# infectious disease

> disease caused by infection of pathogenic biological agents in a host organism

**Wikidata**: [Q18123741](https://www.wikidata.org/wiki/Q18123741)  
**Wikipedia**: [English](https://en.wikipedia.org/wiki/Infectious_disease)  
**Source**: https://4ort.xyz/entity/infectious-disease

## Summary
An infectious disease is an abnormal condition negatively affecting organisms, specifically caused by the infection of pathogenic biological agents within a host organism. These diseases encompass a vast range of conditions transmitted through various mechanisms, including direct contact, airborne particles, contaminated water, and vectors like insects. The category includes specific illnesses caused by bacteria, viruses, fungi, and parasites, affecting humans, animals, and plants.

## Key Facts
*   **Definition**: A disease caused by the infection of pathogenic biological agents in a host organism.
*   **Primary Classification**: It is a subclass of "disease," defined as an abnormal condition negatively affecting organisms.
*   **Transmission Modes**: Includes airborne, waterborne, blood-borne, vector-borne, sexually transmitted, and zoonotic (animal-to-human) transmission.
*   **Pathogen Types**: Caused by bacteria, viruses, fungi, parasites, and protozoa.
*   **Specific Examples**: Includes tuberculosis (caused by *Mycobacterium tuberculosis*), plague (caused by *Yersinia pestis*), and smallpox (an eradicated human disease).
*   **Zoonotic Potential**: Includes zoonosis (transmission between animal species or to humans) and anthroponotic diseases (human-to-animal transmission).
*   **Prevention**: A subset of these conditions are classified as "vaccine-preventable diseases."
*   **Emerging Threats**: Includes "emerging communicable diseases," which involve novel pathogens or new transmission modes.
*   **Historical Impact**: Includes the 1918–1920 flu pandemic caused by the H1N1 influenza A virus and the 16th-century cocoliztli epidemics in New Spain.
*   **Notable Researchers**: Key figures include Alimuddin Zumla (Zambian physician), Yasmine Belkaid (Algerian French immunologist), Martin J. Blaser (American academic), and Didier Pittet (Swiss infectiologue and co-inventor of hydro-alcoholic hand disinfection gel).
*   **Geographic Specifics**: Includes diseases originating in specific regions, such as Bolivian hemorrhagic fever (Bolivia) and Rift Valley fever.

## FAQs
**What are the primary ways infectious diseases are transmitted?**
Transmission occurs through various vectors and mechanisms, including direct contact, airborne particles, contaminated fresh water, and blood or body fluids. Specific modes include sexual transmission, vector-borne spread via insects like ticks and mosquitoes, and zoonotic transfer from animals to humans.

**How are infectious diseases categorized by their causative agents?**
They are classified based on the pathogen type, such as bacterial infectious diseases (e.g., cholera, typhoid), viral infectious diseases (e.g., influenza, Ebola), fungal infections (e.g., candidiasis, blastomycosis), and parasitic diseases (e.g., malaria, schistosomiasis). Some conditions are caused by specific organisms like helminths (worms) or protozoa.

**Which infectious diseases have been eradicated or are considered historical?**
Smallpox is the notable example of an eradicated human disease. Historical impacts include the 1918–1920 flu pandemic and the cocoliztli epidemics in 16th-century New Spain, while conditions like Brill-Zinsser disease represent recurring forms of epidemic typhus after long latency.

**What role do animals play in the spread of infectious diseases?**
Animals serve as hosts for zoonotic diseases, which can transmit to humans, and anthroponotic diseases, which transmit from humans to animals. Specific animal diseases include canine influenza, bovine malignant catarrhal fever, and African horse sickness, while some pathogens like *Bacillus anthracis* (anthrax) affect both humans and animals.

**Are there specific medical conditions related to the immune response or complications of infection?**
Yes, conditions like post-polio syndrome appear decades after the initial illness, while others like Lemierre's syndrome involve infectious thrombophlebitis. Complications can also manifest as specific syndromes such as Fitz-Hugh–Curtis syndrome or subacute sclerosing panencephalitis, a sequela of measles infection.

