April 7 marks World Health Day. This year World Health Day focuses on vector-borne diseases. More than half the world is at risk from vector-borne diseases. What exactly is a vector? A vector is a small organism, like a tick or mosquito, that transmits disease. Malaria, dengue, Chagas Disease and lymphatic filariasis are just four examples of vector-borne infectious diseases.
Come learn about some of these vector-borne diseases and the work that CDC does to prevent, treat, and control these diseases around the world.
(This blog originally posted January 28, 2013.)
Twenty-five years ago, I went to western Kenya as a Centers for Disease Control and Prevention (CDC) Epidemic Intelligence Service (EIS) officer to study an outbreak of severe anemia. No one was sure of the cause. Was it parvovirus, or exposure to an environmental toxin, perhaps? In the hospital there were five or six sick children to a bed, and they were so anemic that their blood looked more like a pinkish fluid than the rich red to which we are accustomed. As it turned out, there was no exotic cause. I was seeing the ravages of drug-resistant malaria at a time when chloroquine, the routinely used antimalarial drug, was failing globally.
That kind of grim hospital scene is much rarer these days, thanks to the enormous investment in malaria programs in Africa over the past decade and the improvements these investments have made possible. Programs that provide proven interventions—artemisinin-based combination therapies (ACTs), insecticide-treated bed nets (ITNs), and indoor residual spraying (IRS)—have achieved a 49% reduction in malaria deaths in the African region and saved 3.3 million lives saved globally. While this is a reason to celebrate, we have much more to do.
Our current tools are grounded in decades of basic, applied, and operational research. These are highly effective, powerful tools; however, the malaria parasites and their mosquito vectors change every day to evade the interventions we use to kill them. Increasing parasite resistance to drugs and increasing mosquito resistance to insecticides are sure bets. Our tools and strategies also need to adapt and evolve. Now is the time to invest in new drugs, insecticides, and approaches for the future. While developing brand new compounds takes many years, understanding how to use better our existing tools—novel combinations of vector control tools, or creative uses of drugs for prevention, for example—can help us continue to stay ahead of our elusive foes.
The Reality of Outbreak Investigations: Dengue in Angola
By Tyler Sharp and Ryan R. Hemme
(This blog originally posted July 18, 2013.)
Wanna know a secret? Here it is. Chances are, the same reason you’re reading this blog is why many folks at CDC do what they do: a fascination with infectious diseases and a desire to help others. Although the work of CDC employees is frequently glamorized in movies like Outbreak and Contagion, we face the same challenges as any other large, complex organization: communication, logistics, funding, and teamwork. These challenges become especially apparent when outbreaks occur, such as during CDC’s recent response to a dengue outbreak in Angola. Based on our experiences in Angola, this blog will dispel 5 myths about outbreak investigation that are often dramatized by Hollywood.
Myth #1 Mystery Disease X
Although Hollywood likes to make it seem like every outbreak is a complete mystery, most of the time when a team goes into the field, preliminary diagnostic testing has already suggested the cause of the outbreak before a foot hits the ground. Nonetheless, whether the cause be viral, bacterial, parasitic, poison or toxin, a critical first step in every outbreak investigation is confirming the cause of the outbreak.
It was no exception when we were sent to Angola to assist the Ministry of Health respond to a recently identified dengue outbreak in May of 2013. Dengue is an acute febrile illness that can cause explosive outbreaks. Although most people that get dengue will only suffer fever, headache, body pain, and possibly minor bleeding from the nose or gums, a relatively small proportion of people will develop severe dengue, which can result in hemorrhage, shock, and even death. By the time we were contacted, there were already dozens of sick people that had tested positive with a dengue rapid diagnostic test. Specimens were sent to CDC and the outbreak was confirmed soon after.
