Maintaining Reduced Exposure To Toxoplasma gondii, By Brad DeWolf from Southwest Ontario Veterinary Services

Toxoplasma gondii (T. gondii) is a zoonotic and protozoan parasite that infects more than one-third of the global human population. Warm-blooded animals can act as hosts but only members of the cat family, such as domestic cats, act as the definitive hosts and have the potential to shed oocysts (infective eggs) into the environment. Human infection occurs through the ingestion of sporulated eggs from the environment (eg kitty litter) or from tissue cysts in undercooked or raw meat from livestock. Occasionally infection can come from ingestion of water or food that contains sporulated oocysts. People with a competent immune system may have mild flu-like symptoms or no symptoms at all.  The consequences of T. gondii infection may be more severe in pregnant women and immunocompromised individuals.  Transplacental transmission of T. gondii may result in spontaneous abortion, premature birth, stillbirth, or neurological or ocular damage to the foetus. Eye lesions from congenital infection are often not identified at birth but occur in 20 to 80% of congenitally infected persons by adulthood . These public health researchers from the Netherlands wanted to revisit the prevalence and risk factors for T gondii infection in the Netherlands. A cross-sectional study conducted in samples collected 2016/2017 was designed similarly to the previous two studies (1995/1996 and 2006/2007) and included a questionnaire and serum sampling among Dutch residents.

The researchers found the following:

  • The decline in T. gondii seroprevalence that had occurred between the 1995/1996 and 2006/2007 surveys (from 40.5% to 26.0%) did not continue into 2016/2017 (29.9%).
  • Seroprevalence increased with age and varied among the various regions of the country.
  • Higher T. gondii seropositivity was associated with increasing age, lower educational level, not living in the Southeast, and eating raw or semi-cooked pork.
  • The incidence of congenital toxoplasmosis was estimated at 1.3 infected /1000 (95% CI 0.9-1.8) live-born children in 2017.

Take Home Messages:

  • While public health efforts aimed at reducing exposure to T. gondii in the Netherlands were quite successful between the 1995/1996 survey and the 2006/2007 survey the exposure rate has not declined and has in fact risen somewhat.
  • Increased public health awareness in the general population is needed to ensure that this infection and its’ related human health costs continues to decline.
  • Pork producers can play a part in the process of reducing T gondii exposure in pork consumers by reducing exposure of their pigs to the infective oocysts that can be shed by cats. These procedures are part of the Canadian Pork Excellence program.

Submitted by Dr. Brad DeWolf

Reference: Oda E van den Berg , Kamelia R Stanoeva , Rens Zonneveld , Denise Hoek-van Deursen  Fiona R van der Klis  Jan van de Kassteele , Eelco Franz , Marieke Opsteegh , Ingrid H M Friesema , Laetitia M Kortbeek  Seroprevalence of Toxoplasma gondii and associated risk factors for infection in the Netherlands: third cross-sectional national study  Epidemiol Infect . 2023 Jul 28;151:e136. doi: 10.1017/S095026882300122X.