The outbreak began in July 1518 when a woman, Mrs. Troffea, began to dance fervently in a street in Strasbourg. This lasted somewhere between four and six days. Within a week, 34 others had joined, and within a month, there were around 400 dancers, predominantly female. Some of these people would die from heart attacks, strokes, or exhaustion. One report indicates that for a period, the plague killed around fifteen people per day.

Historical documents, including "physician notes, cathedral sermons, local and regional chronicles, and even notes issued by the Strasbourg city council" are clear that the victims danced. It is not known why these people danced, some even to their deaths.

As the dancing plague worsened, concerned nobles sought the advice of local physicians, who ruled out astrological and supernatural causes, instead announcing that the plague was a "natural disease" caused by "hot blood". However, instead of prescribing bleeding, authorities encouraged more dancing, in part by opening two guildhalls and a grain market, and even constructing a wooden stage. The authorities did this because they believed that the dancers would recover only if they danced continuously night and day. To increase the effectiveness of the cure, authorities even paid for musicians to keep the afflicted moving.

Historian John Waller stated that a marathon runner could not have lasted the intense workout that these men and women did hundreds of years ago.

Modern theories include food-poisoning caused by the toxic and psychoactive chemical products of ergot fungi, which grows commonly on grains in the wheat family (such as rye). Ergotamine is the main psychoactive product of ergot fungi; it is structurally related to the recreational drug lysergic acid diethylamide (LSD-25), and is the substance from which LSD-25 was originally synthesized. The same fungus has also been implicated in other major historical anomalies, including the Salem witch trials. Waller speculates that the dancing was "stress-induced psychosis" on a mass level, since the region where the people danced was riddled with starvation and disease, and the inhabitants tended to be superstitious. Seven other cases of dancing plague were reported in the same region during the medieval era.

The laughter epidemic began on January 30, 1962, at a mission-run boarding school for girls in Kashasha. The laughter started with three girls and spread haphazardly throughout the school, affecting 95 of the 159 pupils, aged 12–18. Symptoms lasted from a few hours to 16 days in those affected. The teaching staff were not affected but reported that students were unable to concentrate on their lessons. The school was forced to close down on March 18, 1962.

After the school was closed and the students were sent home, the epidemic spread to Nshamba, a village that was home to several of the girls. In April and May, 217 people had laughing attacks in the village, most of them being school children and young adults. The Kashasha school was reopened on May 21, only to be closed again at the end of June. In June, the laughing epidemic spread to Ramashenye girls’ middle school, near Bukoba, affecting 48 girls.

The school from which the epidemic sprang was sued; the children and parents transmitted it to the surrounding area. Other schools, Kashasha itself, and another village, comprising thousands of people, were all affected to some degree. Six to eighteen months after it started, the phenomenon died off. The following symptoms were reported on an equally massive scale as the reports of the laughter itself: pain, fainting, flatulence, respiratory problems, rashes, attacks of crying, and random screaming. In total 14 schools were shut down and 1000 people were affected.

The Tanganyika laughter epidemic of 1962 was an outbreak of mass hysteriaor mass psychogenic illness (MPI)rumored to have occurred in or near the village of Kashasha on the western coast of Lake Victoria in the modern nation of Tanzania (formerly Tanganyika) near the border of Uganda.

In China, traditional treatment based on the causes suggested by cultural beliefs are administrated to the patient. Praying to gods and asking Taoist priests to perform exorcism is common. If a fox spirit is believed to be involved, people may hit gongs or beat the person to drive it out. The person will receive a yang- or yin-augmenting Chinese medicine potion, usually including herbs, pilose antler (stag of deer) or deer tail, and tiger penis, deer penis, or fur seal penis. Other foods for therapy are pepper soup, ginger soup and liquor.

The virus is thought to have been introduced into Eritrea in 1887 by Indian cattle brought by the Italians for their campaign against Somalia. It spread throughout the Horn of Africa, and crossed the Zambezi in March of 1896.

Mass psychogenic illness (MPI), also called mass sociogenic illness or just sociogenic illness, is "the rapid spread of illness signs and symptoms affecting members of a cohesive group, originating from a nervous system disturbance involving excitation, loss, or alteration of function, whereby physical complaints that are exhibited unconsciously have no corresponding organic" cause. MPI is distinct from other collective delusions, also included under the blanket terms of mass hysteria, in that MPI causes symptoms of disease, though there is no organic cause.

