Epidemiology, Infectious Diseases, rare infectious disease, Viruses

3 Rare Infectious Diseases Caused by Viruses | Rare Diseases, Viruses

Author Chandana Balasubramanian , 15-May-2024

Did you know that around 300 million people globally are living with one of the over 7,000 identified rare diseases?


While genetics are behind about 80% of these conditions, viruses also play a key role in causing some of them, including those that are life threatening [1, 2].


Let’s explore how viral infections can trigger these less common but impactful diseases and expand our understanding of their intricate dynamics.


What is a rare disease?

In the United States, the definition of a rare disease stems from the 1983 Orphan Drug Act, which identifies these conditions as those affecting fewer than 200,000 people. The Rare Disease Act of 2002 reaffirmed this definition [3, 4].

Across the Atlantic, the European Union’s legislation from the year 2000 sets the threshold for a rare disease as one that affects fewer than 1 in 2,000 people [3].

The collective impact of many rare diseases on a global scale is profound, affecting millions with devastating health outcomes, significant economic burdens, and challenges in accessing timely and effective treatments.


Why should we be concerned about rare diseases?

Rare diseases affect nearly 300 million people globally, making their impact significant on a worldwide scale. They are also often debilitating [1].

Approximately 80% of those affected struggle to complete daily tasks. This is especially concerning as half of all rare diseases impact children, and tragically, 30% of these children will die before they turn five years old [5].

Getting the right diagnosis for a rare disease can also be a long and frustrating process, often taking 5 to 7 years. During this time, misdiagnoses are common, as initial symptoms may not lead doctors to the correct conclusion until the disease progresses [6].

Additionally, treatments for rare diseases are often as scarce as the conditions themselves, leaving many without standard care therapies. This lack of treatment highlights the urgent need for more research and better support for those affected by these challenging conditions [6].

The broader impact of rare conditions extends beyond the individual, significantly affecting families and communities by imposing economic burdens, complicating chronic care coordination, and necessitating a transition from pediatric to adult care for children with these conditions.

Let’s explore 3 rare infectious diseases caused by viruses.


Subacute sclerosing panencephalitis (SSPE)

Subacute sclerosing panencephalitis (SSPE) is a devastating rare disease triggered by the measles virus, a single-stranded RNA virus from the Paramyxoviridae family.

With no cure or effective treatment, SSPE has a high death rate. Sadly, it mostly affects young children and infants.

SSPE highlights the vital importance of vaccination. The measles vaccine doesn’t just prevent measles; it also protects against SSPE. This shows how valuable the measles vaccine is for long-term health and safety [7].

For pregnant women, this preventive measure is crucial to avoid complications like SSPE and reduce the risk of birth defects.

However, recent trends in vaccine hesitancy and declining rates of the MMR (measles, mumps, and rubella) vaccine have led to a concerning increase in measles cases among children.

This rise in measles infections has led to more SSPE cases. This shows the urgent need for strong vaccination efforts to prevent measles and its serious long-term effects, such as SSPE.


The incidence of SSPE is estimated at 4-11 cases per 100,000 measles cases. However, the rate is higher after infant measles, about 1 in 5,555. Estimates show that it can be 1 in 3,000 for children under 5 and as high as 1 in 609 after infant measles [8].

SSPE does not spread from person to person.

Death rate

The prognosis for Subacute sclerosing panencephalitis (SSPE) is quite severe. Most individuals diagnosed with SSPE will pass away within one to three years. Additionally, in some cases, the disease progresses very quickly, leading to death within just three months of diagnosis [9].

Death is usually due to a high fever or heart or brain failure.

Endemic regions

SSPE is commonly found in regions with low measles vaccination rates, including parts of Africa, Asia, and some areas in Eastern Europe.

  • United States: 4-5 cases of SSPE in a year [10].
  • United Kingdom and Europe: When the United Kingdom experienced a low period of measles infections in the 1990s, there were no cases of SSPE in children under 16 for almost 15 years. However, a resurgence of measles across the European Union from 2016 to 2019 corresponded with the reporting of six pediatric SSPE cases between 2017 and 2019, highlighting the direct impact of measles outbreaks on SSPE incidence [8].
  • Asia: Reports from India suggest a high incidence of SSPE at 21 per million cases [9].


