vector-borne disease

Study: Nearly half of U.S. counties now home to ticks that transmit Lyme disease

kkrisberg — Fri, 22 Jan 2016 17:04:56 +0000

Study: Nearly half of U.S. counties now home to ticks that transmit Lyme disease

It’s been nearly two decades since the last publication of a nationwide survey on the distribution of blacklegged ticks — the primary transmitters of Lyme disease. That survey, released in 1998, reported the tick in 30 percent of U.S. counties. Today, a new study using similar surveillance methods has found the tick in more than 45 percent of counties.

“These kinds of changes tend to be gradual,” study co-author Rebecca Eisen, a research biologist in the Centers for Disease Control and Prevention’s Division of Vector-Borne Diseases, told me. “But when you see the cumulative change over 20 years, it is surprising.”

The study, published earlier this week in the Journal of Medical Entomology, found that the blacklegged tick — scientifically known as Ixodes scapularis and a primary Lyme disease vector in the eastern U.S. — has now been documented in 1,420 of the 3,110 counties within the continental U.S. Its relative in the western U.S., known as Ixodes pacificus, is now in 111 counties. Together, the ticks have now been documented in nearly 50 percent of counties across 43 states. And the new numbers mark a more than 44 percent increase in the number of counties with a documented presence of such ticks since 1998. The study also noted that Lyme disease case counts have also increased steadily, from 10,000 in 1991 to more than 30,000 in 2008, though the true disease burden is likely much greater.

Eisen said her main message to people is to be aware that these vectors are expanding their range and to take precautionary steps to reduce contact with ticks. But before getting too much deeper into the study and its findings, it’s probably a good idea to answer two questions right away.

First, does the expansion of blacklegged tick territory translate into an increased risk of Lyme disease exposure? Not necessarily. Eisen said while blacklegged ticks may now be established in more counties, their host-seeking behavior and the particular animal hosts they seek out still differ according to region. For example, ticks in the South tend to stay immersed in the leaf litter, so they’re less likely to come into contact with people. While ticks in the Northeast are more likely to be on top of leaf litter. Of course, the very different climates contribute to host-seeking and survival behaviors that impact the chance of human encounters as well. As of 2014, the great majority of confirmed Lyme disease cases — 96 percent — were in just 14 states, all of which are in the Northeast, North Central and Mid-Atlantic regions.

The second question: Is this study the first that my local or state health department knows of this trend? Most definitely not, Eisen said. Just about every year, most state health departments post updates on vectors and vector-borne diseases, and local health departments are continuously working to keep their residents aware of risks. However, the updated survey that Eisen co-authored provides public health practitioners with a national overview — a chance to view overall trends and examine distribution changes across state borders. Eisen and study co-authors Lars Eisen and Charles Beard write:

Data on the current geographic distributions of medically important tick vectors, such as I. scapularis and I. pacificus, provide information complementary to epidemiological data on geographic disease case occurrence to inform the medical community and the public of where risk for exposure to tick-borne disease agents may occur. The lack of routine systematic surveillance across the continental United States of ticks of public health importance hampers our ability to define their current geographic distributions and to monitor changes in their ranges and densities over time. Although we are able to report in this paper where I. scapularis and I. pacificus are now known to be present at the county level, our certainty in where the tick is absent is low, especially at the edges of their ranges and in regions where they can be assumed to occur only at low densities.

They go on to write:

Given the lack of systematic surveillance for I. scapularis, one might ask if the range expansion suggested by our data is real or merely an artifact of enhanced tick surveillance and research activities in some areas. A true range expansion of I. scapularis in northern states, as described in this report, is supported by the largely concordant changes in the distribution of human Lyme disease cases captured through mandatory reporting of the disease since 1991.

Overall, the study found that most of the blacklegged tick’s expansion has occurred in the northern U.S., while populations in the southern states have remained pretty stable. The tick’s range in the western U.S. increased only slightly, from 3.4 percent to 3.6 percent of counties. More specifically, I. scapularis has expanded its range northward into upstate New York, Vermont, New Hampshire and northern Maine; westward across Pennsylvania, eastern Ohio and New York; and south- and southwestward into West Virginia, Virginia and North Carolina. For example, in West Virginia, the blacklegged tick was reported in just four counties in 1998, whereas the updated survey found it in 43 counties. On the other side of the country, I. pacificus is now established in 95 counties, the majority of which are located in California, Oregon and Washington (that’s a fairly small increase from the 1998 survey in which that tick was established in 90 counties).

