General information, not a diagnosis Method and limitations

02Agents and transmission

Infectious diseases

An infectious disease is the result of interaction between an agent, a host and an environment. Its transmission, severity and prevention vary according to the disease, time, place and person concerned. Simple benchmarks help us to understand better without drawing an early conclusion.

Clinician exchanging with a patient during a consultation for mild respiratory symptoms
AI-generated illustration, not evidence of a health event. Signs, exposure context and background are evaluated together by a professional.

Understanding an infection

An infection occurs when an infectious agent enters the body and multiplies within it. It may remain asymptomatic, cause mild symptoms or lead to more serious illness. The outcome depends on the agent, the body’s response, and factors such as age, immunity, treatment and other health conditions.

General symptoms such as fever, fatigue, pain or cough are common to many diseases and are never sufficient to identify the agent. The moment of appearance, recent contacts, a trip, professional exposure, clinical examination and, sometimes, analyses are necessary to guide the diagnosis.

It is also necessary to distinguish infection, disease and infectiousness. An infected person may have no symptoms; an infectious disease may not be transmitted directly from one person to another; and the period during which transmission is possible does not always correspond to the period of symptoms.

Clinician and laboratory specialist interpreting diagnostic results together
AI-generated illustration, not evidence of a health event. A biological result makes sense with the clinical context and the interpretation of qualified professionals.

Major categories

Viral infections

Flu, measles, viral hepatitis, COVID-19 or haemorrhagic fever are very different in their spread and severity. Antibiotics are ineffective against viruses. Vaccines, antivirals and other available measures depend precisely on the virus concerned.

Bacterial infections

Tuberculosis, cholera, pertussis or meningococcal infections illustrate distinct transmissions and management. Not all bacteria are dangerous and an antibiotic is useful only when it is correctly indicated, chosen and used.

Mycosis

Mushrooms can cause damage to skin, mucous membranes or deep organs. Some forms are frequent and localized; others mainly affect people who are very vulnerable or appear in care settings. Treatment is based on suitable antifungals.

Parasitic diseases

Malaria, toxoplasmosis, and helminthiasis involve a variety of transmission cycles and pathways. Depending on the parasite, exposure may come from a vector, food, water, soil or animal, which requires different preventive measures.

The directory also distinguishes between two less common cases: prions, poorly conformed proteins involved in certain transmissible neurodegenerative diseases, and Multiple agents, which group a syndrome or exposure that may have several causes. The latter label does not refer to a new family of microorganisms.

Transmission chains

In order for a transmission to occur, several elements usually have to be chained: a source, an exit door, a mode of transport, an entry door and a receptive person. Breaking a single link can significantly reduce the risk, but the useful measure depends on the mechanism actually involved.

The main routes include respiratory droplets and aerosols, direct or indirect contact, water and food, blood and certain biological fluids, and vectors. A disease can take several routes. Hand washing, ventilation, vaccination, vector control or protective equipment are therefore neither the same role nor the same effectiveness in all situations.

Incubation time, i.e. time between exposure and possible symptoms, also varies greatly. It should not be confused with the duration of contaginess. To interpret a contact or decide on a course of action, the specific recommendations of the disease and territory concerned must be followed.

Read the directory ways

The filter indicates the main track chosen to facilitate the search. The same disease may have several; the label does not describe the probability of transmission or the exact circumstances of an exposure.

Respiratory

Particulate matter emitted, in particular, by speaking, coughing or breathing. The proximity, duration and renewal of the air alter the exposure.

Understanding respiratory risk →

Close contact

Direct contact with a person, injury or secretion; some agents may also go through unclean objects. The mechanisms differ according to the disease.

Hand hygiene →

Blood and fluids

Exposure to blood or certain biological fluids by mucous membranes, damaged skin or skin breakage. Not all fluids are at the same risk.

After an exhibition →

Sexual use

Transmission possible during certain sexual contacts, depending on the agent and practices. Screening and prevention methods are chosen for the infection concerned.

Find a source of public health →

Water and food

Ingestion of contaminated water or food; production, storage, cooking and hygiene occur in separate stages.

Food security →

Vector

An organism such as a mosquito or tick can transmit an agent. His presence alone does not prove that this agent is circulating locally.