Myth # 2 Rushing into the field on a moment’s notice
The special red phone in the CDC Director’s office rings, an ominous look draws over their face, and a team is on a plane that evening, right? Not quite. There is a lot of careful planning that has to go into an outbreak response that may last weeks or longer in a country you’ve probably never visited. You have a limited idea of what exactly you’ll be doing once you get there, so you don’t immediately know what equipment and supplies will be needed in the field. In addition, most countries require visas to get in, which can take days or weeks to receive, even in an emergency. Finally, you have to coordinate with the host country to define an appropriate response. What CDC recommends may not be possible for many reasons, from the response being too ambitious to required resources not being available to lack of political support. Therefore, it’s important to pitch the plan to the local officials before arriving in the field. They may not come right out and say it, but hints of trepidation may mean that the plan needs to be revised. For that and many other reasons, flexibility is one of the most important traits that a “disease detective” can have. Before departing for Angola, we proposed to the local health authorities what we believed would be the most informative and feasible response to the ongoing epidemic, and then we tweaked the plan based on the feedback we received from them.
Priority #1 for the Angola dengue response was to raise awareness of the outbreak in the medical community. During dengue epidemics that occur in large, densely-populated cities like Luanda, the capital city of Angola, typically 5–10% of residents will become infected, so it’s not uncommon for hospital emergency rooms to become overrun with patients complaining of fever and body pain. Although there is no specific medication to cure dengue, early initiation of supportive therapy and close clinical monitoring can reduce the case-fatality rate for severe dengue from ~10% to <0.1%. Therefore, clinicians need to know that a dengue epidemic is occurring, the criteria they should use to determine which patients can go home and which need to be hospitalized, and how best to care for those that are hospitalized. The first week that we arrived, Tyler worked with the Ministry of Health to train >150 clinicians in two days, most of whom were sent home with training materials to train their colleagues.
Meanwhile, Ryan worked with staff from the Ministry of Health’s entomology and vector control programs. The Ministry has an established mosquito control program that is operated by very capable staff; however, in Angola the main concern is malaria, which is caused by a different mosquito than the one that transmits dengue, and the two mosquitoes behave quite differently. There are >3,500 species and subspecies of mosquitoes, and each one has a unique biology. Some mosquitoes like the dengue vector Aedes aegypti prefer to lay eggs in water-filled containers, while others will readily lay their eggs in water on the ground. As an entomologist you have to know where to look for the mosquito you are interested in. After another lesson in the importance of being flexible following some snafus with getting our checked baggage, which contained all of our response supplies, Ryan was finally able to work with local staff to provide training and identify surveillance methods to attempt to control the mosquitoes causing the outbreak.
Myth # 3 One of the “disease detectives” always gets infected
Does being in the field put you at greater risk for being infected with whatever bug is causing the outbreak? Probably, but we’re sent into the field with a small pharmacy of pills, sprays and ointments to either prevent us from getting sick or to treat us when we do get sick. Moreover, depending on the cause of the outbreak and what we’ll be doing in the field, we may bring additional personal protective equipment with us to keep us from being infected. Despite being vigilant about wearing mosquito repellent, on our last day in Luanda Ryan got bit by ravenous mosquito. He swatted it dead, examined it to identify it as Aedes aegypti, gave me a worried look and said, “I’m done for.” (Spoiler alert: Thankfully, neither of us ended up getting dengue during this response.)
Myth # 4 CDC saves the day
In the movies, CDC is usually portrayed as a public health SWAT team. They storm in, identify the source of the outbreak, institute harsh but necessary containment measures, and ultimately stop the outbreak. In reality, it rarely works that way. First, CDC is only ever involved in an outbreak response by formal invitation from the state or country in which the outbreak is occurring. Second, CDC never acts alone. In Angola, we worked on the outbreak response with local health officials, foreign governments, USAID, World Health Organization, and local non governmental organizations. CDC is a very competent agency, but we rely on collaboration with local and international partners for a successful response.
Myth # 5 Outbreaks can rapidly spread worldwide
OK, this one is actually pretty accurate. The ease and frequency of international travel has increased the likelihood of cases from any given outbreak being imported into other cities, especially if the outbreak happens in a large, international city like Luanda. Around the end of our second week in the field, a report came online documenting dengue in travelers to Luanda that were diagnosed after returning to their home countries on four different continents. Because of the oil industry, Luanda receives numerous international visitors each year, and some of them were bringing the unwanted souvenir of dengue back home with them. When physicians see a patient with a fever who has recently traveled to Africa, they are likely to suspect malaria, but not dengue. There were also three other dengue outbreaks in Africa in 2013, so the issue of clinical recognition of dengue was not likely to be limited to travelers returning from Angola. Because of this and the rapidly increasing case count, we decided to release an MMWR to notify clinicians in the U.S. and abroad of the need to be vigilant for dengue as a potential cause of fever in residents of and travelers returning from Angola. One of our important findings from the investigation was that genetic analysis of the virus revealed that it had been circulating in this region of Africa for the past 45 years. This meant that this was not a “new” outbreak of dengue, but rather that dengue was actually endemic in Angola and just hadn’t been recognized. These findings were in agreement with to a recent study suggesting that 64 million dengue virus infections occur each year in Africa.