While Eisen’s study doesn’t definitively pinpoint the factors behind expanding tick territories, she said one of the long-term drivers is an expanding deer population. Ticks, she said, like to feed on deer, and deer tend to follow forested areas. So as forests and deer populations expand, so too do ticks. Other drivers include changes in climate conditions that enable ticks to survive and reproduce in new regions, among many other variables, she said. (Click here for more on how public health scientists predict climate change will impact the distribution of vector-borne disease.)

Luckily, there a number of ways to reduce one’s risk of exposure to blacklegged ticks and Lyme disease. For example, Eisen said, avoid areas with high grass and leaf litter; hike in the center of a trail and not on the edges; use repellents containing at least 20 to 30 percent DEET; and shower as soon as possible when returning indoors. All the tips you need can be found on the CDC site.

Next, Eisen and her research colleagues hope to develop a statistical model to help predict where tick expansion might happen in the future. While she said it wouldn’t be surprising to see some additional expansion, she predicts there is an “edge” to the tick’s potential range. Because blacklegged ticks need forests to thrive, that edge is likely where forests runs into prairie lands, high alpine areas and agricultural regions.

“One of the main things I hope people take away (from this study) is the recognition that tick populations change over time, so we need to continually monitor that distribution,” Eisen said. “We need to continue to focus on ways to prevent tick-borne diseases and reduce human encounters. And there’s lots of options on the table.”

To download a full copy of the new study, visit the Journal of Medical Entomology.

Kim Krisberg is a freelance public health writer living in Austin, Texas, and has been writing about public health for nearly 15 years.

kkrisberg Fri, 01/22/2016 - 12:04

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Research

Scientists find high prevalence of Chagas disease in Texas kissing bugs

kkrisberg — Fri, 25 Sep 2015 16:09:10 +0000

Scientists find high prevalence of Chagas disease in Texas kissing bugs

The Centers for Disease Control and Prevention considers it one of five neglected parasitic infections in need of targeted public health action. And while its transmission is still considered rare in the U.S., it seems residents of Texas may be at greater risk than scientists previously thought.

The disease is American Trypanosomiasis, more commonly known as Chagas disease. Chagas is a vector-borne disease in which the parasite is transmitted to animals and people by blood-sucking insects known as “assassin bugs” or “kissing bugs” (here’s what the bugs look like). However, the parasite isn’t transmitted through a bite, per se; as the kissing bug sucks on your blood, it may drop its feces into the wound and it’s in the feces where the parasite is found. Chagas disease is endemic in parts of Latin America, Central America and in Mexico. But the risk of Chagas isn’t entirely clear in the U.S., where some have described Chagas as an emerging disease.

Rosa A. Maldonado, an associate professor of biological sciences at the University of Texas in El Paso, was curious about the risk of Chagas in the U.S. too. She had read studies finding that a significant number of dogs in Texas had tested positive for Chagas and so it made sense that insects must be carrying the parasite as well.

“If animals are infected that means insects have to be infected around here, too,” Maldonado told me.

So, she conducted her own study, the results of which were recently published in the journal Acta Tropica. A colleague told her that there were plenty of kissing bugs at the university’s Indio Mountains Research Station in Hudspeth County out in west Texas, not far from the Mexico border. So with the help of a student, Maldonado collected 39 kissing bugs for testing. She expected that perhaps 40 percent — maybe even half — of the bugs would test positive for the Chagas-causing parasite. But in the end, 24 of the bugs — or 61.5 percent — were carrying the parasite.

“I was expecting it to be high, but not that high,” she said.

Chagas disease has an acute and chronic phase. During the acute phase, symptoms can include fever or swelling; rarely, the disease can cause severe inflammation in the heart or brain. After the acute phase, most people experience a chronic asymptomatic phase. About 20 to 30 percent of infected people will develop debilitating or life-threatening medical problems. CDC estimates that more than 300,000 people in the U.S. have the Chagas parasite, though most contracted it outside the U.S. in endemic countries and only rare cases of domestically acquired Chagas have been documented.

Maldonado’s study noted that an estimated 12 million people are infected with Chagas worldwide. A 2013 Lancet study calculated the annual global economic burden of Chagas at about $7 billion. Maldonado and her study co-authors Munir Buhaya and Steven Galvan write: “Currently, there are no vaccines against Chagas nor effective treatment for the chronic disease. Therefore, improved knowledge of the local epidemiology and ecology is needed to develop a more comprehensive assessment of the magnitude of local transmission risk that will lead to more efficient efforts to prevent transmission.”

