Toxoplasmosis (Toxoplasma gondii) (IgG avidity index)

Toxoplasmosis

is a parasitic infection that can infect humans and animals. The causative agent is Toxoplasma gondii. The pathology is widespread throughout the world. The peak incidence is observed in South America and Africa - about 90% of the population. In Europe and North America, this figure is slightly lower, but still high - from 30 to 50%. The peculiarity of the disease is its asymptomatic course in some cases and clinical forms, which are accompanied by a varied clinical picture with various symptoms.

Toxoplasmosis can be acute or chronic. If the process becomes chronic, the symptoms appear rather sluggishly or are absent altogether. There are also congenital and acquired processes. The disease can be transmitted from mother to child and affects the fetus during fetal development. Such an infection can lead to the death of the embryo or the development of severe defects, because the pathogen affects systems and organs that are just being formed. The acquired form affects internal organs and the nervous system.

Routes of entry of the pathogen into the body

The main source of infection is domestic animals, mainly cats. Communication with them is especially dangerous for pregnant women. There are also intermediate hosts of toxoplasma, other animals in which the pathogen is in the form of cysts. Contact with them does not lead to infection. But eating meat - yes. This applies to pork and lamb. This is another way of infection. The pathogen does not die if the products do not undergo proper temperature treatment. There are known cases of infection being transmitted by insects that bite the skin and suck blood.

The vertical route of transmission is the most dangerous during pregnancy. Its consequences are the most severe and can be fatal. Infection of a woman who has not previously been infected and does not have antibodies is dangerous. The causative agent of toxoplasmosis penetrates the placental barrier and disrupts the condition of the child’s tissues. Toxoplasmosis during pregnancy is one of the indications for its termination.

The following factors increase the risk of infection:

• neglect of hygiene rules;
• contact with the excrement of an infected animal;
• non-compliance with cooking techniques for products of animal origin.

The human body is not the final host for toxoplasma, which means contact with the carrier does not pose a danger to others. The infection is not transmitted through the air or through sexual intercourse. Cases of infection after blood transfusion or organ transplantation are extremely rarely described.

go to analyzes

How does pathology manifest itself?

Initially, the pathology is asymptomatic. The first signs of pathology may appear several months or even years after infection.

In newborns, congenital infection can be recognized by the following signs:

• yellowness of the skin;
• decreased platelet count;
• maculopapular skin rash.

The incubation period of the disease lasts about 2-3 weeks. During this time, most patients produce antibodies - specific substances aimed at combating the pathogen.

Acute toxoplasmosis resembles damage to the brain and its membranes. There is a headache, nausea, general weakness, convulsions are possible, tension in the muscles of the back of the head appears and the patient cannot bend the neck. Next, the optic nerve is damaged and vision deteriorates.

After this, myocarditis may occur. This is an inflammation of the muscle tissue of the heart. The organ ceases to perform its function normally, acute pain in the chest, interruptions in functioning, and rhythm disturbances are observed. The person feels weak and may lose consciousness. The danger of myocarditis is that those tissues that were inflamed can be replaced by scar matter. The condition is called cardiosclerosis and is an irreversible process.

Damage to the digestive organs is accompanied by dry mouth, dull pain in the abdomen, bloating, and impaired passage of gases from the intestines. Appetite decreases, stool may be disrupted.

The disease affects the functioning of the endocrine glands. This is reflected in disruption of the menstrual cycle, in men sexual function decreases, and the functioning of the pancreas is disrupted. A dangerous complication of the disease is recurrent miscarriage, which can remain with a woman for a long time.

Eye complications include uveitis, chorioretinitis, and myopia.

Changes such as muscle pain are observed in the musculoskeletal system. Particularly disturbing is the lower leg, thigh, lower back, neck and arm muscles. The pain occurs so sharply and acutely that the patient stops moving for some time.

Common symptoms include headache, high fever, general weakness, and chills. There is a reactive enlargement of the liver and spleen, the lymph nodes become inflamed, joints and muscles hurt.

The chronic course is accompanied by a less intense clinical picture and may be asymptomatic. If the temperature rises, it is only slightly. You are worried about a dull headache, weakness, memory and mental activity may be impaired.

With an exacerbation of the chronic process, chills and lymphadenopathy are troubling. Complications affect the nervous system and vision. Against the background of toxoplasmosis, the body may be affected by other infections.

