Case-Control Study to Assess the Association between Epilepsy and Toxocara Infection/Exposure

The global prevalence of Toxocara canis among red foxes (Vulpes vulpes): A systematic review and meta-analysis

Red foxes play a crucial role in the life cycle and transmission of zoonotic pathogens, including Toxocara canis; however, comprehensive information on the prevalence of T. canis in red foxes (Vulpes vulpes) is lacking. In this meta-analysis we aimed to evaluate the global and regional prevalence of T. canis among red foxes. We searched PubMed, Scopus, and Google Scholar for studies reporting prevalence of T. canis in red foxes up to April 1, 2024. Using a random-effects model, we estimated pooled prevalences at global, regional, and national levels and assessed heterogeneity through subgroup and meta-regression analyses. The overall pooled global prevalence of T. canis infection in red foxes was 32.1% (95% CI, 28.5-35.6%), with the highest prevalence in Europe (34.6%, 30.9-38.3%) and the lowest in the Eastern Mediterranean (20.0%, 11.0-29.0%). In other regions, prevalences of Toxocara were as follows: Central Asia (33.1%, 26.8-39.4%), North America (23.6%, 10.6-36.6%), Western Pacific (21.3%, 5.2-37.4%), and Eastern Mediterranean & North Africa (20.0%, 11.0-29.0%). However, data from certain geographical regions are very limited (for example Greece, Austria, China and North Africa). Prevalence rates showed a decreasing trend over time. Subgroup analyses indicated higher prevalences in male red foxes (54.1%, 41.4-66.7%) compared to females (37.5%, 29.9-45.1%), and in juvenile red foxes (56.2%, 39.1-73.3%) compared to adults (33.4%, 23.2-43.6%). T. canis worm burdens were generally low, not exceeding an average of 4 worms per fox in most studies. Our findings reveal a substantial prevalence of T. canis infection in red fox populations worldwide (32.1%), highlighting their potentially significant role in perpetuating the transmission of infection to both companion animals and humans. Continued surveillance is essential to mitigate the risk of Toxocara transmission to companion animals and humans. However, a major remaining challenge is to assess the relative importance of the red fox as a contributor to environmental contamination with Toxocara ova. Further research is also needed to address study limitations and provide a complete global picture of T. canis epidemiology in red foxes and other wild animals, especially in underrepresented regions.

Association between Alzheimer's disease and Toxocara infection/exposure: a case-control study

BACKGROUND

Infections may contribute to Alzheimer's disease (AD) risk. Limited evidence suggests Toxocara spp. infection/exposure could influence AD development.

METHODS

We investigated Toxocara seropositivity and AD in Iranian adults using a matched case-control study. Our sample included 90 AD cases and 91 healthy older adults. Anti-Toxocara immunoglobulin G (IgG) antibodies were assessed via enzyme-linked immunosorbent assay. We computed the odds ratios (ORs) and 95% confidence intervals (CIs) through univariable and multivariable analyses, adjusting for potential confounders.

RESULTS

There were 33/90 (36.67% [95% CI 26.75 to 47.48]) anti-Toxocara IgG seropositive individuals identified among the AD cases and 21/91 (23.07% [95% CI 14.89 to 33.09]) among the healthy controls. In univariable analysis, a significant association was identified between anti-Toxocara IgG seropositivity and AD (OR 1.93 [95% CI 1.01 to 3.69], p<0.001). Moreover, the association remained significant (OR 2.18 [95% CI 1.05 to 4.49], p<0.001) in multivariable analysis after adjustment for covariates. There was no association between anti-Toxocara IgG seropositivity and the severity of AD (OR 0.75 [95% CI 0.21 to 2.61], p=0.47).

CONCLUSIONS

Our findings indicated that Toxocara exposure/infection could be a potential risk factor for development of AD. To better understand a real causality between Toxocara exposure/infection and AD and related dementias, follow-up designed and adequately powered studies are needed.

A new perspective on essential tremor: the potential etiologic role of Toxoplasma gondii and Toxocara spp

Our aim was to examine the relationship between Toxoplasma gondii (T. gondii) and Toxocara infection and patients with essential tremor (ET). This study comprised a total of 174 participants, consisting of 99 patients with ET and 75 healthy controls. The presence of anti-T. gondii IgG and anti-Toxocara IgG antibodies was investigated using ELISA. The relationship between the severity of the disease and the seropositivity of T. gondii and Toxocara were examined. The seropositivity rate for anti-T. gondii IgG antibodies among patients and control groups were 43.4% and 12%, respectively (odds ratio [OR]: 5.63; 95% CI: 2.53-12.56). The patient group exhibited a higher seroprevalence of anti-Toxocara IgG antibodies (32.3%) compared with the control group (13.3%; OR: 3.10; 95% CI: 1.41-6.83; p = 0.004). This study suggests that T. gondii and Toxocara infections can contribute to the pathogenic mechanisms underlying ET and could be risk factors for ET.

