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Congenital Toxoplasmosis

Overview

Toxoplasmosis is a part of TORCH group of infections which includes Rubella, Cytomegalovirus, Herpes virus. These can be transmitted from the mother to the fetus during pregnancy and cause congenital infections leading to permanent disability in the fetus and fetus loss in severe cases. The other three causes of congenital infections are viruses whereas Toxoplasma is a protozoan parasite.

Historical Perspective

• In 1908, Nicolle and Manceaux described the parasite in the blood, spleen and liver of a North African rodent–gundi (Ctenodactylus gundi), due to its similar appearance as leishmania they named it Leishmania gondii.
• In 1909, Nicolle and Manceaux renamed the parasite as T. gondii.
• In 1937, Sabin & Olitsky described that Toxoplasma was an obligate intracellular parasite and could be passed onto laboratory animals by intracranial, subcutaneous, intraperitoneal inoculation of brain homogenates (The slurry of tissues and cells which results when cell structure has been mechanically disrupted). They have also suggested that ingestion of Toxoplasma contaminated tissue can result in Toxoplasmosis.
• In 1937 to 1940, Wolf and Cowen have described necrotic and granulomatous lesions on autopsy of a 3 day old infant's brain infected with Toxoplasma. They have also reported that the mothers were asymptomatic but carried antibodies against Toxoplasma and the possibility of congenital transmission was expressed.
• In 1940, Pinkerton and Weinman reported the first fatal case of Toxoplasmosis in an adult.
• In 1948, Sabin and Feldman developed a serological test to identify infected individuals by using antibodies specific to Toxoplasma, called the Sabin Feldman Dye test. The serological test when used in large population studies showed a high proportion of humans and domestic animals carried antibodies against Toxoplasma.
• In 1965, Desmonts described that ingestion of under-cooked and uncooked meat plays a role in the pathogenesis of Toxoplasmosis.
• In 1970, Dubley described the life cycle of the parasite and established that the cats are the definitive hosts and any warm blooded animal can be an intermediate host.

Classification

There is no classification system for Congenital Toxoplasmosis.

Pathophysiology

Pathogenesis

Infective stages of the Parasite

The three infective stages of T. gondii include:

• Tachyzoite: It is the rapidly dividing and invasive form, can invade any vertebrate cell type
• Bradyzoite: These result from the conversion from tachyzoites, they are slowly diving form, and are present in the tissue cysts which can remain in the host throughout the lifetime
• Sporozoite: It is the environmental form present in the oocyts

Mechanism of cell Invasion

• The initial step of invasion is attachment of the tachyzoite to the host cell membrane. A set of protiens help in the adherence and penetration of the host cell membrane, also enhance the growth and virulence of the parasite.
• In the host cell the parasite forms a vacuole where it divides for 6 to 9 cycles after which the parasites are released into the circulation. It is an active process which is dependent on the increase in intracellular calcium stores.

Pathogenesis of Vertical Transmission

• Different modes of transmission of T.gondii to have a primary infection in a healthy mother include:
  • Ingestion of tissue cysts from raw meat and uncooked meat.
  • Ingestion of food, fruits, vegetables or water contaminated by oocysts in the cat feces.
  • Infection after a solid organ transplant, heart transplant patients are at the highest risk as it can contain tissue cysts.
• Once the patient has a primary infection with tachyzoites in the blood stream during pregnancy a possible transplacental infection can take place.
• The tachyzoites colonize in the placenta and can cross the barrier to reach the fetus in 30% of cases leading to the disease.
• The frequency of transmission of the tachyzoites to the fetus is related to the gestational age, with low transmission rates in the first trimester (10-15%) and highest transmission rates in the third trimester(60-90%). However the disease is more severe if the infection is acquired early in the pregnancy.
• The factors influencing the transfer of tachyzoites to the fetus is not well understood.

Microscopic Pathology

• Brain autopsy in patients with congenital diagnosis demonstrates periaqueductal and periventricular vasculitis with necrosis.

Causes

Congenital Toxoplasmosis is caused by a coccidian parasite Toxoplasma gondii. The infective tachyzoites reach the fetus by transplacental route.

