Font: https://www.anmm.org.mx/GMM/2014/n1/GMM_150_2014_1_084-095.pdf

In the bacterial world, there is Borrelia, a spirochetal bacteria with a helical shape present in ticks and lice, and is the cause of Lyme disease and relapsing fever.

What is Borrelia?

Borrelia a spirochete bacteria with a helical shape. 52 species of Borrelia have been identified, all of them transmitted by blood-sucking arthropods, such as ticks or lice.

Borrelia Species Diversity: 

Currently 52 species of Borrelia have been identified but Borrelia burgdorferi It is the best known species that causes Lyme disease, and it is not the only one to transmit this disease.

In Europe, including Spain, Borrelia afzelii and Borrelia garinii They are also common causes of Lyme disease. These species can have different manifestations.

• Borrelia Burgdorferi: It is one of the pathogenic bacteria that can survive without iron, replacing all enzymes of the iron-sulfide family with enzymes that contain manganese, avoiding the problem that many pathogenic bacteria have in obtaining iron.

Once it has infected a vertebrate, a recombination mechanism allows the bacteria to evade the immune system by altering the antigens on its membrane, resulting in the ineffectiveness of the host's adaptive immunity.

• Borrelia Afzelii: It is mainly associated with cutaneous manifestations, such as erythema migrans (EM) and acrodermatitis chronica atrophica. The clinical characteristics of the involvement associated with B. afzelii They are much less specific and more difficult to diagnose. It is only found in Europe.

• Borrelia Garinii: It is particularly associated with neurologically affecting Lyme disease, including cases of meningoencephalitis and, rarely, encephalomyelitis. Unlike B. burgdorferi, it is not found in North America.

Joint pain and inflammation are common symptoms in Lyme disease, but not in most European cases. On the contrary, these present a erythema migrans isolated, while multiple skin lesions have been observed in American Lyme disease.

Role that ticks play in the transmission of pathogens: 

In Spain, the tick Ixodes ricinus is the main transmitter of Borrelia. This tick is also common in other parts of Europe. The distribution and prevalence of this type of tick (Ixodes ricinus) is influenced by environmental factors such as humidity and temperature.

Tick Life Cycle and Transmission: 

Ticks go through several stages in their life cycle (larva, nymph, adult) and can become infected with Borrelia at any stage by feeding on an infected host. However, they are more likely to transmit the bacteria to humans in the nymph stage due to their small size and greater likelihood of going unnoticed when attached to the skin.

Seasonal Prevalence:

In Spain, as in many other parts of Europe, tick prevalence and the risk of Lyme disease are highest during the warmer months, especially in spring and early summer, when nymphs are most active.

Preferred Habitats: 

Ixodes ricinus, the Borrelia-carrying tick, prefers wooded and densely vegetated areas. In Spain, this means that regions with these environments have a higher risk of Lyme disease.

What are the areas of Spain with the highest prevalence of Borrelia infections?

North of Spain:

• Galicia, 
• Asturias
• Cantabria
• Basque Country

These have a humid climate and many natural spaces with dense vegetation, which provides an ideal habitat for Ixodes ticks. These conditions favor a higher prevalence of Lyme disease.

Mountainous Areas: 

• The Pyrenees 
• The Cantabrian Mountains

They are also risk areas due to their forest ecosystems and the abundance of wildlife, which can act as reservoirs for the bacteria.

Natural Parks and Rural Areas: 

Areas with natural parks and rural areas, where there is greater interaction between humans and wildlife, may present a high risk. This includes:

• Regions in Castilla y León
• Parts of Aragon.

Clinical Importance:

The Borrelia species that are of greatest clinical interest are:

• B. burgdorferi: Which is responsible for causing Lyme disease.
• B. recurrentis: What causes relapsing fever due to lice?

Diagnostic Methods:

• Culture in modified Kelly medium and PCR.
• Challenges in cultivation: Low levels and voluminous samples.

The method of diagnosing infections Borrelia The most used is culture on modified Kelly medium. To do this, the most common thing is to use blood samples in cases of recurrent fever, since the levels of bacteria in the blood are very high during febrile periods, or to perform a biopsy of the skin lesions in cases of Lyme disease. 

It can also be detected B. recurrentis directly through blood smears taken during periods of fever.

However, the cultivation of Borrelia It is not always the most appropriate method. This is usually due to low levels of bacteria in the blood and other tissues during infection and the need for large volume samples and qualified personnel to perform biopsies.

PCR assays can be performed, especially in cases of Lyme disease, which require smaller volume samples of blood or synovial fluid. In general, PCR is used to confirm possible infections by Borrelia, identify the specific species and detect co-infections with other tick-borne pathogens. 

Clinical Aspects:

Recurrent fever: Epidemic and endemic. 

The most common symptoms, in addition to fever, are chills, fever, headache and fatigue.

These recurring fevers occur when the bacteria, transmitted by an infected arthropod, reaches the bloodstream of the infected person. After an incubation period of 4 to 18 days in which levels of 10⁸ bacteria per milliliter of blood, the first symptoms of the disease appear.

Lyme's desease: Caused by B. burgdorferi, B. garinii and B. afzelii. 

It mainly affects the skin, nervous system, heart and joints. 

Its main sign is the appearance of a skin lesion, called erythema migrans, between seven and nine days after the tick bite occurs. The erythema usually disappears after a few weeks even without treatment, although it may reappear where the bite occurred or in distant sites.

If the disease is not treated or if inadequate treatment is administered, more serious symptoms such as arthritis, myocarditis or meningitis may appear, as a result of the spread of the bacteria to the joints, heart or nervous system, respectively.

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