Maldonado hypothesizes that Chagas infection is probably underestimated in the U.S., as it’s not well tracked and most doctors probably don’t think to consider Chagas as a cause of related symptoms. She noted that the U.S. Food and Drug Administration has approved diagnostic tools that blood banks can use to test for Chagas, as the disease can be transmitted by blood transfusion. While the agency doesn’t require such testing, many blood banks do test for the disease.

As for the everyday Texan, Maldonado said kissing bugs are hard to find in cities and typically live in wild areas. But if you’re worried, she said to fill in holes and cracks that a bug can use to get inside your home or keep attractive hiding places, such as piles of wood, away from your house. As for Maldonado’s future Chagas research, she plans to do more testing for Chagas in stray dogs and cats in El Paso, which would point to infected kissing bugs in the area as well.

“The good news is that if we keep screening, we can start to raise awareness,” she told me.

To request a full copy of the Acta Tropica study, see this news release from the University of Texas-El Paso.

Kim Krisberg is a freelance public health writer living in Austin, Texas, and has been writing about public health for more than a decade.

kkrisberg Fri, 09/25/2015 - 12:09

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Public Health - General

Researchers develop innovative way to detect fake malaria drugs that could save lives, deter counterfeiting

kkrisberg — Tue, 22 Jul 2014 15:34:00 +0000

Researchers develop innovative way to detect fake malaria drugs that could save lives, deter counterfeiting

It looks like a simple piece of paper and it’s nearly as cheap, ideally costing just pennies. But despite its small size, it’s poised to make an enormous impact and potentially save thousands of lives.

It’s a new test to spot counterfeit versions of the drug artesunate, which is one of the most important drugs used to treat malaria, a mosquito-borne disease that affects hundreds of millions of people every year. Based on the science of microfluidics, researchers at Oregon State University developed an easy-to-use and inexpensive testing kit that patients and health care providers can use to determine if the malaria drug they receive is genuine and how much artesunate is present. Here’s how it works: a single pill is crushed and dissolved in water and then a drop is placed on the testing paper. Users then consult a simple color chart for the results — if the paper turns yellow, artesunate is present. The test takes just minutes and can be done just about anywhere. Findings on the innovative technique were recently published in the journal Talanta.

As the researchers noted in the journal article, drug counterfeiting is responsible for about 20 percent of the 1 million malaria deaths that happen each year. They also cited surveys finding that artesunate counterfeits make up between 38 percent and 53 percent of malaria drugs in Cambodia, Laos, Myanmar, Thailand and Vietnam. The Fake Malaria Drugs Kill project of the Dutch Malaria Foundation estimates that one-third of all malaria drugs sold in Africa are fake. And if that weren’t awful enough, counterfeit drugs can also contribute to the emergence of multidrug-resistant malaria. That’s why this little test could be a really big deal.

“It’s the first time we’ve tried to tackle a public health problem,” Vincent Remcho, an author of the Talanta study and a professor of chemistry and the Patricia Valian Reser Faculty Scholar in the Oregon State University College of Science, said about himself and his colleagues. “(Microfluidics) is a technology that is near and dear to us…to see it be useful in a public health setting is really gratifying.”

So, where did the idea come from? Interestingly, “it all started with a cool radio story,” Remcho told me. His wife, a veterinarian, was driving home when she heard a radio story about counterfeit medicines and malaria in particular. When she got home, she told Remcho that it reminded her of the kind of problems he tackles in his lab, where he and his colleagues build microfluidic devices that perform chemical analyses. Remcho agreed.

In turn, he and his colleagues set out with the intention of creating a test that was cheap, easy to use and wasn’t dependent on a person’s literacy level. The Centers for Disease Control and Prevention had previously developed a colorimetric test for artesunate, but it involved adding and mixing together chemicals in test tubes and isn’t easy to use outside a laboratory. In contrast, the test Remcho helped develop can be easily conducted in resource-poor settings, in remote locations and in the field. Remcho and study co-authors Myra Koesdjojo, Yuanyuan Wu, Anukul Boonloed and Elizabeth Dunfield write:

The chemicals required to perform the assay cost approximately US $.02 per test, which makes it a very practical solution to detect counterfeits. Since the reagents for the colorimetric test are stored on paper in dry form, they are more stable and easier to transport, which provides advantages of easy handling and longer shelf life. Furthermore, while most counterfeiters are producing fake drugs that lack of artesunate, some drugs are made with significantly lower active ingredients, which are incapable of killing all the parasites. This is an effort by the counterfeiters to misleadingly pass the test when a qualitative (positive/negative) evaluation is made to determine the presence of artesunate in the drug. Our test kit allows for quantitative analysis of artesunate tablets by providing a key that comes along with the kit and allows for comparison of the developed yellow color with the intensity of the yellow color corresponding to the approximate concentration of artesunate.

