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Toxoplasmosis

Toxoplasmosis is an important infectious disease of sheep and humans that may result in abortion, stillbirth or foetuses born with congenital infection.

The disease is caused by Toxoplasma gondii, one of the most successful parasites worldwide, as it can infect all warm blooded animals. It is very small, consisting only of a single cell and is transmitted through ingestion of oocysts shed by infected cats or by the consumption of undercooked infected meat with cysts containing bradyzoites. Contamination of the environment (farmland, gardens, rivers and coastal waters) by Toxoplasma oocysts is widespread and the parasite can survive for more than 18 months in cool and moist conditions. 

Toxoplasma gondii is one of the most important causes of abortion in sheep and goats worldwide and in the UK it is the second most frequently diagnosed cause of ovine abortion.  Moredun was involved in conducting the efficacy testing of the only commercially available vaccine worldwide to protect against ovine toxoplasmosis, using a live attenuated “incomplete” strain of T. gondii

Disease in humans, due to T. gondii infection, is usually attributed to infections of the foetus if the mother is infected with the parasite for the first time during pregnancy. Immunosuppressed individuals can also suffer serious disease as a result of Toxoplasma infection where problems can arise from a recrudescence of a previous latent infection.  

Key Points

  • Toxoplasma gondii is the most successful parasite worldwide, capable of infecting all warm blooded animals, including humans.
  • Toxoplasma oocysts have a tough outer shell and can survive in the environment in moist temperate conditions for 2-4 years.
  • Sheep may become infected by ingesting infective oocysts on pasture or in contaminated feed and water.
  • If the parasite infection occurs for the first time during pregnancy, Toxoplasma can cause disease in the placenta and the developing foetus.
  • Infection early in pregnancy may result in abortion, whereas infection later in pregnancy may cause still birth, a mummified foetus or the birth of a live infected and weak lamb.
  • Research at Moredun has shown that as few as 20 sporulated oocysts may cause Toxoplasma abortion in a susceptible ewe.
  • Following infection, sheep develop immunity against the parasite which will protect them against disease in a subsequent pregnancy.
  • There is an effective vaccine to prevent congenital toxoplasmosis in sheep.
  • Cats and members of the cat family are the definitive hosts of the parasite. Cats become infected for the first time usually when they start hunting and eat infected wild rodents and birds and at this time can shed millions of tough shelled oocysts (parasite eggs) into the environment. As young cats are the main shedders of the parasite, it is good practice to have resident, neutered and healthy farm cats.
  • Toxoplasma may also be transmitted to humans from the ingestion of oocysts or from eating undercooked meat containing parasite tissue cysts.  Pregnant women and immuno-compromised individuals are major risk groups and should also avoid contact with ewes at lambing time.

Research at Moredun

Current interests and future aims:

  • Prevalence of Toxoplasma infection in food animals.
  • Prevalence of Toxoplasma in food products.
  • Risks to humans from consumption of contaminated food products.
  • Environmental contamination of Toxoplasma oocysts and parasite survival.
  • Risk of Toxoplasma infection to sea mammals around the UK coastline arising from high levels of environmental contamination.
  • Identification of Toxoplasma genotypes found in UK livestock and wildlife.
  • Establish transmission routes of Toxoplasma through different hosts.
  • Vaccination of food animals to minimise risk of infection to people from infected meat.
  • Detection and quantification of Toxoplasma oocysts in drinking and recreational water.
  • Virulence associated with specific genotypes.
  • Development of a combined Toxoplasma and Chlamydia vaccine to protect against ovine abortion.

 

 

 

Research Funding

Scottish Government

Moredun is conducting research on Toxoplasma gondii within the Scottish Government Strategic Research Programme (2016-2021) looking at developing new diagnostics and determining the prevalence and risk of T.gondii in food animals. 

 

Aquavalens: Protecting the health of Europeans by improving methods for the detection of pathogens in drinking water and water used in food preparation. (European Union)

This is a large EU project, coordinated by the University of East Anglia involving over 40 academic and industrial partners from 13 European countries.  AQUAVALENS is centred on the concept of developing suitable platforms that harness the advances in new molecular techniques to permit the routine detection of waterborne pathogens and improve the provision of hygienically safe water for drinking and food production that is appropriate for large and small systems throughout Europe. Whilst in recent years there has been considerable developments, especially in molecular technology, very few systems are available that meet the needs of water providers. Consequently rather than developing new technologies, the key focus of Aquavalens is to adopt and, where appropriate, adapt existing technologies to develop these detection systems. Moredun’s role in the project is to develop methods to detect Toxoplasma gondii in water supplies.

 

Relationship between seroprevalence in the main livestock species and presence of Toxoplasma gondii in meat (European Food Safety Authority)

This large scale Euroepean project involved 12 participant organisations from 7 European countries and was coordinated by the National Institute for Public Health and the Environment (RIVM) in The Netherlands.  The overall aim of this project is to gain information and knowledge on the presence and infectivity of T. gondii cysts in meat and other edible tissues in main meat‐producing animals and its relationship with T. gondii seroprevalence in animals. Moredun’s role in this project was to look at T. gondii infection in cattle.

Final reports

Relationship between seroprevalence in the main livestock species and presence of Toxoplasma gondii in meat (GP/EFSA/BIOHAZ/2013/01) An extensive literature review. Final report
 
Experimental studies on Toxoplasma gondii in the main livestock species (GP/EFSA/BIOHAZ/2013/01) Final report
 
 

Toxoplasma gondii in the Caribbean

Moredun has a collaboration with Ross University School of Veterinary Medicine in St Kitts to look at the prevalence, genotype and virulence of Toxoplasma gondii in livestock food animals and wildlife on St Kitts and some of the other islands in the Caribbean.

 

Verifying the effectiveness of the water treatment process at removing Toxoplasma gondii oocysts

This project, funded by Scottish Government, is working towards the development of a robust method for extracting T. gondii oocysts from water using samples from Scottish catchments, where T. gondii DNA was previously detected.  These samples will be examined for the presence or absence of T. gondii oocysts and any oocysts identified from these sources will be tested for their viability.

Farming and Veterinary Outreach

For further information about toxoplasmosis please see Moredun Newssheet 6.8 - Control of Chlamydial (Enzootic) and Toxoplasma Abortion in Sheep:

Our scientists regularly give talks and Moredun events and roadshows.  Please see our events page for any forthcoming activities in this area or if you would like to arrange a speaker for an event please contact The Moredun Communications Team.

Public Outreach

The Beasts within Us is an interactive exhibition on Toxoplasma aimed at school children.  This exhibition has been showcased at events such as the Edinburgh International Science Festival.  For more information about Beasts within Us please visit our Inspiring Education page. (add link)