The notion of viral disease dates back to the end of the 19th century, with the discovery of diseases transmissible by ultra-filterable agents. Viruses, initially defined by their size, are found in all animal species, in plants (including algae and fungi), in bacteria (bacteriophages).

The main characteristic of viruses, and to which we owe their discovery, is their ability to pass filters impermeable to bacteria. While the largest viruses infecting humans, the Poxviridae, are between 250 and 300 nm in size, the smaller ones, Parvoviridae, are only 20nm.

Two hundred species are pathogenic in humans. The majority of viral diseases are benign (eg: rhinitis).  Others are quite serious (eg: encephalitis, AIDS, hepatitis, haemorrhagic fevers). Finally, certain viruses play a role in the development of malignant tumors and cancers.



It was in 1953 that André LWOFF stated the three fundamental characteristics that make viruses original entities:

1 /
  viruses contain only one type of nucleic acid

(DNA or RNA) which constitutes the viral genome.

2 /
  viruses reproduce from their genetic material and by replication.



3 /  viruses are endowed with absolute intracellular parasitism.

In appearances of very rudimentary units, viruses constitute a very elaborate form of parasitism. They can only reproduce in living cells; having no energy system, they divert the cellular machinery for their own benefit to replicate and ensure their sustainability. They are, in a way, extremely simple structures, all of whose elements protect a few small pieces of genetic code with the aim of infiltrating a cell in order to parasitize it, then destroy it.

Ultimately, with the help of a few genes, viruses can alter and modify the programs of intracellular functions to their advantage, with the final objective of transforming the infected organism into a contaminating agent, capable of spreading the infection and ensuring survival of the virus.



Probably the most common viral infections are infections

upper respiratory tract. Respiratory infections are

particularly likely to cause severe symptoms in the

infants, the elderly and patients with impaired

cardiac or pulmonary.

Several coronaviruses have been identified that cause respiratory infection

which can be serious. In 2002 and 2003, an outbreak of Severe Acute Respiratory Syndrome (SARS) caused a number of deaths, mainly in China and Hong Kong. In 2012, a new coronavirus, the Middle East respiratory syndrome coronavirus (MERS-CoV), which appeared in Saudi Arabia, can cause severe and sometimes fatal acute respiratory illness. In 2019, another coronavirus (SARS-CoV2) that can cause acute, sometimes fatal respiratory illness emerged in Wuhan, China and is currently spreading around the world.

Respiratory viruses are usually transmitted directly from person to person through contact with infected respiratory droplets.


The  gastroenteritis  is usually caused by viruses and transmitted by the human-to-human fecal route.

The predominantly affected age group depends on the virus:

  • Rotavirus: children

  • Norovirus: children and adults

  • Astrovirus: usually infants and young children

  • Adenovirus 40 and 41: infants

  • Coronavirus-like agents: infants

Local epidemics can occur in children, especially during the cold months.

The main symptoms are vomiting and diarrhea.

No specific treatment is recommended, but supportive treatment, especially rehydration, is important.



Some viruses only cause skin lesions (as in molluscum contagiosum and warts); others also cause systemic manifestations or lesions elsewhere in the body.

Transmission is usually human-to-human; the alphavirus has a mosquito vector.


At least 5 specific viruses (hepatitis A, B, C, D and E viruses) can cause hepatitis; each causes a specific type of hepatitis. The hepatitis D virus can only be infectious in the presence of the hepatitis B virus. Transmission is human-to-human through contact with infected blood or body fluids or by the fecal-oral route in the case of hepatitis A and E (genotypes 1 and 2).

Other viruses can affect the liver as part of the disease process. Common examples are cytomegalovirus, Epstein-Barr virus, and yellow fever virus. Echoviruses, coxsackie viruses, herpes simplex, measles, rubella and chickenpox are less common examples.


Most cases of encephalitis are caused by viruses. These viruses are

many are transmitted to humans by blood-sucking arthropods,

mainly mosquitoes and ticks; these viruses are called arboviruses 

(arthropod viruses). For these infections, prevention involves avoiding

Mosquito bites and tick bites.



Some viruses cause fever and a tendency to bleed (arboviruses, arenaviroses and  Filoviruses.) Transmission may involve mosquitoes, ticks, or contact with infected animals (eg, rodents, monkeys, bats) and people. Prevention consists of avoiding the means of transmission. *


Mucosal infections are the most common type of herpes simplex virus infection. The human papillomavirus induces warts; some subtypes cause cervical cancers, other anogenital cancers, and oropharyngeal cancers. Transmission is human-to-human.


Enteroviruses, which include coxsackie and echo viruses, can cause a variety of multisystem syndromes, as is the case with cytomegalovirus 

Transmission occurs by the fecal-oral route.



Some viruses cause nonspecific symptoms, including fever, feeling sick, headache, and myalgia. Transmission is usually carried out by an insect vector or arthropod. (See also Overview of arboviruses, arenaviroses and filoviruses.)

Rift Valley fever rarely progresses to eye disorders, meningoencephalitis, or a hemorrhagic form (which has a 50% mortality).

some plants against infections: 

- Cypress is a powerful antiviral. It acts as a shield for the cells by preventing viruses from sticking to them, and then it kills them. It is particularly recommended against influenza, but also against herpes. As a preventive or curative treatment, it is consumed in the form of fresh plants.

-  Ginseng  This plant, native to China, is consumed in the form of an infusion to fight against fatigue. But it is also very effective in helping the immune system fight against winter illness.

-  Elderberry In the form of ampoules or tablets, elderberry is consumed throughout the winter to fight against a host of small diseases. Colds, flu, sinusitis or bronchitis do not resist the power of this plant.

-  Thyme Widely used in Europe, and in particular in the Mediterranean, in cooking, thyme is also a health ally. It is because it is particularly rich in vitamin A that thyme is an asset for the immune system. Associated with honey, and consumed in the form of an infusion, thyme will be your best friend in case of colds.

-  The tea tree has always been used by the Aborigines of Australia. Its essential oil will allow you to fight effectively against all forms of bacterial and viral infections.

-  Black radish , Vitamin C is its secret. It is thanks to this that it can fight against fatigue and therefore strengthen your immune system. As a little extra, black radish also helps your skin to maintain good health and fights against the aging of your cells.

-  Blackcurrant Like black radish, is a real mine of vitamin C. Thanks to this, blackcurrant has antioxidant properties that will protect your white blood cells, the very ones that must be efficient to fight against diseases of the winter.

-  Turmeric has been talked about a lot in recent years. And for good reason, this plant, the root of which is consumed, is truly miraculous if used with knowledge. Many studies have shown that turmeric can fight off many bacteria. But be careful not to overdo it, it should be consumed sparingly.

-  Guarana  has toning virtues recognized for a long time. This plant native to Brazil will be your ally if you suffer from temporary fatigue. It is also rich in vitamins, potassium, magnesium, iron and phosphorus, all virtues that will make it a good stimulant for your immune system.

- Cat's claw , also called "Liana of Peru", is a plant whose bark is consumed, in the form of infusion or capsules, and is recognized for its antiviral and anti-inflammatory properties. It is also used to fight cancer.

cerveau (1).png