In addition to the test, students working on the project also developed an iPhone app that can more precisely measure the presence and level of artesunate. The app works by using the phone’s camera to analyze the intensity of the yellow that shows up on the paper strip. Of course depending on the setting, Remcho said the iPhone app may be most useful to health care providers and not necessarily patients. Still, the paper test results can be easily read with the naked eye, he added.

But can the test be cheated? Certainly not easily, Remcho said. If the criminals who manufacture and sell counterfeit malaria drugs wanted to cheat the test badly enough, they might be able to figure out a way. But Remcho hopes the time, effort and cost of finding a way to fool the test will be a deterrent.

Now that the test has been developed and assessed, Remcho is working to get the testing kit out to the people who need it. Beginning this fall and with funding from Grand Challenges Canada, which supports global health projects, Remcho and his colleagues are partnering with the National Institute for Metrology in Thailand to explore the feasibility of widespread use and distribution of the testing kit as well as the ease with which actual malaria patients can use the test. Remcho said he feels very hopeful.

“We want this test to be reliable and trustworthy,” he said. “I’m really hopeful that it goes in that direction. For right now, it kind of remains to be seen how it will evolve…but we’re excited that this technology can do some good.”

According to the World Health Organization, there were an estimated 207 million cases of malaria in 2012 and 627,000 malaria deaths.

To read more about the new counterfeit test, read this press release from Oregon State University or visit the Talanta journal. To watch a video about the toll of counterfeit malaria drugs, visit www.fakedrugskill.org.

Kim Krisberg is a freelance public health writer living in Austin, Texas, and has been writing about public health for more than a decade.

kkrisberg Tue, 07/22/2014 - 11:34

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Drug safety

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Public Health - General

Study: Economic burden of West Nile virus estimated at $778 million

kkrisberg — Fri, 14 Feb 2014 14:45:01 +0000

Study: Economic burden of West Nile virus estimated at $778 million

Most people infected with mosquito-borne West Nile virus don’t experience any symptoms at all. However, the tiny percentage of cases that do end up in the hospital total hundreds of millions of dollars in medical costs and lost productivity.

Published earlier this week in the American Journal of Tropical Medicine and Hygiene, researchers estimated that the cumulative cost of reported hospitalized cases of West Nile virus between 1999 and 2012 totaled $778 million. The study is the first to examine the economic burden of West Nile on infected patients who were hospitalized with conditions such as fever, encephalitis, meningitis and acute flaccid paralysis.

West Nile virus first showed up in the United States in 1999 and has since spread to every state in the country, except for Hawaii and Alaska. Less than one percent of the more than 37,000 documented cases of West Nile virus have resulted in serious neuroinvasive disease such as encephalitis and meningitis, which affect the brain and surrounding tissue. The virus is typically spread when a mosquito feeds from an infected bird and then passes it on to humans. There are no vaccines nor antivirals to prevent or treat the disease, so public health efforts typically focus on reducing the mosquito population and educating people about how to protect themselves against mosquito bites.

Lead study author J. Erin Staples told me the findings — which she characterized as a conservative estimate — could help local officials determine the cost effectiveness of public health and vector control interventions.

“By gathering short- and long-term costs, these data can be used by policy-makers, public health officials, researchers and those in academia and industry to better understand the impact of West Nile virus in their location,” said Staples, a medical epidemiologist within the Arboviral Disease Branch of the Centers for Disease Control and Prevention.

To conduct the study, Staples and her colleagues examined the initial hospital costs as well as lost productivity costs among 80 patients hospitalized with West Nile virus in Colorado in 2003. Of the 80 patients, 38 were followed for five years to gather long-term costs and six patients died. Patients who developed acute flaccid paralysis (partial to full-body paralysis) due to West Nile virus incurred the largest initial and long-term costs. People who experienced paralysis or developed encephalitis had “significantly” higher costs than those who had meningitis or fever. For example, the median initial cost for a person with West Nile virus-induced paralysis was nearly $21,000, while a patient with non-neuroinvasive West Nile virus disease experienced an average expenditure of about $4,500.

