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The Deadly Seven: Where Are These Diseases Now?

Medically reviewed on Jun 12, 2017 by C. Fookes, BPharm

The Black Death: Bubonic Plague

The Black Death ravaged most of Europe and the Mediterranean from 1346 until 1353. Over 50 million people died, more than 60% of Europe's entire population at the time.

Many historians believe it started in the Steppes of Central Asia, a vast area of grassland that even today still supports one of the world's biggest plague reservoirs - an area where rodents live in great numbers and density (also called a plague focus).

Plague is mainly spread through the bite of a flea infected with the plague-causing bacterium, Yersinia pestis. Fleas typically live on small animals such as rats, gerbils, marmots and squirrels and periodically, explosive outbreaks of plague occur among these susceptible hosts. Huge numbers of animals succumb to infection and die. Hungry fleas turn to humans and within three to five days of a bite, fever, headache, chills, and weakness develop. Lymph nodes closest to the bite site swell to form a painful bubo in the variant of plague known as bubonic plague. Infection may spread throughout the blood stream and affect respiration in the lungs. Without prompt antibiotic treatment, 80% of infected people die within five days.

Is Plague Lurking In A Town Near You?

The epidemic of plague in the 14th century was not the only significant plague outbreak recorded in human history. The first reported pandemic broke out in Egypt in 541 and was designated “The Plague of Justinian”. The last major plague event began in the war-torn Yunnan province of China, reaching Hong Kong in 1894.

Even today, plague has not been eradicated, although thanks to the availability of vaccination and antibiotics, few people now die of it. Plague foci still exist in Africa, North and South America, and Asia. Between 2010 and 2015 there were 3248 cases of plague reported worldwide, including 584 deaths. Most cases have occurred in Madagascar, The Democratic Republic of Congo, and Peru.

In the United states alone, 1006 confirmed or probable cases of plague occurred between 1900 and 2012; 80% of which were classified as the bubonic form. In recent years, incidence has ranged from one to seventeen cases (average of seven per year) per year, with most occurring in the rural west.

The Speckled Monster: Smallpox

The origins of smallpox have been lost in prehistory but research suggests it first appeared around 10,000 BC. Telltale pockmarks adorn the the mummified remains of the great Egyptian Pharaoh Ramses V (dated at 1156 BC) and the disease is described in ancient Sanskrit texts.

Smallpox is caused by the variola virus. Humans are the only natural hosts of smallpox and transmission depends upon direct contact with an infected person or infected bodily fluids, contaminated bedding or clothing. Airborne transmission is rare, although is more likely in enclosed settings such as buildings, buses, and trains.

An incubation period of up to 17 days (average 12 to 14) follows exposure to the virus and people are not contagious at this time. Initial symptoms are generally flu-like before small spots start to develop inside the mouth and on the tongue. Within 24 hours a rash starts on the face and quickly spreads before evolving into raised volcano-like pustules filled with a thick, opaque fluid. These pustules may take up to two weeks to scab over, leaving marks on the skin that eventually become pitted scars.

Yearly Death Rate In The 1800's Was 400,000 From Smallpox

During the 18th century, over 400,000 people died annually in Europe from smallpox. Overall fatality rates were around 30%; however, rates were much higher in infants (80-98%), and one third of all survivors went blind.

One thing was obvious among survivors of the disease - they never caught it again. This observation started the human fight against smallpox. First came variolation which involved blowing dried smallpox scabs up a person's nose, deliberately infecting them with the disease.

Inoculation used a lancet to transfer the contents of a smallpox pustule under the skin of a non-immune person. It was a bit risky - some people developed smallpox from the procedure or contracted other diseases such as tuberculosis or syphilis. But fatality rates associated with inoculation were 10 times lower than those associated with naturally occurring smallpox.

In the late 1700s, at least two people acted on the observation that dairymaids who had cowpox, never contracted smallpox. In 1774, Benjamin Jesty used material from cows with cowpox to inoculate his wife and two young sons. In 1796, Dr Edward Jenner used matter from a cowpox-infected young dairy maid to protect an 8-year old boy. Two months later he inoculated the same boy with smallpox, and no disease developed. Dr Jenner's work paved the way for vaccination as we know it today.

A Victory For Vaccination

The last known case of smallpox was in Somalia in 1977. According to the World Health Organization (WHO), smallpox has been successfully eradicated worldwide. This global success is attributed to a mass vaccination campaign that began in 1967 and continued until the WHO announced that the disease had been eliminated.

