Skip to 0 minutes and 10 seconds Hello. In this presentation I will give a brief introduction to ticks and Lyme disease. This presentation is structured as follows. First we will explain what vectors are and what are the main vector-borne diseases existing in the world. Then we will go a bit more in-depth in to the ticks and Lyme disease topic. And finally, we will give a brief introduction to the geographic and environmental factors associated to Lyme disease. But first we need to make a step back. You may ask, what is a vector? Well, a vector is an insect that basically transmits disease, a bacteria, or a virus from one individual to another individual.
Skip to 0 minutes and 51 seconds The World Health Organization has a list of the 14 vector-borne diseases that you can see here in this blue box. You will see some well known names, such as Malaria or Dengue, but here we are going to study the Lyme disease that you can see in yellow a the bottom of the blue box. What all of these diseases have in common is that they have the same transmission patterns. It is the same mechanism that is a vector which is typically a mosquito, a tick, or other different insects that transmit the disease from one individual to another. This is the distribution of Lyme disease in the world.
Skip to 1 minute and 34 seconds As you can see, Lyme disease is the most prevalent vector-borne disease in the northern hemisphere. It was first– the bacteria causing Lyme disease was first isolated in the United States in the village of Lyme in Connecticut. In the ’80s, there was a wave, outbreak, of children having arthritis. So the public health authorities went to this place to investigate a bit more, what was the origin? What was the cause of the arthritis in kids? So they– after some experimentation and research, they discovered for the first time that there was really a bacteria. As I said before, the Malaria bacteria is carried by ticks.
Skip to 2 minutes and 20 seconds And ticks are arthropods that live in nature, typically in deciduous or mixed forests that we can find here in northern latitudes. This is the preferred habitat for ticks because the forest canopy prevents the direct sunlight to reach the ground level, and makes the forest ambiance to be cooler than the outside. And this is good for the ticks because otherwise, if the temperature is too high or there are drought conditions, the ticks desiccate and die. So, usually ticks are monitored using the flagging method, which you can see depicted in the central image, which basically consists of dragging a blanket over all the litter and leaves at the ground level.
Skip to 3 minutes and 5 seconds In the two small images at the right you can see– at the top– an adult tick and below and infant larvae. Just to give a bit more context, the size of an adult tick is half a grain of rice. And the size of a nymph is like the tip of a needle and the larvae are like two small dots on a sheet of paper. So as you can see, it’s very difficult to see ticks in nature, or even if they are biting you. This is the evolution of Lyme disease in the Netherlands from 1994 to 2014.
Skip to 3 minutes and 47 seconds The Dutch National Institute for Public Health and the Environment commissions every four or five years to the general practitioners all over the country, a report where the doctors have to say how many Lyme disease cases they have seen in that year. So, every four or five years we have one of these maps. As you can see, this disease, since the mid ’90s, there is a clear growing pattern in the East half of the country. And also we can see that even though that at the beginning, the South half of the country was more or less free of Lyme disease cases, it is catching up very fast.
Skip to 4 minutes and 33 seconds So now, for each of the red polygons that you can see in the last image, it means that there are 200 cases of Lyme disease every 100,000 inhabitants in this municipality. So the problem is getting bigger and bigger. If we get the data of these reports and we convert it into a chart, we can see a chart like the one at the right. As you can see, the blue shape represents the ticks bites that were reported to general practitioners, and the orange shape represents the number of Lyme disease cases that were diagnosed since the mid ’90s. Here, there are two interesting things to highlight.
Skip to 5 minutes and 23 seconds The first thing is that in 2014 there was a clear decrease in that ticks bite consultations, but there was still an increase, but gentler, in the number of Lyme disease cases. This can be due to different causes. First, it could be an increased awareness of the people about the risk of getting a tick bite in nature, but it also could be an increase in carelessness. So people don’t go to the doctors to report that they got a tick bite. Despite the fact that the tick bites have experienced a 3-fold increase since the mid ’90s, it seems that the number of Lyme disease cases is increasing, but is independent– the growing pattern is independent of the number of ticks bites.
Skip to 6 minutes and 12 seconds Something that makes scientists think that there is still no increase in the infection rate per-tick. At this point you may ask, why is this happening? Well, scientists have established a clear trigger, which is global warming. But it’s not global warming alone, because, yeah, we all know that global warming makes changes in weather dynamics, but also human action, through something called landscape fragmentation, which is the alteration of the landscape by putting together industrial areas, residential areas, and parks and other different land uses, is also affecting the number of tick bites seen in nature.
Skip to 6 minutes and 56 seconds And also, all of these global warming effects also out there, the wildlife dynamics of different small mammals and other species that are also involved in the tick ecology cycle. So the consequences of this is that today the tick season got longer, and we have much more higher tick densities in nature. Also studies at the continent and continental, or at least country level have demonstrated that the geographic distribution of ticks is pushing northwards. So, today there are places that before were not suitable for ticks, and now, just because they are hotter, they are also suitable to sustain tick populations.
Skip to 7 minutes and 46 seconds So, as the highlights of this video, we can say that Lyme disease has a high cost for citizens because it can have a long-lasting sequels translated into muscle and joint pain, and even brain deterioration. And for public health agents, it also can have a high cost because they have to pay for the treatment for a potentially chronical disease. It’s also important to remember that the changes in environmental factors affect the tick population, and that GIS and remote sensing data and other methods are useful to map monitor ticks.
Vector-borne diseases and ticks
In this step you will learn about ticks and Lyme disease. First you will learn what vectors are and what the main vector-borne diseases are. Then you will learn more on ticks and Lyme disease. And finally, you will learn more on the geographic and environmental factors associated to Lyme disease.
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