In terms of lost productivity, higher costs were found among those with meningitis than among those with encephalitis or acute flaccid paralysis. (Though Staples noted that because encephalitis patients tended to be older, lost productivity costs were subsequently lower.) When extrapolated to determine a nationwide average between 1999 and 2012, researchers came to a total cost of $778 million in health care expenditures and lost productivity. Staples emphasized that the study only calculated costs for people who ended up in a hospital, noting that among people who develop a fever and whose cases are reported to CDC, 80 percent don’t get hospitalized.

“The proportion of people (with West Nile virus) who get a fever is very underestimated in our data,” she told me.

In addition, Staples and her study co-authors — Manjunath Shankar, James Sejvar, Martin Meltzer and Marc Fischer — wrote that the “extrapolated costs do not include the costs that were incurred by public health or those related to mosquito control efforts, which are often 25 percent to 50 percent of the total cost during an outbreak response.”

Forecasting when, where and in what severity the vector-borne disease will hit a region is quite challenging (we’ve written previously about what makes West Nile virus control so difficult here). The spread of West Nile virus is affected by so many factors — weather, human behavior, the type and number of birds in an area — that Staples said “we can’t predict how many cases we’ll see — we don’t know if it’ll be a bad year or a large year.” That uncertainty is reflected in the caseload numbers reported to CDC as well: Total West Nile virus cases went from more than 9,800 in 2003 to about 1,300 in 2008 to about 5,600 in 2012. But like most public health issues, surveillance is still key. (CDC uses a system known as ArboNET to track West Nile virus.)

“National surveillance efforts are critical to determining where and when outbreaks of mosquito or tick-borne diseases occur,” Staples said in an American Society of Tropical Medicine and Hygiene news release about the new economic burden study. “Being able to react quickly to an outbreak and put in place preventive measures…is essential to limiting both the public health threat and the long-term economic cost of vector-borne infectious diseases.”

While CDC provides Epidemiology and Laboratory Capacity grants to states to support vector control activities such as surveillance and testing of animal reservoirs, that funding has dramatically decreased from more than $34 million in 2002 to $9.2 million in 2012. In a 2013 survey of health departments conducted by the American Mosquito Control Association, 88 percent of respondents said current funding levels are limiting their ability to deal with diseases such as West Nile virus.

“If you have good surveillance systems in place, you can better know when (a disease) may spill over into humans, and it can help you act more quickly and prevent more cases,” Staples told me. “Staying diligent is the best way to mitigate West Nile virus cases and deaths.”

To access the full West Nile cost burden study, click here.

Kim Krisberg is a freelance public health writer living in Austin, Texas, and has been writing about public health for more than a decade.

kkrisberg Fri, 02/14/2014 - 09:45

CDC reports highest West Nile virus caseload in years, but predicting outbreaks remains a challenge

kkrisberg — Fri, 05 Jul 2013 13:20:21 +0000

CDC reports highest West Nile virus caseload in years, but predicting outbreaks remains a challenge

Last year, reported cases of West Nile virus in the United States hit their highest levels in nearly a decade. It's a good reminder to keep protecting yourself from getting bitten, but it also begs the question: Is this just a sign of a much bigger threat? The answer is just as wily as the pesky mosquito.

According to recent data published June 28 in CDC's Morbidity and Mortality Weekly Report, the federal public health agency received reports of 5,780 nationally notifiable arboviral disease cases in 2012. (Arboviral diseases are those transmitted by arthropods, such as ticks and mosquitoes.) That year's multistate outbreak of West Nile virus accounted for 98 percent of the 5,780 cases and represented the highest reported caseload of West Nile virus since 2003. West Nile reports came in from 48 states, Washington, D.C., and Puerto Rico — the virus has yet to be detected in Hawaii and Alaska. Mosquitoes catch the virus by feeding on infected birds and then pass it on to humans.

Of the 5,674 West Nile cases reported in 2012, 2,873 were neuroinvasive, meaning the virus got into the brain (encephalitis) or spinal cord (meningitis), causing serious health problems. But most people who contract West Nile won't even experience symptoms. The MMWR report states that "extrapolating from the 2,873 West Nile virus neuroinvasive disease cases reported, an estimated 86,000–200,000 non-neuroinvasive disease cases might have occurred in 2012." The report's authors — Nicole Lindsey, Jennifer Lehman, Erin Staples and Marc Fischer — go on to write:

Reported numbers of arboviral disease cases vary from year to year. It is not clear why more (West Nile virus) activity occurred this year than in recent years. The weather, numbers of birds that maintain the virus, numbers of mosquitoes that spread the virus, and human behavior are all factors that can influence when and where outbreaks occur. Because of this complex ecology, it is difficult to predict how many cases of disease might occur in the future and in what areas.

