Toxoplasmosis – Part 2 – Disease pattern, Epidemiology, Diagnosis (Toxoplasma gondii)

Sample

1. Blood to prepare the serum.
2. Store the blood at 2 °C to 6 °C if the test is delayed for more than 7 days.
3. Serum should not be heat-inactivated, because this may give false-positive results.

Indications

1. This is used for the diagnosis of toxoplasma infection.
2. This is advised in infertile women.
3. This is advised in newborn infants.
4. This is advised in immunocompromised patients.

Pathophysiology

1. Toxoplasmosis is caused by the protozoan Toxoplasma Gondii.

2. This causes generalized granulomatous disease and the primary site may be CNS.
3. Toxoplasmosis may be :
   1. Congenital.
   2. Acquired.
4. Toxoplasma can infect :
   1. Humans.
   2. Domestic animals (Cats)
   3. Wild animals.
5. Epidemiology:
   1. This is protozoan which is present in all warmblood animals.
   2. The Toxoplasma gondii was first discovered in North African rodents and has been observed in numerous birds and mammals around the world, including humans.
   3. The cat is the definitive host.
6. Toxoplasma gondii is the most common causative agent of toxoplasmosis.
7. This is found worldwide because so many animals harbor it.
   1. 15 to 20% of the American population has this infection.
   2. The highest record 93% is found in Parisian females who undercooked or raw meat, 50% of cases are seen in their children.
   3. A number of the babies are infected through the transplacental route.
   4. This is also seen in the USA due to undercooked meat.
   5. Oocyst is hardy and can survive for a longer period.
   6. These organisms have no flagella.
8. Toxoplasma has a complete life cycle as coccidian in the filedae (carnivorous animals including cats and big cats).
   1. The definitive host is house cats.
      1. Domestic cats are the source of the disease because the oocysts are often present in their feces.
      2. In the cat, the parasite develops a sexual cycle and eventually, oocysts are excreted in the feces.
      3. Trophozoites are crescent-shaped can spread in the cat organs and tissues.
      4. Later on, these develop into cysts.
9. Antibody to T.gondii varies in a different population. It ranges from 96% in Western Europe to 10 to 40% in the united states if America.
   1. The patients with AIDs are seropositive for T. gondii and roughly 25% to 50% will develop encephalitis.

Source of spread:

1. Humans may acquire the disease by the ingestion of uncooked meat and contaminated material.
2. There may be fecal contamination of:
   1. Food.
   2. water.
   3. Soiled hands.
      1. Inadequate cooked or infected meat.
      2. Raw milk.
      3. Blood transfusion transmission of toxoplasmosis has been recently recognized particularly with white blood cells concentrate.
      4. Patients are at risk are those receiving immunosuppressive agents or corticosteroids.
3. Exposure to feces of cats, or other infected material.
4. This spread due to:
   1. Hand to mouth contamination of infected oocyst in cat feces,
   2. Ingesting contaminated meat.
   3. Transplacental spread during delivery.
5. Transplacental transmission usually takes place in the course of an acute or undiagnosed maternal infection.
6. The expected incidence of congenital toxoplasmosis is 2.7 per 1000 live births.

Signs and symptoms

1. May be asymptomatic.
2. CNS involvement with brain damage, blindness, and death.
3. CDC says that 25 to 70 % of the population is exposed to Toxoplasma because of the presence of the antibody in the serum.
4. CDC recommendations are to check all the pregnant ladies.
5. If the mother has toxoplasma antibodies prior to pregnancy, that may protect the fetus.
6. If the mother develops an infection after the conceivement then the fetus may get the infection through the placenta.

Disease pattern

1. Disease pattern:

   1. After the ingestion of the cysts, this protozoan is obligatory intracellular parasites.
      1. This will spread through the blood and cysts may form in the brain and muscles.
      2. These cysts may be seen in the eye.
   2. The congenital infection which shows:
      1. Hydrocephalus or microcephaly.
      2. Encephalomyelitis.
      3. Chorioretinitis.
      4. Cerebral calcification.
   3. There are lesions in the viscera.
   4. There may be acute enlargement of the lymph nodes.
   5. Severe illness leads to Myocarditis, Pneumonitis, Hepatitis, Meningoencephalitis, and ocular lesions.
   6. Type of toxoplasmosis are:
      1. Congenital toxoplasmosis.
      2. Cerebral toxoplasmosis.
      3. Toxoplasmosis in the immunocompromised patients.

