Lyme disease gets its name from Lyme, Connecticut, where a group of teens suffered from a mysterious arthritic condition in the mid 1970s. By the late 1970s, U.S. scientists had determined that infected blacklegged (Ixodes) ticks transmitted the disease. In 1981, Swiss-American researcher Willy Burgdorfer identified the spirochete bacterium, which was named Borrelia burgdorferi after him.
As a result of these findings, many people think Lyme disease is an American disease. But as early as the 1920’s, Swedish and Austrian doctors had documented the hallmark red rash of Lyme. Earlier reports describe a biting insect and debilitating arthritis that point to Lyme disease in Europe in the 1700’s.
We now know that Lyme disease, known outside North America as borreliosis, occurs on various continents around the world. While borreliosis is usually found more often in specific geographic areas, it’s important to recognize the worldwide distribution of the disease.
Let’s take a closer look at worldwide Lyme Disease by continent.
According to the U.S. Centers for Disease Control (CDC), reported cases of Lyme have been steadily rising since national surveillance began in 1982. In 2008 there were some 30,000 reported U.S. cases of Lyme disease and 35,000 reported cases in 2009. Many believe, however, that these numbers are grossly underreported.
Lyme disease cases are consistently higher in some US states than others. The highest incidence each year happens in Eastern states from Maryland to Maine and in Wisconsin, Minnesota, and parts of northern California and southern Oregon. However, while the geographic range of the blacklegged tick and its reservoir animals is limited, people diagnosed with Lyme live in every U.S. state.
Ticks in the United States carry mainly Borrelia burgdorferi sensu stricto.
In Canada, Lyme borreliosis cases are also increasing. As of 2010, Lyme disease is reportable to provincial and/or national health services. According to the Canadian government, the areas that pose the highest risk of exposure to ticks carrying Borrelia burgdorferi are southern British Columbia, southeastern Manitoba, New Brunswick and Nova Scotia, southern and eastern Ontario, and southern and southeastern Quebec.
It’s important to note that official Lyme statistics can be deceiving. In the U.S. not all doctors who treat people for Lyme report these cases for fear of retribution by medical licensing boards. For more on underreporting in the US, see this Canadian Lyme Association article.
Lyme cases have also been reported in Mexico. In fact, there is some evidence that Borrelia burgdorferi infection may be as endemic to Mexico as it is in the US and Canada, though on a smaller scale.
Europe has a comparable number of borreliosis cases as the U.S. According to the European Commission, Health and Consumers Directorate-General, in 2005 there were over 20,000 reported cases of the disease among the countries of the EU-27 (European Union; some countries not reporting). This figure doubled from the recorded rate 10 years earlier. Certain EU countries have consistently higher numbers of cases than others. Particularly high-risk areas are the Czech Republic, Poland, Slovenia, and other central and eastern European nations. While many European countries have been slow to adopt national borreliosis reporting laws, Slovenia made it a reportable illness back in 1987. In fact, researchers estimate that 40% of ticks in Slovenia carry Borrelia spirochetes.
European ticks carry eight known species of Borrelia namely B. afzelii, B. bavariensis, B. burgdorferi sensu stricto, B. garinii, and B. spielmanii, B. valaisiana, B. lusitaniae and B. bissetii. Only the first five types are known to cause disease in humans. The latter three might cause disease, though further research is needed.
These different types of Borrelia are distributed in different regions of Europe. This could explain why the Lyme symptoms seen in various areas of the continent are different. For example, B. burgdorferi s.s. more often causes neurological symptoms and arthritis, while B. afzelii affects the skin, and B. garinii primarily causes nervous system problems. The North American genospecies B. burgdorferi s.s. is thought to be a transplant from the West; the other types of Borrelia appear to be native to the continent.
The number of cases of borreliosis in Asian countries is more difficult to track. But the infection does occur, primarily in China and Russia and to a lesser extent in Korea and Japan. Cases are typically more concentrated in the northern, temperate regions as in the rest of the world.
The first case of Lyme disease in China was reported in 1986 in Heilongjiang Province. But borreliosis has since been found in virtually every Chinese province. As elsewhere, Borrelia genospecies are more highly concentrated in certain geographic hot spots. For example, the Gansu Province in northwestern China has a high rate of Borrelia-infected rodents and migratory birds. In fact, the numbers seem to be particularly high along the former path of the Old Silk Road that runs through the province. Since the primary genospecies of Borrelia in this region is B. garinii, it is likely that the spirochete migrated from Europe.
Lyme borreliosis is also endemic to the Baltic regions of Russia. The city of Perm in the Pre-Ural Mountain region has a rate about double the rest of Russia. Surveys of the St. Petersburg and Kaliningrad vicinities reveal that 10-30 percent of the Ixodes ticks carry human–disease causing Borrelia, specifically B. afzelii and B. garinii.
Many originally thought that Japan, an island nation, was protected from borreliosis. However, genetic studies of infection show that the spirochete can travel from Mainland China to Japan in migratory birds. The birds then provide a blood meal to local ticks. Or the Chinese ticks hitch a ride on the birds themselves. These ticks then feed on and infect humans or live on Japanese rodents.
South America, Africa, Australia
Lyme disease/borreliosis has rarely occurred in tropical regions, mainly because ticks and their reservoir animals are not common in these areas. When rare cases have been reported, it’s more likely these patients got infected when they traveled outside their country to endemic areas. However, doctors in Brazil are watching a Lyme-like syndrome that seems to be increasing.
The presence of Borrelia species capable of causing human disease in Australia continues to be a matter of debate. Researchers are puzzled by the fact that the Ixodes tick species native to Australia, Ixodes holocyclus, is not capable of carrying or transmitting Borrelia burgdorferi bacteria. Also, the typical reservoir animals in North America and Europe are not found in Australia. Despite thousands of suspected cases of borreliosis in Australia, so far only a handful of patients have turned out to actually have the disease. In these cases, essentially all had traveled to an endemic region outside of Australia.
Some argue, however, that the Australian tick I. holocyclus may be able to carry another as yet unidentified Borrelia species. This could explain why many Australians have symptoms very consistent with borreliosis but fail to show a positive result on current Lyme laboratory tests. The Australian government is funding research into the issue.
In short, Lyme borreliosis appears in many countries besides the U.S. Add to that the fact that in many countries other tick-borne diseases are also on the rise, and it’s clear that tick-borne illnesses are a growing public health problem worldwide.
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