There is a clear preponderance of female victims. The DSM-IV-TR does not have specific diagnosis for this condition but the text describing conversion disorder states that "In 'epidemic hysteria', shared symptoms develop in a circumscribed group of people following 'exposure' to a common precipitant."

Dancing mania (also known as dancing plague, choreomania, St John's Dance and, historically, St. Vitus's Dance) was a social phenomenon that occurred primarily in mainland Europe between the 14th and 17th centuries. It involved groups of people dancing erratically, sometimes thousands at a time. The mania affected men, women, and children who danced until they collapsed from exhaustion. One of the first major outbreaks was in Aachen, in the Holy Roman Empire, in 1374, and it quickly spread throughout Europe; one particularly notable outbreak occurred in Strasbourg in 1518, also in the Holy Roman Empire.

Affecting thousands of people across several centuries, dancing mania was not an isolated event, and was well documented in contemporary reports. It was nevertheless poorly understood, and remedies were based on guesswork. Generally, musicians accompanied dancers, to help ward off the mania, but this tactic sometimes backfired by encouraging more to join in. There is no consensus among modern-day scholars as to the cause of dancing mania.

The several theories proposed range from religious cults being behind the processions to people dancing to relieve themselves of stress and put the poverty of the period out of their minds. It is, however, thought to have been a mass psychogenic illness in which the occurrence of similar physical symptoms, with no known physical cause, affect a large or small group of people as a form of social influence.

Millie McCoy and Christine McCoy (July 11, 1851 – October 8, 1912) were American conjoined twins who went by the stage names "The Carolina Twins", "The Two-Headed Nightingale" and "The Eighth Wonder of the World". The Twins traveled throughout the world performing song and dance for entertainment.

Lucio Godina (March 8, 1908 – November 24, 1936) and Simplicio Godina (March 8, 1908 - December 8, 1936) were pygopagus conjoined twins from the island of Samar in the Philippines.

At the age of 21 they married Natividad and Victorina Matos, who were identical twins. They performed in various sideshow acts, including in an orchestra on Coney Island and in dance with their wives.

After Lucio died of rheumatic fever in New York City, doctors operated to separate him from Simplicio. Simplicio survived the operation, but died shortly thereafter due to spinal meningitis.

Tarantism is a form of hysteric behaviour, popularly believed to result from the bite of the wolf spider "Lycosa tarantula" (distinct from the broad class of spiders also called tarantulas).

A better candidate cause is "Latrodectus tredecimguttatus", commonly known as the Mediterranean black widow or steppe spider, although no link between such bites and the behaviour of tarantism has ever been demonstrated. However, the term historically is used to refer to a dancing mania - characteristic of southern Italy - which likely had little to do with spider bites. The tarantella dance supposedly evolved from this therapy.

In the 1890s, an epizootic of the rinderpest virus struck Africa, considered to be "the most devastating epidemic to hit southern Africa in the late nineteenth century". It killed more than 5.2 million cattle south of the Zambezi, as well as domestic oxen, sheep, and goats, and wild populations of buffalo, giraffe, and wildebeest. This led to starvation resulting in the death of an estimated third of the human population of Ethiopia and two-thirds of the Maasai people of Tanzania.

"Dancing mania" is derived from the term "choreomania", from the Greek "choros" (dance) and "mania" (madness), and is also known as "dancing plague". The term was coined by Paracelsus, and the condition was initially considered a curse sent by a saint, usually St. John the Baptist or St. Vitus, and was therefore known as "St. Vitus's Dance" or "St. John's Dance". Victims of dancing mania often ended their processions at places dedicated to that saint, who was prayed to in an effort to end the dancing; incidents often broke out around the time of the feast of St Vitus.

St Vitus's Dance was diagnosed, in the 17th century, as Sydenham chorea. Dancing mania has also been known as epidemic chorea and epidemic dancing. A disease of the nervous system, chorea is characterized by symptoms resembling those of dancing mania, which has also rather unconvincingly been considered a form of epilepsy. Scientists have described dancing mania as a "collective mental disorder", "collective hysterical disorder", and "mass madness".

In historical culture-bound cases, reassurance and talks on sexual anatomy are given. Patients are treated with psychotherapy distributed according to symptoms and to etiologically significant points in the past. Prognosis appears to be better in cases with a previously functional personality, a short history and low frequency of attacks, and a relatively uncomplicated sexual life.

