Establishment and validation of a guinea pig model for human congenital toxoplasmosis

Background

Toxoplasma gondii is an obligate intracellular parasite with a worldwide distribution. Congenital infection in humans and animals may lead to severe symptoms in the offspring, especially in the brain. A suitable animal model for human congenital toxoplasmosis is currently lacking. The aim of this study is to establish and validate the guinea pig as a model for human congenital toxoplasmosis by investigating the impact of the T. gondii infection dose, the duration of infection and the gestational stage at infection on the seroconversion, survival rate of dams, fate of the offspring, T. gondii DNA loads in various offspring tissues and organs and the integrity of the offspring brain.

Methods

Pregnant guinea pigs were infected with three different doses (10, 100, 500 oocysts) of T. gondii strain ME49 at three different time points during gestation (15, 30, 48 days post-conception). Serum of dams was tested for the presence of T. gondii antibodies using immunoblotting. T. gondii DNA levels in the dam and offspring were determined by qPCR. Offspring brains were examined histologically.

Results

We found the survival rate of dams and fate of the offspring to be highly dependent on the T. gondii infection dose with an inoculation of 500 oocysts ending lethally for all respective offspring. Moreover, both parameters differ depending on the gestational stage at infection with infection in the first and third trimester of gestation resulting in a high offspring mortality rate. The duration of infection was found to substantially impact the seroconversion rate of dams with the probability of seroconversion exceeding 50% after day 20 post-infection. Furthermore, the infection duration of dams influenced the T. gondii DNA loads in the offspring and the integrity of offspring brain. Highest DNA levels were found in the offspring brain of dams infected for  ≥ 34 days.

Conclusion

This study contributes to establishing the guinea pig as a suitable model for human congenital toxoplasmosis and thus lays the foundation for using the guinea pig as a suitable animal model to study scientific questions of high topicality and clinical significance, which address the pathogenesis, diagnosis, therapy and prognosis of congenital toxoplasmosis.

Graphical abstract

Supplementary Information

The online version contains supplementary material available at 10.1186/s13071-021-04890-4.

Serological lessons from the bovine lungworm Dictyocaulus viviparus: Antibody titre development is independent of the infection dose and reinfection shortens seropositivity

Infections with the bovine lungworm Dictyocaulus viviparus, the causative agent of parasitic bronchitis, are accompanied by substantial economic losses due to impacts on production, clinical respiratory disease or even death of diseased cattle. To detect lungworm antibodies in cattle, an enzyme-linked immunosorbent assay (ELISA) based on recombinant major sperm protein (MSP) has been developed. However, it remained unknown whether the infection dose influences antibody levels, and how acquired immunity influences antibody level patterns during reinfections. The latter may lead to low within-herd seroprevalence and thus to negative MSP-ELISA results in examination of bulk tank milk (BTM). Thus, infection experiments with 12 different doses ranging from 10 to 3000 D. viviparus larvae were performed to assess whether the antibody response is dose-dependent. Second, the impact of reinfections on the antibody response was evaluated in infection experiments, and third, antibody patterns in dairy cows during naturally occurring reinfections were assessed in a longitudinal field study based on individual milk samples. Results of this study demonstrate that the rise in MSP antibodies during first infection is dose-independent at infection doses of 25 lungworm larvae and above. However, following reinfections the magnitude and duration of the MSP antibody response are reduced or lacking, depending on the interval to reinfection. The field study revealed short periods of seropositivity as a common pattern in dairy cows subjected to natural D. viviparus reinfections. Low within-herd seroprevalence in dairy herds can thus be a result of continuous reinfections. Low infection doses should not be a barrier to serodiagnosis of lungworm infection in first-time infected cattle.

The effect of host age and inoculation dose on infection dynamics of Angiostrongylus vasorum in red foxes (Vulpes vulpes)

BACKGROUND

Infections and clinical cases of Angiostrongylus vasorum in dogs are found increasingly across Europe, thus rendering knowledge on its infection biology more important. We used red foxes as a carnivore model to examine the effect of host age and infection dose on the establishment of adult A. vasorum in single experimental infections.

METHODS

Fourteen juvenile and fourteen adult red foxes, free of metastrongyloid infections, were given a low (50) or high (200) dose of third-stage larvae (L3) of A. vasorum. Two groups of three foxes of each age group served as uninfected controls. Larval excretion by Baermann and blood parameters were followed for ten weeks. Worm counts were performed at necropsy by sequential perfusion, dissection and Baermann method.

RESULTS

The establishment rate (i.e. recovery in percentage of inoculation dose) of A. vasorum primary infections in red foxes was associated with host age and inoculation dose. In the low dose juveniles, 61% (range 52-72%) of the infection dose was recovered as worms in the pulmonary arteries and heart at necropsy while only 35% (21-50%) were recovered in the high dose. Corresponding establishment rates for adults were 39% (18-98%) and 8% (1-21%). In juveniles, a higher dose resulted in significantly higher adult worm counts, higher larval excretion and more pronounced pathophysiological changes, particularly in coagulation parameters. Earlier onset of patency was also found in the juveniles. In contrast, the larval excretion in high dose adults was very low and two infected animals never reached patency. However, a few adults showed only limited resistance as judged by excretion of larvae. The increase to very high larval excretion levels (> 4,000 larvae per g of faeces) after several months in a single animal, indicated that any potential acquired immunity does not affect worm fecundity.

CONCLUSIONS

Resistance to a primary A. vasorum infection was generally higher in older animals, and this age resistance was reflected in lower worm counts and reduced excretion of larvae. The juvenile red foxes were fully susceptible, as reflected in high establishment rates. Although severe clinical disease was never observed in the foxes, A. vasorum infections in red foxes appear to be chronic and moreover, to resemble infections in dogs. The results underline the red fox as a suitable model as well as natural reservoir for the parasite.