Incidence of patent Toxocara canis infection in bitches during the oestrous cycle

Sources of environmental contamination with Toxocara spp.: An omnipresent parasite

Embryonated Toxocara eggs in the environment are considered to be the most important source of human toxocariasis. These eggs, however, are also a source of infection for the definitive and paratenic hosts. Most available literature focuses on Toxocara canis in dogs, or other canids. There are, however, other Toxocara species with their accompanying definitive hosts. Results from studies that modelled patent infections in dogs, cats and foxes show that although dogs are a very important source for environmental contamination with Toxocara eggs, other sources cannot be ignored. For a good understanding of the relative contributions of different definitive hosts to environmental contamination with Toxocara eggs, computational models should be built and fed with data from different fields of expertise as is discussed in this paper.

Progesterone in vitro increases growth, motility and progesterone receptor expression in third stage larvae of Toxocara canis

The in vitro effect of progesterone in T. canis larvae on their enlargement and motility were evaluated, together to the possible presence of progesterone receptors (PRs). T. canis larvae were cultured in RPMI-1640 with different concentrations of progesterone (0, 20, 40, 80, 400 and 800 ng/mL). Enlargement and increases in motility were dependent on the concentration only from 0 to 80 ng/mL (p < 0.05). The mean percentage of PR + cells in newly obtained larvae as measured by flow cytometry was 8.16 ± 0.4. The number of PR + cells increased depending on concentration from 0 to 80 ng/mL (p < 0.001). Cells obtained from larvae stimulated at any of the studied hormone concentrations showed greater mean fluorescence intensity when compared to non-stimulated cells. Additionally, the expression and location of PR + cells were determined in the larvae. The sequence of an amplicon (420-bp) obtained by PCR from T. canis larvae showed 100% homology with a gene fragment that codes for the PR of the dog. PR + cells were immunolocated using confocal microscopy in the intestinal region of the larvae that had been recently obtained. The results of this study show that T. canis larvae can recognize and respond to the presence of progesterone through a molecule possibly able to bind it. Since we previously observed a similar response to prolactin, we suggest that both hormones could participate sequentially in the reactivation of T. canis larvae in pregnant bitches.

Prolactin as immune cell regulator in Toxocara canis somatic larvae chronic infection

Toxocariasis is a zoonotic disease produced by ingestion of larval Toxocara spp. eggs. Prolactin (PRL) has been considered to have an important role in Toxocara canis infection. Recent evidence has found that PRL directly can increase parasite growth and differentiation of T. canis The present study, evaluated the effect of high PRL levels on the immune system's response and parasites clearance in chronic infection. Our results showed that hyperprolactinemia did not affect the number of larvae recovered from several tissues in rats. Parasite-specific antibody production, showed no difference between the groups. Lung tissue presented eosinophilic granulomas typical of a chronic infection in all the experimental groups. Flow cytometry analysis was made in order to determine changes in the percentage of innate and adaptive immune cell subpopulations in the spleen, peripheric (PLN) and mesenteric (MLN) lymphatic nodes. The results showed a differential effect of PRL and infection on different immune compartments in the percent of total T cells, T helper cells, T cytotoxic cells, B cells, NK cells, and Tγδ cells. To our knowledge, for the first time it is demonstrated that PRL can have an immunomodulatory role during T. canis chronic infection in the murine host.

Endocrine immune interactions during chronic Toxocariasis caused by Toxocara canis in a murine model: New insights into the pathophysiology of an old infection

Toxocara canis is the helminth causing Toxocariasis, a parasitic disease with medical and veterinary implications. Their final host are members of the family Canidae and as paratenic hosts, most of the mammals are sensitive (man, rat, mouse, among others). It has been reported that a pituitary hormone, prolactin, it is responsible for reactivation and migration of larvae to the uterus and mammary gland during the last third of gestation in bitches. In addition, this hormone has been shown to play an important role in the regulation of the immune response. Thus, the aim of this study, was to evaluate the effect of hypophysectomy in the rat model of Toxocariasis, on the immune response against this parasite during a chronic infection, for which parasite loads were analyzed in different organs (lung and brain). Furthermore, serum specific antibody titers, and percentages of different cells of the immune system were also determined. The results showed a decrease in the number of larvae recovered from lung and brain in the hypophysectomized animals. In this same group of animals, there was no production of specific antibodies against the parasite. As for the percentages of the cells of the immune system, there are differences in some subpopulations due to surgery and others due to infection. Our results demonstrated that the lack of pituitary hormones alters parasite loads and the immune response to the helminth parasite Toxocara canis.

