Deer tick life cycle Borrelia bacteria, the causative agent of<unk> , magnified Ixodes scapularis, the primary vector of<unk>  in eastern North America Tick Ixodes ricinus, developmental stages<unk>  is caused by spirochetes, spiral bacteria from the genus Borrelia. Spirochetes are surrounded by peptidoglycan and flagella, along with an outer membrane similar to Gram-negative bacteria. Because of their double-membrane envelope, Borrelia bacteria are often mistakenly described as Gram negative despite the considerable differences in their envelope components from Gram-negative bacteria. The<unk> -related Borrelia species are collectively known as Borrelia burgdorferi sensu lato, and show a great deal of genetic diversity. B. burgdorferi sensu lato is a species complex made up of 20 accepted and three proposed genospecies. Eight species are known to cause<unk> : B. mayonii (found in North America), B. burgdorferi sensu stricto, B. bissettiae (both found in North America and Europe), B. afzelii, B. garinii, B. spielmanii, and B. lusitaniae (all found in Eurasia). Some studies have also proposed that B. valaisiana may sometimes infect humans, but this species does not seem to be important causes of<unk> . Tick life cycle There are three stages in the life cycle of a tick. Larva, nymph, and adult. During the nymph stage, ticks most frequently transmit<unk>  and are usually most active in late spring and early summer in regions where the climate is mild. During the adult stage,<unk>  transmission is less common due to the fact that it is less possible for adult ticks to bite humans and because they tend to be larger in size and therefore can be easily seen and removed. Transmission<unk>  is classified as a zoonosis, as it is transmitted to humans from a natural reservoir among small mammals and birds by ticks that feed on both sets of hosts. Hard-bodied ticks of the genus Ixodes are the vectors of<unk>  (also the vector for Babesia). Most infections are caused by ticks in the nymphal stage, because they are very small and thus may feed for long periods of time undetected. Nymphal ticks are generally the size of a poppy seed and sometimes with a dark head and a translucent body. Or, the nymphal ticks can be darker. (The younger larval ticks are very rarely infected.) Although deer are the preferred hosts of adult deer ticks, and tick populations are much lower in the absence of deer, ticks generally do not acquire Borrelia from deer, instead they obtain them from infected small mammals such as the white-footed mouse, and occasionally birds. Areas where<unk>  is common are expanding. Within the tick midgut, the Borrelias outer surface protein A (OspA) binds to the tick receptor for OspA, known as TROSPA. When the tick feeds, the Borrelia downregulates OspA and upregulates OspC, another surface protein. After the bacteria migrate from the midgut to the salivary glands, OspC binds to Salp15, a tick salivary protein that appears to have immunosuppressive effects that enhance infection. Successful infection of the mammalian host depends on bacterial expression of OspC. Tick bites often go unnoticed because of the small size of the tick in its nymphal stage, as well as tick secretions that prevent the host from feeling any itch or pain from the bite. However, transmission is quite rare, with only about 1.2 to 1.4 percent of recognized tick bites resulting in<unk> . 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<unk>  spirochetes, though it may be implicated in a related syndrome called southern tick-associated rash illness, which resembles a mild form of<unk> . 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<unk>  in the West. Transmission can occur across the placenta during pregnancy and as with a number of other spirochetal<unk> s, adverse pregnancy outcomes are possible with untreated infection; prompt treatment with antibiotics reduces or eliminates this risk. There is no scientific evidence to support<unk>  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<unk> s babesiosis and human granulocytic anaplasmosis (HGA), respectively. Among people with early<unk> , depending on their location, 2–12% will also have HGA and 2–40% will have babesiosis. Ticks in certain regions, including the lands along the eastern Baltic Sea, also transmit viruses that cause tick-borne encephalitis. Coinfections complicate<unk>  symptoms, especially diagnosis and treatment. It is possible for a tick to carry and transmit one of the coinfections and not Borrelia, making diagnosis difficult and often elusive. The Centers for<unk>  Control and Prevention studied 100 ticks in rural New Jersey, and found 55% of the ticks were infected with at least one of the pathogens.
Lyme disease
Cellulitis
Mumps
Bell's palsy
Rabies
Meningitis
Rickettsialpox
Scarlet fever