As we can see, the disease either has no symptoms, which makes it impossible to make a timely diagnosis, or has so many different signs that it is difficult to make a differential diagnosis.

Toxoplasmosis (Toxoplasma gondii) (qualitative DNA determination)

A test to identify the causative agent of toxoplasmosis (Toxoplasma gondii), during which the genetic material (DNA) of Toxoplasma in a blood sample is determined using the polymerase chain reaction method. Toxoplasma gondii is a single-celled parasite that is found in the soil and in the bodies of some animals. It can cause the infectious disease toxoplasmosis. Toxoplasma is very common throughout the world, the infection rate in some countries is 95%. This parasite is capable of infecting mammals, rodents and birds. The route of infection is usually oral. The microorganism can enter the human body through water and food contaminated with parasites, most often through eating raw or insufficiently cooked meat, as well as when cleaning the cat litter of an infected animal and when personal hygiene is not observed. Transmission of the infection from mother to child is also possible through blood transfusion or organ transplantation. The life cycle of a microorganism occurs with a change of hosts. The domestic cat, the definitive host, becomes infected by eating rodents and birds. In the intestines of cats, Toxoplasma divides and forms oocysts. During an active infection, millions of microscopic oocysts are shed in cat feces over several weeks. The oocysts become infectious within a couple of days and remain viable for months. In other hosts, including humans, they undergo a limited life cycle and form inactive cysts in the muscles, brain and eyes. The host's immune system is able to maintain cysts in a dormant state and protect against the development of infection. The "resting stage" can last the entire life of the host until immunodeficiency occurs. In most healthy people, the infection may be asymptomatic or appear as a mild cold. According to some scientific data, toxoplasma infection plays a role in the development of mental illnesses such as schizophrenia and psychosis. Chorioretinitis occurs with toxoplasma damage to the organs of vision. In patients with a weakened immune system, an active infection can be quite severe and cause complications. These are patients with HIV, primary immunodeficiencies, patients undergoing chemotherapy or immunosuppressive therapy after organ transplantation. Symptoms of toxoplasmosis: prolonged fever, headache, swollen lymph nodes, muscle pain, liver enlargement, hepatitis. Intrauterine infection can lead to blindness, encephalomyelitis, growth retardation and even death of newborns. In immunocompromised patients, the infection causes encephalitis (inflammation of the brain with impaired consciousness, headache, fever and local neurological defects). Early diagnosis plays a decisive role in the effectiveness of treatment. Destroying the parasite during chronic infection is difficult. If infected during pregnancy, the risk of transmission of infection to the fetus is 30-40%. Infection in the early stages can lead to miscarriage, stillbirth, or serious neurological damage to the newborn. Most babies infected late in pregnancy do not develop symptoms of toxoplasmosis until several years after birth: hearing loss, severe eye infection, and neurological deficits. Toxoplasmosis is one of the so-called TORCH infections (TORCH - after the first letters of the Latin names of infections: toxoplasma, rubella, cytomegalovirus, herpes), which are dangerous to the fetus. What is analysis used for?

• To determine the activity of toxoplasmosis in pregnant women.
• To assess the risk of fetal infection during pregnancy.
• To study toxoplasmosis infection in immunocompromised patients.
• For differential diagnosis of diseases occurring with fever, encephalitis and damage to the visual organs.

When is the test scheduled?

• If toxoplasmosis is suspected in pregnant women and patients with pathology of the immune system.
• When planning pregnancy (in order to prevent infection of the fetus).
• If the test results for antibodies to toxoplasma are positive.
• When examining children born from mothers with toxoplasmosis.
• When examining for toxoplasmosis, a comprehensive approach from a doctor is required, taking into account the level of IgG and IgM antibodies to identify primary infection or probable chronicity of the infectious process.
• The results of PCR diagnostics are the main criterion for the activity of toxoplasmosis infection, but cannot confirm the absence of toxoplasma in the body.

In what cases is examination necessary?

Diagnosis of toxoplasmosis is indicated in the following cases:

• screening during pregnancy planning and during pregnancy;
• the appearance of lymphadenopathy of unknown origin in those pregnant women who have not previously been ill or have not been diagnosed;\
• fetoplacental insufficiency and other signs of intrauterine infection;
• the occurrence of encephalitis or meningitis in patients with immunodeficiency, cancer, while taking cytostatics or chemotherapy;
• enlarged and painful lymph nodes;
• an increase in the size of the liver and spleen;
• fever for no obvious reason;
• signs of congenital toxoplasmosis in a child.