Differentiating Toxoplasmosis from other Diseases

The most important congenital infections, which can be transmitted vertically from mother to fetus are the TORCH infections. These infections have overlapping features and hence, must be differentiated from Toxoplasmosis  :

Congenital Infection	Cardiac Findings	Skin Findings	Ocular Findings	Hepatosplenomegaly	Hydrocephalus	Microcephaly	Intracranial Calcifications	Hearing deficits
Toxoplasmosis		Petechiae Purpura Maculopapular rash	Chorioretinitis	✔	✔	✔	Diffuse intracranial calcifications
Treponema pallidum		Petechiae Purpura Maculopapular rash	Chorioretinitis Glaucoma	✔
Rubella	Patent ductus arteriosus (PDA) Pulmonary artery stenosis Coarctation of the aorta Myocarditis	Petechiae Purpura	Chorioretinitis Cataracts Glaucoma Microphthalmia	✔	✔	✔		✔
Cytomegalovirus (CMV)	✔	Petechiae Purpura	Chorioretinitis	✔		✔	Periventricular calcifications	✔
Herpes simplex virus (HSV)	Myocarditis	Petechiae Purpura Vesicles	Chorioretinitis	✔	✔	✔		✔
Parvovirus B19	Myocarditis	Petechiae Subcutaneous edema	Chorioretinitis Cataracts	✔

Epidemiology, Demographics

Prevalence

• It is estimated that 25 to 30% of the world's population is infected with Toxoplasma.
• In United States 89% of women in the childbearing age are susceptible to have an acute infection and at risk for transmitting the parasite to the baby if the primary infection occurs during the getational period.
• In United States the age adjusted seroprevalence rate is 22.5%. There is significant variation in the distribution with highest prevalence reported in the North-eastern states and lowest in the western states.
• In countries such as North America, Northern Europe and in Sahelian countries of Africa low seroprevalences of 10% to 30% are observed. In countries of Central and Southern Europe, tropical African countries and Latin America the seroprevalence is around 30 to 50%. This shows the variation within the countries and as well as between the countries.

Incidence

• Toxoplasmosis affects 500 to 4000 new borns every year.
• In United States, Toxoplasmosis affects 1.1 million people every year.

Race

• The prevalence of Toxoplasmosis is higher in non-Hispanic black population and Mexican Americans than non-Hispanic white population.

Age

• A decreasing trend in prevalence is reported in the population of U.S born persons aged between 12 to 49 years; with 14% between the years 1988 to 1994, and 9% in the years 1999 to 2004. This trend is attributed to the improvement of hygienic conditions, changes in farming systems, the consumption of frozen meat, and the feeding of cats with sterilized food.
• The similar decreasing trend of seroprevalence is been reported in France and Netherlands.

Developing Countries

• In countries with poor hygienic measures and using unfiltered surface water for consumption reported higher seroprevalence rates. In these countries the childhood population is at a higher risk of acquiring the infection, the mean age is reported to be 15 years.

Risk Factors

The major risk factors for acquiring the infection is consuming raw meat and ingestion of food contaminated with Toxoplasma oocysts excreted in cat feces.
The risk factors which predispose pregnant women for primary infection include:

• Consumption of raw oysters and clams
• Eating undercooked meat which includes pork, beef and lamb
• Drinking unpasteurized goat’s milk
• Exposure to kitten litter
• Working with meat
• Low socioeconomic status
• Poor Hygiene
• Drinking unfiltered water
• Immunocompromised state

Screening

• Majority of the countries do not follow standard screening for the detection of Toxoplasma infection during the antenatal period.
• In countries such as France, Austria, Brazil standard screening is followed during the antenatal period for detecton of toxoplasmosis .
• Women are tested for antibodies aganist Toxoplasma on their first antenatal visit, and if they are seropositive they are followed up periodically in every trimester to examine the trends in IgG tite levels.
• Women who seroconvert during gestation, fetal testing by amniocentesis and fetal blood sampling is recommended to identify the infection status in the fetus.

