Tag Archives: infectious disease

Forget Ebola, Sars and Zika: ticks are the next global health threat

by Mackenzie Kwak

Ticks carry a wide array of pathogens – and environmental changes mean they are spreading

Since the beginning of our species we have been at war. It’s a continuous, neverending fight against the smallest of adversaries: armies of pathogens and parasites. As we have developed new ways to survive and stop them, they have evolved ever more complex and ingenious methods to thwart our efforts.

Humans have faced numerous attempts to challenge our dominance on planet Earth , and from the Black Death to the Spanish flu, we have weathered them all. However, since the start of the 21st century, with its trend towards global interconnectedness, these onslaughts are ever-increasing. In the past 17 years we have battled Sars, the Ebola virus, Mers, and more recently the mysterious mosquito-borne Zika virus. These diseases seeming to appear from nowhere and rapidly ravage our populations. One commonality is that they almost always originate in animals before jumping across to people, and few parasites are as good at jumping between animals and people as the tick.

Ticks could be best described as the used syringes of the natural world due to their promiscuous feeding habits. Most ticks go through three stages in their lives and feed on a different host at each stage, whilst simultaneously collecting hitchhiking microbes in their blood meals. Ticks also have one of the widest distributions of any vector on Earth – they can be found on every continent, including frigid Antarctica. This combination of ubiquity and a bad habit for accumulating pathogenic microbes make ticks some of the most dangerous vectors on the planet.

So why ticks? And why now?

Partly, it’s because ticks have been understudied for so long that only recently have we begun to realise just how much they affect our health. It took until 1975 for the infamous Lyme disease even to be formally described, and today the list of microbes found within ticks grows ever larger every year as numerous new species are discovered.

An engorged tick removed from a host. Photograph: Astrid860/Getty Images/iStockphoto

Changing ecosystems are also forcing ticks into closer contact with humans. Perhaps the most immediate changes are being driven by land clearing, which is forcing wildlife into closer contact with humans; with wildlife come ticks and the diseases they carry. Climate change has also been implicated: as the climate gets warmer, some ticks are expanding their ranges into places where cool winter temperatures previously limited their distribution. Geographical boundaries are also being eroded as rapid transport links environments which were previously isolated from one another. This presents easy opportunity for ticks to cross borders and spread to new habitats they may not have previously occupied.

In short, our manipulation of the environment has set the stage for a tick-driven health crisis.

Ticks can carry an extremely wide array of human pathogens, including bacteria, viruses, and protozoa. Within the long list of human ailments caused by ticks, several dangerous diseases stand out.

While the recognition of Lyme disease has led to a greater study of the bacteria which cause it and more frequent testing for patients, it has been a double-edged sword, as its notoriety has overshadowed equally important diseases like tick-borne rickettsiosis (TBR). TBR is caused by a number of different bacteria distributed across the globe. Unfortunately, TBR often presents with signs and symptoms similar to Lyme disease, such as rashes, joint and muscle pain, and fatigue. Although deaths are rare when TBR is treated with antibiotics like doxycycline, when the disease is incorrectly diagnosed or adequate medical infrastructure is lacking, mortalities can still occur.

Babesiosis is an emerging tick-borne disease caused by a protozoan called Babesia, a species related to the microbe which causes malaria. The disease is rarely tested for by doctors and the global levels of human infection are unknown, although some researchers believe that they may be much higher than present rates of diagnosis indicate. Infections can be highly variable, with about a quarter of infected adults showing no signs of the disease, while others will die from the infection. In truth the disease is still poorly understood in humans, which is compounded by the fact that several species of Babesia cause the disease and the signs and symptoms can be wide-ranging and often include fever, fatigue, anaemia, and nausea – all common features of other illnesses.

The distinctive “bullseye” marking caused by a bite from a deer tick. Photograph: anakopa/Getty Images/iStockphoto

Crimean-Congo haemorrhagic fever (CCHF) is perhaps the most terrifying disease spread by ticks, as there are no treatments available, and mortality rates can be as high as 40% in infected humans. To put it into perspective, that mortality rate is similar to untreated cases of Ebola or the bubonic plague. The World Health Organisation views CCHF virus as having a high chance of causing human disease epidemics and has accordingly directed considerable funding towards finding a treatment, although to date none have been developed. The wide distribution of tick vectors capable of spreading the disease coupled with the ability of common domestic animals such as sheep and cattle to maintain the CCHF virus in their blood at high levels means the potential for CCHF to expand into new regions like Europe is highly probable.

