In 1906, H. Ricketts began research on spotted fever. In 1909, microorganisms in the form of rods with very small sizes were found in the studied blood preparations. Similar organisms were discovered this year by another researcher, S. Nicol, only in the study of typhoid fever. And since Ricketts died in 1910 just because of typhoid fever, having managed to tell about his discovery before that, the genus of the causative agents of this disease was named after him - Rickettsia, as recognition of the scientist's merit to science.
What are rickettsia
Rickettsiae are small Gram-negative organisms with properties of both viruses and bacteria. From the first they took the possibility of reproduction only inside eukaryotic cells, but at the same time, like bacteria, they need oxygen, have a cell wall and are sensitive to a certain group of antibiotics. These microorganisms are prokaryotes, they do not have a formalizednucleus, no mitochondria.
Description and morphology
Usually, all representatives of this genus are small in size - up to 1 micron. Most often they have a rod-shaped form, but at certain stages it can be filiform and bacillary. Moreover, all changes occur inside the host cells.
Rickettsia are immobile microorganisms, they do not have flagella, and under adverse conditions form small forms that protect them. Often, such forms can stay in the body for up to 10 years, remaining and, under favorable conditions, reactivating.
Rickettsia, chlamydia, mycoplasmas parasitize in a human cell, causing disease, but once in the environment, they immediately die. Their habitat is a living cell with an active metabolism. And if mycoplasmas prefer the mucous membrane of the mouth, pharynx and genitourinary system, rickettsiae live in the epithelial cells and endothelium of the intestinal vessels of their main hosts - insects, and in humans they affect almost all organs and tissues. Chlamydia prefer to settle in the organs of vision, affect the genitals and lungs.
Reproduce, like viruses, rickettsia inside the host cell, only by dividing the mother cell in half (which is characteristic of bacteria). At the same time, the cells infected with the parasite quickly die.
The life cycle of these microorganisms is very simple. This is either a vegetative stage - the cell is actively dividing, or a resting stage.
Rickettsia infections are relatively rare on the European continent. But on the Asian continent, inIn Australia and Tasmania, these infections are widespread.
Classification
As of May 2015, 26 species were included in this genus. At the same time, several species that previously belonged here were excluded and transferred. It should be said that the classification of rickettsia generally accepted by world luminaries has not been fully developed yet.
The study of these microorganisms is very dangerous, since almost all representatives of this genus cause diseases, including fatal ones. Thus, many cases of infection of researchers involved in the study of these microbes have been recorded.
Rickettsioses
Rickettsia causes febrile-type diseases in humans. And the common name for all these diseases is rickettsiosis. Their course, as a rule, is very acute and is accompanied by various types of skin rashes, thrombo-vasculitis or vasculitis.
So what diseases do rickettsia cause? To date, the following are distinguished:
- Epidemic typhus, the second name is typhoid fever.
- Brill-Zinsers disease, or parodic typhus (typhoid rickettsia, after a person has been ill with it for the first time, take a small form; after years and even decades, a relapse of the disease is possible, which received the given name). Most often observed in older people.
- Endemic typhus or rat typhus.
- Brazilian typhus.
- North Asian and Australian tick-borne rickettsiosis.
- Rocky Mountain spotted fever.
- Vesicular rickettsiosis.
- Israeli fever (also known as Marseille fever and Mediterranean spotted fever).
- Mouse typhus (the second name is flea fever, since fleas are the reservoir for transfer).
- Volyn fever.
- Tsutsugamushi, or Japanese fever (the main carriers of the infection are rodents and red ticks).
- Malay scraping fever.
- Sumatran tick-borne typhus.
- TIBOLA, or tick-borne lymphadenopathy, is a recently discovered disease, like the following one.
- DEBONEL, or necrotizing stropalymphadenopathy (caused by the same type of rickettsia. Diseases differ only in symptoms).
Also known:
- Q fever;
- trench fever;
- poxoid rickettsiosis (also called vesicular rickettsiosis);
- Queensland typhus:
- Astrakhan rickettsial fever.
This list is not an exhaustive list of diseases that people can contract.
Routes of infection
Outside the cells, rickettsia are microorganisms that are very unstable to the adversities of the outside world and quickly die from the influence of various factors. That is why they need special carriers. Blood-sucking insects such as fleas, lice and ticks are great for this role.
Since lice and fleas are ubiquitous, the diseases they carry are epidemic in nature, while ticks have their own specific range andthe diseases they cause are endemic.
Rickettsia enter the human body through an insect bite. Pathogens from the gastrointestinal mucosa of a flea, lice or tick pass into the blood, and the result is fever and severe illness. Moreover, for the arthropods themselves, rickettsia are rarely dangerous. There are known cases of transmission of microbial parasites by insects from generation to generation through eggs. Here, arthropods are used simply as a reservoir for storing microorganisms. Moreover, the infection of an insect can occur through the blood of a sick person during a bite.
If the carrier of rickettsia is a tick, then the pathogen can be obtained through a bite if the microorganism is in the salivary glands, or through rubbing into the skin when the insect is simply crushed.
There is a special subspecies, more resistant to environmental conditions, called Coxiella. These rickettsiae provoke diseases both through insect bites and airborne droplets and most often cause one of the three types of Q fever.
And Japanese fever is not transmitted directly from a sick person to a he althy person. An intermediary is required. And most often in his role is a rat or mouse. Their bite can be quite dangerous.