Understanding the research and practical needs required to control toxocariasis in Iran

Human toxocariasis (HT) is a widespread zoonotic infection globally, notably prevalent in tropical areas. Enhancing our understanding of toxocariasis can lead to increased attention towards the socioeconomic impact and control of this neglected zoonosis. We conducted a comprehensive review of all available articles and official documents on toxocariasis in Iran to identify research gaps and critical needs for its control. This review highlights that despite numerous studies exploring various aspects of toxocariasis in definitive and paratenic hosts, as well as humans and environmental contamination, significant data deficiencies and gaps persist across different regions in the country. These gaps involve investigating the worm burden and reinfection rates in definitive hosts, developing more sensitive methods to detect and differentiate of Toxocara species, and understanding the behavior of definitive host animals. Additionally, identifying potential paratenic hosts for HT and exploring the organ-specific affinity and survival duration of Toxocara larvae within these hosts are essential areas for exploration. It's also imperative to comprehend the sylvatic and domestic cycles of the parasite in paratenic hosts. Furthermore, assessing egg density in the environment, exploring potential new sources such as water, and identifying regions with optimal climatic conditions for the survival and development of Toxocara eggs are crucial for the formulation of effective prevention and control strategies. Identifying at-risk groups, developing early diagnosis techniques, employing imaging methods, and identifying long-term complications in humans are also crucial. Community health organizations should prioritize health education for the public and professionals. Furthermore, accurately estimating definitive host populations, monitoring and preventing their movements in public places, implementing regular deworming practices for pets and stray hosts, and recognizing the infection's significance as a health priority are critical. This comprehensive understanding advocates for a holistic "one health" approach to control of HT.

Migratory pattern of zoonotic Toxocara cati and T. canis in experimentally infected pigs

BACKGROUND

Over a billion people are infected with Toxocara canis or T. cati, the roundworms of dogs and cats. Historically, T. canis has been considered the main species responsible for human toxocarosis, but as serodiagnosis cannot discriminate between the two species, this remains unresolved. We used pigs as a relevant large animal model for human infection to assess the migratory pattern of T. cati and T. canis.

METHODS

Pigs were inoculated with T. cati or T. canis eggs or PBS (negative controls) and necropsied 14 or 31 days later. Different organs and tissues were examined for parasites and pathological changes.

RESULTS

Overall, the two parasite species had a similar migration pattern reaching multiple organs and tissues, including the mesenteric lymph nodes, liver, lungs, and diaphragm. We recovered larvae of both species in the brain, suggesting that T. cati also can cause neurological toxocarosis in humans. Both species induced systemic eosinophilia and histopathological changes in the lungs, livers, and mesenteric lymph nodes.

CONCLUSION

This study emphasises the importance of T. cati as a zoonotic agent and the need to develop diagnostic methods that can differentiate between sources of infection in humans.

Toxocarosis in humans: how much of a problem is it in the UK?

Toxocara canis (from dogs) is recognised as a potential cause of human toxocarosis, but Toxocara cati (from cats) and other species (eg, Toxascaris leonina found in foxes) are also possible causes. Most colonisation with Toxocara species does not lead to symptomatic infection in well-cared for adult animals; young and debilitated animals are at greater risk. Humans can acquire infection from infected animals, for example, via soil contaminated with faeces; however, most human infections are asymptomatic, with symptomatic infection being very rare in the UK. The risk of human infection is reduced by measures such as hand washing and responsible disposal of dog faeces. Some organisations recommend regular prophylactic treatment of pet dogs and cats. However, there are concerns that some parasiticides are contaminating the environment. As an example of a One-Health problem there is a potential conflict between the needs of animal health, human health and the health of the wider ecosystem. Also, considering that only about 5% of non-juvenile household dogs shed Toxocara eggs at a given time, it has been questioned whether it is worthwhile to invest in frequent blind treatments. British veterinary organisations have suggested less frequent treatment may be more appropriate and should be based on individual risk assessment and faecal examinations for worms rather than blanket regular prophylactic treatment, which could reduce the impact of parasiticides on the environment without greatly increasing the risks to animal or human health.

The role of helminths in the development of non-communicable diseases

Non-communicable diseases (NCDs) like cardiovascular disease, chronic respiratory diseases, cancers, diabetes, and neuropsychiatric diseases cause significant global morbidity and mortality which disproportionately affect those living in low resource regions including low- and middle-income countries (LMICs). In order to reduce NCD morbidity and mortality in LMIC it is imperative to understand risk factors associated with the development of NCDs. Certain infections are known risk factors for many NCDs. Several parasitic helminth infections, which occur most commonly in LMICs, have been identified as potential drivers of NCDs in parasite-endemic regions. Though understudied, the impact of helminth infections on the development of NCDs is likely related to helminth-specific factors, including species, developmental stage and disease burden. Mechanical and chemical damage induced by the helminth in combination with pathologic host immune responses contribute to the long-term inflammation that increases risk for NCD development. Robust studies from animal models and human clinical trials are needed to understand the immunologic mechanisms of helminth-induced NCDs. Understanding the complex connection between helminths and NCDs will aid in targeted public health programs to reduce helminth-induced NCDs and reduce the high rates of morbidity that affects millions of people living in parasite-endemic, LMICs globally.