While only discovered in 2009, SFTS virus (severe fever with thrombocytopenia syndrome) has sparked widespread fear through much of Asia, especially in Japan where 57 people have died of the disease since 2013. Signs of the disease can range in severity from relatively mild, like fever and diarrhea, to severe, which can include multiple organ failures. The fact that the epidemiology of the disease is so poorly known makes predicting and controlling its spread difficult. It is also known to be carried by at least two cosmopolitan tick species which are spread throughout the world from the UK, to the US, and even Australia. That might sound bad enough, but things are even worse: although the disease typically gets to humans via a tick, from there it can spread to other humans or their pets and back again into ticks who feed on infected hosts.

Ticks are ubiquitous, dangerous, and are coming into ever greater contact with us. We must recognize that the next public health crisis may come from our backyards rather than a remote equatorial jungle in Africa or Asia.


Zoologist Mackenzie Kwak’s research focuses on the biogeography, systematics, and ecology of Australasian ectoparasites. She writes for the science blog on The Guardian, where this blog first appeared.

Opinions expressed by contributors are their own.

The Lyme Disease Divide

How to Make Sense of Conflicting Lyme Disease Facts

 

by Scott Santarella, CEO, Global Lyme Alliance

With the possible exception of HIV, no infectious disease in recent history has been as misunderstood and divisive as Lyme disease.  On one hand, there are tens of thousands of people suffering from debilitating physical and neurological symptoms who are unable to get the help they need from physicians, public health officials and insurance companies. On the other hand, the Infectious Diseases Society of America (IDSA) and the Centers for Disease Control and Prevention (CDC) maintain that Lyme disease is “easy to diagnose, easy to cure” and dismiss the persistence of symptoms over time, even after treatment. It’s no wonder that many people are confused about Lyme prevention, symptoms and treatment fundamentals.

Recently we’ve attended a number of public Lyme discussions held in Lyme endemic states and are both encouraged and concerned about how the disease is being discussed by the public and some in the medical community.

One event we attended focused on the very real threat of Lyme disease and children. Children ages 3-14 have a higher risk of contracting Lyme because they are physically closer to the ground, where ticks are plentiful. Children play in the grass, roll in leaves, run through bushes, thus increasing their exposure to Lyme-infected ticks. But because the symptoms of Lyme can be varied and non-specific—headaches, joint pain, anxiety, confusion, memory loss, anger, insomnia, for example— parents and teachers may not realize their children are ill. And physicians who are not well-versed in Lyme may not attribute it to the illness.

We were glad to hear speakers talk about the challenges in diagnosing Lyme and co-infections. If the disease is left untreated, it can cause a host of problems that can severely affect children’s long-term health, their behavior and school performance. Current Lyme tests are highly inaccurate, so diagnosis should be a combination of testing and a consultation with a Lyme-literate doctor.

Those attending the event walked away with a clear understanding of the true challenges related to Lyme disease in children. And also the importance of being a strong advocate for your child—you know their symptoms better than anyone. However, we attended another talk that was riddled with common misperceptions about the disease’s symptoms, diagnosis and treatment. A few examples:

What We Heard: Lyme is a very treatable, curable disease.
FACT: Although Lyme can be cured if diagnosed and treated in the early stages, up to 20 percent of those who are treated still go on to develop serious chronic symptoms including severe fatigue, muscle and joint pain, insomnia, headaches and “brain fog.”

What We Heard: It takes 36-48 hours for tick to infect a person.
FACT: The longer a tick is attached, the higher the risk of transmission. But it is possible to get Lyme disease even if a tick is attached for less than 24 hours.

What We Heard: If you have Lyme, you will see a clear bull’s eye rash, unless it’s on your back or somewhere hard to see.
FACT: Not everyone who has Lyme exhibits a rash, much less a bull’s-eye rash.  At least 20 percent of patients never develop the rash and fewer than 50 percent of Lyme patients ever recall seeing one. If you are “lucky” enough to see any type of rash, take a picture to show your doctor. A flu-like condition is also a common sign of Lyme infection and it can occur with or without a rash.

What We Heard: There’s a lot of bad press about the tests not being good.
FACT: There is still no reliable diagnostic test for Lyme. The standard blood test lacks sensitivity and is more than 55% inaccurate.

What We Heard: You shouldn’t need more than 4 weeks of antibiotics, 6 at the most if the patient requests it.
FACT: Existing guidelines from the CDC recommend against treating Lyme disease-positive patients with antibiotics for more than 28 days. However, up to 20% of patients treated with this recommended course of antibiotics will have lingering symptoms such as fatigue, pain, or joint and muscle aches. Longer treatment is advocated by the International Lyme and Associated Diseases Society (ILADS), based on a patient’s symptoms.

