In Europe, the main vector is Ixodes ricinus, which is also called the sheep tick or castor bean tick. In China, Ixodes persulcatus (the taiga tick) is probably the most important vector. In North America, the black-legged tick or deer tick (Ixodes scapularis) is the main vector on the East Coast.The lone star tick (Amblyomma americanum), which is found throughout the Southeastern United States as far west as Texas, is unlikely to transmit the Lyme disease spirochetes, though it may be implicated in a related syndrome called southern tick-associated rash illness, which resembles a mild form of Lyme disease.On the West Coast of the United States, the main vector is the western black-legged tick (Ixodes pacificus). The tendency of this tick species to feed predominantly on host species such as the Western Fence Lizard that are resistant to Borrelia infection appears to diminish transmission of Lyme disease in the West.Transmission can occur across the placenta during pregnancy and as with a number of other spirochetal diseases, adverse pregnancy outcomes are possible with untreated infection; prompt treatment with antibiotics reduces or eliminates this risk.There is no scientific evidence to support Lyme disease transmission via blood transfusion, sexual contact, or breast milk. Tick-borne coinfections
Ticks that transmit B. burgdorferi to humans can also carry and transmit several other parasites, such as Babesia microti and Anaplasma phagocytophilum, which cause the diseases babesiosis and human granulocytic anaplasmosis (HGA), respectively. Among people with early Lyme disease, depending on their location, 2–12% will also have HGA and 2–40% will have babesiosis.
The specific approach to their use is dependent on the individual affected and the stage of the disease. For most people with early localized infection, oral administration of doxycycline is widely recommended as the first choice, as it is effective against not only Borrelia bacteria but also a variety of other illnesses carried by ticks. People taking doxycycline should avoid sun exposure because of higher risk of sunburns. Doxycycline is contraindicated in children younger than eight years of age and women who are pregnant or breastfeeding; alternatives to doxycycline are amoxicillin, cefuroxime axetil, and azithromycin. Azithromycin is recommended only in case of intolerance to the other antibiotics. The standard treatment for cellulitis, cephalexin, is not useful for Lyme disease. When it is unclear if a rash is caused by Lyme or cellulitis, the IDSA recommends treatment with cefuroxime or amoxicillin/clavulanic acid, as these are effective against both infections. Individuals with early disseminated or late Lyme infection may have symptomatic cardiac disease, Lyme arthritis, or neurologic symptoms like facial palsy, radiculopathy, meningitis, or peripheral neuropathy. Intravenous administration of ceftriaxone is recommended as the first choice in these cases; cefotaxime and doxycycline are available as alternatives.Treatment regimens for Lyme disease range from 14 days in early localized disease, to 14–21 days in early disseminated disease to 14–28 days in late disseminated disease. Neurologic complications of Lyme disease may be treated with doxycycline as it can be taken by mouth and has a lower cost, although in North America evidence of efficacy is only indirect.