Introduction

Toxoplasma gondii is a protozoa that infects nucleated cells of vertebrate hosts⁽¹⁾, including birds, wild and domestic animals, and also human beings⁽²⁾. In breeders, such as goats, not only does T. gondii lead to fever, but it is also responsible for great economic losses due to abortions, weak newborns, and perinatal mortality⁽³⁾.

Several studies have shown that the strain of T. gondii can be classified into three major genotypically distinct groups, type I (virulent), II and III (non-virulent or low virulence), which can infect animals and humans, and apparently differ in their virulence, biological behavior and epidemiological patterns occurrence. There is a predominance of type II strains in human toxoplasmosis and the most common type III in animals^(4,5).

Brazil has a goat herd of over 13 million animals, yet little is known about goat toxoplasmosis. Also, the possibility of human transmission due to goat breeding management activities is worrisome⁽⁶⁾. Muday and Mason⁽⁷⁾ were the first researchers to describe this disease as a major cause of goat reproductive losses. Besides, although not well documented, the losses seem to be even higher, clinically attacking both young and adult animals⁽⁸⁾. According to Cavalcante et al.⁽⁹⁾, factors such as the increase in the age of the animals, the number of felines among goat herds, and the types of breeding facilities contribute to increasing the risk of stock contamination. The major route of transmission of toxoplasmosis in goats, as well as in most domestic species, is the ingestion of sporulated oocysts of the parasite⁽¹⁰⁾ found in the environment.

Information on the seroprevalence of antibodies against T. gondii in goats has been reported in many countries, suggesting that this species is an important host^(11-13). Serological surveys indicate that stock seropositivity ranges from 28.9% to 92.4% in Brazil, showing a high prevalence in that domestic species^{(11; 14-17)}.

Although there are some studies reporting the occurrence of clinical changes in goats infected with T. gondi^(18-20), there was no information found to correlate the effects of toxoplasmic infection in clinical, hematological and seminal parameters in male goats experimentally infected with this parasite, what this study aimed to investigate.

Material and Methods

The present study was carried out at the Animal Health Research Center (CPPAR) at School of Agrarian and Veterinary Sciences, Universidade Estadual de São Paulo (FCAV/UNESP), Jaboticabal campus, São Paulo, Brazil. Every procedure was approved by the university Animal Ethics and Wellness Committee from UNESP's School of Agriculture and Veterinary in Jaboticabal, São Paulo state, Brazil, under the protocol N. 010850-08.

This study used "P"⁽²¹⁾and "RH"⁽²²⁾ T. gondii strains kept at CPPAR, FCAV/UNESP. "P" strains were genotypically characterized by using PCR-RFLP segment of locus SAG2 located in chromosome VIII as a genetic marker and classified as Type III⁽²³⁾. "RH" strains were previously characterized as Type I by using the same analysis of loci SAG1, SAG2, new SAG2, SAG3, BTUB, GRA6, c22-8, c29-2, L358, PK1 and Apico^(24-25).

Nine male goats of undefined breed, serologically negative for T. gondii, aged between one and two years, healthy and in good physical condition, were selected in a specialized rearing facility in the town of Pitangueiras, in the state of São Paulo, Brazil. Serology titers obtained by indirect immunofluorescence (IFI) were considered positive starting at a 1:16 dilution. These nine animals were then kept in proper individual stalls of CPPAR for four weeks prior to the experiment, with water and food at will, with the purpose of letting them adapt to the breeding management conditions and to the facilities.

Serological exams were carried out during the experimental period as follows: acidified buffered antigen test⁽²⁶⁾ for brucellosis, and microscopic agglutination test⁽²⁷⁾ for leptospirosis.

The animals were identified, sorted and randomized into three groups with three animals in each, and they were kept isolated until the end of the experiment, as follows: GI (A, B and C) - non-inoculated controls; GII (D, E and F) subcutaneously infected with 1 x 10⁶ RH strain tachyzoites per animal; and GIII (G, H and I) orally infected with 2 x 10⁵ P strain oocysts per animal.

In order to confirm the real infection arising from inoculum administration: 1x10⁶ RH strain tachyzoites, subcutaneously (GII), and 2x10⁵ P strain oocysts, orally (GIII), blood samples from infected (GII and GIII) and uninfected (GI) goats were collected for serological follow-up using IFI⁽²⁸⁾ two days prior to inoculation (-2^nd), and on days 3^rd, 5^th, 7^th, 11^th, 14^th, 21^st, 28^th, 35^th, 42^nd, 49^th, 56^th, 63^rd and 70^th after inoculation (DAI). Serology titers obtained by indirect immunofluorescence (IFI) were considered positive starting at a 1:16 dilution.

