This story is part of a partnership between MedPage Today and VICE News.
When 2015 began, the world was still focused on the Ebola outbreak in West Africa. Our attention soon shifted, however, to a much smaller outbreak that started in an unlikely place: Disneyland, where unvaccinated visitors triggered a rash of measles cases that ultimately sickened 147 people across the US.
A grim medley of viral and bacterial infections went on to make headlines this year in different parts of the globe, illustrating the many ways that infectious diseases can emerge and spread.
"Infectious diseases evoke a kind of fear that's very, very deep in our brains," said Dr. Myron Cohen, director of the Institute for Global Health and Infectious Diseases at the University of North Carolina School of Medicine. "Health is the most precious thing you have. No matter how much you're worried about everything else, it all pales when health is compromised."
Here are the most significant outbreaks of 2015:
Middle East Respiratory Virus (MERS)
Often compared with the notoriously lethal SARS virus, MERS, or middle east respiratory virus, has continued to spread and kill people in 2015.
The World Health Organization detected MERS in 15 countries in 2015: China, Germany, Iran, Jordan, Kuwait, Oman, Qatar, South Korea, Saudi Arabia, Thailand, the Philippines, and the United Arab Emirates.
The most recent reported cases were two deaths and a 47-year-old man in critical condition in Saudi Arabia in November, according to the World Health Organization (WHO). But the organization has learned of more than 1,600 laboratory-confirmed cases, including 584 deaths, since the virus was first discovered three years ago.
Typical MERS symptoms include cough, fever and shortness of breath, but many people have more severe complications, including pneumonia and kidney failure, according to the Centers for Disease Control and Prevention. Those who died often had underlying medical conditions, but some people have no symptoms at all, or only mild cold-like symptoms.
Still, the virus has yet to capture America's attention.
"MERS is going to remain on the back burner as long as a small number of people in Middle Eastern countries develop it," Cohen said.
Scientists aren't sure yet exactly how MERS is transmitted, but it has been found in some camels, and some MERS patients have reported contact with camels. With that in mind, WHO has recommended that people with weakened immune systems and other high-risk groups avoid contact with camels, raw camel milk or urine, and undercooked meats, especially camel meat.
Avian Influenza (H7N9)
Two humans were reported to be infected with the avian influenza virus H7N9 earlier this month in China, according to WHO. The first was patient was a 74-year-old man who bought poultry at a market and raised it at home. The second was a 60-year-old man with a history of slaughtering domestic poultry. Both men were in severe condition as of December 17.
Humans contracting avian influenza have been reported almost every month in China, but two cases in Canada prompted North Americans to fear the virus in February 2015. Before becoming symptomatic, the patients had been traveling through China and were exposed to live poultry but did not touch it, according to WHO. Neither were hospitalized, however, and both recovered in self-isolation to prevent any further transmission.
'Infectious diseases evoke a kind of fear that's very, very deep in our brains.'
"I think it's something we can't get complacent about because… if the avian flu strain goes person-to-person, it could result in a pretty significant pandemic," said John Brownstein, director Health Map, a web tool that collects infectious disease information from thousands of sources. "It could be catastrophic."
Cholera is often associated with wartime conditions and poor infrastructure, and that was no exception in 2015.
The Democratic Republic of the Congo (DRC) reported nearly 20,000 cases since January 2015, according to WHO. Villages housing refugees were hit hardest.
"Cholera is a disease of environmental distress," Cohen said. "The bacteria benefit from public health catastrophe."
It can be treated with rehydration salts, or, for severe cases, intravenous fluids and antibiotics. There's also a move to administer oral cholera vaccines to people at risk.
The virus was reported in the DRC, Iraq, Haiti, and Tanzania in 2015.
Madagascar had an outbreak of bubonic plague over the summer. Ten of the 14 patients died, but no new cases of the bacterial disease were reported after late August.
The bacteria that causes plague is mostly found in wild rodents, but it is spread via infected fleas that bite humans. The bacteria migrates to the lungs, causing pneumonia, which then makes the virus transmissible to other people by coughing. Although it can be treated with antibiotics, WHO calls it "one of the most deadly infectious diseases" because patients can die within 24 hours.
Still, for it to make a 1300s-style comeback, humans would have to have regular, close contact with infected rodents, which is unlikely today, Cohen said.
Health workers have had an effective tool against malaria for decades, but that didn't stop the disease from making a comeback in the United States this year.
The Centers for Disease Control and Prevention reported 189 cases in 24 states and Washington, DC as part of five separate outbreaks since January 1. The largest of these outbreaks was linked to visitors to Disneyland in California who had not received the two recommended doses of the measles vaccine.
"The measles outbreak in the United States is a function of the belief systems about vaccine compliance," Cohen said, pointing the finger at celebrity anti-vaccine advocates and a disproven and retracted study.
There was also a much smaller measles outbreak in Chile.
When the year began, the Ebola outbreak in West Africa was just starting to show signs of slowing. In January, reported cases started to dip below 100 per week, but the virus would infect another 6,500 people in 2015.
The end of the outbreak has come in fits and starts. Liberia was declared Ebola-free in May 2015, but when a teenage boy died in June, officials discovered that the virus had returned. Then, health officials went back to trying to track down and contain people with the virus.
In March, a woman died of Ebola after having had unprotected sex with an Ebola survivor. She would become one of about 20 people suspected of contracting Ebola sexually.
October 2015 was the first week without a single new Ebola case in Guinea, Liberia, or Sierra Leone.
Since the outbreak began in 2014, there have been nearly 29,000 cases and more than 11,000 deaths, according to WHO. Officials have also learned that the virus can linger in areas of the body protected from the immune system, such as eyeballs and testicles.
WHO declared Sierra Leone Ebola-free in early November and Guinea Ebola-free on Tuesday, December 29. No new Ebola cases have been reported in Liberia since late November.
Watch the VICE News documentary The Fight Against Ebola:
Diseases caused by bites from infected insects are known as vector-borne diseases, and they were on the rise in 2015. They include Dengue fever, chikungunya, malaria, West Nile, and Zika, which has been spreading in South and Central America over the last three months.
Brownstein, who also serves as chief innovation officer of Boston Children's Hospital, said the symptoms vary, but can include fever, rash, and joint pain.
"What's interesting is that it's a collection of things not seen before, things that are reemerging and things that are taking global hold," Brownstein said, adding that this may be the result of a combination of warmer climate, reduced mosquito control, and other factors. "Zika is starting to take hold as a newly emerging mosquito-borne virus. It's a new thing we're going to see more of starting next year."
Follow Sydney Lupkin on Twitter: @slupkin