Symptoms of diseases
Diseases caused by rickettsiae can manifest themselves in different ways, but the general symptoms can still be distinguished. They are as follows:
- headache and muscle pain of unknown origin;
- fever;
- various typesrash, and at the site of the insect bite, a small scab forms, which blackens over time, when pressed on it, its rigidity is felt;
- inflammation of the lymph nodes and their increase in size;
- dry cough.
Severe rickettsiosis usually always occurs with fever and delirium, the patient's breathing is heavy and labored. Diagnosis of pathology is often very difficult. Diagnosis can be made by taking a skin biopsy from the site of the bite. When infected, a papule always forms on its surface, which then turns black.
Fever begins approximately on the fourth day after infection, but its appearance may be delayed for a longer period. The patient develops a state of apathy. Lymph nodes (first those next to the bite, then the rest) become inflamed and enlarged.
A week after the first signs of the disease, typical signs of rickettsiosis begin to appear - high fever and dry cough, which develops into bronchitis or pneumonia, photophobia, conjunctivitis appear. Due to the heat, a delusional state may develop, as well as partial or complete hearing loss. A small papular rash appears on the skin, especially on the limbs, but it also happens on the trunk.
If you do not start treatment, the fever will persist for two weeks. The possibility of death is up to 40% of all cases of infection. Moreover, the risk of death depends on age, type of disease and the immune capabilities of the human body.
Microbiological diagnostics
Early diagnosis speeds up the healing process. A quick diagnosis of rickettsia is a biopsy of the scab. But it can be confirmed only with the help of antibody secretions in mice after inoculation of the blood of a sick person.
Another way of diagnosing is carried out using the serological method. But the results should be interpreted with great caution, as cross-reactivity between strains of different bacterial species is common.
One of the most common rickettsia tests is the Muser-Neil test. In this case, the venous blood of a patient at an early febrile stage is injected into the abdomen of a guinea pig. If the disease is confirmed, the animals show symptoms of fever, tissue necrosis, and scrotal swelling in male gilts. Most often, if the diagnosis is confirmed, the animal dies.
Immunity against rickettsiosis
Even with such a small size, this genus of microorganisms has some antigens (AG), most often of a lipopolysaccharide nature. The same AG was found in the rickettsia of the bacterium Proteus, which is located quite far in the systematic table from the genus Rickettsia. Therefore, if a person has suffered one of the diseases caused by any species of a given genus, other pathogens of the same genus, carrying the same antigen, are no longer terrible. After all, cross-immunity develops in the human body.
Treatment
Depending on the disease, methods of treatment are selected. And only qualifiedan infectious disease specialist can make the correct diagnosis and prescribe treatment. For various rickettsial fevers, the administration of antipyretics, such as Aspirin, Prednisolone, or another glucocorticosteroid, antibiotic (Rifampicin or Levomethicin), is prescribed.
At the same time, it is necessary to detoxify the body by infusion, within 3 days of gemodez, intravenous administration of glucose solution for 3 days and drinking plenty of water up to 2.5 liters per day of oralit solution for five days.
With this scheme of taking drugs, the temperature returns to normal on days 9-11. After about two weeks, body aches and muscle pain were removed, and after three weeks the rash on the body disappeared, which meant an almost complete recovery.
Another treatment regimen is proposed for the treatment of tick-borne typhus:
- Taking antibiotics of the tetracycline and (or) chloramphenicol group, to maintain - cardiovascular drugs in moderate dosage.
- If the disease begins to be aggravated by a delusional state, or other severe symptoms are noticed, then a five percent glucose solution is additionally administered intravenously to reduce the toxicity of the body.
- In rare cases, additional hormones and cardiac glycosides are administered.
With this treatment regimen, full recovery occurs approximately in a month.
Q fever is treated by oral antibiotics, "Levomycetin" and a tetracycline group drug at the same time. If within three or four days it is not noticedimprovements, then glucocorticoid drugs are additionally introduced. With the appearance of such a side effect as the myocardium, cardiac and vasopressor drugs are additionally introduced. Detoxification agents are administered intravenously (glucose and saline). Treatment lasts about half a month.
Treatment of rickettsiosis must necessarily take place in a hospital, under the supervision of infectious disease specialists. It is much more difficult to treat diseases that caused rickettsia, chlamydia in pregnant and lactating women, since this category of patients is contraindicated in taking the tetracycline group of drugs. In this case, a more gentle, but less effective "Chloramphenicol" is used (breastfeeding should be stopped during treatment).
Children under eight years of age with rickettsiosis are treated with "Chloramphenicol" for ten days, and older ones, like adults, with the doxycycline group, only the dose is taken less.
Prevention
To date, an attenuated vaccine against epidemic typhus and Q fever has been developed and used in medicine.
But not everyone has the opportunity to get vaccinated when going on vacation to countries where there are foci of rickettsiosis infections. Therefore, by following a few simple rules, you can protect yourself and your family from them.
- If you are going to a park, square, forest, zoo or any other place where contact with ticks, fleas or other vectors is possible, wear long sleeves and a wide-brimmed hat on your head.
- Be sure to use insect repellent.
- Be sure to check yourself and your children for insect bites. Pay special attention to the back of the head, groin, armpits and under the knees - a favorite place for tick bites.
- When visiting places infected with some kind of rickettsiosis, be sure to wear clothing soaked in dimethyl phthalate.
- Do you like spending the night outdoors in tents? Then sleep on a cot, not on the ground.
- Are there suspicions about the disease of someone close to rickettsiosis? Immediately, without hesitation, contact an infectious disease specialist.
- Compliance with the rules of personal hygiene has not been canceled.
