Eradication of Infectious Diseases and Risk of Re-Emergence

The eradication of infectious diseases means that diseases like smallpox that are passed from person to person have been reduced to zero worldwide. By contrast, the elimination of an infectious disease like polio means that it has been reduced to zero in a specific area or geographical region.

To date, only one disease—smallpox—has been eradicated worldwide, while several others have been declared eliminated. Even so, some previously eliminated diseases like measles have experienced a resurgence due to vaccine hesitancy and anti-vaccine sentiments that increased after the COVID-19 pandemic. Others have re-emerged due to poverty and failures in public health.

Dracunculiasis (Guinea Worm Disease)

Dracunculiasis (Guinea worm disease) is a parasitic infection transmitted by the ingestion of larvae in contaminated water. Dog feces are common vectors for infection.

Guinea worm disease doesn’t cause symptoms at first, but, around a year after the infection, painful blisters will begin to form on the feet and legs. As the blisters rupture, narrow worms several inches long begin to work their way out of the skin.

Although Guinea worm disease doesn’t cause death or long-term disability, it can cause extreme pain and distress as the worms exit the body over the course of several weeks. Severe gastrointestinal symptoms and fever are also common.

Due to mass treatment programs involving a cocktail of three antiparasitic drugs (as well as the containment of stray dogs), the global incidence of dracunculiasis has dropped from 3.5 million in 1986 to 54 in 2019. Even so, Angola, Chad, South Sudan, Ethiopia, Mali, and Cameroon are still faced with the disease.

There is no vaccine for Guinea worm disease.

Hookworm

Hookworms are among a group of parasitic worms that cause a type of infection known as helminthiasis. Hookworms are found in many parts of the world, typically those with poor access to clean water and sanitation. The infection occurs when the larvae come in contact with and penetrate the skin.

Hookworm infection occurs in the intestines and typically starts with a localized rash. This is soon followed by other symptoms, including abdominal pain, diarrhea, loss of appetite, weight loss, and anemia-induced fatigue.

In the early part of the 20th century, an estimated 40% of people living in the southern United States had hookworms. Indoor plumbing and improved sanitation halted its spread, and today helminthiasis is no longer the endemic disease it once was.

Today, an estimated 576 to 740 million people around the world are affected by hookworms, resulting in over 65,000 deaths each year. Even so, improvements in community sanitation and hygiene have reduced the global incidence of hookworms.

Lymphatic Filariasis

Lymphatic filariasis (LF) is a chronic parasitic infection spread by mosquitos. The parasites, called filarial worms, are deposited in the lymphatic system where they cause no disease.

However, in some people, the parasitic worms can “clog” the lymphatic system and lead to a condition known as elephantiasis in which the arms, legs, breasts, or genitals swell to an enormous size.

From 2000 (when the global effort started) to 2020, 8.6 billion cumulative treatments were delivered at least once to more than 910 million people in 68 countries. In 2019, 538 million people were treated for LF in 38 countries. The mass drug effort has thus far lead to the elimination of LF in six endemic countries.

While officials with the World Health Organization (WHO) suggest that the campaign has averted 9.5 million infections, over 120 million people are believed to be infected with this difficult-to-eliminate parasite.

Malaria

Malaria, a mosquito-borne disease affecting millions worldwide, is caused by a parasite of the genus Plasmodium. Symptoms develop anywhere from seven to 30 days after exposure, leading to shaking chills, headache, muscle aches, and tiredness. The severity of symptoms can vary by the species of Plasmodium.

In 2021, the WHO estimated there were around 247 million new cases of malaria worldwide, with over 619,000 deaths.

Malaria containment efforts are mainly focused on the use of preventive medications (like chloroquine), mosquito repellents and netting, and mosquito eradication.

These preventive efforts—along with improved malaria treatments and a malaria vaccine—have begun to pay off, leading to a steep reduction in the number of malaria-related deaths since the 1.2 million deaths that occurred between 1990 and 2013.

Despite these gains, new infection and death rates have stagnated in recent years.

Measles

Measles is a highly infectious disease caused by the measles virus. It is spread through respiratory droplets produced from coughing or sneezing. Symptoms usually develop 10 to 12 days after exposure and last for a week to 10 days. They include fever, cough, runny nose, inflamed eyes, and a widespread rash.

In developed countries, one in four people with measles will require hospitalization and one in 1,000 will die. In parts of the developing world, the fatality rate can be as high as 30%. In 2018 alone, over 134,000 measles-related deaths were reported worldwide.

Measles can be stopped with the MMR (measles, mumps, rubella) vaccine widely given to children in the United States.

Since the measles vaccine was first licensed in 1963, the incidence of the disease has steadily declined to where it was officially declared eliminated in the United States in 2000. The same was seen in Canada, the United Kingdom, and parts of Europe.

Global vaccination efforts have led to a 65% reduction in the annual incidence of measles, from 28,340,700 in 2000 to 9,828,400 in 2019. Deaths have also dropped by 62%, from 539,000 in 2000 to 207,500 in 2019.

Mumps

Mumps is a highly contagious infection caused by the mumps virus. It starts with flu-like symptoms such as fever, headache, tiredness, muscle pain, and loss of appetite before eventually causing painful swelling on one side of the face (due to swelling of the parotid gland). Complications include deafness, infertility, seizures, and kidney injury. Death is rare.

Mumps is found worldwide, with over 500,000 cases reported annually. Mumps cases typically peak in late winter or early spring.

Due to the efficacy and widespread use of the MMR vaccine, the annual number of mumps infections in the United States has dropped from over 150,000 cases in the mid-1960s to around 1,000 now. With that said, mumps has never been eliminated in the U.S., unlike measles or rubella.