Notable outbreaks

From 2016 to 2019, as a significant measles epidemic swept through Europe, 6 cases of pediatric subacute sclerosing panencephalitis were reported (between 2017 to 2019) [8].

These cases highlight the serious long-term consequences of measles outbreaks, particularly the risk of developing SSPE in children exposed to the virus at a young age.


SSPE is a progressive neurological disorder primarily affecting children and young adults, often leading to death within one to three years of diagnosis.

Symptoms typically manifest in individuals who have a measles infection at a very young age, usually before the age of two. The condition progressively impairs neurological functions, reflecting its severe impact on the brain.

Early signs of SSPE

  • Mild memory loss and cognitive decline
  • Behavioral changes, such as increased irritability
  • Myoclonic jerks: motor issues, including uncontrollable jerking movements
  • Seizures
  • Potential blindness [12].


Advanced stages of SSPE

  • Muscle stiffness and loss of ability to walk
  • Progression to a comatose state and then a persistent vegetative state [12].


Death is typically due to fever, heart failure, or when the brain loses control over the nervous system [12].


Diagnosis of SSPE involves evaluating clinical symptoms, measuring anti-measles antibody titers in cerebrospinal fluid or serum, and using EEG and neuroimaging results [13].


Unfortunately, there is no cure for SSPE and no treatment. This makes it even more important for more people to get the measles vaccine and prevent getting an SSPE infection.

Ongoing clinical trials are crucial for the development of future treatments, offering hope for those affected by rare disorders like SSPE.


SSPE prevention is best through timely measles vaccination for children and maintaining high vaccination coverage in the community.

The measles vaccine is typically a part of the MMR vaccine, which also protects against mumps and rubella (also known as German measles).



Ebola is a rare disease with severe health consequences, including a high fatality rate of up to 90% [14]. Ebola can spread between humans and can quickly become a global threat without strong surveillance and effective public health measures.

In fact, that’s why Ebola is considered a Category A disease by the Centers for Disease Control and Prevention (CDC) for its potential to be a bioweapon and cause a pandemic [15].

Ebola is caused by infection with one of the four ebolaviruses within the Ebolavirus genus of the Filoviridae family (the deadly Marburg virus is a part of this family) [14].


Ebola incidence varies by region and year. The disease was first documented in 1976 in Sudan, Africa.

Death rate

Ebola has an average mortality rate of 50%, ranging from 25%-90% [14].

Endemic regions

Ebola is endemic to rural areas in Sudan, the Democratic Republic of Congo, Gabon, the Republic of the Congo, and Uganda [16].

Notable outbreaks

Ebola outbreak map, GIDEON infectious diseases database

Ebola outbreaks map 1976-2023. GIDEON Infectious diseases.

2014-2016: West Africa saw the largest Ebola outbreak that spanned several countries. According to the World Health Organization (WHO), it was the biggest one since the disease was first discovered [14].

Get the complete list of Ebola outbreaks and information on 30,000+ disease outbreaks on GIDEON, a leading infectious disease database.


Ebola symptoms include:

  • Fever
  • Severe headache and muscle and joint pain
  • Weakness and fatigue
  • Sore throat
  • Loss of appetite
  • Abdominal pain, diarrhea, and vomiting
  • Unexplained bleeding, bruising, or hemorrhaging [17].


It can be difficult to diagnose Ebola early because even though it is a rare disease, symptoms are similar to those of the flu, malaria, and other common illnesses.


Ebola is diagnosed through laboratory tests detecting the virus’s genetic material or antibodies in blood samples. Early symptoms may also prompt initial clinical suspicion.


Ebola treatment includes supportive care with fluids, electrolytes, and oxygen therapy. Experimental treatments like antiviral drugs and monoclonal antibodies may also help.