Recurrent patent infections with Toxocara canis in household dogs older than six months: a prospective study

BACKGROUND

To reduce environmental contamination with Toxocara canis eggs, the current general advice is to deworm all dogs older than six months on average four times a year. However, only a small proportion of non-juvenile household dogs actually shed T. canis eggs, and some dogs shed eggs more frequently than others. The identification of these frequent shedders and the associated risk factors is an important cornerstone for constructing evidence-based deworming regimens. The purpose of this study is to identify risk factors associated with recurrence of periods of shedding Toxocara eggs in a cohort of household dogs older than six months.

METHODS

We performed a prospective study (July 2011 to October 2014) on shedding Toxocara eggs in a cohort of 938 household dogs older than six months from all over the Netherlands. The median follow-up time was 14 months. Monthly, owners sent faecal samples of their dogs for Toxocara testing and completed a questionnaire. Dogs were dewormed only after diagnosis of a patent infection (PI). Survival analysis was used to assess factors influencing the time to first diagnosed PIs (FPI) and the time to recurrent PIs (RPI).

RESULTS

The overall prevalence of PIs was 4.5 %, resulting in an estimated average incidence of 0.54 PIs/dog/year. No PI was diagnosed in 67.9 % of the dogs, 17.5 % of the dogs went through only one PI and 14.6 % had > 1 PI. Prevalence of PIs always peaked during wintertime. Increased hazards for first diagnosed PIs were associated with coprophagy, geophagy, walking off-leash for ≥ 80 % of walking time, reported worms in the faeces, feeding a commercial diet and suffering from urologic or respiratory conditions. Median time to reinfection was nine months. Factors associated with increased hazards for recurrent PIs were taking corticosteroids, changing dog's main purpose, and proxies for veterinary care-seeking behaviours.

CONCLUSIONS

We concluded that targeted anthelmintic treatments in household dogs may be feasible as PIs tend to (re)occur in specific periods and in groups of dogs at high risk. Moreover, recurrent PIs appear to be influenced more by factors related to impaired immunity than environmental exposure to Toxocara eggs.

The in vitro effect of prolactin on the growth, motility and expression of prolactin receptors in larvae of Toxocara canis

The in vitro effect of prolactin (PRL) on the growth and motility of Toxocara canis larvae was assessed. Additionally, the expression and location of prolactin receptors (PRL-Rs) were determined in the larvae. Larvae of T. canis were incubated with different concentrations of PRL for different periods of time. The stimulated larvae accelerated their enlargement and increased their motility. The mean percentage of PRL-R+ cells in non-stimulated larvae, measured by flow cytometry was 7.3±0.3%. Compared with non-stimulated larvae, the mean fluorescence intensity (p<0.05) increased in larvae incubated with 40ng/mL of PRL for 10 days. A 465-bp length fragment was amplified from larvae gDNA by PCR. The sequence of this fragment showed 99% similarity with the gene fragment that codes for the PRL-R of the domestic dog. A high concentration of PRL-Rs was immune-located in the posterior region of the larval intestine; therefore, the intestinal cells in this region were most likely the targets for this hormone. Based on these results, PRL-Rs were identified in T. canis larvae, and the in vitro stimulation with PRL increased the number of these receptors, accelerated the growth and modified the activity of larvae. All of the above suggest that T. canis larvae are evolutionarily adapted to recognize the PRL of their definitive host and furthermore might explain the reactivation of tissue-arrested larvae during the gestation of bitches, which does not occur in gestating females of other species.