In fact, the only country to ever declare mumps eliminated was Finland back in 1997. In order for elimination and “herd immunity” to be achieved, WHO advised that over 95% of a given population needs to be vaccinated.

Onchocerciasis (River Blindness)

Onchocerciasis (river blindness) is the second-most common cause of blindness worldwide. The parasitic infection involves a worm, called Onchocerca volvulus, that is transmitted to humans by black flies that breed near fast-flowing rivers and streams.

Once inside a body, the worms can produce thousands of larvae that spread to the eyes and skin causing vision loss as well as itching, skin nodules, and “lizard skin.”

While extremely rare in the United States, river blindness causes widespread vision loss in parts of the world where the disease is endemic. An estimated 99% of cases occur in Africa.

In 2017, an estimated 21 million people were infected with Onchocerca volvulus. Of these, 1.2 million experienced permanent vision loss or blindness.

Prevention and treatment are key to reducing the incidence of onchocerciasis. The prevention of river blindness can be achieved in part with insecticides like DEET and permethrin. Mass treatment programs involving the twice-yearly use of the antiparasitic drug ivermectin may further reduce the number of symptomatic infections in heavily hit populations.

In 2018, drug treatment was delivered to 151 million people with 100% coverage in some regions. While no country in Africa is free of the disease, four of six endemic countries in Latin America have declared river blindness eliminated. It is hoped that perseverance will lead to the same on the hard-hit African continent.

Polio

Polio, also known as poliomyelitis, is an infectious disease caused by the poliovirus which is spread primarily through sewage-contaminated water. Up to 95% of infections are asymptomatic (without symptoms). However, in 0.5% of cases, the infection can damage nerves and membranes surrounding the brain and spinal cord, causing paralysis in the legs and sometimes the face.

Most people with polio survive, but 5% to 10% of those who become paralyzed die due to paralysis of the diaphragm and respiratory arrest.

Polio has been around for centuries and first reached epidemic proportions in 1916 in New York City, causing over 2,000 deaths in its five boroughs. By the 1940s, around 35,000 people in the United States were permanently disabled by the poliovirus every year.

That all changed in 1955 with the widespread release of the Salk polio vaccine. Subsequent versions progressively reduced the annual incidence of infection to where polio was all but eliminated by the early 2000s in many developed countries.

Of the three types of poliovirus, type 2 and type 3 were declared eradicated in 2015 and 2018, respectively. The last evidence of type 1 transmission in Nigeria was reported in 2018. Afghanistan and Pakistan are the only two countries where polio is still endemic.

In the United States, polio was declared eliminated in 1979.

Rubella

Rubella (also known as German measles) is a respiratory virus that manifests with a rash, fever, swollen glands, and joint aches. Those most seriously affected are infants of mothers infected during pregnancy. Congenital rubella causes possible heart, liver, spleen, and brain damage as well as deafness and cataracts.

During the last major rubella epidemic in the United States (1964 to 1965), an estimated 12.5 million people were infected, 11,000 pregnant women lost their babies, and 2,100 newborns died.

Rubella can be prevented with a rubella vaccine, which was first licensed in 1969 and is included in the MMR vaccine. As a result of mandatory vaccinations in all 50 states and the District of Columbia, rubella was declared eliminated in 2004.

Several other developed countries have not fared as well.

From 2018 to 2019, a total of 4,622 cases of rubella were reported in Japan due to the unavailability of the MMR vaccine. Because of manufacturing problems that led to cases of aseptic meningitis in the 1980s and 90s, the vaccine has not been available there since 1993. In 2023, the widespread distribution of a newly approved MMR vaccine aims to reverse the trend in Japan.

Smallpox

Smallpox, a disease transmitted through droplets (usually expelled by coughing) as well as person-to-person contact, was the first infectious disease declared eliminated with the use of a vaccine.

In 1977, the world saw the last natural case of smallpox, which involved a man in Somalia with a mild form of the virus (called Variola minor). The last natural case of the more deadly variant (V. major, which kills 30% of those infected) was reported in a toddler in Bangladesh in 1975.

Global vaccination efforts and the building of herd immunity eventually led to smallpox’s eradication.

Despite the continued absence of smallpox worldwide, the United States keeps millions of doses of the vaccine in storage just in case. One of the concerns is the threat of bioterrorism given that Russia and the United States were said to have produced tons of the virus as a biological weapon in the Soviet era.

Yaws

Yaws is a chronic bacterial infection caused by Treponema palladium pertenue, a bacteria related to syphilis. Yaws is spread by skin-to-skin contact and most commonly affects children in tropical regions of Africa, Asia, and Latin America.

Yaws infection starts with an isolated skin sore that, if scratched, can cause the bacteria to spread. If left untreated, the sores can cause scarring and disfigurement on the face, arms, legs, and buttocks.

Late-stage disease often manifests with bone pain, swollen fingers, and destruction of the tissues of the nose, upper jaw, palate, and throat.

A campaign of mass antibiotic treatment nearly eradicated yaws in the 1950s and 1960s. Even so, over 300,000 new cases were reported in 15 countries between 2008 and 2012, and yaws is considered endemic in 15 of them.

There is no vaccine for yaws.

Summary

Smallpox is the only infectious disease to be declared eradicated in the world. With continued global effort, polio may be poised to eventually do the same having been eliminated from the United States and other countries.

Diseases that have been eliminated to varying degrees but not eradicated include guinea worm disease, hookworm, lymphatic filariasis, malaria, measles, mumps, river blindness, rubella, and yaws.