Indications for the study and the type of analysis are prescribed by the attending physician, for which you need to undergo a clinical examination.

general characteristics

The detection of both IgG and IgM antibodies in the serum is usually interpreted as evidence of a recent primary infection, since, as is known, the disappearance of IgM antibodies is usually about 3 months from the onset of the infectious process. But the period of circulation of IgM antibodies during infection with Toxoplasma gondii, trace amounts of IgM antibodies in some cases are detected for 18 months or more. The presence of specific IgM antibodies in the blood of a pregnant woman does not always confirm primary infection during pregnancy. Avidity (Latin - avidity) is a characteristic of the strength of the connection of specific antibodies with the corresponding antigens (determined by the number of binding sites and the strength of binding). Detection of high-avidity IgG antibodies in the blood allows us to exclude recent primary infection with toxoplasmosis. Low-avidity IgG antibodies in tocoplasmosis are, on average, detected within 3-4 months from the onset of infection, but sometimes are developed over a longer period.

Modern methods of laboratory diagnostics

Today, the diagnosis of toxoplasmosis is based on the following studies:

• Serological method (ELISA);
• REEF;
• NRIF(IgM, IgG)
• PCR;
• Parasitological method;
• Allergological method.

Each method has its own specific indications for use. Let's take a closer look at them.

Serological method (ELISA)

This is an immunological study based on the “antigen-antibody” reaction. The method allows you to evaluate the qualitative and quantitative indicators of the pathogen in the blood. The reaction occurs thanks to specific reagents that are added to the patient's blood serum. If the antibodies in the blood react to the antigen that is in the reagent, then the diagnosis can be considered confirmed. The technique is widespread and is used to confirm clinical signs of toxoplasmosis.

REEF

The immunofluorescence reaction is based on the property of immune complexes to be illuminated by an immunofluorescent substance. If a reaction occurs, the medical worker sees a specific glow, evaluates its intensity and quantitative indicators. Surface and intracellular antigens can be assessed. The method is included in express diagnostics, does not take much time and is often used to make a diagnosis. A prerequisite is specific laboratory equipment and staff skills.

NRIF(IgM, IgG)

The indirect immunofluorescence method is not used so often. It allows you to determine the type of antibodies in different serum titers. Immunoglobulins of type M indicate an acute stage of the process, and class G antibodies are a sign of a chronic course or a previously suffered disease. Diagnosis should be carried out efficiently, because the use of low titers can easily be mistaken for a false positive result.

PCR

The polymerase chain reaction method is the most accurate and modern way of making a diagnosis. The study is quite expensive, as it requires specific laboratory equipment. The basis of diagnosis is the detection of nucleic acid sections of the genetic material of the pathogen, which makes the diagnosis as accurate as possible.

Parasitological method

The essence of the study is the direct detection of the pathogen in biological material. For this purpose, blood, saliva, cerebrospinal fluid, and biopsy specimens are examined. Microorganisms can be detected using special staining. The method has mixed reviews. On the one hand, it is possible to confirm the presence of a pathogen, but it is difficult to say how long the patient has been sick and at what stage of the process. In addition, the absence of parasites in the studied material does not always mean that the patient does not have toxoplasmosis.

Allergological method.

An allergy test is performed with intradermal injection of toxoplasmin. If the reaction is positive, this indicates that the patient is really sick and requires a more thorough examination. The test becomes positive starting from the fourth week of illness.

Toxoplasmosis (Toxoplasma gondii) (IgG avidity index)

Determination of the avidity of IgG antibodies to Toxoplasma gondii in the blood - determination of avidity - a method of establishing the stage of infection, is a method of confirming or excluding recent infection with Toxoplasma gondii. Main indications for use: detection of infection in pregnant women, checking previously obtained results during examination for toxoplasmosis (excluding false positive results).

