How is Borreliosis or Lyme disease transmitted?

The borreliosis It is an infectious disease caused by bacterium Borrelia burgdorferi. The bacterium is transmitted by tick bites infected and produces fever, headache, fatigue and skin rashes.

Also known as Lyme's desease, as this is the city where it was discovered. The first cases diagnosed as borreliosis occurred between 1975 and 1977 in Old Lyme, Lyme and East Haddam, in Connecticut (United States).

In Europe it is considered a endemic disease in many countries, where the prevalence can reach 4%, although immunological tests can be positive in more than 25% of the population in some regions, indicating that they have been infected by the bacteria (not all people develop symptoms of the disease).

The life cycle of the tick

During the hottest time of the year, between the end of spring and summer, the tick eggs (order Ixodida) and individuals emerge in the larval stage. The larvae They look for small animals as their first host, such as birds and rodents.

On these hosts, the larvae feed and develop until the second stage of the tick's life, the stage of nymph. When the following spring arrives, the nymphs look for a second hostusually larger mammals such as deer, dog, cat, human and other mammals.

During this second spring and summer the nymph becomes an adult and will lay eggs completing the life cycle.

The entire cycle usually lasts two years, although it may require more time if conditions are unfavourable. Similarly, if conditions are favourable, especially in warm or hot weather, the cycle can be accelerated.

transmission to human

Ticks come into contact with Lyme disease bacteria (Borrelia burgdorferi) during the larval and nymphal stages when their hosts are infected birds and small mammals that carry the bacteria in their blood.

The bacterium remains in the tick digestive system and from there he goes to his Salivary glands.

Subsequently, the nymph will leave the first host in search of the second host where it will become an adult. When she bites him to feed on her blood, will inject the bacteria into the host's bloodstream and infect the host.

Both nymphs and adult ticks can change hosts and transmit the disease to other animals. However, most cases of borreliosis are associated with nymphal bites. The greatest risk is in late spring and summer, when ticks are most active.

It was previously thought that female ticks did not pass the bacteria to their eggs, but it appears that some species of ticks do and their larvae can also transmit the disease, although infestation by tick larvae in humans is very rare.

Other forms of transmission

In addition to humans, the bacteria can be transmitted from ticks to other mammals, for example cats and dogs, but the disease is not usually transmitted from animal to animal, including from animals to humans and between humans.

It is not spread by touching, kissing, through the air, or through contaminated food. This is why Lyme disease is often considered It is not a contagious disease.

However, host-dependent microorganisms, such as Borrelia burgdorferiusually specialize in one transmission route, in this case through tick bites, but that does not mean that they cannot be transmitted through other routes.

It is commonly said that Lyme disease is not transmitted through intimate and sexual contact or during pregnancy, but there are data and documented cases that suggest that congenital vertical transmission and sexual transmission are possible, although much more difficult. than in other infectious diseases.

Thus, among other routes of transmission of Lyme disease can be found:

  • contaminated blood transfusion
  • Pregnancy
  • Fluid exchange during intercourse
  • Exposure to feces from animals or infected people
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