For sporadic Western cases, careful diagnostic workup including searching for underlying sexual conflict is common. The choice of psychotherapeutic treatment is based on the psychiatric pathology found.

Melancholia (from , '), also lugubriousness, from the Latin "lugere", to mourn; moroseness, from the Latin "morosus", self-willed, fastidious habit; wistfulness, from old English "wist": intent, or saturnine, was a concept in ancient and pre-modern medicine. Melancholy was one of the four temperaments matching the four humours. In the 19th century, "melancholia" could be physical as well as mental, and melancholic conditions were classified as such by their common cause rather than by their properties.

According to Balaratnasingam and Janca, “mass hysteria is to date a poorly understood condition. Little certainty exists regarding its” cause.

Besides the difficulties common to all research involving the social sciences, including a lack of opportunity for controlled experiments, mass sociogenic illness presents special difficulties to researchers in this field. Balaratnasingam and Janca report that the methods for “diagnosis of mass hysteria remains contentious. According to Timothy Jones of the Tennessee Department of Public Health, the effects resulting from MPI “can be difficult to differentiate from [those of] bioterrorism, rapidly spreading infection or acute toxic exposure.”

These troubles result from the residual diagnosis of MPI. Singer, of the Uniformed Schools of Medicine, puts the problems with such a diagnosis thus:

“[y]ou find a group of people getting sick, you investigate, you measure everything you can measure . . . and when you still can't find any physical reason, you say 'well, there's nothing else here, so let's call it a case of MPI.'” There is a lack of logic in an argument that proceeds: “There isn't anything, so it must be MPI.” It precludes the notion that an organic factor could have been overlooked. Nevertheless, running an extensive number of tests extends the probability of false positives.

British psychiatrist Simon Wesseley distinguishes between two forms of MPI:

- mass anxiety hysteria “consists of episodes of acute anxiety, occurring mainly in schoolchildren. Prior tension is absent and the rapid spread is by visual contact.”

- mass motor hysteria “consists of abnormalities in motor behaviour. It occurs in any age group and prior tension is present. Initial cases can be identified and the spread is gradual. . . . [T]he outbreak may be prolonged.”

While his definition is sometimes adhered to, others such as Ali-Gombe et al. of the University of Maiduguri, Nigeria contest Wesseley's definition and describe outbreaks with qualities of both mass motor hysteria and mass anxiety hysteria.

An evolutionary psychology explanation for this disorder, as well as for conversion disorder more generally, is that the symptom may have been evolutionarily advantageous during warfare. A non-combatant with these symptoms signals non-verbally, possibly to someone speaking a different language, that she or he is not dangerous as a combatant and also may be carrying some form of dangerous infectious disease. This can explain that conversion disorder may develop following a threatening situation, that there may be a group effect with many people simultaneously developing similar symptoms, and the gender difference in prevalence.

have been proposed among "possible causes" of the disease. For instance, the above-mentioned declaration produced by the April 2013 International Conference which took place in San Salvador said that:

The nature of multifactorial problems is, that the observed disease can be caused from regionally different sets of risk factors, e.g. agrochemicals and heavy metals are ubiquitous in endemic and non-endemic areas, feature proteinuria, or have not been related previously to CKD but only to acute kidney injury. Mesoamerican volcanic soils, for instance, are rich in arsenic and cadmium (e.g. CKDu miners).

Mesoamerican nephropathy (MeN) is a currently unexplained epidemic of chronic kidney disease of unknown origin (CKDu), prevalent in the Pacific Ocean coastal low lands of the Mesoamerican region, including southern Mexico, Guatemala, El Salvador, Nicaragua, Honduras and Costa Rica. In rural areas of Nicaragua the disease is colloquially called creatinina.

This CKD epidemic in Central America spans along a nearly 1000 kilometer stretch of the Pacific coast. In El Salvador and Nicaragua alone, the reported number of men dying from this painful disease has risen five-fold in the last 20 years, although some researchers believe hidden cases have always been there and this increment in official data could be partially due to the recent increase in reports and improved case search, pushed by the growing social and political interest in the disease. In El Salvador, the disease has become the second leading cause of death among adult men, and according to a recent editorial, it has been estimated that this largely unknown epidemic has caused the premature death of at least 20,000 men in the region. Science Magazine reports: "In El Salvador alone, PAHO's latest figures say CKD of all causes kills at least 2,500 people in the country each year".

