Historical Outbreaks: What have we learned?

Below are three examples of zoonotic diseases that have jumped to human populations in recent history.  All of these diseases are considered newly emerging and are still being researched thoroughly today.  A few examples that are not mentioned below but are still of great importance are Dengue Virus and West Nile Virus.  These viruses are of mosquito vector based transmission and are currently of great concern throughout the United States and the world.  As populations increase and continue to tax the Earth's resources we will continue to build dams and create large areas of intense irrigation to provide water to these areas.  Today about 2.5 billion people, or 40% of the world’s population, live in areas where there is a risk of dengue transmission.  Dengue is endemic in at least 100 countries in Asia, the Pacific, the Americas, Africa, and the Caribbean. The World Health Organization (WHO) estimates that 50 to 100 million infections occur yearly, including 500,000 DHF cases and 22,000 deaths, mostly among children.  These open bodies of water provide the perfect breeding ground for Aedes aegypti and other disease carrying mosquitos.  The following examples illustrate what can happen when populations expand into previously uninhabited areas.


Machupo: 1962-1967 Outbreak 

In July of 1962 San Joaquin, Bolivia was in a state of panic.  A viral outbreak was in its midst, unlike one the people of the many small villages that dotted the area had seen before.  The patients awoke in sweat, running very high fevers and were afflicted with near paralytic exhaustion and excruciating pain.  Their eyes were a light shade of crimson and their blood was flowing freely from the many small capillaries that dotted their skin.  These rashes were in fact microscopic holes through which water and blood protein flowed freely.  Their throats were raw bloodied.  This was the war zone in which the CDC scientists from MARU and NIH encountered that summer.  What they saw was clearly a new form of hemorrhagic fever, much like they had seen in Junin years earlier, but this virus was clearly a whole new animal.  The virus was killing 10-20 percent of the patients it infected.  People were dying and it was their job to figure out just where the virus originated and what the vector of transmission was.  Karl Johnson and company worked relentlessly for years to try to uncover the mystery surrounding the Machupo River Valley epidemic.

Through years of tireless research, insect and animal trapping, the team was finally able to uncover what the vector of transmission was; a species of rodent known as the Calomys field mouse.  This particular type of field mouse was endemic to the region but had never left the safety of the lush jungle surrounding the village until Bolivia's social revolution occurred in 1952, when the residents of San Joaquin found themselves without the food and supplies that had become accustomed to receiving.  In the villagers hast to grow corn and other crops they began clearing large plots of jungle in the area.  This in turn disrupted the natural habitat of the Calomys field mouse and provided the rodent with a new food source; corn.  The mouse population swelled during the 1950's and eventually invaded the town of San Joaquin in the early 1960's.  By the time the first victims had succumbed to the virus, the mice could be found anywhere the towns people had readily stored food and, or grain.  The mice would feed feverishly at night while the villagers slept and in doing so would urinate in the villager's homes.  The virus would then be transmitted through inhalation of the dried urine, consumption or through any cuts in the victims skin that came in contact with it.

This is one of many examples of a zoonotic transmission of a virus due to a population of people invading a once uninhabited plot of land.  Clear cutting the forest and planting new crops inadvertently contributed to the deaths of hundreds of people in the Machupo River Valley area.  Machupo continues to pose a very real threat to people within this region and there is still no vaccine.  Rodent control has proven to be the most effective measure of containment.    

                 
Lassa:

In February of 1969 near Jos, Nigeria an American nurse named Lily "Penny" Pinneo was treating patients in the midst of an unknown viral hemorrhagic fever outbreak.  Several of her colleagues, including doctors had fallen ill and some had already succumbed to the infection but she worked tirelessly to help the now exploding number of infected patients flooding the St. Charles Mission Hospital in which she worked.  The infected patients first complained of sharp backaches and muscle spasms.  This was quickly followed by an extremely sore throat, development of ulcers in the lining of the pharnyx and fevers soaring as high as 107 degrees fahrenheit.  This was followed by dehydration, the inability of blood to clot and lack of proteins in their urine.  Finally the infected patients start to show signs of hemorrhaging and irregular heartbeats.  Those that succumbed to the infection normally went into uncontrolled convulsions and multi organ failure and quickly died thereafter.  This unknown disease afflicting the region was a newly classified arenavirus known as Lassa.  Nurse Pinneo had been tending to another sick nurse when she too fell ill three days later.  Miraculously she survived after a vicious battle with the virus.

Jordi Casals of Yale University went to work immediately trying to evaluate what the new virus may be as its origin and classification was still unknown.  He cross checked the new virus against antibodies from several hundred of the viruses he had in his collection.  It turned out that none of the antibodies reacted to the virus and the virus itself was extremely deadly with a mortality rate of greater than 50 percent.  It also looked nothing like any of the viruses he had studied previously such as Marburg.  Unfortunately Jordi was forced to shut down his study of the novel virus because he somehow became infected and luckily recovered but his lab assistant wasn't so lucky.  He died a few days after contracting the illness.  To this day they still have no idea how his assistant came in contact with the virus.  The outbreak in Jos eventually came to an end but officials in the CDC knew that another outbreak was eminent and this time they were ready to jump at the first sign of trouble to try to pinpoint the origin of the virus.