Inmazeb and Ebanga are two monoclonal antibody therapies approved for Ebola [18].

Early medical care increases survival chances.


Preventing Ebola involves vaccination, good hygiene, and avoiding contact with infected individuals.

There is a single-dose Ebola vaccine called ERVEBO (rVSVΔG-ZEBOV-GP) approved by the US FDA to be administered to people at the highest risk of getting an Ebola infection.

Clinical trials show that the vaccine reduced the mortality rate by half. However, the vaccine is not commercially available yet [19].

Addressing nutritional deficiencies is also crucial in the prevention strategy for rare diseases like Ebola, as it strengthens the body’s resistance to infections and mitigates the risk of complications.


Herpes simplex encephalitis (HSE)

Herpes simplex encephalitis (HSE) is a severe condition caused by herpes simplex viruses, specifically HSV-1 and HSV-2, which are large double-stranded DNA viruses in the Herpesviridae family [20].

This rare disorder is significant because about 57% of American adults are infected with HSV-1, the main cause of HSE, though most never show symptoms. If symptoms develop, the rare disease can be fatal, making early diagnosis and treatment crucial [2-].

While the herpes virus can spread from person to person, encephalitis occurs when the virus enters the brain. As a result, HSE, specifically, cannot be transmitted between individuals.


The annual incidence of HSE is about 2 to 4 cases per million people worldwide [20].

Death rate

Without treatment, up to 70% of patients die, and even with proper treatment, mortality is still 20% to 30% [20].

Endemic regions

HSE is not endemic to any particular region and can occur anywhere.

Notable outbreaks

No notable outbreaks. Sporadic occurrences have been reported.


Symptoms of HSE include:

Initial HSV infection

  • Painful, recurring blisters or ulcers
  • Fever
  • Body aches
  • Sore throat (oral herpes)
  • Headache
  • Swollen lymph nodes near the infection [21].


HSE-specific symptoms

  • Affects the temporal lobes and the limbic system
  • Meningeal congestion
  • Extensive lesions in immunocompromised patients
  • Lesions in the brainstem, cerebellum, and cerebral cortex [21].



HSE diagnosis is through PCR-based testing of cerebrospinal fluid, which detects the presence of HSV DNA [22].


There is no cure for herpes simplex encephalitis. Treatment involves antivirals to help reduce the severity of symptoms [20, 22].


There is no vaccine to help prevent HSE. Younger children and older adults are at the highest risk of getting an HSE infection.



Understanding rare diseases caused by infectious agents like viruses is crucial for public health. Tracking, studying, and finding better ways to prevent and treat these conditions can save lives and reduce suffering. SSPE, Ebola, and HSE are three such rare disorders, each presenting unique challenges.

SSPE, resulting from measles infection, shows the importance of vaccination. Ebola, with its high fatality rates and potential for global spread, highlights the need for rapid response and robust public health measures.

HSE, a viral infection caused by herpes simplex viruses, demonstrates the importance of early diagnosis and treatment to prevent severe brain damage or death.

By investing in research and improving diagnostic tools, we can enhance our ability to combat these rare diseases. Increased awareness and education can lead to better prevention strategies and more effective treatments, ultimately reducing the impact of these devastating illnesses. For those seeking more detailed information on symptoms, causes, treatments, and support, the NORD Rare Disease Database is a valuable resource for patients and families.


The GIDEON difference

GIDEON is one of the most well-known and comprehensive global databases for infectious diseases. Data is refreshed daily, and the GIDEON API allows medical professionals and researchers access to a continuous stream of data. Whether your research involves quantifying data, learning about specific microbes, or testing out differential diagnosis tools– GIDEON has you covered with a program that has met standards for accessibility excellence.

Learn more about more rare diseases and viral infections on the GIDEON platform.


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Chandana Balasubramanian

Chandana Balasubramanian is an experienced healthcare executive who writes on the intersection of healthcare and technology. She is the President of Global Insight Advisory Network, and has a Masters degree in Biomedical Engineering from the University of Wisconsin-Madison, USA.

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