Forum for Nordic Dermato-Venereology Nr 3, 2018 | Page 16

Review Ticks and Humans P aul -E rik U ggeldahl Suvikatu 8, FIN-80200 Joensuu, Finland. E-mail: [email protected] Hard ticks, especially Ixodes ricinus in Europe, carry different microbes, which can cause the diseases described in my babesiosis article (1). However, most bites by blood-sucking ticks do not result in infection. The body has a self-curing tendency, but if signs and symptoms of borreliosis, ehrlichiosis or babesiosis develop, patients should be treated according to current recommendations. The conditions termed chronic Lyme borreliosis or post-Lyme syndrome, requiring several months or even years of antibiotic therapy, have not been proven. The question of subclinical infection has been dis- cussed, especially in borreliosis, where seroconversion can develop with no clinical symptoms of the disease. Few doctors are sufficiently familiar with the symptoms of tick-borne diseases (2). Thus collaboration and consultation with experts, especially regarding Lyme borreliosis (Lyme disease) (3), are important. Hopefully such contact could be established also with vets, who are, or should be, familiar with borrelia, ehrlichia and babesia. Taxonomy Ticks (Metastigmata) are giant mites, all of which are blood-sucking parasites, in contrast to the abundant micro- scopic mites (Acari), most of which are harmless to humans. Hard ticks are in the majority (family Ixodidae). If these vectors were mosquitos there would be less fear concerning the infec- tors themselves and the diseases they can pass on. Mosquito and tick bites As a consequence of mosquito bites half a million people die each year from malaria. However, deaths following hard tick bites are rare. Not a single person has died from Lyme borreliosis in the Nordic countries, but the recommendation of treatment with massive doses of antibiotics is a threat for life. A mosquito bite is painful, but a tick bite is not, due to substances with anaesthetic and antihistamine effect in the saliva of the ticks. Near neighbours We have to accept the existence of ticks, as well as mosquitos, often close to us (4, 5). Living in a city is no guarantee of not 78 being bitten, since the green spaces in cities are good habitats for a multitude of hosts for ticks, such as mice, rats, rabbits and hares. The conditions may be perfect for the lifecycle of ticks, e.g. as in Central Park in Manhattan in the middle of New York. Stages of Ixodes ricinus The stages of Ixodes ricinus are: the egg, larva, nymph and adult ticks; male and female. Of the adult ticks only the fe- male sucks blood. The male couples with the female during her meal or shortly afterwards. In borreliosis approximately 10% of nymphs are infected with B. burgdorferii, and for adult females at least double this proportion are infected. However, because nymphs are 40 times more frequent than adult ticks, they are the most important vectors of disease in borreliosis and other tick-borne diseases (6). Before they have had a meal of blood, all stages of the tick are very small; the larvae are roughly the size of a full stop on this page. You could find the size in Ref 7, on page 1152. At this page, the framed picture is of importance. The text is in Finnish but reads from left: The adult female, the male, nymph and the minuscule larvae. The text under the ticks: “Ticks in natural size”. Reservoir- and reproduction hosts Reservoir hosts are vertebrates from which the larvae, nymphs and adult female ticks suck blood containing live microbes. As a result the ticks become infected. In borreliosis the reservoir hosts are mainly small rodents. Migrating birds can also act as reservoir hosts. Reproduction hosts have no microbes in their bloodstream. They are often large mammals, such as the deer family. How- ever, there are many other reproduction hosts, such as do- mestic animals, cattle, horses, dogs and cats. Humans are also reproduction hosts, but they are not essential for the lifecycle of ticks, and are poor hosts as, in general, people spend most of the day indoors. This means that most ticks that attach to people drop off indoors and not in the soil. Reproduction hosts may develop symptoms of the diseases mentioned in this arti- cle: borreliosis, ehrlichiosis and babesiosis. As in ehrlichiosis Forum for Nord Derm Ven 2018, Vol. 23, No. 3