Rarest Diseases in the World

Diseases have affected the population for thousands of years and will likely continue to do so. They may come in the form of bacteria, viral or any number of other problems with bodily systems. How rare individual diseases are, is often very difficult to classify as different definitions can be used. Some diseases which are deemed ‘rare’ may not be rare everywhere in the world. One disease may be rare in one country but still considered an epidemic in others. The diseases presented are therefore a conglomeration of what may be considered ‘rare diseases’ that affect human beings in the world today.

What is rare?

The most basic definition for a rare disease is one that only affects a small portion of the population. Other definitions include a disease that a normal doctor may not see more than one instance of in the course of their entire lifelong practice. In the United States, the National Institute of Heath considers a disease rare if less than 200,000 people suffer from it. Based on that definition, there are about 7,000 different rare diseases in the US and almost one in ten people suffer some form of a rare disease. The European Union considers a rare disease as having less than 1 in 10,000 people suffering from it, which is similar to the United States definition when considering the population of the United States but not very similar when it comes to the countries in Europe.


Lamins are proteins in the body that are part of many different functions and regulations of the cells. Problems with these proteins can result in over fifteen rare genetic disorders which are known as laminophathies. The effects of laminopathies on the body can be quire harmful to sufferers and one of the most harmful of the disorders is Progeria. Also known as Hutchinson-Gilford Progeria syndrome, Progeria causes the premature aging of the body. Only around 1 in 8,000,000 children develop Progeria and few live past the age of the thirteen.


Unfortunately, some rare disease are inherited or can be inherited. Examples of two of these diseases are Von Hippel-Lindau syndrome (VHL) and Fibrodysplasia ossificans progressive (FOP). VHL is a genetic condition whereby tumors spontaneously grow in different areas of the body. Most of the tumors are benign but untreated tumors can cause many other problems which could lead to death. The only treatment is to surgically remove the tumors that could cause problems. Only about 1 in every 35,000 people are affected by VHL.

FOP is far rarer than VHL and affects the body’s connective tissue (tendons, ligaments, muscle). After receiving an injury to the connective tissue, instead of healing, the tissue will actually transform into bone or bone will grow in the damaged area. There is unfortunately no cure for this disorder and 1 out of 2 million people suffer from this debilitating condition.


Proteins called prions, pronounced ‘pree-ons’, are responsible for several rare human diseases if they are transformed into abnormal prions. The abnormal prions are transmissible and affect the healthy prion proteins which are found predominantly in the brain but also other areas of the body, in lower amounts. The abnormal Prions unfold the prion proteins which results in brain damage and a progression of symptoms which is always fatal. Two neuro-degenerative diseases caused by these pathogens are Kuru and Creutzfeldt-jakob disease (CJD).

Kuru is a very rare prion disease that only occurs in a remote area of New Guinea in members of the Fore tribe. As a result of the historic practice of cannibalism and consuming the dead members of the tribe, many members contracted Kuru. The name means ‘laughing disease’, which was so named because of the fits hysterical laughter that the infected individuals experienced. There have been no new cases since the 1950s when cannibalism was abolished in the area and the only way to become infected would be to eat the brain of an already infected tribe member.

CJD is a rare disease that occurs naturally in populations. Normal prions may spontaneously become transformed into abnormal prions or become transformed because of an inherited mutation. Within one year of the onset of CJD, patients will usually die. Only about 1 to 2 people per 1,000,000 will develop this disorder. In addition to CJD, there also exists Variant CJD which is linked to Mad Cow disease and can develop from the ingestion of contaminated meat. However, even if contaminated meat is ingested, this does not mean that Variant CJD will occur.


Viruses are responsible for several rare diseases in the world. Two examples of rare viral disease are Ebola and Polio. The initial infection by the Ebola virus, also known as Ebola hemorrahagic fever, is believed to be the result of zoonotic (animal-borne) transfer from an infected animal. Once infected, a person can spread the disease to others through several means which can result in an outbreak. Direct contact with an infected person’s secretions, blood, or contaminated objects can result in transmission. Aside from cases in areas of Africa, the Ebola virus is quite rare in every other continent.

Polio, short for poliomyelitis, was a worldwide epidemic in the mid 1800s to the mid 1950s that caused damage to the nerves which could result in full or partial paralysis. Spread by the poliovirus, the infection entered through the nose or mouth and was transferred though contact with the mucus or faeces of an infected person as well as through person-to-person contact. Since the development of the polio vaccine, few cases occur in most developed countries and it has essentially been removed from many countries; however there are still outbreaks of the virus in undeveloped countries of the world.


Bacteria are also responsible for causing several rare diseases around the world. Two such diseases are leprosy and the bubonic plague. Leprosy, also known as Hanson’s disease, is caused by the bacterium mycobacterium lepraa and has been known to be around for thousands of years. The bacteria cause lesions and sores on the skin as well as cause sensation loss which could lead to permanent nerve damage. About 250,000 new cases of leprosy are diagnosed each year worldwide with only 100 to 200 cases in the United States and other developed countries. Leprosy is treatable but not every area in the world has access to the antibiotics required to get rid of it.

The bubonic plague, also known as the Black Death, has caused several epidemics that have been recorded as early as the 1300s. The bacterium responsible is Yersinia pestis, sometimes shortened to Y-pestis, and it typically infects small rodents or mammal and can be transferred to humans by fleas or through handling an infected animal. The plague can then be spread to other people by direct person-to-person contact or through water droplets in coughs. Responsible for killing millions over the course of several epidemics, the bubonic plague still remains in existence today in isolated areas all over the world but early treatment can increase the chances of surviving this rare disease.

Laboratory diseases

Though considered eradicated, some diseases that were once epidemics still exist today and can be considered rare diseases. A select number of laboratories in the world do keep samples of many diseases for study and one example would be small pox. The variola virus, which causes small pox, is very contagious and was often fatal to those that were infected. It has been around for thousands of years and was spread by face-to-face contact for prolonged periods as well as direct contact with fluids from an infected person or contaminated objects. Though eradicated worldwide as an epidemic in 1977, there have been several accidental exposures of the virus to unfortunate researchers that have occurred since the. A vaccine was once given out but after the eradication, routine vaccinations for small pox were stopped.

Fields’ condition

Quite possibly the rarest of all known diseases in the world is Fields’ condition. This disease was only recently discovered in two twins from the United Kingdom. Since it has never been seen before and only two patients have been diagnosed with it, it has basically affected two people out of all the world’s population. Fields’ condition is characterized by continued muscular degeneration but other symptoms could develop over time.