August 1, 2025 Author : Saraiva da Cunha (infectious diseases) Lyme disease, also named Lyme borreliosis, is a zoonosis , meaning a disease of animals which can be transmitted to humans . It was first identified in the city of Lyme, in the United States. It is the main tick-borne infection in temperate areas of Europe , the United States, and Asia. It is caused by certain bacteria from a complex called Borrelia burgdorferi . These bacteria are transmitted by infected ticks of the species Ixodes ricinus , the second most common in Portugal. In our country, this tick is widespread throughout the territory. The ticks live in wooded areas with high relative humidity . They are highly resistant and detect their hosts efficiently, attaching them when they are near. In Portugal, adult forms peak in activity during the fall and winter months, while immature forms (larvae and nymphs) occur mainly in the spring and summer months . In the younger stages of its life cycle, Ixodes ricinus preferred hosts are rodents and birds and in the later stages, the deer. Humans and domestic animals (such as dogs and horses) are accidental hosts . Ticks become infected when they feed on the blood of birds and other animals carrying Borrelia burgdorferi . When they feed on the blood of humans and domestic animals , ticks inject saliva and, if infected, they transmit Borrelia burgdorferi . Ticks prefer hidden areas of the skin, such as the knees, armpits, groin, waist, neck, and head to attach and bite the hosts. Lyme borreliosis is not contagious and is not transmitted between people ; transmission is always carried by the vector Ixodes ricinus . Symptoms of Lyme disease The initial symptoms of Lyme borreliosis vary and may include: Nonspecific, flu-like symptoms such as fatigue, malaise, fever, headache, muscle and joint pain. Erythema migrans , which is a characteristic skin reaction. t occurs in about 60%-80% of infected people . It begins after 3-30 days in the area of skin where the tick was attached and then expands, sometimes reaching several centimeters. The skin becomes red , either uniformly or with a central discolored area, which may or may not itch or burn. Over time, the redness may become more intense. Erythema migrans is usually a single lesion, but in about 20% of cases, multiple lesions occur. If the disease is not detected early and treated appropriately with antibiotics, it can lead to later symptoms and complications . These occur six weeks to a few months after infection, can persist for years, and primarily involve: The central nervous system , which is the most serious complication. Lyme neuroborreliosis occur in about 10% of cases , and can cause, for example, facial paralysis and severe neuropathic pain, especially in older people. The joints, with joint inflammation of one or more joints; The heart; The skin, with multiple erythema migrans lesions and nodule formation, usually on the hands, feet, knees, and elbows. Diagnosis and treatment The diagnosis of Lyme borreliosis is based on symptoms, history, and risk of exposure to ticks and can be confirmed by blood tests. In most people, treatment of Lyme disease in its early stages with antibiotics is very effective in controlling symptoms and preventing the disease from progressing. However, symptoms such as headache, joint pain, and fatigue may persist for several months or years after treatment, but they generally disappear gradually. Prevention In Portugal, only Lyme neuroborreliosis has been considered a notifiable disease since 2021 , which is why the true extent of Lyme disease in our country is unknown . There are no commercially available vaccines against Lyme borreliosis in humans, although several are under investigation. Agricultural workers and people living in rural areas are, of course, at higher risk of having tick-borne diseases. However, Ixodes ricinus ticks can also be found in any area with vegetation and high relative humidity, such as gardens and urban parks, so anyone who spends time in places where ticks may be present is at risk of infection . In areas where ticks may be present, everyone should wear insect repellent and light-colored protective clothing - long pants, socks (preferably untucked), and shoes - because this makes ticks less likely to attach to the skin. Additionally, should walk on trails , whenever possible, because they have less vegetation. Keeping areas near homes and animal houses clear of vegetation and following pet deworming programs are also important measures to control ticks. Ticks only begin feeding on blood about 24 hours after attaching to the skin, and Borrelia transmission usually occurs within 48 hours. Therefore, bathing and carefully inspecting the skin (and clothing) after being in areas where ticks may be present is good practice, and special attention should be paid to the most hidden areas, like skin folds. Ticks attached to the skin should be removed whole with tweezers, so it may be necessary to seek help to do it correctly. References European Centre for Disease Prevention and Control. Borreliosis . Relatório REVIVE 2024. Culicídeos,ixodídeos e flebótomos: rede de vigilância de vetores. Centro de Estudos de Vetores e Doenças Infeciosas Doutor Francisco Cambournac. Lisboa: Instituto Nacional de Saúde Doutor Ricardo Jorge, 2025. Meet the infectious diseases clinical team from Hospital da Luz network . The content published in the Health Guide is intended for the general public and is provided for informational and educational purposes only. It does not replace individual medical assessment, diagnosis, or personalized clinical advice from a qualified healthcare professional. The content is produced or reviewed by physicians and other healthcare professionals at Hospital da Luz and is based on the knowledge available at the time of publication or the most recent update, as indicated at the beginning of each item.
