Overview
AIDS is a medical condition caused by the human immunodeficiency virus (HIV) that damages the body’s immune system. HIV originated from the simian immunodeficiency virus (SIV), which affects monkeys. It is believed that SIV jumped from monkeys to humans numerous times before the virus we know today appeared and spread around the world. The early origins of HIV date back to 1920s Kinshasa, in the Democratic Republic of the Congo, but the disease was first recognized in 1981.
Pathogen Characteristics
HIV is spread through direct contact with certain bodily fluids. Sexual intercourse and injection drug use are the two most common channels for transmission. The virus can also be passed from mothers to their babies during pregnancy, childbirth, and breastfeeding, and can be acquired from contaminated blood transfusions or organ/tissue transplants. HIV/AIDS affects specific cells of the immune system, called CD4 cells.
Clinical Illness
Initial infection with HIV causes flu-like symptoms, after which the disease enters a period of clinical latency, averaging ten years. During clinical latency, a person may have no symptoms, but can still transmit the disease to others. Once the disease has progressed to a point where there are very few CD4 cells, a person is considered to have AIDS. A weakened immune system makes an infected person highly susceptible to opportunistic infections, including infection with other pathogens that are more severe in a person with HIV/AIDS. Without treatment, survival with AIDS is three years on average.
Prevention and Treatment
There are several methods available for testing and diagnosing HIV infection. HIV is preventable by avoiding contact with the bodily fluids of an infected person, such as with the use of a condom during sex, or by never sharing needles. The risk of infection can be reduced by choosing less risky sexual behaviors, such as oral sex over vaginal or anal sex. (Anal sex is the highest-risk sexual activity for HIV transmission). Male circumcision lowers the risk of a man becoming infected with HIV from an infected sexual partner.
There is no vaccine for HIV; however, effective treatment exists. The first antiretroviral drugs were developed in the late 1980s, and more highly effective drugs became available in 1995. Known as antiretroviral therapy (ART), HIV treatment suppresses the HIV viral load in the body, slowing or stopping damage to the immune system. Today, most HIV-positive people on ART live long, healthy lives.
HIV treatment can also help prevent transmission of the virus to an uninfected partner. The concept of treatment as prevention is fairly recent, but the strategy has been in use since the 1990s in the form of prevention of mother-to-child transmission. A person living with HIV can significantly reduce her risk of transmitting HIV to her baby with the proper use of ART during pregnancy, labor, and delivery; by having a cesarean section, and avoiding breastfeeding. The first substantial evidence supporting treatment as prevention was published in 2011.
Pre-exposure prophylaxis (PrEP) refers to the use of medication to help prevent an uninfected person from becoming infected with HIV. Some of the same medications used to treat HIV are used for PrEP. PrEP is only recommended for those at significant risk of becoming infected with HIV and is most effective when combined with other prevention measures.
Major Outbreaks
Over the past 35 years, HIV/AIDS has infection over 78 million people and taken nearly 40 million lives. In 2013, there were 35 million people living with HIV/AIDS globally. That year, 1.5 million people died from the disease. Approximately 19 million of people living with HIV do not know that they are infected. Over 70% of people living with HIV/AIDS are in sub-Saharan Africa.
Lessons and Notable Achievements
When HIV/AIDS was first recognized in the 1980s, the disease was spreading rapidly and a positive diagnosis meant almost certain death. The number of new HIV infections peaked in 1997 and the number of AIDS-related deaths peaked in 2005. Since 2005, with the identification and use of effective prevention and treatment, there has been a 29% decrease in AIDS-related deaths. From 2001-2013, there was a 33% decrease in the number of new HIV infections, and a 40-fold increase in access to ART between 2002-2012. 9.7 million people living with HIV were accessing HIV treatment in 2012.
References
Overview
Ebola is a severe disease caused by an Ebola virus. There are five strains of Ebola virus, four of which can infect humans. Ebola was first discovered in 1976 in the Democratic Republic of the Congo (DRC). The virus is animal-borne and the most likely animal reservoir is bats. Ebola is primarily found in Africa.