## Why It Matters
Infectious diseases represent a fundamental biological challenge that affects the health of all living organisms, from humans to livestock and wildlife. Understanding these conditions is critical for public health, as they drive the development of vaccines, antibiotics, and hygiene protocols like the hydro-alcoholic disinfection gel invented by Didier Pittet. The study of these diseases reveals complex ecological interactions, such as the role of vectors in spreading malaria or the impact of climate on emerging pathogens. Furthermore, the eradication of diseases like smallpox stands as a monumental achievement in medical history, demonstrating the potential of global cooperation and scientific intervention. The persistence of these diseases continues to shape economic stability, demographic trends, and the evolution of medical science.

## Notable For
*   **Eradication Success**: Smallpox is the only human disease to be completely eradicated through global vaccination efforts.
*   **Pandemic History**: The 1918–1920 flu pandemic remains one of the most devastating global health events in recorded history.
*   **Diverse Pathogen Spectrum**: It is the only category encompassing diseases caused by bacteria, viruses, fungi, parasites, and prions simultaneously.
*   **Zoonotic Interface**: It uniquely bridges human and animal health, highlighting the critical role of veterinary medicine in human disease prevention.
*   **Vector Complexity**: Includes diseases transmitted by diverse vectors, from mosquitoes (dengue, malaria) to ticks (Lyme disease, tick paralysis) and fleas (plague).
*   **Latency and Recurrence**: Features diseases like Brill-Zinsser disease, which can reactivate decades after the initial infection due to immunosuppression.
*   **Global Disparity**: Many bacterial and parasitic infections, such as typhoid fever and yaws, remain common in developing countries, highlighting global health inequities.
*   **Innovation in Prevention**: The field has driven the invention of specific medical technologies, such as the hydro-alcoholic hand gel, to combat transmission.

## Body

### Classification and Pathogens
Infectious diseases are broadly defined as abnormal conditions negatively affecting organisms caused by pathogenic biological agents. The primary classification divides these conditions by the type of pathogen involved. Bacterial infectious diseases include cholera, an infection of the small intestine, and typhoid fever, a bacterial disorder contracted through contaminated food or drink. Viral infectious diseases encompass influenza, caused by the influenza virus, and severe acute respiratory syndrome (SARS), a viral respiratory disease. Fungal infectious diseases result from fungi affecting animals or humans, such as candidiasis caused by *Candida* species and blastomycosis caused by *Blastomyces dermatitidis*. Parasitic infectious diseases are caused or transmitted by parasites, including helminthiasis (worm infections) like ascariasis and schistosomiasis, and protozoan diseases like amebiasis and giardiasis.

### Transmission Mechanisms
The spread of infectious diseases occurs through diverse pathways. Airborne diseases are transmitted through the air via pathogen concentration, including respiratory tract infections and tuberculosis. Waterborne diseases are caused by microorganisms in contaminated fresh water, such as cholera and cryptosporidiosis. Blood-borne diseases spread through contamination by blood and body fluids, including hepatitis B and C. Vector-borne diseases rely on intermediate organisms; for example, Lyme disease is spread by blacklegged ticks, while dengue fever is transmitted by mosquitoes. Sexually transmitted infections (STIs) are transmitted through human sexual behavior, including syphilis, gonorrhea, and chancroid. Zoonotic diseases can be transmitted from one animal species to another or to humans, such as rabies and brucellosis. Conversely, anthroponotic diseases involve pathogens capable of transmitting from humans to non-human animals.

### Specific Disease Entities and Symptoms
The knowledge base details a vast array of specific conditions. Respiratory infections include pneumonia (inflammation of lung alveoli), bronchopneumonia, and the common cold. Skin infections range from impetigo and cellulitis to fungal conditions like tinea pedis (athlete's foot) and scabies. Gastrointestinal infections include rotaviral gastroenteritis and amoebic dysentery. Neurological infections include bacterial meningitis, viral encephalitis, and Rasmussen's encephalitis. Specific syndromes include Lemierre's syndrome (infectious thrombophlebitis of the internal jugular vein) and Fitz-Hugh–Curtis syndrome. Some diseases are characterized by specific symptoms, such as tetanus (muscle spasms), diphtheria (infectious disease), and botulism (human and animal disease).

