Toxo Test - Toxoplasma antibodies

The antibodies to Toxoplasma, called by the abbreviation Toxo-test, are antibodies directed towards parts of the Toxoplasma Gondii, a parasite obligate intracellular protozoan capable of infesting humans and animals, causing Toxoplasmosis.

There Toxoplasmosis it is a disease that usually affects people who are immunocompromised, that is, with low immune defenses.

The disease is transmitted from animal to man: usually the infection occurs through the ingestion of eggs (oocysts), which occurs mainly by consuming improperly washed vegetables or raw meat.

The disease can cause flu-like symptoms in some people, but most people who are immunocompetent (that is, with normal immune defenses) do not develop any symptoms, and the disease resolves. In people with compromised immune systems (such as AIDS, patients undergoing chemotherapy or taking immunosuppressive drugs, such as transplant recipients), it is possible thatToxoplasma infection manifests itself with greater severity, giving non-specific symptoms (headache, confusion, blurred vision, incoordination) up to severe lung and intestinal problems.

Toxoplasmosis is also a very harmful disease if taken in pregnancy: even in women with a normal immune system, contact with the parasite Toxoplasma gondii durbefore first quarter pregnancy can result in miscarriage or stillbirth, in the second trimester can cause hydrocephalus and late forms of chorioretinitis, while in the third quarter usually there is an asymptomatic evolution or a less severe clinical manifestation such as neonatal jaundice due to hepatic and splenic suffering.

There diagnosis of Toxoplasmosis is performed with the measurement of antibodies to Toxoplasma (Toxo test).

Immunoglobulin M (IgM): they appear first and can therefore be considered a sign of a recent infection; they generally disappear after 6-12 months from the infection, even if for some individuals these are not antibodies developed following the infection but natural antibodies already present.

IgM have a lower affinity than immunoglobulin G (IgG) and competition problems can occur in their presence. False positives can be found in individuals positive for the rheumatoid factor or for anti-nucleus antibodies (ANA). The presence of IgM is, therefore, necessary but not sufficient to suspect a recent Toxoplasma gondii infection.

Immunoglobulin A (IgA): they appear after IgM and before or after the appearance of the first IgG. Generally IgA also disappears after 6-12 months, but can reappear in case of reactivation of the infection, even without the simultaneous reappearance of IgM. The positivity of the serum for IgA and IgM allows a diagnosis of certainty for a recent toxoplasmosis (ie acquired in a period of less than 6 months). If IgA is present in the absence of IgM, a reactivation of an old infection is conceivable.

Immunoglobulin G (IgG): cthey appear later. The first IgG are specific to the parasite's membrane and not greedy until the second week. Subsequently the IgG are specific for the cytoplasm of the parasite and the greed appears from the 3rd-5th week. The antibody titre of anti-membrane IgG generally stabilizes in 3-12 months, for anti-cytoplasmic IgG in 6-18 months. Non-greedy antibodies gradually disappear after 3 months. IgG lasts for the entire life of the individual, their concentration can increase in case of re-infection (in the absence of IgM and IgA) or reactivation (with or without IgA).

Unfortunately, in immunosuppressed subjects the results are purely indicative, as their immune system is unable to produce antibodies in the correct way. Furthermore, in case of negativity, cerebral toxoplasmosis cannot be excluded with certainty.

So to summarize:

  • Positive IgM: acute, current or recent infection. The persistence of specific IgMs (2-12 months and beyond) makes the interpretation problematic and therefore it is necessary to re-examine IgM and IgG after 3 weeks.
  • Positive IgG: previous infection, or in progress, depending on whether there are positive IgM (recent infection) or negative (previous infection).
  • Positive IgA: acute infection, can be primary (with positive IgM) or a reactivation (negative IgM). In the newborn with suspected or confirmed toxoplasmosis during pregnancy: congenital toxoplasmosis.



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