Spotted Fever - Tick-Borne Disease

Spotted fever is a disease that arises when a person is bitten by a tick infected by the bacterium Rickettsia rickettsii.

Spotted Fever
Spotted Fever
 

Rocky Mountain spotted fever is a disease that occurs throughout the Americas, affecting countries from Canada to Argentina. In Brazil, most cases in concentrated in the Southeast, and there are isolated cases in states of other regions such as Bahia, Ceara, Santa Catarina, Parana, Rio Grande do Sul, Federal District, Goias and Mato Grosso do Sul. São Paulo and Minas Gerais are the states with the highest number of reported cases.

Although a typical rural disease, in recent years, the number of urban cases have been increasing. The disease is not very common, accounting for about 40 to 100 cases a year across the country.

Spotted fever responds well to treatment with antibiotics, but if not promptly treated, it can cause serious damage to internal organs such as the kidneys, liver and heart and cause death. The problem is that, precisely because it is not a very common disease, it is often not properly identified, which delays the establishment of an adequate treatment and makes the annual mortality rate be around 15-35%.

The first signs and symptoms of infection are high fever, headache and malaise. A few days later, skin lesions, blemishes calls may appear in the limbs and trunk, hence the name of the disease is spotted fever.

Star tick - tick spotted fever

Amblyomma ticks
Amblyomma ticks
 
Any tick species can be host bacterium Rickettsia rickettsii, including ticks attacking dogs, as is common in the USA. In Brazil, however, the main vector of Rocky Mountain spotted fever is the tick species Amblyomma cajennense, better known as tick star, who is a tick that usually parasitize horses, oxen and capybaras.

Other tick species Amblyomma also been recognized as vectors of spotted fever in Brazil, including Amblyomma aureolatum (common in dogs) and Amblyomma dubitatum (common in capybaras).

Ticks have a life span ranging from 18 to 36 months, and once infected by the bacterium Rickettsia rickettsii, so remain for life, and may also pass the infection vertically, from one generation to another tick. Another way of infection of ticks is through intercourse with infected male or female or when the tick bites an animal previously infected with Rickettsia rickettsii.

Human transmission of spotted fever

Humans become infected with rickettsii Rickettsia when they are bitten by an infected tick. There spotted fever transmission directly from one person to another.

For transmission of the bacteria occur, the tick must be at least 4 to 10 hours adhered to the skin. As juveniles (larva and pupa) are smaller and have a less painful bites, they tend to be more dangerous than adult ticks, which often be identified and removed before the time required to forward Rickettsia rickettsii.

Interestingly, up to 1 in 3 patients with Rocky Mountain spotted fever does not remember being bitten by ticks in no time, which highlights the importance of non-recognition of arachnid presence attached to the skin in the process of transmission of the disease.

Transmission can also occur if the tick is removed from the skin inappropriately. To be crushed, for example, large amounts of bacteria come in contact with damaged skin due to leakage of gastric contents of the tick, which is rich in Rickettsia rickettsii. This form of transmission can also occur when a person tries to remove wrongly ticks of other animals such as horses, cattle or dogs, and ends up contaminating.

Symptoms of rocky mountain spotted fever

The incubation period of the spotted fever ranges from 2 to 14 days, depending on the amount of bacteria was inoculated.

The table usually start up a non-specific way, with high fever, headache, body pain, general malaise, nausea and vomiting. At the beginning of the frame is very difficult to distinguish the spotted fever of various other common febrile diseases, including the most known viruses.

Around the 3rd day of the disease, 90% of patients develop typical spotted fever rash, which are more reddish specks (stains) from 1 to 6 mm, those that disappear when pressed with the fingers. Lesions usually appear in the wrists and ankles and will be spreading towards the trunk. Palms and soles are also frequently affected. As the days passed, the lesions become more violet and fail to vanish pressure (become petechiae). At this time, the lesions may coalesce, forming purplish plaques (bruises).

The absence of the rash within 72 hours makes early diagnosis very difficult. Unless the patient comment something about a recent tick bite, it is unlikely that the spotted fever is one of the differential diagnoses of the doctor to examine the patient at the beginning of symptoms. Only 10 to 15% of patients have a rash on the first day of symptoms.