What We Heard: It’s very atypical with late Lyme disease for one’s hands and feet to be affected.
FACT: Although knee pain is most common in late-stage Lyme, the disease can cause pain and tingling in other body parts. In addition to Lyme, a tick can carry other tick-borne co-infections as well such as Babesia, Bartonella and Ehrlichia and transmit them in a single bite. When a patient suffers from atypical symptoms, a doctor must also consider possible co-infections as the cause.

What We Heard: Getting a tick tested for Lyme is unnecessary unless you think it helps the town learn how many cases of Lyme disease it has from ticks.
FACT: Some doctors will not treat a patient until symptoms of Lyme disease have manifested and this loss of precious treatment time often results in more severe symptoms. Tick testing can help you make treatment decisions before symptoms arise since testing may reveal the presence of other disease-causing co-infections the tick is carrying and transmitting.

The challenges in diagnosing Lyme and its co-infections early make it difficult for both the patient and the clinician. Knowing the facts about the disease can help. Your best option is strong prevention, but that’s not fail-proof. If you feel that you or someone you love may have Lyme, learn the symptoms and contact a Lyme-literate doctor for guidance. Please explore our website for the latest information, resources and support.

Scott Santarella

 

 

 

Tick-borne Infections on the Rise in Gray Wolves

by Mayla Hsu, Ph.D., GLA Science Officer

As the majority of emerging infectious diseases stem from wildlife, the rise of tick-borne Infections in gray wolves is a good indicator of the future of Lyme and other tick-borne diseases.

 

Wild gray wolves evoke images of unfettered nature and animals loping freely through forests and meadows. But a new study of wolf populations in northwest Wisconsin shows that a high percentage of them are actually infected with tick-borne infections, which suggests that they are potentially suffering ill health.

Many of us know that rodents like squirrels and mice, as well as larger animals like white-tailed deer, are hosts for Ixodes scapularis, the tick that transmits Lyme disease. The bacteria that cause Lyme disease (Borrelia burgdorferi), anaplasmosis (Anaplasma) and ehrlichiosis (Ehrlichia), grow in these host animals and colonize the ticks who bite them to take blood meals. When infected ticks then bite humans, we too become infected by the bacteria, and get sick.

Scientists analyzed 373 blood samples drawn from wild gray wolves between 1985 and 2011. Using the Snap 4Dx test, which is used by veterinarians to test for tick-borne illnesses in dogs, they looked for antibodies that recognize these microbes. Their presence indicates past exposure to the pathogens. Overall, they found antibodies to B. burgdorferi in 65.6% of animals, Anaplasma antibodies in 47.7% and Ehrlichia antibodies in 5.7%. These findings show that tick-borne pathogens are common in gray wolves in Wisconsin, and as expected, the American dog tick Dermacentor, and I. scapularis tick vectors that transmit them were routinely found on the animals.

While the sex of the wolves was unrelated to the percentage infected, their age was important. A higher proportion of adult wolves had B. burgdorferi, Anaplasma, and Ehrlichia antibodies than pups. This is unsurprising, since greater age means increased probability of being bitten by ticks. Also, adult wolves move greater distances, with greater exposure to questing ticks, compared to pups, who generally stay near their den.blog_tick-borne-gray-wolves-2

The research also showed a 50% increase in the prevalence of B. burgdorferi between 1985 and 2011 among gray wolves.  The counties in which wolf exposure has increased the most are among the Wisconsin counties in which human Lyme disease has also expanded the most.  By contrast, the prevalence of heartworm, a parasitic disease spread by mosquito bites, did not change during this time frame, suggesting that conditions favorable to ticks, but not mosquitoes, may be driving disease spread.

Why should we care about tick-borne diseases in wild wolves? They are free-ranging animals whose exposure to ticks is greater than that of pets or humans. They go places that we don’t go, and humans do not remove ticks from them as they do from domestic dogs. Thus, they can be regarded as sentinels of infectious diseases in wilderness spaces. Nationally, the Lyme disease epidemic in humans is expanding, particularly in the Northeast, Wisconsin and Minnesota. Several studies suggest that climate change may favor the growth of ticks and mosquitoes. So, information about vectors and microbes in wild animals everywhere will help us to plan and implement measures for safeguarding public health. In the last 75 years, 71.8% of emerging infectious diseases came from wildlife.

But aside from illnesses that we as humans may acquire, the health of gray wolves is important for another reason. They are predators and preserve ecosystem health, by preventing the overpopulation of prey species. Whether gray wolves become severely sick from tick-borne illness isn’t well known, with a few documented cases of captive wolves losing weight after Borrelia infection. So far, it appears that the wild wolf population, rebounding from near-extinction, has not been harmed by tick-borne microbes. However, we have a responsibility to remain vigilant to health threats to all species and in all habitats, not just our own.