Pathogen Characteristics
Ebola is introduced to humans through direct contact with infected animals and can then spread through person-to-person transmission. A person can become infected with Ebola through direct contact with: the blood or body fluids of a person who is sick with or has died from Ebola; objects (like needles and syringes) that have been contaminated with body fluids from a person who is sick with Ebola or the body of a person who has died from Ebola; infected fruit bats or primates; and possibly from contact with semen from a man who has recovered from Ebola.
The average case fatality rate for Ebola is 50%, and the range has varied between outbreaks from 25% to 90%. Healthcare workers are at the highest risk for infection with Ebola because of the risk of coming into contact with bodily fluids of a person with the disease.
Clinical Illness
Symptoms appear 2 to 21 days after infection with Ebola and include fever, vomiting, headache, muscle pain, diarrhea, fatigue, abdominal pain, and bleeding or bruising. According to the CDC, “People who recover from Ebola infection develop antibodies that last for at least 10 years.” However, it is not known if immunity is provided for other strains of the virus.
Prevention and Treatment
Prevention for Ebola involves strategies to reduce the risk of animal-to-human transmission and the risk of human-to-human transmission, including avoiding contact with bats and non-human primates, including meat prepared from these animals; avoiding contact with infected persons, including the bodies of those who have died from Ebola; and practicing safe and careful hygiene including handwashing and the use of alcohol-based sanitizers.
Treatment for Ebola involves supportive medical care, including rehydration and maintaining blood pressure. Several experimental vaccines and treatments for Ebola are under development at the time of this writing.
Major Outbreaks
The largest Ebola epidemic occurred in West Africa in 2014 to the present, primarily affecting Liberia, Sierra Leone, and Guinea, where the outbreak began. With over 28,000 cases and 11,000 deaths, this epidemic is larger than all previous outbreaks combined. This outbreak was characterized by weak health systems, significant population migration, and population density in urban areas, as well as high-risk cultural practices (e.g. burial practices) which allowed the virus to spread out of control. At its peak, it affected people in 10 countries, including some in Europe and North America.
Prior to the outbreak in West Africa, there have been 34 incidences of Ebola since it was discovered in 1976, including three cases of laboratory contamination (in England and Russia); four in which there were no human cases (the US, Italy, and the Philippines); three in which only one person was infected (DRC, Cote d’Ivoire, and Uganda); and three others in which people were exposed but did not get sick (the US and Philippines), leaving 21 other outbreaks. Until 2013, Ebola infection in humans was concentrated in central Africa in just a few countries: DRC, Uganda, Gabon, Republic of the Congo, and South Sudan. The most recent of these outbreaks happened in DRC concurrently with the West African epidemic in 2014 and infected 66 people with a case fatality rate of 74%.
Lessons and Notable Achievements
Once believed to be deadly virus not capable of widespread transmission, the West African Ebola epidemic shattered this misconception. This epidemic highlighted the importance of strong health systems and robust surveillance and preparedness. Wide disparities in survival rates between developed and developing countries parallel differences in health system capacity. Before 2014, there was 1 doctor for every 100,000 people in Liberia, 2 in Sierra Leone, and 10 in Guinea. In the US there were 242, and in France, 338.
References
Overview
Influenza is a viral illness that attacks the respiratory system. Influenza types A and B are the viruses that cause seasonal influenza. Influenza viruses change constantly, through small changes in the genes of the virus over time (both A and B) and through large, abrupt changes (A only). These shifts can result in novel subtypes of the virus to which humans have little or no immunity.
Influenza A can infect a wide range of animals, but while most can only be infected by specific subtypes, birds are susceptible to all influenza A. Influenza A can be transmitted to people from birds directly, or through intermediary species, such as swine. An epidemic occurs when a new virus is able to spread easily from person-to-person.
