Many of the infectious diseases that human beings suffer have an animal origin; it is what we call zoonoses . In fact, some of the great pandemics that in the remote or recent past have spread to practically all countries are of zoonotic origin.
HIV originates from the simian immunodeficiency virus . The influenza A (N1H1) pandemic jumped to humans from birds. The two coronavirus epidemics prior to 2020, the first SARS and MERS , reached humans, probably from bats, and from camelids, respectively. And although we are still not sure which was the original vector that gave rise to SARS-CoV-2 , we know that it also has an animal origin.
But among the zoonoses, not all are pandemics that, once present, expand massively. Some zoonoses require vectors to carry the disease. Such was the case of the black plague, transmitted by fleas that in turn were associated with rats. Although once sick, the person could infect others through droplets or by direct contact with infected tissues.
Other examples of diseases transmitted by insects are sleeping sickness, transmitted by the tsetse fly, or malaria, caused by a blood parasitic microorganism called Plasmodium falciparum , transmitted from individual to individual by the bite of a mosquito.
Tick-Borne Diseases
Not all ticks carry disease, nor are all diseases carried by any tick . Generally, each disease is associated with a species or group of species of ticks.
Of all the tick-borne diseases, the most common is Lyme disease . In Spain it is transmitted by the common tick ( Ixodes ricinus ), one of the most abundant in the natural environment, especially when it is hot. It measures between 2 and 4 millimeters when it is not swollen, and up to one centimeter after feeding. The most striking marker of Lyme disease is a very red erythema at the site of the bite , which usually appears within a few days, and never after a month. It gradually expands and becomes lighter in the center, taking on the shape of a ring . If left untreated, the consequences of Lyme disease can be fatal, leading to consequences as serious as multiple sclerosis or dementia.
Mediterranean spotted fever is usually transmitted by ticks of the genus Rhipicephalus (such as the brown dog tick, R. saguineus ), although species of the genus Hyalomma and the aforementioned I. ricinus are potential carriers, too. It has an incubation period of between 4 and 21 days, beginning with fever, malaise, and photophobia . It is very common for an eschar or a blackish spot to appear in the area of the bite, even before the fever appears. Again, prompt attention is essential, as the disease can progress to severe forms and lead to hepatitis, meningoencephalitis, or kidney failure.
Debonel/Tibola disease is a very recently discovered disease, but it turns out to be one of the most common. It is transmitted by species of the Dermacentor genus, generally D. marginatus , called hard ticks, and unlike the previous cases, this disease is more common in the winter and spring months. These ticks only bite the upper half of the body, most often the head. The infection begins with a blackening of the bite area, which ends up forming an eschar , similar to boutonneuse fever, but usually larger. An erythema reminiscent of Lyme disease forms around it, due to its growing annular shape. Fever is unusual.
Other diseases that have ticks as vectors, but are less common in Spain, are anaplasmosis —also transmitted by I. ricinus— , which initially causes fever and flu-like symptoms, tularemia , transmitted by Dermacentor marginatus —in winter—, and the rare but extremely dangerous Crimean-Congo fever , transmitted by Hyalomma marginatum , although it can be spread from person to person.
Avoiding ticks
As has been seen, there is great specificity in tick-borne diseases, and ticks often do not carry any pathogens. However, when in doubt, the maxim “ prevention is better than cure” should always be applied. The best we can do against these diseases is, as usual, to take preventive measures. If the tick doesn’t attach to your skin, the pathogens don’t enter your body. That is why certain precautions must be taken on field trips, especially in areas with very leafy bushes or ferns, where ticks may be patiently waiting for their prey.
Good shoes, high socks and long pants are basic and surprisingly effective preventive measures. If you go to an area where the vegetation is very high, it is recommended to combine it with long- sleeved garments, to prevent them from becoming anchored in the arms. Any area of exposed skin is an invitation for the tick to make unwelcome company for you, and keeping it well covered is a powerful deterrent.
Of course, our pets are also possible carriers of ticks—in fact, they can get Lyme disease, too. If we go to the field with them and they enter areas of high vegetation, we must carefully check the body of our furry friend , to ensure that he has not returned from the excursion with unwanted stowaways. There are certain products for dogs, such as collars or pipettes, that repel ticks ; if they are of good quality, they give very good results, so if you foresee a risky trip, it is better to prevent.
On returning from the field, it is advisable to take a good shower and check the whole body in search of these small parasites, which look for dark, warm and humid places, such as the armpits or the groin, and some species hide in areas with hair or copious hair. If the tick falls out with the shower water without problems, it is because it had not anchored itself to your skin . But, if it is already nailed, you should not extract it to the braves.
I have a tick, what do I do now?
Above all, keep calm and do not do crazy things . Safely removing a tick from the skin is no easy task. Unlike mosquitoes and fleas, which stick a hollow stylet—similar to a miniature hypodermic needle—and suck blood quickly, ticks stick their entire rostrum, which has harpoon-like lateral expansions directed backwards. That allows them to enter very well, but makes it difficult to extract.
Trying to remove them by pulling or twisting them to “unscrew” them can cause their heads to break off and remain inside the skin, thus being a source of infections. In addition, squeezing her body can cause her to empty her content and, if she were a carrier of a disease that she had not yet transmitted, transmit it. These rules apply to humans, and also to pets.
Home remedies are also not recommended . Neither apply Vaseline, nor oil, nor try to drown it in water, much less approach a lighter or a lighted match; in general they are completely ineffective and, sometimes, they entail more risks than the supposed benefits that are expected.
The process of removing a tick is a first aid task that must be carried out by someone with experience. If you do not have it, it is best to go to a health center, or to a veterinarian , if the affected person is your animal companion.
Normally, tweezers are used, with which the tick is grabbed from the head or mouth, which is the most sclerotized and hardest part, where it does not break. The tick is pulled outward, in a slow, steady motion. Avoid giving strong jerks , and be careful not to crush the animal. First of all, that the head does not stay nailed.
Once the tick has been removed, it is advisable to wash the area with plenty of soapy water . You also have to wash the instruments, and if a drop of blood has fallen on bare skin, wash it too. If during the extraction, the tick breaks and remains embedded in the skin, medical attention must be immediate.
Once removed, the tick is not discarded; it is kept for 32 days, while the patient is monitored to detect symptoms compatible with some pathology. That is the maximum incubation time for Lyme disease, the rest act earlier. If any symptoms compatible with any of the diseases are observed, you should go to the doctor, and if possible, take the tick in a jar. Let us remember that there are species that only transmit certain diseases ; if it is Ixodes ricinus , we know that it may be Lyme disease, but never tularemia; if, on the other hand, we are dealing with a specimen of Dermacentor marginatus , tularemia is possible, but Lyme disease is ruled out. In other words, identifying the species can serve to reduce possible diseases and improve diagnosis .
REFERENCES:
Oteo Revuelta, JA et al. 2016. Spectrum of tick-borne diseases. Primary Care Pediatrics, 18, 47-51.
SEMTSI et al. 2017. Guide to action against tick bites (p. 5). Ministry of Health, Social Services and Equality.
