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Vaccination challenges and strategies against long-lived Toxoplasma gondii

Loh FK, Nathan S, Chow SC, Fang CM

Vaccine, 2019 07 09;37(30):3989-4000.
PMID: 31186188 DOI: 10.1016/j.vaccine.2019.05.083

Since the discovery of Toxoplasma gondii in 1908, it is estimated that one-third of the global population has been exposed to this ubiquitous intracellular protozoan. The complex life cycle of T. gondii has enabled itself to overcome stress and transmit easily within a broad host range thus achieving a high seroprevalence worldwide. To date, toxoplasmosis remains one of the most prevalent HIV-associated opportunistic central nervous system infections. This review presents a comprehensive overview of different vaccination approaches ranging from traditional inactivated whole-T. gondii vaccines to the popular DNA vaccines. Extensive discussions are made to highlight the challenges in constructing these vaccines, selecting adjuvants as well as delivery methods, immunisation approaches and developing study models. Herein we also deliberate over the latest and promising enhancement strategies that can address the limitations in developing an effective T. gondii prophylactic vaccine.

Matched MeSH terms: Toxoplasmosis/prevention & control
Fulltext Toxoplasmosis in HIV/AIDS: a living legacy

Nissapatorn V

Southeast Asian J Trop Med Public Health, 2009 Nov;40(6):1158-78.
PMID: 20578449

Toxoplasmosis has historically been considered one of the most important opportunistic infections detected in HIV/AIDS patients. The prevalence rates of latent Toxoplasma infections in HIV-infected patients has been found to vary greatly from 3% to 97%. Prevalence has been found to be related to ethnicity, certain risk factors, and reactivation of toxoplasmosis. Prior to antiretroviral therapy, toxoplasmic encephalitis (TE) was the most common focal cerebral lesion detected in AIDS patients with Toxoplasma infection, occurring in approximately half of Toxoplasma-seropositive patients. Other forms of dissemination have also been reported in AIDS patients in sites such as the eyes, lungs, heart and spinal cord. Anti-Toxoplasma therapy and chemoprophylaxis have shown effectiveness in reducing the incidence of TE, while noncompliance has been identified as a cause of relapse in these settings. Toxoplasmosis is one of the most common neuropathological complications found at autopsy. Rapid progress in the development of highly active antiretroviral therapy (HAART) has changed the observed patterns with TE, for which there has been a marked decrease in overall incidence. Subsequently, TE has been found to be significantly associated with the so-called "neurological immune restoration inflammatory syndrome" (NIRIS). Toxoplasma screening programs are recommended for all newly diagnosed HIV-positive patients. Chemoprophylaxis should be considered in HIV-infected patients who have a CD4 < 200 cells/mm3, particularly in settings where resources are limited and there is not access to HAART. TE remains a cause of morbidity and mortality among AIDS patients.

Matched MeSH terms: Toxoplasmosis/prevention & control
Fulltext Protective immune response in BALB/c mice induced by DNA vaccine of the ROP8 gene of Toxoplasma gondii

Parthasarathy S, Fong MY, Ramaswamy K, Lau YL

Am J Trop Med Hyg, 2013 May;88(5):883-7.
PMID: 23509124 DOI: 10.4269/ajtmh.12-0727

Toxoplasmosis in humans and other animals is caused by the protozoan parasite Toxoplasma gondii. During the process of host cell invasion and parasitophorous vacuole formation by the tachyzoites, the parasite secretes Rhoptry protein 8 (ROP8), an apical secretory organelle. Thus, ROP8 is an important protein for the pathogenesis of T. gondii. The ROP8 DNA was constructed into a pVAX-1 vaccine vector and used for immunizing BALB/c mice. Immunized mice developed immune response characterized by significant antibody responses, antigen-specific proliferation of spleen cells, and production of high levels of IFN-γ (816 ± 26.3 pg/mL). Challenge experiments showed significant levels of increase in the survival period (29 days compared with 9 days in control) in ROP8 DNA vaccinated mice after a lethal challenge with T. gondii. Results presented in this study suggest that ROP8 DNA is a promising and potential vaccine candidate against toxoplasmosis.