Pathogen Characteristics
Influenza is contagious and spreads from person-to-person via saliva droplets. This can happen through the air when an infected person sneezes or coughs–up to six feet away–and from contact with a contaminated surface and then with the nose or mouth. Influenza affects everyone; however, certain groups of people are at greater risk, including children under five, adults over 65, and pregnant women, as well as people with certain medical conditions.
Clinical Illness
Infection with influenza can be mild to severe. Symptoms typically come on suddenly and may include fever, cough, sore throat, runny nose, body aches, and fatigue. Vomiting and diarrhea are more common in children than adults. According to the CDC, “Most healthy adults may be able to infect other people beginning 1 day before symptoms develop and up to 5 to 7 days after becoming sick. Children may pass the virus for longer than 7 days. Symptoms start 1 to 4 days after the virus enters the body.” Most people recover within a few days to a week. In severe cases, influenza can be fatal.
Prevention and Treatment
A vaccine is used to prevent seasonal influenza. However, as the virus is constantly changing, the vaccine does not protect against novel strains. Hand washing and other safe hygiene practices can help prevent infection. While most people recover without treatment, antiviral medications for influenza exist and can help lessen the severity of an infection.
Major Outbreaks
The 1918 influenza pandemic, known as the Spanish flu, spread simultaneously in Europe, Asia and North America, and it believed to have originated in Asia. It spread in three waves over a period of one year, infecting approximately one third of the world’s population and killing 20-50 million people. The death rate of this pandemic was high at 2.5%. The Spanish flu was also unique in that death rates among 15-34 year olds–a population that is typically relatively healthy–were 20 times greater than in previous outbreaks.
Other influenza pandemics include the 1957 Asian Influenza that killed 1-2 million people; the 1968 Hong Kong pandemic resulting in 750,000 deaths; Highly Pathogenic Avian Influenza A H5N1 virus, which re-emerged in humans in 2003 and has infected over 700 people since; and the H1N1 or “swine flu” pandemic of 2009 that caused 200,000 deaths.
Seasonal influenza epidemics are estimated to result in about 3 to 5 million cases of severe illness, and about 250,000 to 500,000 deaths annually. According to the CDC, “Over a period of 31 seasons between 1976 and 2007. Estimates of flu-associated deaths in the United States range from a low of about 3,000 to a high of about 49,000 people.”
Lessons and Notable Achievements
The influenza vaccine protects against the main viruses that scientists determine will be most common that year. Despite the development of an effective annual vaccine, influenza has significant pandemic potential due to its constant genetic shifts and ease of transmission. It is estimated that if a pandemic with the pathogenicity of the 1918 virus were to emerge today, it would cause over 100 million deaths worldwide, underscoring the need for vigilant surveillance and preparedness.
References
Overview
SARS is a respiratory illness caused by a coronavirus. Coronaviruses are common viruses that normally cause mild illness in humans. SARS was first identified in Asia in 2003. It was found to have jumped to humans from palm civets, at an exotic live animal market in Guangdong, China.
Pathogen Characteristics
SARS is transmitted from person-to-person through respiratory droplets in the air, such as from the cough or sneeze of an infected person. Infection can also occur from contact with surfaces or object contaminated with infectious droplets.
Clinical Illness
Diagnosis of SARS is made based on likelihood of exposure. The incubation period is 2 to 7 days after which a high fever develops followed by a lower respiratory infection involving cough and difficulty breathing. Other symptoms may include headache and body ache, and in some cases, diarrhea. Most patients develop pneumonia. The case fatality rate of SARS was estimated by WHO to be 14 to 15%.
Prevention and Treatment
Proper hygiene, including hand washing and cough etiquette (i.e. covering one’s cough or wearing a mask) can help prevent infection with SARS.
Treatment for SARS involves minimizing symptoms and providing support medical care, as well as preventing or treating pneumonia or other infections that may occur.
Major Outbreaks
After first appearing in China in 2003, SARS spread to 29 countries in a matter of months. It was later traced back to a 44-year old seafood seller who was hospitalized in Guangzhou and passed virus to 19 relatives and 50 hospital staff. Three weeks later, a doctor from that hospital travelled to Hong Kong to attend a wedding and infected 17 more people. From there, the virus spread to Singapore, Vietnam, the Philippines, Australia, Canada, and beyond. By the time it was contained, 8,098 people were infected and 774 died. The worst hit countries were China, Hong Kong, Taiwan, and Singapore.