Understanding vectors →

Animal / zoonosis

Possible exposure by bite, scratch, secretion, animal products or working contacts, depending on species and agent.

Understanding zoonoses →

Environment

Exposure to an agent present in a medium, e.g. water, soil or dust. Environmental detection alone does not demonstrate a human infection.

Read an environmental signal →

Sporadic / rare cases

Classification label for diseases whose occurrence is not limited to an ordinary route of transmission between people. See the official fact sheet for specific circumstances.

View the sheets →

When to ask for help

Consult a professional when a symptom is unusual, persists, worsens or occurs after a known exposure. A return trip, bite, tick bite, contact with blood, consumption of a suspicious food or the presence of several cases around you are useful information to report.

More rapid attention may be required in an infant, an elderly, pregnant, immunocompromised or chronically ill person. In the event of significant respiratory difficulty, confusion, loss of consciousness, convulsions, severe bleeding or other signs of distress, contact the emergency department immediately.

AntibioticUnnecessary or incorrect intake promotes bacterial resistance. Do not use any remaining antibiotic and do not share a treatment. Understanding Antimicrobial Families →

Frequently Asked Questions

Are all infections contagious?

No. An infection can be acquired from the environment, an animal, a food or a vector without being transmitted directly between people. Even when a disease is contagious, the ease and conditions of transmission vary. Therefore, the risk should not be inferred from the name of the disease alone.

Do antibiotics act against viruses?

No. Antibiotics target bacteria and do not treat viral infections. They should not be taken "in case" from a former treatment or shared with another person. Their choice, dose and duration should be prescribed according to the appropriate prescription.

What is the difference between epidemic and pandemic?

An epidemic is an increase in cases beyond what is expected in a given population or area. A pandemic is an epidemic that spreads to several countries or continents with sustained transmission. These words describe, above all, a geographical spread and are not sufficient alone to indicate the individual severity of a disease.

03Comparative data

124 diseases, verifiable benchmarks

Filter by agent family or route of exposure. The fact sheets summarize general principles and refer to a health authority; they do not allow for diagnosis or therapeutic decisions.

46Virus

42Bacteria

23Parasite

11Mushrooms

1Prion

1Multiple agents

Quick searches

The research focuses on the name, agent, transmission, prevention and source of each sheet.

124 displayed diseases

Documentary data · external sources

VirusWHO

Mpox

Virus monkeypox

Transmissible viral zoonoses, especially in close contact with lesions, fluids or contaminated objects.

Transmission/exposure
Close contact · Animal / zoonosis · Mother and child transmission
Prevention
Avoid contact with lesions, follow health instructions and use vaccination when proposed.
Read the detailed sheet →
Guides for this exhibition
See the WHO fact sheet
VirusWHO

Hepatitis B

Hepatitis B virus

Infection of the liver transmitted by blood and certain biological fluids, which may become chronic.

Transmission/exposure
Blood and fluids · Sexual use · Mother and child transmission
Prevention
Vaccination, sterile equipment, donation testing and precautions when exposed to blood.
Read the detailed sheet →
Guides for this exhibition
See the WHO fact sheet
VirusWHO

HIV infection

Human immunodeficiency virus

Infection targeting the immune system, controlled by antiretroviral treatment but without common healing to date.

Transmission/exposure
Blood and fluids · Sexual use · Mother and child transmission
Prevention
Preservatives, screening, sterile equipment, PrEP or PEP when indicated and effective treatment.
Read the detailed sheet →
Guides for this exhibition
See the WHO fact sheet
VirusWHO

Zika virus infection

Zika virus

Arbovirose mainly transmitted by Aedes mosquitoes, with a particular risk of complications during pregnancy.

Transmission/exposure
Vector · Sexual use · Mother and child transmission
Prevention
Protection against stinging, reduction of larval gites and sexual precautions after possible exposure.
Read the detailed sheet →
Guides for this exhibition
See the WHO fact sheet
VirusCDC

Chickenpox

Varicella zoster virus

Very contagious viral infection with rash; the virus can then remain latent and reactivate as shingles.

