Toxoplasmosis is caused by an intracellular protozoan, Toxoplasma gondii, which has a wide geographical distribution. The main infection routes are ingestion of cysts from raw or badly-cooked meat, ingestion of oocysts from substrates contaminated with the feces of infected felines and congenital transmission by tachyzoites. The congenital form results in a severe systemic disease, because if the mother is infected for the first time during gestation, she can present a temporary parasitemia that will infect the fetus. Conventional tests for establishment of a fetal diagnosis of toxoplasmosis include options from serology to PCR. Toxoplasmosis is usually diagnosed by antibody detection. In acute infections, increased levels of IgG and IgM antibodies usually appear within the first or second week of infection . High levels of specific IgG antibodies indicate that the individual has been previously infected. However, these antibodies do not distinguish a recent infection from one acquired a long time before. Detection of specific IgM antibodies can help determine if infection was recent ; however, these antibodies can persist for months or even years after acute infection . This fact has limited the use of this method, because it is not possible to determine if the patient has an acute infection, which can put the fetus at risk, or if the infection had occurred months before .ELISA and ISAGA are the most widely-used techniques for detection of IgA antibodies. Whenever the serological result is negative, prenatal and follow-up care must be intensified in order to prevent infection of the mother. As the mother rarely develops infection symptoms, but rather has a temporary parasitemy, serological diagnosis should be periodical, throughout pregnancy in seronegative women, in order to be aware of a possible infection

Positive IgM test results should be confirmed by reference laboratories, which are able to determine the time since infection using specific tests, such as IgG avidity, or by serological profile (Sabin-Feldman reaction, capture ELISA-IgM, ELISA-IgA, ELISA-IgE and differential agglutination) [34].

The test for IgG avidity is an auxiliary test to determine if the infection is acute or previously acquired when the IgM serological reaction is positive in an asymptomatic patient. The test is based on the greater strength of ionic bindings between antigen and antibody produced from old infections when compared to recent ones [35]. Depending on the method used, pregnant women with high avidity antibodies are those who have been infected at least 3-5 months earlier. This is most useful in pregnant women in their first months of gestation who have a positive test for both IgG and IgM toxoplasma antibodies. When avidity is low or boderline it may be misleading and a more careful interpretation is critical. Low-avidity results may persist for as long as 1 year [36].

Pre-natal ELISA

Practically  IGM is the most used one, PCR mya be used in  the lab

By rising titer of IgM ELISA

to MOHMOUD : would you elaborate By rising titer of IgM ELISA

I would suggest a molecular method. Thus, PCR if you have the facility to do. This will definitely detect active infection and not exposure.

The serological tests (e.g. ELISA, 'dye test', agglutinations and immunofluorescence) may be used to indirect diagnosis, detecting IgM in recent infections or evaluating the anti-Toxoplasma IgG affinity in chronic cases. Among the direct diagnosis technics (searching the etiological agent), the PCR is the most commonly used, since the culture of the protozoan or the xenodiagnosis are laborious.

Serological anti-IgM test which is the more sensitive and easily to perform. You can use both commercially or in house-made antigen. PCR is also a very sensitive test, but requires a more sophisticated laboratory structure.

In some situation  we have to  do PCR e.g.  in  the ligour

Diagnosis is made by various serlogic procedures. Other techniques include e.g. PCR or isolating the Toxoplasma in tissue culture..However, in the diagnosis of toxoplasmosis immunological tests are the method of choice. Some diagnosis options for toxoplasmosis:

if serum sample is negative - women is susceptible to infection; recommend avoid exposure and request serology

antibodies found in single serum sample - women is infected at some time in the past; you have to examine other serum samples collected 2-4 weeks after the first;

if AB  16-fold increase in second serum sample it indicates acute infection;

titer of 1:2 to 1: 512 - infection in the past; probably immune; titer of 1: 1,024 or higher need to monitor neonate for infection;

the presence of IgM antibody in single serum sample cannot be used to indicate recent exposure; moreover the great problem with Toxoplasma-specfic IgM is lack of specificity

If women is pregnant and IgG and IgM are positive then an avidity IgG test schould be carried out. High avidity result in the 3-4 months of pregnancy usually rules out infection in early pregnancy. Low avidity IgG mainly indicates recent infection although in some patients low avidity IgG persist for many months after infection.

The diagnosis is difficult to perform on history and physical examination. The doctor should always think of this diagnosis in patients with:

fever

lymphadenopathy (enlarged lymph nodes - swollen lymph nodes)

malaise

history of contact with cats or eating uncooked meat or little.

In adults the disease can be asymptomatic, however the parasite can reach the fetus through the placenta and fetal compromise the future.

Blood tests are used for diagnosis of acute infection (current) or chronic. Many people have or had toxoplasmosis and no symptoms.

Women who have had the disease are not at risk of reinfection during pregnancy. Only immuno-suppressed patients can reactivate the disease during pregnancy.

In pregnant women it is customary to order tests for the detection of two types of antibodies, IgG and IgM:

IgG is the marker of immunity to the parasite.

IgM is the marker of acute infection by the parasite.

Pregnant women who have positive IgG antibodies have immunity to the disease.

Dear Walter Filho

Thanks for your comprehensive comments. I think  we  need to add PCR for inutero infections

Mothers suspected of T. gondi infection, the parasite can be detected by serological  test  from amniotic fluid for IgG, IgM, IgA and avidity test.  PCR can be instituted  by testing amniotic fluid during pregnancy.

If confirmed positive, spiramycin should be given a dose of 3 g/day throughout confinement to reduce the risk of infecting the fetus via the placental route.

i am agree with Dear Johari

Walter Filho: Ig M is not anymore considered as an indicator of acute infection, exept for the situation when specific Ig M against T.gondii are present while Ig G are not. Otherwise, when both Ig g and Ig M are present in a patient serum we will diagnose the condition as persistent  T.gondii infection, which has no clinical relevance if the patient is an immune competent one. In my studies I found that about 1/3 of women are having persistent Ig M.

Ig A are a little bit more reliable for detecting acute infectio, as is the avidity test, if the avidity is high you can exclude a recent infection.

PCR is highly reliable to diagnose the condition in mother but this will not tell you anything about the situation of the foetus or new-born. 

There is a long discussion about the risk/benefit rate when performing amniocentesis.

Iam  agree with  Carmen Costache 

OK. Grateful for the information.

From zoonotic point of view, toxoplasmosis is a  zoonosis of public health importance. I published online an article about serological and molecular studies of ovine and human toxopasmosis:

 www.Sjournals.com

Scientific Journal of Veterinary Advances (2013) 2(11) 157-168

ISSN 2322-1879

doi: 10.14196/sjvs.v2i11.1080

Hello there,

As Walter Filho said, IgG and IgM are the markers of immunity to the parasite and acute infection by the parasite, respectively; So you should pay special attention to the titer of these two factors by means of serological tests such as ELISA.