Tick-borne diseases
Ticks are hematophagous mites that can transmit a number of diseases to humans, which present a non-specific clinical picture, with flu-like symptoms. Sometimes severe, these diseases require specific treatment and management. For this reason, it is important to make a diagnosis.
We will focus on two such tick-borne diseases, namely Lyme borreliosis (Lyme disease) and babesiosis.
Main diseases transmitted by ticks:
Bacteria
– Spirochetes: Lyme borreliosis, tick-borne relapsing fever
– Rickettsioses: Mediterranean spotted fever, rocky mountain spotted fever, ehrlichiosis, tularemia
Viruses
– Tick-borne meningoencephalitis, Crimean-Congo hemorrhagic fever
Protozoa
– Babesiosis
Lyme borreliosis
Lyme borreliosis is the most common bite infection in Europe. It is characterised by great clinical, but also bacteriological and antigenic, polymorphism.
Lyme borreliosis is a non-contagious bacterial infection caused by a spirochete, Borrelia burgdorferi sensu lato, which is transmitted to humans by Ixodes tick bites. The disease is present wherever vector agents exist: in Europe (Ixodes ricinus), the USA and Central America (I. scapularis), Asia (I. persulcatis), and in the western USA (I. pacificus).
Ixodes live in wetlands and deciduous forests. These creatures are most active in the spring and early autumn. Humans are an incidental host. The bacterium is present in the tick’s intestine, attached by an OSP A protein, and is transmitted after passing through the salivary glands. The bacterium then diffuses through the skin. The Borrelia species encountered in human pathology are B. afzelii (the main species in France), B. burgdorferi (the main species in the USA) and B. garinii.
The rate of infestation of ticks by Borrelia ranges from 3-30%, with large regional disparities. After being bitten by an infected tick, the risk of transmission (seroconversion) is 10%. Several techniques can be used for biological diagnosis.
Babesiosis
Babesiosis is an infection caused by the protozoan Babesia spp. It is often asymptomatic in immunocompetent individuals or results in a malaria-like illness with a fever and haemolytic anaemia, but can be severe in splenectomised or immunosuppressed patients. Types of patient management and treatment are known.
The spectrum of tick-borne diseases is increasing with the advancement of knowledge. Lyme disease is the most common tick-borne disease in Europe; however, when faced with “atypical Lyme disease”, other tick-borne pathogens should be considered.