So while West Nile virus was first detected in the United States in 1999 in New York and even though it's had the attention of scientists ever since, the mosquito-borne disease still remains a bit of a mystery.

"Last year's case numbers are probably just a fraction of what really happened," said A. Marm Kilpatrick, assistant professor in the Department of Ecology and Evolutionary Biology at the University of California-Santa Cruz.

With declines in federal funding support for surveillance activities, it's difficult to get a concrete handle on just how much West Nile virus is spreading, Kilpatrick told me. He said that while about 40,000 cases of West Nile have been reported since it first showed up in the U.S., researchers estimate that about 2.5 million people have actually been infected, with the overwhelming majority experiencing no symptoms. (And people who are infected with the virus, whether they develop symptoms or not, are believed to gain lifelong immunity.) What we do know is that so far West Nile virus has infected more than 300 species of birds, more than 60 species of mosquitoes and about 30 mammals — "it can infect just about anything," Kilpatrick noted.

Beyond case numbers, trying to predict how the virus and its host will move, what communities are vulnerable, and where virus hotspots might pop up are formidable challenges. Because so many environmental and biological factors affect the virus and its spread, forecasting a particular year's West Nile threat is more a process of educated guessing.

For example, according to a 2012 Lancet article Kilpatrick co-authored on the dynamics and drivers of vector-borne zoonotic diseases, the appearance of such diseases locally is driven by a combination of environmental and social conditions, ranging from poverty and conflict to temperature and rainfall to land use and development. And even those influences are still the subject of ongoing research, Kilpatrick told me.

For example, he said, one major hypothesis is that the effects of climate and warming temperatures will enable the virus to replicate more quickly inside its mosquito host, which can lead to bigger epidemics among humans. But the research so far isn't rigorous enough to make a definitive cause-and-effect connection, Kilpatrick said. There's also the hypothesis that lots of rainfall will lead to more mosquito breeding, which could then lead to more West Nile virus. But even that isn't for sure, as too little or too much rain could disrupt breeding patterns — Kilpatrick called it the "Goldilocks theory."

So what if an area experiences a serious epidemic one year — such as last year in Dallas, where the mayor actually declared a state of emergency — is that a solid predictor? Maybe, maybe not. An epidemic one year could mean the local human and bird population built up an immunity to the virus, thwarting the virus the following year, Kilpatrick said. Or there could be enough young birds born that second year with no immunity that West Nile virus makes a repeat visit.

"There are so many pieces to the story," Kilpatrick said. "The reason I have a job is that figuring out the dominant factor is not a trivial matter."

In Louisiana, where residents often joke that the mosquito is the official state bird, 155 cases of neuroinvasive West Nile virus were reported in 2012. Gary Balsamo, state public health veterinarian and assistant state epidemiologist with the Louisiana Office of Public Health, said that referring to neuroinvasive numbers is the most accurate way to gauge the ebb and flow of West Nile virus. He told me that even though medical diagnosis of the virus is improving, the 2012 caseload numbers represent a "real increase, so something was going on."

"Still, we can't really pinpoint any one factor responsible for that," said Balsamo, who's also president-elect of the National Association of State Public Health Veterinarians. "Over the years, people have tried to come up with methods to model (the spread of West Nile virus), but I'm not sure anyone's done that great of a job simply because the disease is so multifactorial."

Full of marshes, wetlands and mosquitoes, Louisiana is no stranger to arboviruses, Balsamo noted, and so surveillance and reporting of neuroinvasive disease cases as well as awareness among physicians to test for West Nile is well established. Still, the "best predictor of whether we'll have cases is the calendar...regardless of what happened the previous year," he said. In other words, summer is West Nile season so protect yourself from mosquitoes.

"We've told people in the past that we don't have really good predictive models so it's best to simply avoid mosquito bites," Balsamo said. "This disease is affected by climate, by rainfall, by terrain...there are so many factors in play here that I don't know if we'll ever get really good at predicting it. So whenever you have something like that the best lesson is to always be vigilant."

To learn more about West Nile virus and how to protect yourself, visit CDC. For a copy of the recent MMWR report, click here.

Kim Krisberg is a freelance public health writer living in Austin, Texas, and has been writing about public health for more than a decade.

kkrisberg Fri, 07/05/2013 - 09:20

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