Natural History, Complications, Prognosis

Natural History

Congenital Toxoplasmosis is due to transplacental transmission of infective tachyzoites to the developing fetus. The severity of clinical manifestation is dependent on the timing of the infection during gestation. Early gestational infection results in a miscarriage, still birth or a new born with neurological abnormalities. Late gestational infection is asymptomatic in majority of children at birth but they develop neurological abnormalities and vision changes in the 1st or 2nd decade.

Complications

If left untreated congenital Toxoplasmosis results in mental retardation, seizures, motor difficulties, severe vision loss, hydro or microcephalus and hearing loss.

Prognosis

Prognosis of congenital Toxoplasmosis is dependent on the severity of the disease. Severe infection causes death at an early age, asymptomatic infection at birth will present in the 1st or 2nd decade with progressive chorioretinitis with poor prognosis.

Diagnosis

The presence of intracranial calcifications, hydrocephalus and chorioretinitis is a classic traid of congenital Toxoplasmosis.

History and Symptoms

The severity of manifestations in the newborn are dependent on the fetal age when the infection occurred and the trimester of pregnancy the mother gets infected. The disease is severe in mothers who acquire infection in the first trimester.

Symptoms in the Mother

• Acute infection of Toxoplasma in an asymptomatic women can be easily missed as they present with flu like symptoms, lymph node swelling in the neck and rarely a skin rash.
• Early gestational infection results in a miscarriage or a still birth.

Symptoms in newborn

The clinical manifestations in the newborn are dependent on the month of gestation the infection has occurred - earlier the infection more severe the disease.

Infection in early pregnancy

Neuro-ocular symptoms are typical presenting features in Congenital Toxoplasmosis.

• Involvement of the CNS can present with psycho-motor retardation and seizures.
• Chorioretinitis presents with impaired vision.
• Obstruction in the ventricles results in accumalation of CSF, causing enlargement of the head and increased intracranial pressure symptoms such as vomiting, headache, confusion and double vision.
• Jaundice
• Focal neurological deficits
• Feeding difficulties

Infection later in the pregnancy

• Majority of the infected newborns remain asymptomatic at birth.
• Children develop psycho-motor retardation and retinochoroiditis later in life.
• Loss of vision is a common symptom and is seen in 95% of infants due to chorioretinitis.

Laboratory Findings

Prenatal Diagnosis

• During the period of gestation Toxoplasma is diagnosed by the presence of parasite in the amniotic fluid or in the fetal tissue by DNA amplification, microscopy or by isolation of the organism.
• The most commonly used diagnostic test is the PCR of the amniotic fluid and a positive test is diagnostic of congenital Toxoplasmosis.

Postnatal Diagnosis

The most commonly used diagnostic investigation for early dectection is the serological detection of antibodies (IgG, IgM and IgG) in the serum of the infant. A combination of all the antibodies is done as the maternal IgG can cross the placenta and give false positive result.

• In the postnatal period the gold standard for diagnosis of Congenital Toxoplasmosis is the persistence of Toxoplasma IgG by 12months of age.
• During the postnatal period the standard to rule out diagnosis is the the absence of Toxoplasma IgG at 12months of age in the absence of treatment.

Imaging Studies

• Imaging studies such as CT and MRI of the brain demonstrate periventricular calcifications, hydrocephalus and microcephaly.

Principles and various methods used for the diagnosis of congenital toxoplasmosis:

Principle	Detection	Method	Findings supporting the diagnosis of Toxoplasmosis
Toxoplasma specific humoral responses	IgG, IgM, IgA	Dye test, ELISA, ELISA-like assays,ISAGA, immunofluorescence, agglutination	Positive IgM after 5 days of life and in the absence of blood transfusions Positive IgA after 10 days of life Persistence of Toxoplasma IgG beyond 1 year of age
	IgG, IgM, and IgA to specific Toxoplasma antigen	Western blot	Presence of specific bands only seen in the newborn or bands with higher intensity than maternal ones for IgG and/or IgM and/or IgA in a reference laboratory
Toxoplasma nucleic acid amplification	DNA	PCR	Positive result in any body fluid (e.g: amniotic fluid, cerebrospinal fluid, peripheral blood, urine)
Immunohistochemistry of Toxoplasma specific antigens in tissue	Antigens	Immunoperoxidase	Positive result in any tissue(e.g., brain or other fetal tissue)
Visualization by microscopy	Visual identification of tachyzoites and/or cysts	Stains such as hematoxylin/eosin, Giemsa	Positive identification in a reference laboratory
Isolation of Toxoplasma	Whole live parasite	Inoculation in peritoneal cavity of mice	Detection of live cysts from any body fluid or tissue that has been inoculated in mice in a reference laboratory
Brain imaging	Brain calcifications Hydrocephaly Microcephaly	Ultrasound, CT, brain MRI	Findings can be suggestive but are not diagnostic of congenital Toxoplasmosis since other etiologies may result in similar findings
Retinal exam	Inflammation in choroidal and retinal layers	Ophthalmological exam	Retinochoroidal lesions can be highly suggestive or, at times, diagnostic of congenital Toxoplasmosis

