet impact insulin resistance and sensitivity in obese individuals? Researchers evaluate the associations between adherence to the Mediterranean diet, insulin secretion, resistance, and sensitivity in obese individuals.

Day-to-day painkiller use doesn't lower empathy levels, but misuse might, according to recent survey The association between low empathy and prosocial behavior on the one hand and analgesic consumption.

SARS-CoV-2 virus found to migrate within neurons and infect the brain
by Pasteur Institute

Clinical profile of hamsters infected with SARS-CoV-2 original virus (Wuhan), the recombinant Wuhan/ΔORF7ab or the variants of concern (VoC) Gamma, Delta, and Omicron/BA.1. A, B Body weight variation over four days post-infection. C Lung weight measured at 4 dpi. D, E Clinical score over four days post-infection. The clinical score is based on a cumulative 0–4 scale: ruffled fur; slow movements; apathy; and absence of exploration activity. F Lung weight-to-body weight ratio measured at 4 dpi. A–F Horizontal lines indicate median and the interquartile range (n = 8/group). B, C, E, F Kruskal-Wallis test followed by the Dunn’s multiple comparisons test (the adjusted p value is indicated when significant). G, H Olfactory performance measured at 3 days post-infection (dpi). The olfaction test is based on the hidden (buried) food finding test. Curves represent the olfactory performance of animals during the test (G) and bars represent the final results (H) (n = 8/group). Chi-square test for trend (the adjusted p value is indicated when significant). See Supplementary Figs. 1, 2. Credit: Nature Communications (2023). DOI: 10.1038/s41467-023-40228-7
The emergence of different variants of SARS-CoV-2 has produced a wide range of clinical profiles and symptoms in patients. For the first time, researchers at the Institut Pasteur and Université Paris Cité have demonstrated, in an animal model, a characteristic common to several SARS-CoV-2 variants: the ability to infect the central nervous system.

The study confirms that SARS-CoV-2 is capable of infecting human neurons in vitro and migrating into axons, the nerve cell projections that carry information. The results were published in the journal Nature Communications.

The neurological symptoms associated with SARS-CoV-2 infection have changed with the evolution of the virus and the emergence of new variants. At the start of the COVID-19 pandemic, anosmia was identified as one of the typical symptoms of infection, but it was less frequently associated with infections caused by the omicron/BA.1 variant. Does this variability in symptoms indicate a greater or lesser affinity of SARS-CoV-2 for the nervous system?

In this study, researchers from the Institut Pasteur and Université Paris Cité have demonstrated, in an animal model, that a panel of SARS-CoV-2 variants of interest (the original strain of the virus first detected in Wuhan and the gamma, delta and omicron/BA.1 variants) can enter the central nervous system and remain there during the acute phase of the infection.

The researchers observed that all these variants spread to the central nervous system and infect the olfactory bulb, a structure located in the cranial cavity that processes olfactory information before transmitting it to the cortex.

"In this study, we demonstrated that infection of the olfactory bulb is common to all variants and not linked to any particular one, nor to any particular clinical manifestation such as anosmia," explains Guilherme Dias de Melo, first author of the study and researcher in the Institut Pasteur's Lyssavirus, Epidemiology and Neuropathology Unit.

Moreover, the researchers identified a genetic sequence linked to anosmia in the ancestral (Wuhan) virus. When this genetic sequence, which encodes the ORF7ab protein, is deleted or truncated—which is the case in certain variants less likely to produce anosmia—the incidence of olfactory loss in infected animals is lower even though the degree of neuronal infection via the olfactory bulbs remains unchanged.

"This suggests that anosmia and neuronal infection are two unrelated phenomena," says Guilherme Dias de Melo. "If we follow this line of reasoning, it is quite possible that even an asymptomatic—and therefore clinically benign—infection is characterized by the spread of the virus in the nervous system."

The researchers then looked at how SARS-CoV-2 reached the olfactory bulb and observed that neurons appeared to be the ideal route. An in vitro microfluidic cell culture system enabled the researchers to observe human neurons organized in a particular way. The neurons are arranged so as to allow detailed observation of the transport of molecules within the axon.

Using this method, the researchers found that, once inside the neuron, the virus is able to move in both directions along the axon, either in an anterograde direction, i.e. from the cell body to the axon terminals, or in a retrograde direction, from the axons to the cell body.

"The virus seems to effectively exploit the physiological mechanisms of the neuron to move in both directions. The SARS-CoV-2 variants we studied—the ancestral Wuhan variant, gamma, delta and omicron/BA.1—infect neurons in vitro and are capable of moving along axons."

"Through this study, we have characterized the neurotropism of SARS-CoV-2. For all the variants studied, brain infection via the olfactory bulb seems to be a common feature of SARS-CoV-2," concludes Hervé Bourhy, last author of the study and head of the Institut Pasteur's Lyssavirus, Epidemiology and Neuropathology Unit.

"The next step will be to understand, from the animal model, whether the virus is able to persist in the brain beyond the acute phase of infection, and whether the presence of the virus can induce persistent inflammation and the symptoms described in cases of long COVID, such as anxiety, depression and brain fog."