George Stilwell Veterinarian Professor, Faculdade de Medicina Veterinária da Universidade de Lisboa Tick fever , also known as Mediterranean spotted fever, is a zoonosis , that is, a disease that can be transmitted from animals to humans. It is not a common disease, but it can be serious and even fatal. Mortality is estimated in 2.5%. The disease is more common in countries in the Mediterranean basin, sub-Saharan Africa, India, and countries along the Black Sea. It is often thought that ticks are the cause of tick fever in humans. However, it is not the ticks that are responsible, not even the dogs. Tick fever is caused by a microorganism : a bacteria named Rickettsia conorii Transmission of tick fever In people, the infection occurs when people are bitten by a tick of the species Rhipicephalus sanguineus that carries , in its salivary glands, the bacterium Rickettsia conorii . Rhipicephalus sanguineus , also known as the dog tick, is an external parasite. Its main hosts are dogs. However, when a person is be bitten by a tick, this does not mean that the tick was passed directly from a dog. It is even more likely that ticks reach people from vegetation , for example when walking in the countryside or in areas with high vegetation. That is, we can have our dogs well dewormed and still be bitten by a tick that transmits tick fever. Traditionally, tick fever was more common in warm months, as these were associated with a greater presence of ticks on dogs and in fields. However, with the less accentuated climatic differences between the seasons of the year and with high temperatures continuing into autumn and even winter, it is increasingly difficult to establish a period of risk for tick fever. What is the role of dogs in tick fever? Ticks can transmit various microorganisms to dogs. Some can cause serious illness and even death to animals. But this does not happen with Rickettsia conorii . For some time, there was a doubt about the role of dogs in the cycle and spread of tick fever. However, it is now known that dogs are indeed competent reservoirs for Rickettsia conorii . It has been shown that dogs: Become infected if bitten by ticks of the species Rhipicephalus sanguineus that carry the bacterium Rickettsia conorii ; If they are infected with Rickettsia conorii they can pass this infection on to other ticks that are not infected and which bite them. Ticks can become infected with Rickettsia conorii either from a dog or from any wild animal. Due to their proximity to man and because they are the preferred host of the tick Rhipicephalus sanguineus , dogs pose a greater risk. Therefore, the proximity of positive dogs for antibodies to the bacterium that causes tick fever has been considered a risk factor for the disease in humans. Some (few) dogs infected with Rickettsia conorii can develop a disease with a clinical picture similar to human tick fever. However, the susceptibility of dogs to clinical illness (ie, with symptoms) is low and appears to vary by breed . Prevent tick fever We know that more than 70% of human diseases can be considered zoonoses. Therefore, cooperation between all those involved in human and animal health care has a decisive contribution to prevent and combat these threats. Prevention and/or early detection of infections in animals can prevent their transmission to humans or the introduction of pathogens into the food chain. Tick fever is an exemplary disease for demonstrating the validity and importance of this One Health concept. Prevention is essentially based on good health and hygiene practices , which obviously include that of domestic animals. In animals With regard to ticks and tick fever, keeping the external deworming program for dogs updated allows to reduce: The risk of dogs becoming infected with the bacteria Rickettsia conorii ; The risk of transmitting this infection to uninfected ticks; The population of potentially infected ticks close to humans. In addition to external deworming of dogs, it is also advisable to: Check dogs regularly for ticks and additionally after walks in fields with high vegetation, especially in endemic regions. Maintain regular surveillance of animals by the veterinarian, to prevent or early identify the presence of the Rickettsia conorii and perform an appropriate treatment. There are currently no vaccines against tick fever (neither for animals nor for humans) and drug prevention is not recommended. In people The most important measures to prevent tick fever are related to the permanence, for leisure or work, in areas of high vegetation , in which case: Wear full-body clothing to prevent ticks from reaching the skin easily; Prefer light-colored garments to facilitate tick identification; Prefer closed shoes ; Carry out a careful inspection of the skin after being in these risky places , remembering that ticks are experts in lodging (and biting) in areas of the body where they go most unnoticed. Know the main symptoms – sudden onset, about 1 week after the infection, of high fever, flu-like symptoms, presence of a painless black sore at the tick bite site (which can be areas of difficult visibility, as in scalp), a few days later a skin rash with small raised red patches that usually starts on the lower limbs and ends up covering practically the entire body. A timely evaluation by a physician is crucial as early treatment is important for the evolution and recovery of the disease. Also know that Tick fever is endemic in the Mediterranean area. Southern Europe is considered the main endemic region . The disease has been associated with natural Rickettsia conorii infection in dogs since human tick fever was described in 1910 in Tunis. Eight subspecies of Rickettsia conorii are currently recognized. In Portugal , tick fever is caused by two strains of the bacteria: Malish and Israel. These strains show minor antigenic and phenotypic differences and may cause distinct clinical signs and differences in disease severity. 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.