Table adopted from Laboratory Diagnosis of Congenital Toxoplasmosis

Approach for the management of Congenital Toxoplasmosis

Approach during pregnancy with known seropositive status

Screening programs benefit the clinicians with information regarding maternal serological and amniotic fluid PCR test results, precise gestational age at which the mother was infected, and detailed anti-Toxoplasma treatment history which play a vital role in the management of congenital Toxoplasmosis.

IgG/IgM(ideally performed in the first trimester

Negative IgG and IgM

Positive IgG Negative IgM

Positive IgM Negative IgG

Positive IgG and IgM

No serologic evidence of Toxoplasma infection Risk of congenital Toxoplasmosis only if the woman aquires infection during the pregnancy Counsel about the preventive measures for T.gondii

<18 weeks of gestation Infection aquired in the past and prior to the pregnancy Risk of infection is zero unless the patient is immunocompromised ≥18 weeks of gestationIt is difficult to establish the timing of infection

Repeat IgG and IgM in 1 to 3weeks

Serum should be sent to reference laboratory for confirmatory testing

Follow up testing is indicated during gestation to detect seroconversion

≤ 18 weeks of gestation No further action indicated >18 weeks of gestationCompare to previous serological tests

Negative IgG and Positive IgM Does not have clinical relevance

Positive IgG and IgM Seroconverted and fetus is at risk Initiate treatment and consider PCR

Maternal Infection Status

❑ No maternal infection acquired during pregnancy and remains seronegative one month after birth or ❑ Maternal infection acquired prior to pregnancy

❑ Maternal infection acquired during pregnancy and ❑ Positive PCR of amniotic fluid

❑ Maternal infection acquired during the pregnancy and a negative amniotic fluid PCR or ❑ Amniocentesis was not done

No Infant Follow up

Confirmed diagnosis of Congenital Toxoplasmosis

❑ Testing for IgG, IgM, IgA at birth by Western blot or by conventional serologies at ≥ 10 days of life ❑ If diagnosis not made at initial testing, follow up testing with IgG, IgM, IgA at 1 month age and every 2 months thereafter is indicated

❑ Initiate Treatment and ❑ Order a serological test for IgG, IgM and IgA to further confirm the diagnosis and to rule out a false positive PCR test result

Presence of any one of the below criteria is diagnostic of congenital Toxoplasmosis: ❑ Presence of IgM and/or IgA ≥ 10 days of life and/or during the follow up test samples ❑ In new born presence of specific band or bands with higher intensity than maternal ones for IgG/IgM/IgA on Western blot ❑ Persistant increase in IgG titer without treatment ≤ 12months of age

❑ Diagnosis of Toxoplasma is excluded if: ❑ The absence of IgG titer without treatment is documented ≤ 12months of age

❑ Confirmed diagnosis of Congenital Toxoplasmosis ❑ Inititate Treatment

Diagnosis exlcuded

Approach to the patient with unknown Toxoplasma serology status

❑ Suspicion of acquired infection and/or ❑ Clinical signs at birth ❑ As antenatal screening is not performed during gestation, parallel testing of maternal serum with the newborn serum should be done

❑ Maternal serum is Toxoplasma seronegative at birth and confirmed to remain negative 1 month after birth or ❑ Confirmation of maternal infection acquired prior to gestation