About 10% of patients do not have a rash at any stage of the disease, making its diagnosis a challenge. In very dark skinned patients, the problem is similar, since the emergence of the rash may not be as obvious.

If the disease is not recognized in the early days, it can become serious. By the time the rash appears, the doctor needs to think about the diagnosis and should institute treatment with appropriate antibiotics.

If treatment is not started, the disease progresses, and the skin areas that are irrigated by small blood vessels, such as the tips of fingers and ears, may suffer necrosis. The bacterium spreads through the body and begins to affect internal organs such as kidneys, heart, lungs and liver. The central nervous system is also commonly affected by infection, may cause meningitis (the picture can look a lot like meningococcal meningitis), encephalitis, seizures and coma. Patients with neurological involvement are those that evolve with worse prognosis.

Diagnosis of rocky mountain spotted fever

The diagnosis of spotted fever usually has more utility from the epidemiological point of view of view than to assist the physician in treatment.

Serology, which is the presence of antibodies in the blood, is the test most commonly used to establish the diagnosis of spotted fever. The problem is that IgG and IgM antibodies against Rickettsia rickettsii only come from the 7th day of illness, which is too late. The physician should not wait for the serology results to decide the treatment.

A biopsy of skin lesions is an alternative. In places with many technical features, the result can be obtained in a few hours. But there are few places that can provide results as fast.

Treatment of spotted fever

Without treatment, the mortality rate of spotted fever reaches 75%. Studies show that the watershed is the 5th day of illness. Patients starting treatment with antibiotics before the 5th day have up to 5 times more chances of being cured without sequelae than patients who only start treatment after the 5th day of illness.

When the picture becomes severe, with involvement of multiple organs, especially the nervous system, antibiotics institution may no longer be very effective. And those lucky ones who still manage to be cured can have consequences such as deafness or paralysis of limbs.

Fortunately, not all cases evolve disastrously. There are milder forms of the disease, which can heal spontaneously after 2 or 3 weeks of symptoms. However, most cases does not behave as benign. Do not expect to see if the patient will present severe or mild form because the wait can be fatal. Similarly, if the clinical and epidemiological history the doctor suspects spotted fever, you must not wait for the appearance of the rash to confirm it, let alone the results of laboratory tests. If the doctor suspects spotted fever, you should start the antibiotics, even not sure of the diagnosis.

For example, if the patient has early symptoms of the disease, especially high fever and malaise, and has a recent history of tick bite, it is enough to initiation of treatment. Similarly, if the patient has symptoms of an area that have recently registered spotted fever cases, it has also permits the physician to begin treating.

However, it is important to note that the mere fact of having been bitten by a tick is no reason to start treatment. It is estimated that only 1% of ticks in endemic areas are infected with Rickettsia rickettsii. And outside the endemic areas, virtually no tick is contaminated. So if the patient has no symptoms of Rocky Mountain spotted fever, it should not be treated for Rocky Mountain spotted fever.

If the doctor have doubts, it is not wrong to get more of an antibiotic aimed at treating the most serious diagnostic hypothesis. Therefore, the doctor can get antibiotics targeting spotted fever, meningococcal meningitis, for example. Both are infections with high mortality rate and need early treatment.

The antibiotic of choice for the treatment of Rocky Mountain spotted fever is doxycycline, which can be administered orally or intravenously, depending on severity. Treatment is continued until 72 hours after the disappearance of fever, which usually occur in the 2nd or 3rd day of treatment. In most cases the treatment usually lasts 7 days.

An alternative is chloramphenicol, which is the most appropriate antibiotic for pregnant with Rocky Mountain spotted fever, because doxycycline is contraindicated in pregnancy. Chloramphenicol of the problem is the risk of serious side effects such as bone marrow aplasia, an event that occurs in 1 out of every 25,000 people treated. Therefore, all people not pregnant, treatment should be done preferably with doxycycline.

Most patients respond quickly to treatment, and the mortality rate is very low when the antibiotic is started within 5 days.

Once cured, most patients develop immunity against Rickettsia rickettsii for the rest lives and there is no risk of having the disease again.

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