The people affected by the epidemic are mainly young and middle-aged male laborers in the agricultural sector, particularly sugarcane workers. The disease has also been found to be prevalent in other occupations with a high risk of heat stress, implying strenuous work (miners, construction, port and transportation workers) in the high temperatures of the coastlands. The epidemic appears to affect particular Pacific coastal regions of Nicaragua, El Salvador, Costa Rica, and Guatemala.

John Crompton proposed that ancient Bacchanalian rites that had been suppressed by the Roman Senate in 186 BC went underground, reappearing under the guise of emergency therapy for bite victims.

The phenomenon of tarantism is consistent with mass psychogenic illness.

Although the popular belief persists that tarantism results from a spider bite, it remains scientifically unsubstantiated. Donaldson, Cavanagh, and Rankin (1997) conclude that the actual cause or causes of tarantism remain unknown.

The earliest known report of "bakanae" is from 1828; it was first described scientifically in 1898 by Japanese researcher Shotaro Hori, who showed that the causative agent was fungal.

The fungus affects rice crops in Asia, Africa, and North America. In epidemic cases yield losses may reach up to 20% or more. A 2003 publication from the International Rice Research Institute estimated that outbreaks of bakanae caused crop losses that were 20% to 50% in Japan, 15% in Thailand and 3.7% in India.

The infection is treated with antibiotics. Intravenous fluids and oxygen may be needed to stabilize the patient. There is a significant disparity between the untreated mortality and treated mortality rates: 10-60% untreated versus close to 0% treated with antibiotics within 8 days of initial infection. Tetracycline, Chloramphenicol, and doxycycline are commonly used. Infection can also be prevented by vaccination.

Some of the simplest methods of prevention and treatment focus on preventing infestation of body lice. Complete change of clothing, washing the infested clothing in hot water, and in some cases also treating recently used bedsheets all help to prevent typhus by removing potentially infected lice. Clothes also left unworn and unwashed for 7 days also cause both lice and their eggs to die, as they have no access to their human host. Another form of lice prevention requires dusting infested clothing with a powder consisting of 10% DDT, 1% malathion, or 1% permethrin, which kill lice and their eggs.

Boanthropy is a psychological disorder in which a human believes himself or herself to be a bovine.

Epidemic typhus is a form of typhus so named because the disease often causes epidemics following wars and natural disasters. The causative organism is "Rickettsia prowazekii", transmitted by the human body louse ("Pediculus humanus humanus").

As of 2017 there is no commercially available vaccine. A vaccine has been in development for scrub typhus known as the scrub typhus vaccine.

HIV/AIDS is a major public health concern and cause of death in many parts of Africa. Although the continent is home to about 15.2 percent of the world's population, more than two-thirds of the total, some 35 million infected, were Africans, of whom 15 million have already died. Sub-Saharan Africa alone accounted for an estimated 69 percent of all people living with HIV and 70 percent of all AIDS deaths in 2011. In the countries of sub-Saharan Africa most affected, AIDS has raised death rates and lowered life expectancy among adults between the ages of 20 and 49 by about twenty years. Furthermore, the life expectancy in many parts of Africa is declining, largely as a result of the HIV/AIDS epidemic with life-expectancy in some countries reaching as low as thirty-four years.

Countries in North Africa and the Horn of Africa have significantly lower prevalence rates, as their populations typically engage in fewer high-risk cultural patterns that have been implicated in the virus's spread in Sub-Saharan Africa. Southern Africa is the worst affected region on the continent. As of 2011, HIV has infected at least 10 percent of the population in Botswana, Lesotho, Malawi, Mozambique, Namibia, South Africa, Swaziland, Zambia, and Zimbabwe.

In response, a number of initiatives have been launched in various parts of the continent to educate the public on HIV/AIDS. Among these are combination prevention programmes, considered to be the most effective initiative, the abstinence, be faithful, use a condom campaign, and the Desmond Tutu HIV Foundation's outreach programs.

According to a 2013 special report issued by the Joint United Nations Programme on HIV/AIDS (UNAIDS), the number of HIV positive people in Africa receiving anti-retroviral treatment in 2012 was over seven times the number receiving treatment in 2005, "with nearly 1 million added in the last year alone". The number of AIDS-related deaths in Sub-Saharan Africa in 2011 was 33 percent less than the number in 2005. The number of new HIV infections in Sub-Saharan Africa in 2011 was 25 percent less than the number in 2001.