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. Nicholas, only when studying typhoid fever. And since Ricketts died in 1910 precisely because of typhoid fever, having managed to talk about his discovery before that, the genus of the causative agents of this disease was named in his honor - Rickettsia, as a recognition of the scientist's merit in science.
What is rickettsia?
Rickettsiae are small-sized gram-negative organisms that have the 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 specific group of antibiotics. These microorganisms are prokaryotes, they lack a formed nucleus, and there are no mitochondria.
Description and morphology
Usually, all representatives of this genus with small sizes are up to 1 ΞΌm. 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.
Rickettsiae are immobile microorganisms, they do not have flagella, and under adverse conditions form small forms that protect them. Often, such forms can be in the body for up to 10 years, persisting and, under favorable conditions, activating again.
Rickettsia, chlamydia, mycoplasmas parasitize in the human cell, causing disease, but, once in the environment, they die immediately. Their habitat is a living cell with an active metabolism. And if the mucous membranes of the mouth, pharynx and urogenital system prefer mycoplasmas, rickettsia live in the epithelial cells and endothelium of the intestinal vessels of their main hosts - insects, and almost all organs and tissues are affected in humans. Chlamydia prefer to settle in the organs of vision, affect the genitals and lungs.
Like viruses, rickettsia multiply inside the host cell only by dividing the mother cell in half (which is characteristic of bacteria). In this case, cells infected with the parasite die quickly.
The life cycle of these microorganisms is very simple. This is either a vegetative stage - the cell actively divides, or a resting stage.
On the European continent, infections caused by rickettsia are relatively rare. But on the Asian continent, in Australia and in Tasmania, these infections are widespread.
Classification
As of May 2015, 26 species were included in this genus. At the same time, several species that belonged here earlier were excluded and transferred. It should be said that the classification of rickettsia generally accepted by world luminaries has not yet been fully developed.
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 have been recorded by researchers involved in the study of these microbes.
Rickettsioses
In humans, rickettsia causes a febrile illness. And the common name for all these diseases is rickettsioses. Their course, as a rule, is very acute and is accompanied by various types of skin rashes, thrombovasculitis or vasculitis.
So what diseases cause rickettsia? To date, the following are distinguished:
- Epidemic typhus, the second name is typhoid fever.
- Brill-Zinsers disease, or sporadic typhus (typhoid rickettsia, after a person is ill with it for the first time, take a small form; after years and even decades, a relapse of the disease is possible, which was given the name given). Most often seen in older people.
- Endemic rash or rat typhus.
- Brazilian typhus.
- Tick- borne rickettsiosis of North Asia and Australia .
- Rocky Mountain Spotted Fever.
- Vesicular rickettsiosis.
- Israeli fever (also called Marseilles fever and Mediterranean spotted fever).
- Typhoid fever (the second name is flea, since fleas are the transfer reservoir).
- Quintan.
- Tsutsugamushi, or Japanese fever (the main carriers of the infection are rodents and red mites).
- Malayan typhoid fever.
- Sumatran tick-borne typhus.
- TIBOLA, or tick-borne lymphadenopathy, is a disease discovered recently, just like the following.
- DEBONEL, or necrotic strupalymphadenopathy (caused by the same type of rickettsia. Diseases differ only in symptoms).
In addition, the following are known:
- Q fever;
- trench fever;
- smallpox rickettsiosis (also called vesicular rickettsiosis);
- Queensland typhoid:
- Astrakhan rickettsial fever.
This list is an incomplete list of the diseases that people can get.
Infection pathways
Outside the cells, rickettsia is a microorganism that is very unstable to the hardships of the outside world and quickly dying from the effects 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 that they carry are epidemic, while ticks have their own specific habitat and the diseases caused by them are endemic.
Through an insect bite, rickettsia enters the human body. Pathogens from the gastrointestinal mucosa of fleas, lice or ticks pass into the bloodstream, and the result is a fever and a serious illness. Moreover, for the arthropod rickettsia themselves are rarely dangerous. Cases of transmission of parasites-microbes by insects from generation to generation through eggs are known. 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 tick is the carrier of rickettsia, then the pathogen can be obtained through a bite, if the microorganism is in the salivary glands, or by rubbing it into the skin when the insect is simply crushed.
There is a special subspecies that is more resistant to environmental conditions, called Coxiella. These rickettsia diseases are provoked both through insect bites and by airborne droplets and most often cause one of the three types of Q fever.
And Japanese fever is not transmitted directly from the patient to a healthy person. Must have an intermediary. And most often in his role is a rat or mouse. Their bite can be very dangerous.