Larval development of Toxocara canis in dogs

The parasitic roundworm Toxocara canis is present in dog populations all over the world. Due to its zoonotic potential, this roundworm is of special interest not only for veterinarians, but also for medical practitioners. In the present review, current knowledge of infection routes and the subsequent development of larvae within the canine host is summarised. Furthermore, information about the clinical, pathological, enzymatic, haematological and histopathological changes was collected, giving a broad overview of current knowledge of the infection. Although the data collected over the years give an idea of what happens during the larval development of T. canis, many questions remain open. Nevertheless, it is important that we continue our efforts to further understand the biology of this versatile and compelling parasite and try to improve and optimise strategies to prevent the infection in dogs and thereby to protect humans from this infection.

Ovariectomy during the luteal phase influences secretion of prolactin, growth hormone, and insulin-like growth factor-I in the bitch

A decline in circulating progesterone concentration plays an important role in the ethiopathogenesis of pseudopregnancy in the bitch. Because growth hormone (GH) and prolactin (PRL) are essential for normal mammogenesis and the secretion of these hormones is influenced by changes in the circulating progesterone concentration, the purpose of this study was to investigate the effects of mid-luteal phase ovariectomy on the 6-h pulsatile plasma profiles of GH and PRL and the basal plasma concentrations of GH, PRL, and insulin-like growth factor-I (IGF-I) in six beagle bitches. Ovariectomy was followed by only mild or covert signs of pseudopregnancy. The sharp decrease of the plasma progesterone concentration was accompanied by decreased basal plasma concentrations of GH and IGF-I and a rise in basal plasma PRL concentration. GH and PRL were secreted in a pulsatile fashion both prior to and after ovariectomy. The mean basal plasma GH concentration was significantly higher before ovariectomy than on days 1 and 7 after ovariectomy. The mean area under the curve above the zero level (AUC(0)) for GH was significantly higher before than at 7 days after ovariectomy. The mean area under the curve above basal level (AUC(b)) and the frequency of GH pulses at 7 days after ovariectomy were significantly higher than before and 1 day after ovariectomy. Both the mean basal plasma PRL concentration and the mean AUC(0) for PRL increased after ovariectomy. In conclusion, ovariectomy of bitches in the mid-luteal phase stops progesterone-induced GH release from the mammary gland, as evidenced by the lowering of basal plasma GH levels, the recurrence of GH pulsatility, and the lowering of circulating IGF-I levels. The sudden lowering of plasma progesterone concentration is probably a primary cause of a prolonged increase in PRL secretion. These observations underscore the importance of similar, albeit less abrupt, hormonal changes in the cyclical physiological alterations in the mammary gland and in the development of pseudopregnancy.

Secretion of growth hormone and prolactin during progression of the luteal phase in healthy dogs: a review

In some dogs the long exposure to high circulating progesterone levels during each oestrous cycle may result in a syndrome of growth hormone (GH) excess, i.e. acromegaly. The progesterone-induced GH production in dogs with acromegaly originates from the mammary gland. Also in healthy cyclic bitches, the pulsatile secretion pattern of GH changes during progression of the luteal phase, with basal GH secretion being higher and pulsatile GH secretion being lower when plasma progesterone concentration is high. This may be explained by partial suppression of pituitary GH release by progesterone-induced GH production in the mammary gland. Progesterone also modulates the secretion of prolactin in the bitch. In pregnant and overtly pseudopregnant bitches, the plasma prolactin concentration starts to rise about 1 month after ovulation, which is when the plasma progesterone concentration begins to decline. Also in healthy cyclic bitches, most prolactin is released during the second half of the luteal phase. The changes in GH and prolactin release during the luteal phase may promote the physiological proliferation and differentiation of mammary gland tissue in the bitch. In the early part of the luteal phase progesterone-induced mammary GH initiates proliferation of the mammary epithelium, whereas in the late luteal phase, when progesterone concentrations decrease, prolactin release increases and promotes lobuloalveolar differentiation.