2. Clinical presentation:
   1. Primary infection:
      1. Many patients may remain asymptomatic especially children.
   2. Later on, this results in generalized infection:
      1. The patient may have fatigue, enlargement of the lymph nodes,
      2. Patients may have chills and fever.
      3. The Patient may have a headache and myalgia.
      4. Chronic cases may develop a maculopapular rash.
      5. Severe symptoms may be seen in patients with encephalomyelitis, myocarditis, or hepatitis.
   3. Spontaneous recovery follows acute febrile disease, the organism can localize and multiply in any organ of the body or circulatory system.
   4. Types of T.gondii infections are:
      1. Acquired infection.
         1. This is frequently mild.
         2. There are chills, fever, headache, enlarged of the lymph nodes, and extreme fatigue.
         3. The chronic form of toxoplasmic lymphadenopathy may exist.
         4. Reactivation of cerebral toxoplasmosis may be seen in AID’s patients.
         5. In AID’s patients, encephalitis is seen. In these patients, CD4+ cell numbers fall below 100 x 109/L.
      2. Congenital infection.
         1. It results in central nervous system malformation.
         2. There may be prenatal mortality.
         3. In infants who are serologically positive  at birth, may fail to display:
            1. Neurological abnormalities.
            2. Ophthalmic abnormalities.
            3. generalized illness at birth.
         4. 75% of the cases congenitally infected newborn is not seropositive or not diagnosed at birth:
            1. The disease remains dormant.
            2. Or discovered when the patients will develop:
               1. Chorioretinitis.
               2. Unilateral blindness.
               3. Neurological abnormalities.
      3. Complications of congenital toxoplasmosis
         1. Hydrocephalus.
         2. Microcephaly.
         3. Chronic retinitis.
         4. Convulsion.
      4. How to prevent congenital toxoplasmosis:
         1. Avoid touching the mucous membrane of the mouth and eye while handling raw meat.
         2. Wash hands thoroughly after handling raw meat.
         3. Cook the meat at >66 °C.
         4. Wash the kitchen surfaces that come in contact with the raw meat.
         5. Wash thoroughly the fruits and vegetables before eating.
         6. Prevent access to flies, cockroaches, and other insects to vegetables and fruits.
         7. Avoid contact or wear gloves when handling the cat feces contaminated materials

Normal

• Negative = Titer = < 1:16
  • T.Gondii DNA not detected by PCR.
• The titer of 1:256 or more indicate recent exposure or recent infection
• The titer of 1:1024 or more indicates active disease.

 Diagnosis

• The culture of the T. gondii is very difficult, so the diagnosis is supported by the serology.
• Serology of Toxoplasmosis
  1. The enzyme-linked immunofluorescent assay (EIA) is considered the method of choice for the detection of IgM which indicates acute infection.
     1. The various methods or techniques used for T. gondii antibody are:
        1. Enzyme-linked immunoassay (EIA).
        2. Indirect hemagglutination (IHA).
        3. Indirect fluorescent antibody (IFA).
        4. Sabin-Feldman dye test
        5. Complement fixation test.
  2. IgG antibody titer represents present or past infection.
  3. IgM antibody is needed to confirm the present infection.
     1. Antibody IgM titer <1:16  =  shows no exposure to virus.
     2. Antibody IgM titer >1:4 to 1:256  = acquired infection in last 18 months.
     3. Antibody IgM >1: 1024  = Acquired infection in last 4 months
• Because of difficulty in growing the Toxoplasma, serological tests are recommended.

IgM (antibody)

1. Rises about after one week of infection
2. The peak level is about 2 to 3 months.
3. Declines in around one year when may not be detected.
4. A high level indicates acute infection.
5. Rising titer also indicates an acute infection.
   

   Toxoplasma IgM antibody (serology)

IgG (antibody)

1. It begins to rise after 2 weeks of infection.
2. The peak level is in about 2 to 3 months.
3. Its level declines in about 6 months but persists in blood at a low level.
4. A low level indicates past infection.
5. A low level protects the fetus from infection.
   

   Toxoplasmosis antibody (serology)

Interpretations

1. 4 fold titer rises in IgG over 4 weeks indicates acute infection.
2. IgM high titer also indicates acute infection.
3. The elevated titer of IgM and IgG > 1:1000 indicate acute infection.
4. A low and persistent level of IgG indicates past infection.

Toxoplasma antibody interpretation:

IgG antibody	IgM antibody	Interpretation
Negative	local evidence of toxoplasmosis infection
Negative	Positive	Positive for early  infection or false positive so repeat the test
Positive	Negative	Past infection 6 months or more
Positive	Positive	Positive recent infection within the last 12 months

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