Disease symptoms
Diseases caused by rickettsia can occur in different ways, but general symptoms can still be distinguished. They are as follows:
- headache and muscle pain of unknown origin;
- fever;
- various types of rashes, and in the place of an insect bite a small-sized scab forms, which blackens over time, when pressed, its stiffness is felt;
- inflammation of the lymph nodes and their increase in size;
- dry cough.
Severe rickettsioses usually always occur with fever and delirium; the patientβs breathing is heavy and difficult. Diagnosis of pathology is often of great difficulty. The diagnosis can be made through a skin biopsy from the site of the bite. On its surface during infection, a papule is always formed, which then turns black.
Fever begins 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 increase in size.
A week after the first signs of the disease, typical signs of rickettsiosis begin to appear - intense fever and dry cough, which develops into bronchitis or pneumonia, photophobia, conjunctivitis appears. 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 body.
If treatment is not started, then the febrile state 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 the age, type of disease and immune capabilities of the human body.
Microbiological diagnosis
Early diagnosis can speed up the treatment process. A quick diagnosis of rickettsia is a scab biopsy. But it can only be confirmed by the isolation of antibodies in mice after vaccination of the blood of a sick person.
Another diagnostic method is carried out using the serological method. But the results should be interpreted with great caution, because cross activity is often found between strains of various types of bacteria.
One of the most common tests to detect rickettsia is the Museur-Neil test. In this case, venous blood of the patient is introduced into the abdomen of guinea pig at an early febrile stage. If the disease is confirmed, the animals develop symptoms of fever, tissue necrosis, and the scrotum swells in male pigs. Most often, if the diagnosis is confirmed, the animal dies.
Rickettsiosis immunity
Even with such small sizes, this genus of microorganisms has some antigens (AH), most often lipopolysaccharide nature. The same AH was found in the rickettsia of the bacteria Proteus, which is located quite far from the Rickettsia genus in the systematic table. Therefore, if a person has suffered one of the diseases caused by any kind of this genus, other pathogens of the same genus, carrying the same antigen, are no longer terrible. Indeed, in the human body cross-immunity develops.
Treatment
Depending on the disease, treatment methods are selected. And only a qualified infectious disease specialist can make the correct diagnosis and prescribe treatment. For various rickettsial fevers, the administration of antipyretic drugs is prescribed, for example, Aspirin, Prednisolone, or another glucocorticosteroid, antibiotic (Rifampicin or Levomethicin).
At the same time, it is necessary to carry out detoxification of the body by infusion, for 3 days of haemodesis, intravenous administration of glucose solution for 3 days, and heavy drinking up to 2.5 liters per day of oralit solution for five days.
With this regimen, the temperature returns to normal for 9-11 days. After about two weeks, aches in the body and muscle pain were removed, and after three weeks the rash on the body disappeared, which meant an almost complete recovery.
For the treatment of tick-borne typhus, another treatment regimen is proposed:
- Acceptance of antibiotics of the tetracycline and (or) chloramphenicol group, for maintenance - cardiovascular agents 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, hormones and cardiac glycosides are additionally administered.
With this treatment regimen, a full recovery occurs approximately in a month.
Q fever is treated with oral antibiotics, Chloramphenicol and a tetracycline group at the same time. If no improvement is noticed within three to four days, glucocorticoid drugs are additionally administered. When such a side effect as the myocardium appears, cardiac and vasopressor drugs are additionally introduced. Detoxification agents are administered intravenously (glucose and saline). The treatment lasts about a crescent.
Treatment of rickettsioses 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, as the tetracycline group of drugs is contraindicated in this category of patients. In this case, a more gentle, but less effective "Chloramphenicol" is used (breast-feeding during treatment should be discontinued).
Children under eight years of age with rickettsiosis are treated with Chloramphenicol for ten days, while older ones, like adults, are treated with a doxycycline group, only a smaller dose is taken.
Prevention
To date, a vaccine has been developed and is being used in medicine that has been attenuated against epidemic typhus and against Q fever.
But not everyone has the opportunity to get vaccinated, going on vacation to countries where there are foci of infection with rickettsioses. Therefore, following a few simple rules, you can protect yourself and your family from them.
- If you go to a park, square, forest, zoo or any other place where contact with ticks, fleas or other carriers is possible, wear long-sleeved clothing and a wide-brimmed hat on your head.
- Be sure to use insect repellents.
- Be sure to inspect yourself and your children for insect bites. Pay special attention to the back of the head, inguinal region, armpits and places under the knees - a favorite place for a tick bite.
- When visiting places infected with any kind of rickettsiosis, be sure to wear clothing soaked in dimethyl phthalate.
- Do you like to spend the night outdoors in tents? Then sleep on the cot, not on the ground.
- There are suspicions of the disease of someone close to rickettsiosis? Immediately, without hesitation, contact the infectious disease specialist.
- Compliance with the rules of personal hygiene has not been canceled.