Although the disease has been eliminated, both the Centers for Disease Control and Prevention (CDC) and the WHO have concerns that the virus could be used for bio-terrorism. This topic has been dramatized in movies, books and TV shows. Although the possibility of smallpox being used as a biological weapon deserves consideration, the actual risk is likely very low. However, strategies are in place to protect the public should this ever happen and large quantities of the smallpox vaccine have been stockpiled.

Severe Acute Respiratory Syndrome (SARS)

Time Magazine, 5th May 2003

The history of SARS was short but not so sweet.

SARS generated widespread panic in 2003 and was caused by a previously unknown coronavirus (SARS-CoV) - the same family of viruses that causes a cold. Symptoms began two to ten days after coming into contact with the virus and included a high fever, headache, body aches, sometimes diarrhea. But the main symptom of concern was the severe breathing difficulties associated with SARS, and almost all those infected developed pneumonia. By the end of 2003, 774 people had died out of the 8,098 infected people notified to WHO. Many more people needed to be hospitalized for breathing assistance.

SARS is spread through close contact with infectious droplets released during a cough or sneeze. SARS started in Asia, and researchers have identified the most likely source as wild Chinese Horseshoe bats that had been caught and brought to market. These bats harbored a SARS-like virus that subsequently infected civets before mutating; which meant that humans were now susceptible to the virus. Within a year, the infection had spread to more than two dozen countries before it was contained through public health measures.

Risk Of SARS And Similar Illnesses Remain A Public Health Concern

One of the most concerning facts about viruses, particularly those of the coronavirus virus family, is their ability to rapidly mutate (change).

Worldwide, surveillance is ongoing for another outbreak of SARS. In the U.S., the CDC has joined forces with critical federal and healthcare providers to create guidelines and policies that outline the appropriate local and national response should transmission of SARS-CoV recur.

Middle East Respiratory Syndrome (MERS), is another coronavirus infection that can be fatal. Outbreaks of MERS are ongoing, with 25 cases reported in Saudi Arabia between the 21st April and the 29th May, 2017. MERS can cause severe respiratory and kidney failure, and may be linked to contact with dromedary camels.

Avian Influenza: Not Just One For The Birds

Just like humans, birds get the flu.

Bird flu - also called Avian influenza - is common and several major outbreaks have occurred sporadically worldwide since the disease was first recorded in Italy in 1878. It took until 1955 to discover that the virus causing bird flu was an influenza type A virus.

Avian influenza occurs naturally among wild aquatic birds and can easily spread to more susceptible farmed poultry - millions of chickens, geese, and turkeys were destroyed to prevent further spread of the disease following the outbreaks that occurred in 2015 and 2016.

Avian flu viruses rarely infect humans. The exceptions are the H7N9 and H5N1 strains of influenza A. H7N9 is considered the influenza A virus with the greatest potential public health impact. Currently, China is experiencing its fifth outbreak of influenza A H7N9 virus, with 688 human cases reported since May 23, 2017. Poultry have been confirmed as the source.

Ebola: On The Radar Again

Ebola is a severe, often fatal disease (death rates average 50% [range 25-90%]), caused by the Ebola filovirus. There are five different types of ebola virus, four of which are known to cause disease in humans.

Ebola was first discovered in 1976 and bats are thought to be the most likely reservoir (natural permanent host) of the virus. The virus readily spreads to humans, and from human-to-human. Direct contact (through broken skin or mucous membranes) with an infected person or animal (either living or dead), or with objects such as contaminated needles and syringes is the most common way Ebola is spread. Cases of sexual transmission from people who have survived the virus have also been reported, months after their recovery.

Symptoms may appear from two to 21 days (average 8-10 days) after exposure to the virus and include fever, severe headache, muscle pain and weakness, diarrhea, vomiting, bleeding and bruising, and death. Survivors develop antibodies that protect them from further infection for at least 10 years. The most significant outbreak of Ebola in recorded history occurred from 2014 to 2016, predominantly in Guinea, Sierra Leone and Liberia.

Ebola: Risk is Low As Long As Sensible Precautions Are Taken

Reports issued by the CDC indicate that 28,616 people were infected with confirmed or probable Ebola, and 11,310 died over the course of the 2014-2016 outbreak. In the U.S., eleven people were documented as having Ebola; four of whom had developed symptoms once back in the Unites States. Seven of the 14 had been medically evacuated from other countries. Two died.