Transmission/exposure
Respiratory · Close contact · Mother and child transmission
Prevention
Vaccination when recommended and removal of contact with particularly vulnerable people.
Read the detailed sheet →
Guides for this exhibition
See the CDC sheet
VirusWHO

Nipah Virus Infection

Henipavirus nipahense

Emerging zoonose related to frugivorous bats, transmissible by animals, contaminated food or between people.

Transmission/exposure
Animal / zoonosis · Water and food · Close contact
Prevention
Avoid potentially contaminated foods, strengthen animal biosecurity and apply care precautions.
Read the detailed sheet →
Guides for this exhibition
See the WHO fact sheet
VirusCDC

Cytomegalovirus infection

Human Cytomegalovirus

Often a silent infection, with special challenges during pregnancy and in immunocompromised people.

Transmission/exposure
Close contact · Blood and fluids · Mother and child transmission
Prevention
Hygiene after contact with young children, transfusion safety and appropriate follow-up of people at risk.
Read the detailed sheet →
Guides for this exhibition
See the CDC sheet
VirusCDC

Infection with parvovirus B19

Parvovirus B19

Infection often benign in children but may be problematic during pregnancy or with certain blood diseases.

Transmission/exposure
Respiratory · Blood and fluids · Mother and child transmission
Prevention
Respiratory hygiene, hand washing and medical assessment after exposure to risk during pregnancy.
Read the detailed sheet →
Guides for this exhibition
See the CDC sheet
VirusCDC

Hand, foot and mouth disease

Enterovirus, including coxsackievirus

Common viral infection in young children, with oral lesions and rash of the hands or feet.

Transmission/exposure
Close contact · Respiratory · Water and food
Prevention
Washing hands, cleaning surfaces and limiting the sharing of contaminated objects.
Read the detailed sheet →
Guides for this exhibition
See the CDC sheet
VirusCDC

Adenovirus infection

Human adenoviruses

Group of infections that may affect the respiratory tract, eyes or digestive system.

Transmission/exposure
Respiratory · Close contact · Water and food
Prevention
Hand hygiene, adapted disinfection and proper maintenance of swimming pools and community facilities.
Read the detailed sheet →
Guides for this exhibition
See the CDC sheet
BacteriaCDC

Anthrax

Bacillus anthracis

Bacterial zoonose associated with persistent spores acquired by contact, ingestion or inhalation depending on the context.

Transmission/exposure
Animal / zoonosis · Environment · Water and food
Prevention
Veterinary control, professional protection and immediate management of any suspected exposure.
Read the detailed sheet →
Guides for this exhibition
See the CDC sheet
BacteriaCDC

Clostridioides difficile infection

Clostridioides difficile

Intestinal infection often associated with the care or disturbance of the microbiota after use of antibiotics.

Transmission/exposure
Close contact · Environment
Prevention
Reasonable use of antibiotics, washing of hands with water and soap, and disinfection of sporicid in the premises concerned.
Read the detailed sheet →
Guides for this exhibition
See the CDC sheet
BacteriaCDC

Shiga-toxin-producing E. coli infection

Escherichia coli STEC

Digestive infection that may be related to food, water, animals or fecooral transmission.

Transmission/exposure
Water and food · Animal / zoonosis · Close contact
Prevention
Sufficient meat cooking, pasteurized milk, plant washing and hygiene after animal contact.
Read the detailed sheet →
Guides for this exhibition
See the CDC sheet
ParasiteCDC

Toxoplasmosis

Toxoplasma gondii

Parasitosis often asymptomatic but presenting special issues during pregnancy or immunodepression.

Transmission/exposure
Water and food · Animal / zoonosis · Mother and child transmission
Prevention
Cook meat, wash plants and hands, and follow specific advice when pregnant.
Read the detailed sheet →
Guides for this exhibition
See the CDC sheet
ParasiteWHO

Chagas disease

Trypanosoma cruzi

Parasitosis mainly present in Latin America, transmitted by triatomine bugs but also by other routes.

Transmission/exposure
Vector · Water and food · Blood and fluids
Prevention
Vector control, improved habitat, food security and screening for donations and congenital transmission.
Read the detailed sheet →
Guides for this exhibition
See the WHO fact sheet
ParasiteWHO

Echinococcosis

Echinococcus spp.

