The third subunit is a survey of current emerging or re-emerging infectious diseases. The background information in this section is intended to provide examples of six key emerging infectious diseases, in addition to the re-emergence of
Y. pesits
outlined in subunit two above. As previously stated, the background information may become outdated as scientists gain a better understanding of the infectious agents being addressed. It is highly recommended that current research be used to supplement any presentation of these materials.
SARS: Severe Acute Respiratory Syndrome
SARS, or severe acute respiratory syndrome, emerged in Asia in February 2003 and spread worldwide before the outbreak was later contained that year. The causative agent for SARS is a coronavirus SARS-CoV, a zoonotic virus that moved into human populations from infected avian populations.
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This disease presents with dangerous respiratory complications in addition to myalgia and fever. If the infection is left untreated, the virus may cause viral pneumonia and, in some cases, death.
While the outbreak is credited as occurring early in the year 2003, the first signs of emergence were in late November 2002 when a farmer was brought into First People's Hospital of Foshan to be treated for respiratory distress.
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The patient died shortly after being admitted into the hospital. The hospital and Chinese government failed to report the novel virus to the World Health Organization, This delay in notification allowed the virus to spread slowly through China as a 'flu outbreak'.
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By the time it started to make worldwide news, there were already numerous deaths.
In February 2003, an American business man flying from China to Singapore started to show symptoms of respiratory distress.
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He was admitted into The French Hospital of Hanoi, Vietnam where he died as did his attending doctor Carl Urbani who reported the case to the WHO and Vietnamese government.
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By this time, SARS had spread globally, with cases occurring in the United States and Eastern Europe.
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Shortly after, on March 29
th
2003, there was a super-spread event. Sixteen individuals who lodged the 9
th
floor of the Hotel Metropole in Hong Kong were infected with SARS-CoV.
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They subsequently traveled to Canada, Singapore, Taiwan, and Vietnam spreading the disease to more people. By July 31
st
, 2003, the SARS pandemic was considered to be under control, though no vaccine was developed to prevent future outbreaks.
MERS: Middle Eastern Respiratory Syndrome
MERS
,
Middle Eastern Respiratory Syndrome, is a novel coronavirus outbreak. Like SARS, MERS-CoV affects the pulmonary system of those who it infects causing severe respiratory complications. MERS-CoV was first reported in Saudi Arabia in 2012 and has since developed into media-worthy proportions in 2014.
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As of the time this paper is being scripted, 288 people have died from the virus and 830 confirmed cases, mostly in Saudi Arabia. This virus has been documented in several countries including the United Kingdom, Italy, the Philippines, Egypt, and Iran.
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While a majority of patients are asymptomatic, those who do show symptoms face a 30% mortality rate.
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MERS is another zoonotic virus spread from camels to humans. Recently, there is some evidence that MERS may be airborne, increasing ease of transmission between hosts.
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Similar to the SARS virus, there is currently no vaccine available and treatments aim to eliminate the symptoms of MERS rather than MERS itself.
Ebola
Ebola
is, arguably, one of the scariest emerging and re-emerging diseases known. Ebola, and its sister virus Marburg, are part of the
filovirus
family. There are multiple strains of Ebola three of which are fatal to humans and nonhuman primates and one strain (Reston) which as of yet is not fatal to humans. Ebola is a hemorrhagic virus presenting initially with flu like symptoms but rapidly progressing into hemorrhaging, rashes, damage to the liver, and coagulopathy.
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Patients entering the terminal stages of Ebola present with profuse bleeding from the inside the mouth, expectant from the lungs, and from the anus. Diffuse bleeding send the body into shock, leading to death in over 80% of cases in the most virulent strain.
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In total, the infection can run its course between two to three weeks time.
Ebola, and viruses like Ebola are considered 'hot viruses' and often pop up in populations and quickly burn out as they run out of hosts to support the virus. Like the previous diseases discussed, Ebola is a zoonotic disease. Transmission is initially spread by contact with infected body fluids of animals like chimpanzees, fruit bats, antelope, or porcupine.
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This wide range of animal hosts has made it difficult to pin down the natural reservoir for this virus.
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Once Ebola transmits into the human population, it is transmitted from person to person through contact with infected body fluids. There have also been documented cases of sexually transmitted Ebola from males to females up to seven weeks after a man has recovered from the illness, indicating longevity of the virus even after the patient is asymptomatic.
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Most recently, the CDC announced an outbreak of Ebola on March 25
th
, 2014 in several southeast districts of Guinea. Initially, a total of 86 cases were reported with 59 deaths.
6
The
Zaire ebolavirus
strain was indicated as the culpable pathogen.
6
By April 23
rd
, 2014 the virus spread to Liberia.
6
As of July 20
th
, 2014, the Guinea Ministry of Health has reported a cumulative death total of 314 patients out of the 415 suspected and confirmed cases.
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There is currently no vaccine available for this virus although several are being developed. Part of the reason why viral vaccines are so difficult to produce is the mutability of viruses. Viruses replicate very quickly and, without the same methods to check for accurate DNA replication, often acquire mutations. This allows for the virus to quickly evolve resistance from the vaccine as its genetic information mutates.
