Changes

==Description==

==Description==

[[File:Borreliose.png|thumb|Map of the areas where ''Borrelia spp'' are endemic<br><small>Copyright Percherie 2006 Wikimedia Commons]]</small>

[[File:Borreliose.png|thumb|Map of the areas where ''Borrelia spp'' are endemic<br><small>Copyright Percherie 2006 Wikimedia Commons]]</small>

Lyme disease descibes the clinical syndrome caused by infection with ''[[Borrelia burgdorferi]]'' sensu lato in humans, dogs, horses, cattle and sheep.  The disease is named after the town of Lyme[http://townlyme.org/ Lyme] in Connecticut, USA where clinical cases were first described in humans in 1975.  Since its identification, analysis of historical samples of ticks has shown that ''B. burgdorferi'' has been present in Europe and North America since at least the start of the twentieth Century<ref>Marshall WF 3rd, Telford SR 3rd, Rys PN, Rutledge BJ, Mathiesen D, Malawista SE, Spielman A, Persing DH. '''Detection of Borrelia burgdorferi DNA in museum specimens of Peromyscus leucopus.''' ''J Infect Dis. 1994 Oct;170(4):1027-32.''</ref><ref>Hubbard MJ, Baker AS, Cann KJ. '''Distribution of Borrelia burgdorferi s.l. spirochaete DNA in British ticks (Argasidae and Ixodidae) since the 19th century, assessed by PCR.''' ''Med Vet Entomol. 1998 Jan;12(1):89-97.''</ref>.  Currently, the bacterium is known to be present in Europe, Asia and North America (see image) and the prevalence of antibodies to ''B. burgdorferi'' sensu lato in French dogs was 1.09% when this was investigated in 2009<ref>Pantchev N, Schaper R, Limousin S, Norden N, Weise M, Lorentzen L. '''Occurrence of Dirofilaria immitis and tick-borne infections caused by Anaplasma phagocytophilum, Borrelia burgdorferi sensu lato and Ehrlichia canis in domestic dogs in France: results of a countrywide serologic survey.''' ''Parasitol Res. 2009 Aug;105 Suppl 1:S101-14.''</ref>.

Lyme disease descibes the clinical syndrome caused by infection with ''[[Borrelia burgdorferi]]'' sensu lato in humans, dogs, horses, cattle and sheep.  The disease is named after the town of[http://townlyme.org/ Lyme] in Connecticut, USA where clinical cases were first described in humans in 1975.  Since its identification, analysis of historical samples of ticks has shown that ''B. burgdorferi'' has been present in Europe and North America since at least the start of the twentieth Century<ref>Marshall WF 3rd, Telford SR 3rd, Rys PN, Rutledge BJ, Mathiesen D, Malawista SE, Spielman A, Persing DH. '''Detection of Borrelia burgdorferi DNA in museum specimens of Peromyscus leucopus.''' ''J Infect Dis. 1994 Oct;170(4):1027-32.''</ref><ref>Hubbard MJ, Baker AS, Cann KJ. '''Distribution of Borrelia burgdorferi s.l. spirochaete DNA in British ticks (Argasidae and Ixodidae) since the 19th century, assessed by PCR.''' ''Med Vet Entomol. 1998 Jan;12(1):89-97.''</ref>.  Currently, the bacterium is known to be present in Europe, Asia and North America (see image) and the prevalence of antibodies to ''B. burgdorferi'' sensu lato in French dogs was 1.09% when this was investigated in 2009<ref>Pantchev N, Schaper R, Limousin S, Norden N, Weise M, Lorentzen L. '''Occurrence of Dirofilaria immitis and tick-borne infections caused by Anaplasma phagocytophilum, Borrelia burgdorferi sensu lato and Ehrlichia canis in domestic dogs in France: results of a countrywide serologic survey.''' ''Parasitol Res. 2009 Aug;105 Suppl 1:S101-14.''</ref>.

The bacterium is transmitted by ticks of which the most common is ''[[Ixodes spp.|Ixodes ricinus]]'' in the UK.  ''I. ricinus'' is a three host tick that acquires ''B. burgdorferi'' bacteria when it obtains a blood meal from small rodents as a larva and then transmits it to large mammals as a nymph or adult.  Lyme disease therefore occurs when domestic animals and humans enter areas of tick habitat and ticks must be attached for at least 48 hours for the organisms to multiply and transfer to the mammalian host.

The bacterium is transmitted by ticks of which the most common is ''[[Ixodes spp.|Ixodes ricinus]]'' in the UK.  ''I. ricinus'' is a three host tick that acquires ''B. burgdorferi'' bacteria when it obtains a blood meal from small rodents as a larva and then transmits it to large mammals as a nymph or adult, demonstrating trans-stadial transmission.  Lyme disease therefore occurs when domestic animals and humans enter areas of tick habitat and ticks must be attached for at least 48 hours for the organisms to multiply and transfer to the mammalian host.

===Pathophysiology===

===Pathophysiology===

The virulence of the borreliae is associated with changes in expression of outer membrane proteins (OMP) after introduction into the mammalian host.  In the majority of hosts, the bacteria remain at the site of introduction but do not cause clinical disease.  Antibodies are produced in response to the bacteria but, despite this, they are not eliminated and they may persist for the life of the host.  In a small proportion of infected animals, the bacteria multiply and migrate through the connective tissues and disseminate via the blood stream.  The migrant bacteria localise particularly in the skin, joints, brain, nerves, eyes and heart and clinical syndromes may involve any of these organs.  The immune response to the bacterial OMPs cross-reacts with epitopes present of host proteins and the lesions that are observed in Lyme disease may in part be caused by this immune response.

The virulence of the borreliae is associated with changes in expression of outer membrane proteins (OMPs) after introduction into the mammalian host.  In the majority of hosts, the bacteria remain at the site of introduction but do not cause clinical disease.  Antibodies are produced in response to the bacteria but, despite this, they are not eliminated and they may persist for the life of the host.  In a small proportion of infected animals, the bacteria multiply and migrate through the connective tissues and disseminate via the blood stream.  The migrant bacteria localise particularly in the skin, joints, brain, nerves, eyes and heart and clinical syndromes may involve any of these organs.  The immune response to the bacterial OMPs cross-reacts with epitopes present of host proteins and the lesions that are observed in Lyme disease may in part be caused by this immune response.

It is not currently known why only a small proportion of infected animals develop clinical disease.

It is not currently known why only a small proportion (5-10%) of infected animals develop clinical disease.

==Signalment==

==Signalment==