On the 9th of June, 2016, the World Health Organization (WHO) declared the end of Ebola outbreak in Liberia. This came 42 days after the last confirmed Ebola patient in Liberia tested negative for the disease for the second time.

There is always a risk of Ebola in countries with very weak health systems and where the virus is prevalent in wild animals. However, the risk to most is very low as long as travelers avoid sick people, body fluids, and Ebola treatment centers. Although there is no treatment for Ebola, an experimental vaccine, called rVSV-ZEBOV, has been shown to be highly protective against the virus in a major trial involving 11 841 people in Guinea. Among the 5837 people who received the vaccine, no Ebola cases were recorded 10 days or more after vaccination, compared with 23 cases in the group that did not receive the vaccine.

Leprosy: A Feared Disease That Features In The Old Testament

Leprosy is an infection caused by the slow growing bacterium, Mycobacterium lepraehas. It has a long incubation period - two to three years (range 6 months to 40 years) and symptoms usually start as a numbness or loss of feeling in a defined area of skin - reflecting the affinity of the bacterium for nerve cells.

Despite not being very contagious, leprosy has been feared and misunderstood throughout its history. Initially thought to be a curse or a punishment from God, leprosy sufferers were stigmatized, forced to wear special clothing or ring bells to warn others when they were approaching. Symptoms vary from person to person, and tend to progress with time; ranging from mild, indeterminate hypopigmented skin lesions to blindness, deformity and severe facial disfigurement.

Still Prevalent, But Curable With Prolonged Treatment

Leprosy is still prevalent today, affecting about 12 million people in low lying, humid, tropical and subtropical areas found near the equator. Seventy percent of all cases occur in three countries; India, Indonesia and Myanmar. In the U.S. about 100 new cases of leprosy are reported to the CDC each year, most of which involve immigrants from developing countries. However, in 2015, two people acquired leprosy after contact with a nine-banded armadillo. Approximately 15% of armadillos in southern Texas and Louisiana have been found to harbor the bacteria.

Drug treatment of leprosy is prolonged and complicated and usually involves a combination of antibiotics (such as dapsone, rifampin, and clofazimine) for at least six months, in most cases longer. In some countries, thalidomide - a drug most famous for causing birth defects in the 1950s and 60s - is used to treat complications of leprosy such as erythema nodosum leprosum.

Although leprosy is curable, deformities and nerve damage that occur before treatment begins are often irreversible.

The Most Dreaded Childhood Disease Of The 1940-50s: Polio

Polio is a crippling infectious disease that is often fatal. Children under the age of five are especially susceptible. Although periodic epidemics occurred during the late 19th century, it was the spike in prevalence that occurred in the 1940s and early 1950s that triggered the start of the worldwide campaign of polio vaccination.

Polio is caused by the very contagious and resilient poliovirus and spreads from person-to-person, most commonly though contact with infected feces. Feces can remain infectious for several weeks, as can food, water, or objects contaminated by feces. Approximately 72% of people who catch polio show no symptoms. Twenty-five percent develop flu-like symptoms (for example, sore throat, fever, tiredness, headache, nausea, abdominal pain) within a week or two after infection. A small proportion of these people will go on to develop more severe symptoms such as paresthesia (burning or prickling limb pain), meningitis (infection of brain and spinal cord), limb weakness, and paralysis that may lead to permanent disability and death if the respiratory muscles are affected.

Polio: Vaccination Is Key To Global Eradication

Polio can be prevented through immunization, and since 1988, the World Health Assembly has resolved to eradicate polio worldwide. Latest surveillance figures show that excellent progress has been made with a 79% reduction in the number of polio cases reported worldwide compared with the number of cases reported in 2014. Substantial gains toward polio eradication were made in 2015, with a 79% decrease in the number of polio cases reported worldwide compared with the number of cases reported in 2014. In 2015, a total of 74 wild poliovirus cases were identified; 54 in Pakistan and 20 in Afghanistan.

There U.S. has not reported a case of naturally occurring paralytic polio (wild poliovirus) since 1979, when an outbreak occurred among the Amish in several Midwestern states. Over the period spanning 1980 through 1999, 62 confirmed cases of paralytic polio were reported. Eight of these were acquired outside of the U.S. and 154 were vaccine-associated, mostly caused by contact with feces contaminated with the live oral poliovirus vaccine (OPV). OPV is no longer used as a polio vaccine in the U.S., although several overseas countries still use it. The inactivated poliovirus vaccine (IPV) is now the preferred vaccine.

Finished: The Deadly Seven: Where Are These Diseases Now?

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