Countries with reported<unk>  cases.<unk>  occurs regularly in Northern Hemisphere temperate regions. There is evidence that tick populations and<unk>  occurrence are increasing and spreading into new areas, due in part to the warming temperatures of climate change. Africa In northern Africa, B. burgdorferi sensu lato has been identified in Morocco, Algeria, Egypt and Tunisia.<unk>  in sub-Saharan Africa is presently unknown, but evidence indicates it may occur in humans in this region. The abundance of hosts and tick vectors would favor the establishment of<unk>  infection in Africa. In East Africa, two cases of<unk>  have been reported in Kenya. Asia B. burgdorferi sensu lato-infested ticks are being found more frequently in Japan, as well as in northwest China, Nepal, Thailand and far eastern Russia. Borrelia has also been isolated in Mongolia. Europe In Europe,<unk>  is caused by infection with one or more pathogenic European genospecies of the spirochaete B. burgdorferi sensu lato, mainly transmitted by the tick Ixodes ricinus. Cases of B. burgdorferi sensu lato-infected ticks are found predominantly in central Europe, particularly in Slovenia and Austria, but have been isolated in almost every country on the continent. Number of cases in southern Europe, such as Italy and Portugal, is much lower. Diagnosed cases in some Western Countries, such as Iceland, are rising. United Kingdom In the United Kingdom the number of laboratory confirmed cases of<unk>  has been rising steadily since voluntary reporting was introduced in 1986 when 68 cases were recorded in the UK and Ireland combined. In the UK there were 23 confirmed cases in 1988 and 19 in 1990, but 973 in 2009 and 953 in 2010. Provisional figures for the first 3 quarters of 2011 show a 26% increase on the same period in 2010. It is thought, however, that the actual number of cases is significantly higher than suggested by the above figures, with the UK's Health Protection Agency estimating that there are between 2,000 and 3,000 cases per year, (with an average of around 15% of the infections acquired overseas), while Dr Darrel Ho-Yen, Director of the Scottish Toxoplasma Reference Laboratory and National<unk>  Testing Service, believes that the number of confirmed cases should be multiplied by 10 "to take account of wrongly diagnosed cases, tests giving false results, sufferers who weren't tested, people who are infected but not showing symptoms, failures to notify and infected individuals who don't consult a doctor." Despite<unk>  (Borrelia burgdorferi infection) being a notifiable<unk>  in Scotland since January 1990 which should therefore be reported on the basis of clinical suspicion, it is believed that many GPs are unaware of the requirement. Mandatory reporting, limited to laboratory test results only, was introduced throughout the UK in October 2010, under the Health Protection (Notification) Regulations 2010. Although there is a greater number of cases of<unk>  in the New Forest, Salisbury Plain, Exmoor, the South Downs, parts of Wiltshire and Berkshire, Thetford Forest and the West coast and islands of Scotland, infected ticks are widespread, and can even be found in the parks of London. A 1989 report found that 25% of forestry workers in the New Forest were seropositive, as were between 2% and 4–5% of the general local population of the area. Tests on pet dogs carried out throughout the country in 2009 indicated that around 2.5% of ticks in the UK may be infected, considerably higher than previously thought. It is thought that global warming may lead to an increase in tick activity in the future, as well as an increase in the amount of time that people spend in public parks, thus increasing the risk of infection. North America Many studies in North America have examined ecological and environmental correlates of the number of people affected by<unk> . A 2005 study using climate suitability modelling of I. scapularis projected that climate change would cause an overall 213% increase in suitable vector habitat by 2080, with northward expansions in Canada, increased suitability in the central U.S., and decreased suitable habitat and vector retraction in the southern U.S. A 2008 review of published studies concluded that the presence of forests or forested areas was the only variable that consistently elevated the risk of<unk>  whereas other environmental variables showed little or no concordance between studies. The authors argued that the factors influencing tick density and human risk between sites are still poorly understood, and that future studies should be conducted over longer time periods, become more standardized across regions, and incorporate existing