Determination of the avidity of IgG antibodies to Toxoplasma gondii is used to confirm or exclude recent primary Toxoplasma infection. The detection of high-avidity antibodies indicates previous infection. If a low level of high-avidity antibodies is detected in the serum, this indicates a “fresh” infection. It is known that during the immune response, one of the body’s defense reactions is the production of specific antibodies (IgM, IgG, IgA). The resulting antibodies have an affinity for the antigens (bacteria, viruses) that stimulated their formation. This affinity is characterized by the strength of the antigen-antibody bond, called avidity. Over time, avidity increases, which formed the basis of the test for detecting low- or high-avidity IgG antibodies. The test results are expressed as an avidity index. In some cases, immunoglobulins of the IgM class (an indicator of early infection) can circulate in the blood for a long time, which casts doubt on the diagnosis of recent infection. Typically, IgM antibodies circulate in the blood for up to 3 months, but sometimes they can be detected for up to a year. In such cases, the detection of antibodies in the blood makes it difficult to confirm the primary infection of the pregnant woman. Clarification is especially important in early pregnancy. The risk of death or development of fetal pathology is higher with primary infection with Toxoplasma during pregnancy, compared with chronic or past infection. TORCH infections - this term refers to a number of infections that pose a danger to the development of the fetus during pregnancy. TORCH is an abbreviation consisting of the first letters of the Latin names of infectious agents: Toxoplasma - toxoplasma, Rubella - rubella, Cytomegalovirus - cytomegalovirus, Herpes simplex - herpes. Main indications for use: clinical signs of TORCH infection, pregnancy planning, miscarriage (miscarriages, stillbirths), hepato-splenomegaly of unknown origin, clinical picture of infectious mononucleosis, differential diagnosis with viral hepatitis. Antibodies of the IgM and IgG classes to the pathogens of these infections are determined. It should be taken into account that the detection of low-avidity or high-avidity antibodies is not complete evidence of recent infection and vice versa. Given the importance of interpreting the results obtained during pregnancy, it is necessary to take into account all factors (other laboratory tests, clinical picture) and, if necessary, repeat studies.

Toxoplasmosis during pregnancy

Diagnosis of toxoplasmosis is included in the study of TORCH infections, which are the most dangerous during this period. Regular testing allows you to confidently manage your pregnancy. The effect of Toxoplasma on the fetus depends on the period of gestation. Infection can lead to significant deformations that are incompatible with life, resulting in termination of pregnancy or recurrent miscarriage. During pregnancy, a woman must especially observe safety rules and limit contact with pets that have not passed veterinary control. The consumption of animal products should occur only after complete heat treatment.

Chapter 5. DIAGNOSIS OF TOXOPLASMOSIS

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4.1.6. Analysis results

Appearance

Toxoplasmosis is a systemic disease caused by the protozoan Toxoplasma gondii. This parasite is widespread and capable of infecting many species of mammals, especially common in the tropics and less common in cold, arid areas. Serological studies in human populations show rates of Toxoplasma infection ranging from less than 1% of young adults in some areas to 90% of older adults in others. The main routes of transmission to humans are congenital and oral, through consumption of contaminated food, and contact with domestic animals, especially cats [43-46]. Less common, but of greater clinical importance, is person-to-person transmission through contaminated blood products and tissue transplants [47].

One of the situations in which toxoplasmosis poses a serious danger is primary infection during pregnancy [48-51]. The risk of severe consequences for the fetus is higher the earlier in pregnancy a woman is infected with toxoplasmosis, but during the same period the probability of infection of the fetus is lower. Conversely, in later stages of pregnancy, the percentage of transmission of toxoplasmosis to the fetus is very high, but the risk of severe damage to the fetus is reduced. The potential risk of fetal infection with toxoplasma is 6% at the beginning of the first trimester of pregnancy, 40% at the end of the first and during the second trimester of pregnancy and reaches 72% in the third [52-54]. If a woman had toxoplasmosis before pregnancy (at least six months before), toxoplasmosis does not threaten her unborn child.

The most common clinical manifestations of the disease are self-limiting febrile lymphopathy, occurring subclinically or with mild clinical manifestations in healthy adults. However, infection of a patient with a suppressed immune system or a developing fetus can have very serious consequences. Opportunistic infections of toxoplasmosis or reactivation of a subclinical infection in a patient with a suppressed immune system can cause encephalitis, pneumonia and myocarditis, often fatal.

The consequences of a woman's infection include miscarriage and stillbirth if infection occurs during the first three months of pregnancy, and irreversible neurological damage to the newborn if infection occurs in the second and third trimester of pregnancy.