Since 2004, there have not been any known cases of SARS worldwide.
Lessons and Notable Achievements
The 2003 epidemic was marked by an inadequate initial government response in China that exacerbated widespread fear of and misinformation about the disease. The consequences of fear and panic–eventually totalling $40 billion in economic damages–underscore the importance of accurate and timely communication, both among public health professionals and with the public. SARS also demonstrated the potential of big data for early detection of outbreaks. The Global Public Health Intelligence Network, an early warning tool that uses informal information was developed in the mid 1990s in response to outbreaks of plague and Ebola. It demonstrated its potential in 2002 when it detected SARS days ahead of official reports.
References
Overview
Smallpox had a long history of infecting humans and decimating societies before it was eradicated from the planet in 1979. Caused by the variola virus, smallpox is believed to have first appeared around 10,000 BC. It likely originated in Egypt or India, but having come about in prehistoric times, no one really knows. The earliest evidence of smallpox infection in humans is from around 3,000 years ago in the remains of Egyptian mummies. Humans are the only known hosts or reservoirs of smallpox.
Pathogen Characteristics
Smallpox is highly contagious and spreads from person-to-person via saliva droplets in the air or through direct contact with skin lesions. It has a relatively long incubation period (7 to 17 days), becoming infectious once an individual develops a fever. In the 20th century, smallpox caused 300 to 500 million deaths. It killed people of all ages, both rich and poor.
Clinical Illness
Variola comes from the Latin word varius or varus, meaning “stained” or “mark on the skin” because of the characteristic rash and fluid-filled blisters it causes on the face, hands, arms, and body. The blisters turn into scabs that eventually fall off, and can leave permanent scarring. The rash is accompanied by a high fever, headache, fatigue, and in some cases, vomiting.
Prevention and Treatment
As early as 430 BC, it was understood that survivors of smallpox became immune; accordingly, they often became caretakers for the sick. Edward Jenner is well known for the development of the smallpox vaccination, but the practice of inoculation with smallpox preceded Jenner by many years. Inoculation, also called variolation, is the practice of purposeful introduction of the virus under the skin of unexposed people. It was developed independently in several countries from Africa to India and China before it was introduced in Europe in the 18th century. Despite its risks, inoculation with smallpox provided immunity to many people. Jenner himself was inoculated at 8 years old in 1757.
In 1796 Jenner carried out the experiment that would lead to the successful eradication of the disease. He found that inoculation with cowpox, a virus closely related to variola that infected cows, provided immunity for smallpox in humans. The new procedure was called vaccination, after vacca, meaning cow. By the early 1800s it was being used in most of Europe and had been introduced in the United States. In the years that followed, vaccination was continuously improved upon, and by the 1950s the smallpox vaccine was being produced consistently in large quantities.
Major Outbreaks
Smallpox caused a scourge of epidemics between its appearance and the 17th century, playing a role in the formation and collapse of civilizations all over the world, from the Romans to the Incas. By the mid-18th century, smallpox was endemic throughout most of the world and caused 400,000 deaths each year in Europe alone. Mortality ranged from 10% to 50% in most epidemics, and up to 90% in previously unexposed populations, such as among native North Americans in the 1500 and 1600s when European settlers brought the disease across the ocean with them.
Lessons and Notable Achievements
The development of an effective and easy to use vaccine made it possible for the world to embark on an eradication campaign, which began in 1967. At the time, there were an estimated 50 million cases of smallpox each year. The devastating effects of the disease led to the remarkable global effort, led by the World Health Organization, to eradicate the disease. It took 10 years to rid the world of smallpox and the last known case was in Somalia in 1977. In 1979 the disease was officially declared eradicated. Today, smallpox only exists in two high-security laboratories in the United States and Russia.
References