❑ PCR of CSF, urine, whole blood depending on the clinical signs in the baby

❑ Testing for IgG, IgM, IgA by conventional serologies ≥10 days of life

No infant follow up

Positive

Negative

If diagnosis is not made on the initial testing

Presence of IgG plus IgM and/or IgA

❑ Confirmed Diagnosis ❑ Initiate Treatment

❑ Follow up testing with IgG, IgM, IgA at 1 month age and every 2 months thereafter is indicated

❑ Confirmed Diagnosis ❑ Initiate Treatment

Presence of any one of the below criteria is diagnostic of congenital Toxoplasmosis: ❑ Presence of IgM and/or IgA >10 days of life and/or during the follow up test samples ❑ Persistant increase in IgG titer without treatment ≤12months of age

❑ Diagnosis of Toxoplasma is excluded if: ❑ The absence of IgG titer without treatment is documented ≤ 12months of age

❑ Confirmed Diagnosis of Congenital Toxoplasmosis ❑ Initiate Treatment

Diagnosis Excluded

Treatment

Medical Therapy

The principle for medical therapy of Congenital Toxoplasmosis is based on the timing of diagnosis.

• Pregnant women diagnosed with primary Toxoplasma infection: Spiramycin should be initiated and identification of infection status in the fetus by amniocentesis and fetal blood sampling should be done. If fetal infection is ruled out, spiramycin should be continued throughout the pregnancy.
• In patients with established fetal infection: Pyrimethamine, sulfadiazine, and folinic acid should be given throughout the pregnancy and is shown to decrease infection of the placenta and the fetus in utero, the neurological sequalae and ocular symptoms.However, it does not reduce the rate of transmission and the regimen is contraindicated in the first trimester of pregnancy due to the teratogenic effect.
• In infants with established infection, low or high dose pyrimethamine with sulfadiazine throughout the first year of life, showed better outcomes compared to untreated infants.

Follow Up

• Infants with congenital Toxoplasmosis should be followed up regularly to examine for presence of motor abnormalities, cognitive outcomes, vision impairment, formation of new eye lesions, and hearing loss.

Surgical Therapy

There are no surgical management measures for the treatment of congenital Toxoplasmosis.

Prevention

Primary Prevention

Prevention is the best way to reduce the transmission of disease. The following are recommended by the CDC to reduce the risk of transmission of Toxoplasma from the environment.

• Avoid drinking untreated drinking water.
• Wear gloves when gardening and during any contact with soil or sand because it might be contaminated with cat feces that contain Toxoplasma.
• Wash hands with soap and warm water after gardening or contact with soil or sand.
• Teach children the importance of washing hands to prevent infection.
• Keep outdoor sandboxes covered.
• Feed cats only canned or dried commercial food or well-cooked table food, not raw or undercooked meats.
• Change the litter box daily if you own a cat. The Toxoplasma parasite does not become infectious until 1 to 5 days after it is shed in a cat's feces.
• If you are pregnant or immunocompromised: Avoid changing cat litter if possible. If no one else can perform the task, wear disposable gloves and wash your hands with soap and warm water afterwards.
• Keep cats indoors.
• Do not adopt or handle stray cats, especially kittens. Do not get a new cat while you are pregnant.

Reducing the risk of transmission from meat

To prevent risk of toxoplasmosis from food:

• Cook food to safe temperatures. A food thermometer should be used to measure the internal temperature of cooked meat. Do not sample meat until it is cooked.
• For Whole Cuts of Meat (excluding poultry): Cook to at least 145° F (63° C) as measured with a food thermometer placed in the thickest part of the meat, then allow the meat to rest* for three minutes before carving or consuming.
• For Ground Meat (excluding poultry): Cook to at least 160° F (71° C); ground meats do not require a rest time.
• For All Poultry (whole cuts and ground): Cook to at least 165° F (74° C), and for whole poultry allow the meat to rest for three minutes before carving or consuming.

Secondary Prevention

• Countries such as France and Austria recommend prenatal screening for Toxoplasma, by antibody measurement in the pregnant mother to establish the status of infection.
• Pregnant women with active infection are treated with spiramycin, it is shown to reduce the transplacental transmission by 60%.