All in all, this investigation was an excellent example of the international team pulling together to get the job done quickly and correctly, and brought attention to a neglected tropical disease of significant public health importance. It was also a lesson to us that, unfortunately, reality isn’t always what Hollywood would have us believe.
Chagas disease and the kissing bug
By Dr. Susan Montgomery, DVM, MPH
(Adapted from a blog originally posted June 5, 2012.)
The kissing bug, also known as a triatomine, can be infected by Trypanosoma cruzi, the parasite that causes Chagas disease. Chagas disease is found in many parts of Latin America, where an estimated 8 million people have this disease. It is not widespread in the United States, but CDC estimates at least 300,000 people in the United States are infected by Trypanosoma cruzi and have Chagas disease.
Chagas can cause cardiac disease including stroke and arrhythmias, and gastrointestinal disease over time. It can take several years to decades for the infection to take its toll on the human heart and stomach.
Most people with Chagas disease have no apparent symptoms, so people infected don’t know they have it. When people are diagnosed, with the exception of those who are already very sick, it can be treated with drugs CDC gives to health care providers.
Often people find out they have it when donating blood, as blood banks use the FDA’s guidelines to test and notify donors. In addition to blood transfusions, the parasite is also transmitted through organ and tissue transplants. CDC has collaborated with transplant experts to publish recommendations for testing organ donors and monitoring organ recipients to prevent Chagas disease so that transplant centers can help protect their patients from the parasite.
The parasite also can be transmitted from infected mothers to their babes. It’s important for health care providers to know about Chagas disease so that pregnant women who might be at risk for Chagas disease can be tested. Babies born to infected mothers can be monitored and treated if they are infected.
Lymphatic filariasis: Spotlight on elimination in Haiti
(Blog originally posted June 14, 2013.)
Lymphatic filariasis (LF), sometimes known as elephantiasis, is delivered by mosquitoes infected by young, blood-borne parasites. The worms lodge in a person’s lymph nodes, causing fluid to pool in their legs and testicles, forcing them to swell dramatically. LF affects over 120 million people in 73 countries throughout the tropics and sub-tropics of Asia, Africa, the Western Pacific, and parts of the Caribbean and South America.
Humans are the only known host for the parasite in Haiti, which means it’s an ideal infectious disease to eliminate. Once we eliminate it from people, it can’t be brought back by animals carrying the parasite, which is the case for many infectious diseases.
LF wasn’t always in Haiti or the Americas; it was imported through slave trade. The costly disease is still endemic in four countries in the Americas; one shares an island with Haiti, the Dominican Republic, which will also benefit from Haiti’s efforts. LF has been gone from the United States since the 1930s but also remains in some areas of Brazil and in Guyana.
Haiti has some of the worst rates of LF in the world. As much as 50 percent of schoolchildren in some parts of the country were infected before CDC started the elimination program 20 years ago. Haiti and its partners are implementing an innovative and manageable drug treatment program to stop the spread of this infectiousparasitic disease.
An added benefit of the treatment, called mass drug administration, is that it kills other intestinal parasites that cause nutritional and growth deficiencies. As a result of this treatment, children will now perform better at school and experience less diarrhea and other health problems.
The Haitian Ministry of Health has been working with CDC and other important partners to deliver this community-wide treatment since 2000: we’ve trained hundreds of public health workers, not just to administer the drugs, but to monitor the program and verify results so we know when to stop treatment.
The treatment program is also a public health best buy. It costs only about 50 cents a dose. Although it can’t cure those with the disease, now future generations will live free from suffering the pain and ostracization.
For more information about these vector-borne diseases, visit the following: