Page 30 - Eclipse - RVC Alumni Magazine - Autumn 2020

OTHER RESEARCH NEWS
Improving interventions against toxoplasmosis
Approximately one in three people worldwide have been exposed to the apicomplexan protozoan parasite Toxoplasma gondii, which causes acute and latent infections in all endotherms.
Hosts are infected via the consumption
of raw/undercooked meat harbouring infectious bradyzoites, or via the ingestion of sexual-stage oocysts, containing infectious sporozoites, which are shed in cat faeces and contaminate crops and water sources. Infection during pregnancy via either of these routes can result in vertical transmission to the foetus.
Infections are thought to be most severe in immunocompromised individuals, including HIV/AIDS and organ transplant patients. However, outbreaks of toxoplasmosis in immunocompetent adults have also been known to cause
a range of symptoms, and increasing evidence suggests a role of latent infection in the aetiology of severe behavioural and neuropsychiatric disorders, including schizophrenia.
The predominance of the two major horizontal routes of infection (bradyzoite vs. oocyst) varies globally according to climate, culinary and hygiene factors.
protein (TgERP). Anti-TgERP antibodies were thought to persist for less than a year in human sera, restricting TgERP serology’s use to detecting recently acquired oocyst infections. However, recent serosurvey data from a highly endemic region of Brazil questioned this notion. In light of this data, we aimed to provide the first quantitative estimate of anti-TgERP antibody duration, in order to understand the utility and limits of this serological marker for informing context- specific toxoplasmosis interventions.
To this end, we developed a mathematical model that tracked the serostatus (seronegative or seropositive) of a human population from birth to older age. The model considered anti-TgERP antibodies (of unknown longevity) and antibodies that are raised against the motile tachyzoite stage in each infected individual (thought to have lifelong duration). The model accounted for imperfect diagnostic sensitivity and specificity, and different profiles of the rate of infection over age.
By fitting our model, using a robust statistical method, to population data on the presence of these two antibodies over a range of ages, we were able to estimate the duration of anti-TgERP antibodies. Contrary to previous expectations, we found that TgERP antibodies persist for many years in human sera, with estimates ranging from 8.3 to 41.1 years depending on the assumed diagnostic sensitivity and specificity.
Pending confirmation in other settings
with differing disease endemicities, our findings suggest that TgERP serology could be a valuable tool for epidemiological surveys in T. gondii-endemic settings
and for providing a stronger evidence- based approach to the implementation of toxoplasmosis interventions.
The full research article, which has been published in Clinical Infectious Diseases, can be found here: rvc.uk.com/toxoplasmosis
Among humans, approximately 190,000 cases of congenital toxoplasmosis occur annually and, among livestock,
T. gondii causes 23% of ovine abortions in Europe and the USA. Complications resulting from congenital infection include abortion and stillbirth, chorioretinitis, hydrocephalus and intracranial calcifications.
30
BioRender and Greg Milne
Distinguishing between these two routes is important for informing context-specific control initiatives and potentially even for differential clinical prognosis of patients.
Recent oocyst infections can be identified by the presence of host IgG antibodies raised against the sporozoite- specific T. gondii embryogenesis-related