During primary infection with Toxoplasma gondii, the immune system begins to produce class M antibodies. Current methods can detect them only 14 days after infection [55]. Over the next few months, the level of IgM decreases and is present in the body for no more than 1 year [56, 57]. Antibodies of this class are not formed during reactivation of the infection. Therefore, qualitative determination of Toxoplasma IgM provides rapid confirmation of acute or recent infection [58-61]. Since class M antibodies do not cross the placenta, they are used as markers of fetal infection during pregnancy [53, 54, 62–65]. Moreover, testing for the presence of IgM antibodies in a newborn simultaneously with testing maternal IgM allows for early diagnosis of congenital toxoplasmosis.

Since the severity of the consequences of infection with toxoplasmosis depends on the stage of pregnancy, establishing a specific time of infection is essential. To specify the moment of infection of a pregnant woman, comparison of the results of detection of IgM with the titer and avidity of IgG is widely used throughout the world [66-72].

In contrast to the IgM class, the level of class G antibodies increases within 14 days after the first determination of IgM and remains constant indefinitely [55, 73]. IgG antibodies to Toxoplasma can be present in the body throughout life. Therefore, a constant titer of IgG antibodies indicates earlier infection, while a fourfold or more increase in titer is a sign of active infection. Since class G antibodies cross the placenta, serial repeated determination of the level of IgG antibodies in the infant will help distinguish congenital infection (constant level) from neonatal infection (increasing titer).

Detection of class M antibodies to Toxoplasma should be carried out using the BPT ImmunoComb TOXO IGM ELISA according to the instructions included with the kit. For the general scheme of setting up the analysis, see Chap. 4.1, table 3, figure 3.

The results of the analysis appear as blue-gray dots on the surface of the comb tooth. Qualitative assessment of the result is carried out visually, by comparing the intensity of staining of the lower spot of each sample with the intensity of staining on a tooth with a positive control, or automatically on the CombScan III™ device (see 4.1.6.).

The sensitivity and specificity of the ImmunoComb TOXO IGM test was studied on a panel of 480 serum samples in comparison with the ELISA reference test. Questionable results were verified by indirect immunofluorescence and agglutination reactions. The results are summarized in Table 5.

Table 5. Study results

*Includes one sample positive by ELISA but negative by both other tests.

Based on these results, the following test indicators were calculated:

• Sensitivity 97.7%,
• Specificity 100.0%.

Quantitative determination of class G antibodies to Toxoplasma should be carried out using the BPT ImmunoComb TOXO IGG ELISA according to the instructions included with the kit. For the general scheme of setting up the analysis, see Chap. 4.1, table 3, figure 3.

The results of the analysis appear as blue-gray dots on the surface of the comb tooth. Quantitative assessment of the results is carried out visually using the CombScale scale or automatically on the CombScan III tm device (see 4.1.6.). A result with an antibody G concentration greater than or equal to 10 IU/ml (IU/ml) is considered positive.

The sensitivity and specificity of the ImmunoComb TOXO IGG test was studied on the example of 489 serum samples in comparison with the ELISA reference test and immunofluorescent analysis. The results are summarized in Table 6.

Table 6. Study results

Based on these results, the following test indicators were calculated:

• Sensitivity 97.5%,
• Specificity 97.2%.

Modern methods of treatment

Unfortunately, it is very difficult to completely eliminate the parasite from the body. Toxoplasma forms cysts in which they can persist in tissues for a long time. They are resistant to medications. Patients with compromised immune status require especially intensive treatment.

Antibacterial agents, chemotherapy drugs, and their combinations are used. Also, treatment is aimed at increasing immunity.

During pregnancy, treatment is carried out no earlier than 12-16 weeks. Chemotherapy drugs are used. For sufficient effect, two courses are carried out with a break of 1-1.5 months. If the patient became infected before pregnancy and has no clinical signs of pathology, treatment is not carried out. The intake of medications is controlled not only by the infectious disease specialist, but also by the doctor who is managing the pregnancy.

Reasons to undergo diagnostics at SZTsDM

The center's laboratory is equipped with the latest diagnostic equipment. Analyzes are performed quickly and efficiently. The medical centers employ highly qualified specialists, which allows for comprehensive and effective diagnostics. The patient can not only establish the fact of the disease, but also undergo an extensive examination of the body, as well as treatment. For our doctors there is no disease of a separate system - they assess the patient’s full condition and treat it, not pathology. It is possible to receive the results of the study by personal email or receive them in printed form at the medical center.