Matched MeSH terms: Toxoplasmosis/prevention & control
Toxoplasmosis: prevalence and risk factors

Nissapatorn V, Noor Azmi MA, Cho SM, Fong MY, Init I, Rohela M, et al.

J Obstet Gynaecol, 2003 Nov;23(6):618-24.
PMID: 14617462

A total of 200 pregnant women were recruited in this cross-sectional study. The overall seroprevalence of toxoplasmosis in pregnant women was found to be 49%, in which 39%, 4% and 6% for anti-Toxoplasma IgG, IgM and both anti-Toxoplasma IgG and IgM antibodies, respectively. We found the differences in Toxoplasma seroprevalence rates among the races were significant: the highest rate was in the Malays (55.7%), followed by the Indian (55.3%) and the Chinese (19.4%) (P<0.05) populations. An increase in Toxoplasma seroprevalence with increasing parity was detected (P<0.05). Women with no children had a prevalence of 39.7%, while women with one or more than two children had a prevalence of 44.2% and 62.9%, respectively. In this study, there was no significant association between Toxoplasma seroprevalence and various possible risk factors in pregnant women (P>0.05). When multivariate analysis was performed, no significant association between Toxoplasma seroprevalence and history of contact with cats, consumption of undercooked meat and blood transfusion was found (P>0.05). We did not find any newly diagnosed cases of acute acquired toxoplasmosis in pregnancy during the study period.

Matched MeSH terms: Toxoplasmosis/prevention & control
Fulltext A community-based survey of Toxoplasma gondii infection among pregnant women in rural areas of Taiz governorate, Yemen: the risk of waterborne transmission

Mahdy MA, Alareqi LM, Abdul-Ghani R, Al-Eryani SM, Al-Mikhlafy AA, Al-Mekhlafi AM, et al.

Infect Dis Poverty, 2017 Feb 13;6(1):26.
PMID: 28190399 DOI: 10.1186/s40249-017-0243-0

BACKGROUND: Toxoplasma gondii is a zoonotic coccidian parasite causing morbidity and mortality. In Yemen, T. gondii infection has been reported among pregnant women seeking healthcare in the main cities. However, no data are available on the prevalence of T. gondii infection and its associated risk factors among pregnant women in the rural communities of the country. Thus, the present study aimed to determine the seroprevalence of T. gondii and identify its risk factors among pregnant women in the rural communities of Taiz governorate, Yemen.
METHODS: A total of 359 pregnant women living in the rural communities of Taiz governorate were enrolled in this study by house-to-house visits. Data were collected using a pre-designed questionnaire, and blood samples were collected and tested for the detection of anti- T. gondii IgM and IgG antibodies by enzyme-linked immunosorbent assay.
RESULTS: The prevalence of T. gondii infection among pregnant women in this study was 46.2% (166/359). Bivariate analysis identified the age of ≥ 30 years (odds ratio [OR] = 1.7; 95% confidence interval [CI] = 1.09-2.65, P = 0.019) and unimproved water sources (OR = 2.2; 95% CI = 1.10-4.55, P = 0.023) as factors associated with T. gondii infection among pregnant women. The multivariable analysis, however, identified unimproved water sources as an independent risk factor (adjusted OR = 2.4; 95% CI = 1.16-5.0, P = 0.018) associated with T. gondii infection among pregnant women.
CONCLUSIONS: Pregnant women in the rural communities of Taiz, Yemen are at high risk of contracting T. gondii infection. Unimproved water sources (wells, water streams and water tanks) are significantly associated with T. gondii infection and should be considered in prevention and control strategies, especially among pregnant women.

Matched MeSH terms: Toxoplasmosis/prevention & control