Infections In Pregnancy /

Toxoplasmosis

01 In Brief

Toxoplasma gondii is a common parasitic infection that is asymptomatic in most healthy people. Mothers who are infected for the first time in pregnancy can transmit it to their unborn baby .The risk of transmission and severity of the infection in the fetus depends on when in pregnancy the infection occurs. The parasite only reproduces in domestic cats so preventive measures are important to minimise the likelihood of infection.

02 What Do I Need To Know?

• Toxoplasmosis is an infection caused by the parasite Toxoplasma gondii and it causes a mild flu like illness and in many cases is asymptomatic. However it can rarely cause serious abnormalities in a baby born to an infected mother in pregnancy.  It is one of the most common parasites in the world.

THE LIFE CYCLE OF THE PARASITE

• Toxoplasmosis is a single cell parasite that can infect most animals and birds. It is unique as it can only reproduce in the bowel of the domestic feline (cat). The cat becomes infected when it eats infected prey (e.g. birds or mice), contaminated raw meat especially lamb, pork or venison or infected soil. The parasite then multiples in the cats bowel and after 2-3 weeks the cats then begins to excrete eggs in its faeces. Within 24 hours the eggs develop into mature, highly infectious cells that can survive in soil for months. In the first 24 hours after they develop they are not infective.
•  If the eggs are ingested by another animal or human the cells enter the bowel, are absorbed and rapidly into the blood stream then multiply forming cysts which lodge mainly in the brain and muscles. If you are healthy your immune system ensures that the cysts remain inactive. They are only reactivated if your immune system is low e.g. HIV. 

CONGENITAL TOXOPLASMOSIS

• Congenital Toxoplasmosis is the disease that occurs when the parasite is transmitted from an infected mother to the fetus. The risk of transmission and severity varies depends on when in pregnancy the mother is infected;
  • If the mother acquires the infection 4-6 months before pregnancy she will develop immunity and transmission to the unborn fetus will not occur.
  • If the infection is acquired in the first trimester of pregnancy, transmission to the fetus rarely occurs. If it does occur there is a high chance of miscarriage. On the rare occasions that the fetus survives, infected infants develop major birth defects with abnormalities of the brain such as hydrocephalus, intracranial calcification, chorioretinitis, and signs of generalised infection with enlargement of the liver and spleen, jaundice and a low platelet count.
  • If the mother is infected in the third trimester then transmission is fairly common and is asymptomatic in around 85% of cases. The newborn may not show signs of infection but can still develop symptoms in their teens or later. Symptoms include hearing loss, intellectual disability and serious eye infections.

ROUTES OF TRANSMISSION

• You can only be infected with Toxoplasmosis from the faeces of an infected cat, sources include;
  • Infected cat faeces e.g. in the soil or cat's litter box or touching anything that has come in contact with the faeces. Hence gardening without gloves poses a risk as does cleaning litter boxes.
  • Ingesting contaminated food or water especially unpasteurised milk and meats such as lamb, venison or pork.
  • Contaminated food utensils or unwashed fruit or vegetables. 

• Tests for Toxoplasmosis immunity in pre-pregnancy or pregnancy are not usually done routinely. You may wish to discuss this with your doctor if you are high risk. It may show that you have already been infected in which case you cannot pass it onto your baby.

• During pregnancy your doctor may decide to test for Toxoplasmosis. Interpretation of the tests is complex. 
  •  A negative test may mean either that you haven't been infected or that you are in the early stages and antibodies are not yet developed.  A repeat test a few weeks later may be required to help clarify this.
  • A positive test may indicate past or a recent infection in pregnancy
  • Tests may be performed on the fetus, if there is a concern that the baby may have Congenital Toxoplasmosis. These include testing the fluid around the baby e.g. by amniocentesis or a detailed ultrasound looking for fetal abnormalities.

• Rarely treatment is offered in pregnancy, it is such a specialised area and  an infectious disease specialist is usually consulted.

PREVENTION

The best treatment is prevention :

If you own a cat

03 What Others Say

• Excellent in depth fact sheet from the Mayo Clinic

http://www.mayoclinic.com/health/toxoplasmosis/DS00510

• Well referenced fact sheet from the Organisation of Teratology Specialists, Illinois US

http://www.otispregnancy.org/files/toxoplasmosis.pdf

04 I Want To Know More

• Prevalence survey in Western Australia of over 10,000 pregnant women showing that 35% had been previously infected and were immune, and 11 had evidence of active infection but none of the newborns showed clinical signs of congenital Toxoplasmosis.

http://www.ncbi.nlm.nih.gov/pubmed/2046568

• Excellent review in the American Family Physician Journal

http://www.aafp.org/afp/2003/0515/p2131.html

05 Clinicians Tools and Resources

• Information regarding Toxoplasmosis ans treatment from the Illinois Teratogen Service

http://www.fetal-exposure.org/resources/index.php/2003/12/01/toxoplasmosis-update/

Last updated: 09/08/2011 by Dr Elizabeth Hallam*

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