The CDC got their opportunity in 1972 when another outbreak began to take hold in Liberia.  Cassals and two other scientists from the CDC were sent to investigate the outbreak and find patient zero.  After months of intense investigation the team was able to find the vector of transmission; Mastomys natalensis, a type of rat endemic to the region.  This type of rat had previously been repressed due to competition with a larger species of black rat; Rattus rattus.  This species of rat had been either driven out of the villages or consumed by the people thus allowing the smaller species to flourish.  Also, as the populations grew in these areas they planted more crops and clearcut miles of lush jungle to allow for more crop production.  This, along with a new found shelter for the mice provided by the villagers homes allowed the population to explode.  As was the case with Machupo, the virus was spread through the urine of the animals and was inhaled or consumed by the victims.  Lassa still poses a major problem throughout much of Africa and there is still no vaccine available and very few treatments are effective.  Clear cutting and crop planting have created very suitable habitats for the disease carrying vector and again, rodent control has proven to be the most effective measure in these areas.  


Ebola: Yambuku, Zaire 

In September of 1976 a new and terrifying outbreak was underway in Yambuku, Zaire.  This was an outbreak unlike anyone had seen before and the villagers were terrified.  A total of 26 people had been infected, 16 were dead, 8 were still sick and four had fled the local hospital in terror.  The disease gripping the region was a new and very deadly hemorrhagic fever.  The disease was characterized by a soaring 102.2 degree Fahrenheit fever, frequent vomiting of black digested blood, diarrhea streaked with blood, bloody gums and nose bleeds.  Many of the patients lost all cognitive ability and were so dehydrated they appeared dazed and incoherent.  Frequent abdominal from internal bleeding and joint pain also afflicted the infected patients with death following approximately three days after the initial infection.  The acting president at the time of the outbreak; President Mobutu quarantined the entire Bumba region and instituted martial law in an attempt to contain the outbreak.  At around the same time another outbreak with similar circumstances was beggining to take shape in Maridi, Sudan.  The WHO requested that blood and tissue samples be sent to them from both outbreaks for further analysis.  Once the samples reached Geneva they were sent to the CDC and other high security laboratories in the U.K.

Scientists from all over the world wanted a chance to figure out what virus was causing this novel outbreak.  Several different groups of scientists received blood samples from the two outbreaks, one such group included a young post-doc named Peter Piot.  The Belgian post-doc and his colleague; van der Goen tested the samples against several different antibodies, including yellow fever and all of the tests turned out negative.  They also attempted to infect Vero monkey cells only to discover they had all died within ten days of infection.  After coming up empty handed Piot decided to prepare samples for analysis under an electron microscope.  What he saw was much like the image depicted above, a completely new and novel virus.  Unfortunately further research was halted by the CDC because the pathogen was deemed to hot for their low level security labs.  Piot and his colleagues then left for Zaire to enter the belly of the beast.  They joined several scientists from the CDC and the WHO in the region.  Karl Johnson (the same Karl Johnson involved in the Machupo outbreak), a very famous virologist working for the CDC was also dispatched to Zaire.  Meanwhile the CDC continued there work on the novel virus in their maximum security labs.

On October 10th, 1976 two scientists who had been working on the virus at the CDC; Patricia Webb and Fred Murphy made the announcement that the virus causing the outbreaks in Zaire and Sudan was Marburg like in nature and that all of the samples sent for analysis should only be sent to the CDC and the WHO so they can be worked with in the, what is now known as the BSL4 laboratories.  Meanwhile in Zaire and Sudan the outbreaks raged on.  Mortality rates in Zaire hovered around 90% and just over 50% in Sudan.  Epidemiologists and virologists from across the world had found their way to Zaire to attempt to uncover the origin of the mysterious virus.  Through months of tireless work the scientists were able to uncover the spread of transmission was in fact blood to blood.  Once they deduced this they were able to institute new procedures for how to deal with infected patients in the local hospitals.  The main problem was sanitation; many of these hospitals only received five syringes per day and those syringes were used on 300 to 600 patients per day.  The scientists were also able to proclaim that the two outbreaks were distinctly different from each other but they were both caused by the newly named Ebola virus.  Unfortunately they were not able to uncover the origin of the epidemic and scientists today can only speculate where the disease originated.  They have however, found evidence of the virus in the guano of fruit bats indigenous to the area.

In later outbreaks of Ebola scientists have found that the consumption of bushmeat, specifically monkey meat has led to numerous outbreaks in the region.  It has also been noted that Ebola is currently causing an epidemic among the gorilla populations in Zaire and Sudan and is responsible for a large number of deaths in the region.  As the population continues to increase in the region food demands will as well.  This will cause people to look toward bushmeat and other resources for food sources and push people deeper into previously uninhabited areas thus causing more outbreaks of this extremely deadly virus.  

*All of the images above were found via the CDC or Google Image search.        

Here are some links for further information about the viruses from the CDC:


Lassa:
http://www.cdc.gov/ncidod/dvrd/spb/mnpages/dispages/lassaf.htm

Ebola:
http://www.cdc.gov/ncidod/dvrd/spb/mnpages/dispages/ebola/qa.htm

Machupo:
http://www.cdc.gov/ncidod/dvrd/spb/mnpages/dispages/arena.htm

Source:


Garrett, Laurie.  1994  The coming plague : newly emerging diseases in a world out of balance / Laurie Garrett  Farrar, Straus and Giroux, New York :