Flu, cold, Covid-19 or dengue: understand differences and symptoms

The summer rains bring with them an explosion of cases of a disease already known among Brazilians: dengue.

Fever, headaches and body aches, tiredness and malaise are some of its symptoms.

But these are also often manifestations reported by those who contract Covid-19, flu or even colds.

So, how to differentiate each of these diseases?

Some signs, such as how symptoms evolve, may even give some clues, but only a blood test can confirm the diagnosis, warn health experts.

In common, all these diseases are caused by viruses.

However, they are different: Covid-19 is caused by Sars-CoV-2, from the coronavirus family; the flu, caused by the influenza family virus; the cold, caused by rhinovirus, adenovirus and parainfluenza; and dengue, by flavivirus.

And in the case of Covid-19, flu and colds, there is another unifying element: the mode of transmission is through droplets of respiratory secretions from an infected person. Dengue is transmitted by the Aedes aegypti mosquito.

Check out other differences below.

Dengue

It is a viral infection transmitted mainly through the bite of a female mosquito infected with a flavivirus, usually Aedes aegypti (also responsible for the transmission of chikungunya, yellow fever and Zika virus).

There are four serotypes (DENV-1, DENV-2, DENV-3, DENV-4), each with different interactions with human antibodies. That is, people have four possibilities of being infected.

Its classic symptom is high fever, which appears abruptly at the beginning of the infection. In the case of Covid-19, this sign is not necessarily the first and in many cases it may not even appear.

Respiratory symptoms, quite common in Covid-19, are also rare “in dengue, which does not usually cause respiratory symptoms such as coryza (runny nose), nasal obstruction (clogged nose) or cough”, explained infectious disease specialist Melissa Falcão, consultant at Brazilian Society of Infectious Diseases, in a recent interview with BBC News Brasil.

In fact, in the current context, with several epidemics in the country at the same time, the specialist points out that in the case of respiratory symptoms, health professionals responsible for the patient “must always make the differential diagnosis between Covid-19 and the flu caused by the virus of Influenza A H3N2, which can only be done safely through specific laboratory tests”.

Dengue usually lasts four to ten days, but its impact can last for weeks. It can be non-serious (with or without warning signs) or severe, and the diagnosis can be made by clinical examination and confirmed by a blood test.

• Dengue is not serious without an alarm signal: presence of common symptoms such as nausea, fever, redness in the body, vomiting, headaches, in the muscles, joints and around the eyes.
• Non-severe dengue with alarm signs: it is the phase after the fever ceases to start one or more symptoms considered to be alarming, such as persistent vomiting, bleeding, accumulation of fluid in the body cavities, such as the lungs and heart, dizziness, increased liver and blood concentration.
• Severe dengue: Presence of one or more manifestations, may present with shock (pallor and prostration, sweating and drop in blood pressure), difficulty breathing due to plasma leakage (fluid out of blood vessels), severe impairment of organs such as kidneys , liver, brain and heart, major bleeding, among others.

“The period of plasma leakage and shock takes from 24 to 48 hours, it is quick to install and short-lived, and can lead to death, if not properly treated, within 12 to 24 hours”, explains Falcão.

Finally, she explains that the expression “hemorrhagic dengue”, which became popular, is no longer used because of “the lack of precision in the identification of serious cases in the previous classification, leaving many serious cases unnoticed, since its very name suggested that to be serious, there had to be hemorrhage, which is not true”.

Covid-19

In all variables, infection with the Sars-CoV-2 coronavirus can occur without or with symptoms, which have been changing a lot depending on the variant linked to the infection.

Covid-19, a disease caused by this virus, can present itself in three forms: mild, moderate or severe. The diagnosis can be made by clinical examination and laboratory tests on samples taken from the nose, mainly.

The most common symptoms (when talking about the “version” of the virus at the beginning of the pandemic, in 2020) were dry cough, fever, tiredness and loss of smell and taste.

The World Health Organization (WHO) also listed less common symptoms (headache, throat, diarrhea, red and itchy eyes, and skin rash) and severe symptoms (shortness of breath, loss of mobility and speech, chest pain and mental confusion).

But over time, five variants of concern of the coronavirus have emerged: alpha, beta, gamma, delta and omicron.

The main symptoms of the delta variant, for example, are similar to those of alpha, such as cough, headache, sore throat, nasal obstruction, runny nose, abdominal pain and skin manifestations.

In the case of the omicron variant, the most contagious of them, the most common signs identified by researchers are: sore throat, fatigue, runny nose, sneezing and headache and in other parts of the body – loss of smell and taste has become much more common. unusual. Sudden, continuous coughing, shortness of breath, and a high fever are still significant symptoms, in addition to diarrhea and chills.

The worsening of symptoms of Covid-19 is not usually as accelerated as it is in the case of dengue, but even the omicron, considered less serious than other variants of Covid-19, can still kill. It is worth remembering that in the last week of January 2022, about 300 people died a day from the disease, more than dengue killed in the entire year of 2021.

In addition, it is important to note that these symptoms are the most common, according to surveys and studies by experts around the world, but that does not mean that they are the only ones. There are dozens of signs associated with the disease (such as skin lesions, hair loss, mental confusion and anxiety), both at the time of infection and later, in the condition known as long Covid (which affects millions of patients around the world for weeks, months or even years).

The flu

Influenza is caused by the influenza virus, which has an extensive family with hundreds of mutations.

This is why the flu vaccine needs to be updated and given every year.

The flu can have symptoms very similar to those of Covid-19, but its incubation period tends to be shorter, that is, the symptoms appear quickly (from one day to the next, often) and the worsening of the condition tends to be sharp.

In the case of Covid, the incubation period is longer – the organism can take up to five days to show symptoms, which explains the large number of so-called “false negatives”, that is, people infected with the coronavirus, but who get negative diagnosis when performing the test. In addition, without showing symptoms, the individual can end up infecting other people.

The most common symptoms of the flu are: cough (usually dry), fever, headache, body aches and malaise and tiredness. Sore throat, diarrhea (especially in children) and runny nose or nasal congestion (stuffy nose) may occur.

Loss of taste and smell is not a common manifestation in cases of influenza virus infection, unlike Covid-19.

Despite this, as mentioned earlier, this symptom is no longer being reported more frequently in infections by the ômicron variant, the most prevalent in Brazil.

colds

Colds are caused by other types of viruses: rhinovirus, adenovirus and parainfluenza.

Unlike the flu, the onset of symptoms tends to be gradual and they are usually mild.

Sore throat, runny nose and nasal congestion are some of its most common manifestations.

A mild cough may develop, as may a fever (usually low), but these are infrequent symptoms. Diarrhea, headache and shortness of breath are also rare.

Colds usually get better in a few days.

_{With a report by Cristiane Martins, from London}