### Animal and Veterinary Diseases
Infectious diseases significantly impact animal populations. Canine influenza affects dogs, while bovine malignant catarrhal fever afflicts cattle. Avian influenza is caused by viruses adapted to birds, and duck plague is a viral infection in ducks. Equine diseases include African horse sickness, an insect-borne reovirus infection, and Eastern equine encephalitis. Other animal-specific conditions include louping ill, varroosis (a disease of honeybees), and Aleutian disease in mustelids. Some diseases, like glanders, are primarily horse diseases but can be transmitted to humans.

### Historical and Emerging Contexts
Historical data highlights the impact of past epidemics. The 1918–1920 flu pandemic was a global event caused by the H1N1 influenza A virus. The cocoliztli epidemic refers to 16th-century epidemics in New Spain. Emerging communicable diseases are defined as infectious diseases of emerging pathogens, often novel in their outbreak range or transmission mode. Examples of emerging or re-emerging threats include Ebola hemorrhagic fever, Marburg virus disease, and Lassa fever.

### Notable Researchers and Contributors
Several individuals are linked to the study and management of infectious diseases. Alimuddin Zumla is a Zambian physician. Yasmine Belkaid is an Algerian French immunologist. Martin J. Blaser is an American academic. Didier Pittet is a Swiss infectiologue and epidemiologist who co-invented the hydro-alcoholic disinfection gel for hands. Ernest William Goodpasture was an American pathologist and physician (1886–1960). Adaora Adimora was an American doctor and academic (1956–2024). Peter Daszak is a zoologist and disease ecologist. Alice Catherine Evans was an American microbiologist. Max Wolff was a German physician. Aza Rakhmanova is an AIDS and Hepatitis expert. Salim Abdool Karim is a South African researcher. Elfatih Eltahir is a Sudanese American geophysicist and climate scientist. Theophil Yanovsky is another contributor noted in the data.

### Complications and Sequelae
Infections can lead to long-term complications or secondary conditions. Post-polio syndrome is a group of disabling signs appearing decades after poliomyelitis. Subacute sclerosing panencephalitis is a rare sequela from measles infection. Brill-Zinsser disease is a mild form of epidemic typhus that recurs after a long latency period. Congenital conditions include congenital syphilis, which results in multisystem infection in the fetus, and congenital cytomegalovirus infection. Other complications include abscesses (localized pus collection), empyema (pus in anatomical cavities), and granuloma inguinale.

### Geographic and Environmental Factors
Certain diseases are tied to specific geographic regions or environmental conditions. Bolivian hemorrhagic fever originates in Bolivia. Rift Valley fever affects humans and animals in Africa. Kyasanur forest disease is a human disease. Argentine hemorrhagic fever and Venezuelan hemorrhagic fever are specific to their regions. Environmental factors also play a role, such as the transmission of Lyme disease through tick bites in specific habitats.

### Prevention and Treatment
Vaccine-preventable diseases are a specific subset that can be prevented by vaccines. Antibiotics are noted as a treatment for typhoid fever. The development of hydro-alcoholic disinfection gel by Didier Pittet represents a key intervention in preventing transmission. Understanding the material basis of diseases, such as the deficiency of ornithine translocase in certain metabolic disorders (though not strictly infectious, it is linked in the data), helps in diagnosis. Genetic resistance to malaria is also a noted factor in human disease susceptibility.

## References

1. Comparing national infectious disease surveillance systems: China and the Netherlands
2. Impact of infectious diseases on population health using incidence-based disability-adjusted life years (DALYs): results from the Burden of Communicable Diseases in Europe study, European Union and European Economic Area countries, 2009 to 2013.
3. Disease Ontology
4. Monarch Disease Ontology release 2018-06-29
5. Nuovo soggettario
6. Freebase Data Dumps. 2013
7. [Nuovo soggettario](https://thes.bncf.firenze.sbn.it/termine.php?id=66523)
8. [Registros de autoridad de "Materia" de la Biblioteca Nacional de España. Spain open data portal](https://www.bne.es/media/datosgob/catalogo-autoridades/materia/materia-UTF8.zip)
9. YSO-Wikidata mapping project
10. Quora
11. [Source](https://www.abs.gov.au/AUSSTATS/abs@.nsf/DetailsPage/1297.02008?OpenDocument)
12. [Source](https://thenextweb.com/vocabulary/infectious-disease/)
13. FactGrid
14. KBpedia
15. [Source](https://vocabs.ardc.edu.au/viewById/316)
16. All Science Journal Classification Codes