Human-to-human transmission (HHT) is an epidemiologic

vector Vector most often refers to: *Euclidean vector, a quantity with a magnitude and a direction *Vector (epidemiology), an agent that carries and transmits an infectious pathogen into another living organism Vector may also refer to: Mathematic ...

, especially in case the disease is borne by individuals known as superspreaders. In these cases, the

basic reproduction number In epidemiology, the basic reproduction number, or basic reproductive number (sometimes called basic reproduction ratio or basic reproductive rate), denoted R_0 (pronounced ''R nought'' or ''R zero''), of an infection is the expected number of ...

of the virus, which is the average number of additional people that a single case will infect without any preventative measures, can be as high as 203.9. Interhuman transmission is a synonym for HHT. The

World Health Organization The World Health Organization (WHO) is a specialized agency of the United Nations responsible for international public health. The WHO Constitution states its main objective as "the attainment by all peoples of the highest possible level of ...

designation of a pandemic hinges on the demonstrable fact that there is sustained HHT in two regions of the world.

Synopsis

Relevant

pathogens In biology, a pathogen ( el, πάθος, "suffering", "passion" and , "producer of") in the oldest and broadest sense, is any organism or agent that can produce disease. A pathogen may also be referred to as an infectious agent, or simply a ger ...

may be

viruses A virus is a submicroscopic infectious agent that replicates only inside the living cells of an organism. Viruses infect all life forms, from animals and plants to microorganisms, including bacteria and archaea. Since Dmitri Ivanovsky's ...

bacteria Bacteria (; singular: bacterium) are ubiquitous, mostly free-living organisms often consisting of one Cell (biology), biological cell. They constitute a large domain (biology), domain of prokaryotic microorganisms. Typically a few micrometr ...

, or

fungi A fungus ( : fungi or funguses) is any member of the group of eukaryotic organisms that includes microorganisms such as yeasts and molds, as well as the more familiar mushrooms. These organisms are classified as a kingdom, separately from ...

, and they may be spread through breathing, talking, coughing, sneezing, spraying of liquids, toilet flushing or any activities which generate aerosol particles or droplets or generate

fomites A fomite () or fomes () is any inanimate object that, when contaminated with or exposed to infectious agents (such as pathogenic bacteria, viruses or fungi), can transfer disease to a new host. Transfer of pathogens by fomites A fomite is any ...

, such as raising of dust. A 2007 study showed that influenza virus was still active on stainless steel 24 hours after contamination. Though on hands it survives only for five minutes, the constant contact with steel almost certainly transmits infection. Transfer efficiency depends not only on surface, but also on pathogen type. For example,

avian influenza Avian influenza, known informally as avian flu or bird flu, is a variety of influenza caused by viruses adapted to birds.

survives on both porous and non-porous materials for 144 hours. The pathogens may also be transmitted by poor use of cutlery or improper sanitation of dishes or bedlinen. Particularly problematic are toilet practices, which lead to the fecal-oral route. STDs are by definition spread through this vector.

List of HHT diseases

Examples of some HHT diseases are listed below.

Controlled

* measles:

vaccine A vaccine is a biological preparation that provides active acquired immunity to a particular infectious or malignant disease. The safety and effectiveness of vaccines has been widely studied and verified.

available * mumps: vaccine available *

chicken pox Chickenpox, also known as varicella, is a highly contagious disease caused by the initial infection with varicella zoster virus (VZV). The disease results in a characteristic skin rash that forms small, itchy blisters, which eventually scab ...

: vaccine available * small pox * bubonic plague: slim non-nil risk *

pneumonic plague Pneumonic plague is a severe lung infection caused by the bacterium ''Yersinia pestis''. Symptoms include fever, headache, shortness of breath, chest pain, and coughing. They typically start about three to seven days after exposure. It is one ...

: 1910-11 Manchurian plague *

tuberculosis Tuberculosis (TB) is an infectious disease usually caused by '' Mycobacterium tuberculosis'' (MTB) bacteria. Tuberculosis generally affects the lungs, but it can also affect other parts of the body. Most infections show no symptoms, i ...

Norovirus Norovirus, sometimes referred to as the winter vomiting disease, is the most common cause of gastroenteritis. Infection is characterized by non-bloody diarrhea, vomiting, and stomach pain. Fever or headaches may also occur. Symptoms usually devel ...

* monkeypox * SARS-CoV-1 * MERS *

Avian flu Avian influenza, known informally as avian flu or bird flu, is a variety of influenza caused by viruses adapted to birds.

* Sexually transmitted infections (STIs) or sexually transmitted diseases (STDs): ** Syphilis, aka French pox

Uncontrolled

SARS-CoV-2 Severe acute respiratory syndrome coronavirus 2 (SARS‑CoV‑2) is a strain of coronavirus that causes COVID-19 (coronavirus disease 2019), the respiratory illness responsible for the ongoing COVID-19 pandemic. The virus previously had a ...

References

Sources

* * {{Concepts in infectious disease Epidemiology Parasitology Infectious diseases Sanitation Hygiene Global health Epidemics