knowledge of regional<unk>  ecology. Canada The range of ticks able to carry<unk>  has expanded from a limited area of Ontario to include areas of southern Quebec, Manitoba, northern Ontario, southern New Brunswick, southwest Nova Scotia and limited parts of Saskatchewan and Alberta, as well as British Columbia. Cases have been reported as far east as the island of Newfoundland. A model-based prediction by Leighton et al. (2012) suggests that the range of the I. scapularis tick will expand into Canada by 46 km/year over the next decade, with warming climatic temperatures as the main driver of increased speed of spread. Mexico A 2007 study suggests Borrelia burgdorferi infections are endemic to Mexico, from four cases reported between 1999 and 2000. United States CDC map showing the risk of<unk>  in the United States, particularly its concentration in the Northeast Megalopolis and western Wisconsin. In 2019, according to the CDC, there were approximately 35,000 confirmed and probable cases in the U.S. with incidences occurring in almost every state. The CDC is currently conducting research on evaluation and diagnostics of the<unk>  and preliminary results suggest the number of new cases to be around 300,000.<unk>  is the most common tick-borne<unk>  in North America and Europe, and one of the fastest-growing infectious<unk> s in the United States. Of cases reported to the United States CDC, the ratio of<unk>  infection is 7.9 cases for every 100,000 persons. In the ten states where<unk>  is most common, the average was 31.6 cases for every 100,000 persons for the year 2005. Although<unk>  has been reported in all states about 99% of all reported cases are confined to just five geographic areas (New England, Mid-Atlantic, East-North Central, South Atlantic, and West North-Central). New 2011 CDC<unk>  case definition guidelines are used to determine confirmed CDC surveillance cases. Effective January 2008, the CDC gives equal weight to laboratory evidence from 1 a positive culture for B. burgdorferi; 2) two-tier testing (ELISA screening and Western blot confirming); or 3) single-tier IgG (old infection) Western blot. Previously, the CDC only included laboratory evidence based on (1) and (2) in their surveillance case definition. The case definition now includes the use of Western blot without prior ELISA screen. The number of reported cases of the<unk>  has been increasing, as are endemic regions in North America. For example, B. burgdorferi sensu lato was previously thought to be hindered in its ability to be maintained in an enzootic cycle in California, because it was assumed the large lizard population would dilute the number of people affected by B. burgdorferi in local tick populations; this has since been brought into question, as some evidence has suggested lizards can become infected. Except for one study in Europe, much of the data implicating lizards is based on DNA detection of the spirochete and has not demonstrated that lizards are able to infect ticks feeding upon them. As some experiments suggest lizards are refractory to infection with Borrelia, it appears likely their involvement in the enzootic cycle is more complex and species-specific. While B. burgdorferi is most associated with ticks hosted by white-tailed deer and white-footed mice, Borrelia afzelii is most frequently detected in rodent-feeding vector ticks, and Borrelia garinii and Borrelia valaisiana appear to be associated with birds. Both rodents and birds are competent reservoir hosts for B. burgdorferi sensu stricto. The resistance of a genospecies of<unk>  spirochetes to the bacteriolytic activities of the alternative complement pathway of various host species may determine its reservoir host association. Several similar but apparently distinct conditions may exist, caused by various species or subspecies of Borrelia in North America. A regionally restricted condition that may be related to Borrelia infection is southern tick-associated rash illness (STARI), also known as Masters<unk> . Amblyomma americanum, known commonly as the lone-star tick, is recognized as the primary vector for STARI. In some parts of the geographical distribution of STARI,<unk>  is quite rare (e.g., Arkansas), so people in these regions experiencing<unk> -like symptoms—especially if they follow a bite from a lone-star tick—should consider STARI as a possibility. It is generally a milder condition than<unk>  and typically responds well to antibiotic treatment. In recent years there have been 5 to 10 cases a year of a<unk>  similar to<unk>  occurring in Montana. It occurs primarily in pockets along the Yellowstone River in
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