Parasitic zoonose acquired by ingestion of eggs from the environment or contaminated animal hosts.

Transmission/exposure
Animal / zoonosis · Water and food · Environment
Prevention
Dog vermifugation, slaughterhouse hygiene, hand washing and safety of water and food.
Read the detailed sheet →
Guides for this exhibition
See the WHO fact sheet
ParasiteWHO

Taeniasis and cysticercosis

Taenia solium

Tenasis follows the ingestion of pigs containing larvae; cysticercosis follows the ingestion of eggs of the parasite by the fecooral route.

Transmission/exposure
Water and food · Animal / zoonosis · Close contact
Prevention
Sanitation, hand washing, meat inspection, sufficient cooking and carrier treatment.
Read the detailed sheet →
Guides for this exhibition
See the WHO fact sheet
ParasiteCDC

Cryptosporidiosis

Cryptosporidium spp.

Diarrhoeal infection transmitted by resistant oocysts in water or by contact with infected people and animals.

Transmission/exposure
Water and food · Close contact · Animal / zoonosis
Prevention
Hand hygiene, safe water and respect for temporary exclusions from bathing after diarrhea.
Read the detailed sheet →
Guides for this exhibition
See the CDC sheet
MushroomsWHO

Sporotrichosis

Sporothrix spp.

Subcutaneous mycosis acquired after inoculation from plants or, in some areas, from contact with infected cats.

Transmission/exposure
Environment · Animal / zoonosis · Close contact
Prevention
Gloves and protective clothing for exhibiting activities, and veterinary care of infected animals.
Read the detailed sheet →
Guides for this exhibition
See the WHO fact sheet
BacteriaCDC

Genital chlamydia

Chlamydia trachomatis

Sexually transmitted infection often without symptoms, which can lead to complications of reproductive health; transmission to the newborn is possible at delivery.

Transmission/exposure
Sexual use · Mother and child transmission
Prevention
Preservatives, exposure-specific screening, prescribed treatment and partner management as recommended.
Read the detailed sheet →
Guides for this exhibition
See the CDC sheet
MushroomsCDC

Infection with Candida auris

Candida auris (Candidozyma auris)

Yeast can cause serious infections and can be transmitted between patients in the care setting. Symptoms-free porting is possible; resistance to antifungals is common.

Transmission/exposure
Close contact · Environment
Prevention
Specialized care measures: hand hygiene, equipment management and adapted disinfection. Report a history of portage or infection to the health care team.
Read the detailed sheet →
Guides for this exhibition
See the CDC sheet
BacteriaCDC

Group B streptococcal infection

Streptococcus agalactiae

Bacteria that can be worn without symptoms and cause serious infections, especially in the newborn.

Transmission/exposure
Flora of the organism · Mother and child transmission
Prevention
Screening during pregnancy and prevention during childbirth according to local recommendations; rapid management of infection.
Read the detailed sheet →
Guides for this exhibition
See the CDC sheet

04Proceed to action

Deepening prevention by exposure

A route of transmission describes a possibility of exposure; useful measures always depend on the agent, place and recommendations applicable. These guides explain the general actions associated with the main contexts.

Air and close contacts

Understand the role of indoor air, duration of exposure and mask when indicated.

Improve ventilation →
Choose and wear a mask →
Limit transmission to home →

Water and food

Identify the stages of preparation, storage and consumption that may affect the risk.

Food hygiene →
Check drinking water →

Vectors

Adapt protection to mosquitoes or ticks present locally, without assuming that they all transmit the same disease.

Protecting from mosquitoes →
Reaction to tick bite →

Animals and exhibitions

After a bite or biological exposure, immediate actions and the timing of assessment count.

After a bite →
After an exhibition →

Cross-cutting prevention

Hand hygiene and vaccination, when recommended, complement the specific measures for each disease.

Hand hygiene →
Understanding vaccination →

Interpret a result or alert

A disease sheet has stable markers. An ongoing test or situation is read with its method, date and context.

Understanding tests →
Read health data →
See the official watch →

Further reading

These publications help you verify the concepts discussed. Disease records and directory entries each identify their sources.

The content modification date does not mean that every source has undergone a new medical review. Verification method and scope.