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In 2012, two companies that were working on an oral Ebola vaccine were informed that they needed to halt work because funding had been cut to the programs. Since Ebola tends to burn out quickly, and it is often easily contained using relatively simple protocol, it is more likely that the consumer base for an Ebola vaccine is relatively small. This makes producing the drug expensive without the payout that many pharmaceutical companies look to gain.
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Another vaccine being developed more recently in 2014 uses surface proteins from the Ebola capsid to invoke an immune response. However, this vaccine is only in a pre-clinical evaluation. After pre-clinical evaluation, it must go through a series of clinical trials, putting an Ebola vaccine several years away.
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Poliovirus and Poliomyelitis
Polio is considered to be one of the first diseases that mankind eradicated. Polio is a viral infection caused by a virus called poliovirus, a member of the picornaviridae family.
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This virus causes poliomyelitis—a transmittable disease that may enter into the central nervous system and cause paralysis of both voluntary and involuntary muscles. Interestingly, a majority of infected hosts are asymptomatic and do not express the paralysis that it is associated with. A quarter of those infected may have flu like symptoms and some stiffness which resolves over several weeks. Only 1% of people who are infected with the disease actually develop any sort of paralysis.
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As patients age, so too does death rate as the virus spreads into the respiratory muscles causing suffocation.
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The height of the polio epidemic was in the late 1940s through the early 1950s.
11
According to CDC records, over 35 thousand people were crippled yearly by the virus, many of them children.
7,10
Quarantines were used to separate the ill from the potentially infected and travel between cities was often restricted to prevent the spread of the virus.
4
There is no cure for polio, only supportive measures aimed at reducing some of the symptoms. Most treatments included a combination of pain killers and physical therapy along with braces.
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As the disease traveled towards the lungs, respiratory distress was reduced with respirators or negative pressure ventilators like the iron lung.
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It wasn't until the early 1960s when Dr. Albert Sabin developed the oral polio vaccine that the United States began to recover.
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By 1979, polio was eliminated from the United States.
7,10
Nine years later, the CDC, WHO, UNICEF and several other national organizations and governments band together to form the Global Polio Eradication Initiative (GPEI).
10
Outlined in their plan are four pillars: immunization of infants with the oral polio vaccine, providing supplementary immunization, surveillance for wild poliovirus in populations, and campaigns aimed at targeting any poliovirus outbreaks.
10
Currently, the CDC reports that GPEI has reduced the amount of polio outbreaks to 99% with the Americas, Europe, South East Asia and the Western Pacific marked as polio free.
7,10
There are currently only three countries where polio outbreaks happen with frequency—Afghanistan, Nigeria, and Pakistan.
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MRSA and other Drug Resistant Bacteria
When Alexander Fleming discovered one of his
Staphylococcus aureus
petri dishes was contaminated with mold, he did not know that he had discovered the next line of defense against disease. What Fleming discovered was a secretion called penicillin, a compound that had antibiotic effects that killed bacteria. Antibiotics work by preventing the formation of bacterial cell walls or by preventing the bacterial cells from reproducing.
By the late 1960s, antibiotics were prescribed for a wide range of previously uncontrollable infectious diseases.
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In addition, improvements in the sanitization infrastructure in major cities had improved dramatically, further eliminating conditions that contributed to the spread of bacteria and viruses. Penicillin and other antibiotics were so promising in controlling disease that in 1967 the United States of America Surgeon General William Stewart declared that, "We have basically wiped out infection in the United States."
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Not too long after that bold statement, a strain of penicillin resistant staph
was found in a patient. Now, almost all strains of staph are resistant to penicillin. Other forms of antibiotic resistance have been noted in dozens of species of bacteria indicating that bacteria are keeping pace with our medical developments.
Antibiotic resistant bacteria, like MRSA or methicillin-resistant
Staphylococcus aureus
, are a serious health concern. Often, resistant forms of bacteria are acquired as nosocomial infections—secondary infections developed after entering into a hospital.
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Sometimes, infections are acquired by coming into contact with an infected person outside of the hospital. These infections can spread unchecked through a patient and are notoriously difficult to treat because the drugs that are most effective no longer work.
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While many cases of resistant bacterial infections occur in patients that have weakened immune systems, anyone who has come into contact with these bacteria can be susceptible.
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MRSA and other antibiotic resistant bacteria have evolved as a response to the flood of antibiotics. If used correctly, antibiotics can kill bacterial infections. However, many people misuse or overuse prescriptions, exposing bacterial populations to the drug without entirely removing the population. As a result, bacteria that are naturally resistant survive the infection and recolonize the host in a secondary infection.
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These bacteria are spread from person-to-person and cause further infections. Constant exposure to antibiotics has driven an evolutionary arms race between antibiotic and bacterium, creating these super-bugs.
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Teaching strategies and resources for this sub-unit include exposing students to news paper articles about each of these diseases. Creating an Infectious Emerging Disease wall with the lifecycle of the virus or bacterium, transmission, hosts and reservoirs, and any other pertinent information may be a helpful activity for teaching students about these diseases. With the large number of emerging or re-emerging infectious diseases available, it may be worthwhile to assign this subunit as an individual research project.