With the purpose of following up possible clinical changes arising from experimental infection of the animals, respiratory and cardiac frequency and rectal temperature were taken two days prior to inoculum administration (-2^nd), and on the 3^rd, 5^th, 7^th, 11^th, 14^th, 21^st, 28^th, 35^th, 42^nd, 49^th, 56^th, 63^rd and 70^th DAI.

Concomitantly with serological and clinical assessment, a laboratory study of each animal was performed using hematological examinations. Therefore, 1 mL of blood samples was collected by puncturing the jugular vein using 40x12 needles, in consonance with the technique proposed by Rosenfeld⁽²⁹⁾, and the automated hemograms were performed at Clinical Pathology Laboratory at Veterinary Hospital Governador Laudo Natel at FCAV/UNESP.

Parasitemia was assessed using white mice by inoculation of the leukocytic layer⁽³⁰⁾ of goats' blood in mice and serology was used to determine if antibodies developed against T. gondii. Mouse serum was considered positive for sample that reacted at a diluition of >64.

For nearly two months, all animals were submitted to semen collection with an electroejaculator. Ejaculate samples obtained two days before inoculation and on 3^rd, 5^th, 7^th, 11^th and 14^th DAI and then weekly until the end of the experiment were evaluated for the following sperm parameters: volume, motility, concentration, morphology and vigor⁽³¹⁾. Immediately after ejaculation, semen samples were placed in a water bath (38 to 40 °C) to ensure sperm integrity.

To evaluate sperm motility and vigor, approximately 10 p,L of semen were used prior to dilution and placed on a slide with a coverslip⁽³¹⁾. These exams were conducted in triplicate for each of the samples. The motility data were expressed as a percentage and vigor data, on a scale of 0 to 5.

For sperm concentration analysis (sperm/mL), in accordance with the methodology described by Chemineau et al.⁽³¹⁾, 20 p,L of semen from each goat were diluted in 980 p,L of saline solution containing 0.1% formol. The seminal volume was verified by direct observation using a 5 mL test tube.

For spermatic pathologies evaluation, 50 µL semen aliquots were separated from each sample and diluted in 1 mL of 0.1% formol saline solution. Next, 200 cells/goat/collection were counted in accordance with the methodology adopted by Chemineau et al.⁽³¹⁾.

Pre- and post-inoculation clinic parameters were analyzed as a split-plot in time, taking inoculated and control groups into account. F-test was used for treatment effect and Tukey test was used to compare the treatments.

Seminal parameters were evaluated among the experimental groups (control, infected with tachyzoites and infected with oocystes) using analysis of variance (ANOVA), followed by the Bonferrom's post hoc test for parametric data. In addition, for nonparametric data, we used Kruskal-Wallis test, followed by the post hoc Dunn's test. The statistical analysis were performed using the software Statistica 8.0 (STATSOFT, Tulsa, OK, USA), and p-values of <0.05 were taken to be significant.

Results and Discussion

The serological titers⁽²⁸⁾ shown in Table 1confirm the development of toxoplasmic infection with fast immune response from 11^th DAI (titer ≥ 1:64), as reported by Nishi et al.⁽¹⁸⁾ and Santana et al.⁽³²⁾ in similar studies.

We could also observe the highest serological titer was of 1:4096 from 14^th to 42^th DAI in the group of animals infected with 1.0 x 10⁶ tachyzoites, and on the 21^st and 35^th DAI in the group of animals infected with 2 x 10⁵ oocysts. Although there were changes in antibody titers of animals that received T. gondii,throughout the experiment there was a visible decrease in this titer after serological peaks in each inoculated animal. As expected, the animals inoculated with saline showed no growth of T. gondii infection throughout the experimental period.

According to Dubey et al.⁽³³⁾, the mean rectal temperature of adult goats in normal physiological conditions may reach up to 40.5 °C. In this study, as shown in Figure 1, a mild episode of hyperthermia could be noticed on the 5^th DAI in the group of animals inoculated with oocysts (GIII).

Figure 1: Mean rectal temperature in non-inoculated male goats (GI) and in male goats experimentally inoculated with 1 x 10⁶ tachyzoites (GII) and with 2 x 10⁵ oocysts of Toxoplasma gondii (GIII) 

Even though there were changes in the mean rectal temperatures in the experimental groups on the course of the experiment, they were within the normality range of the studied species. The hyperthermia episode was similar to the findings of Nishi et al.⁽¹⁸⁾, who reported this change as being one of the most evident clinical signs in goats orally inoculated with 10⁵ oocysts of T. gondii. Dubey et al.⁽³³⁾, Chhabra et al.⁽²⁰⁾ and Dubey⁽¹⁹⁾ have also observed similar clinical symptomatologies, as well as the death of an animal inoculated with oocysts⁽¹⁹⁾.

Although there have been changes in cardiac and respiratory frequencies at several dates throughout the experiment, for the groups GI, GII and GIII, these changes were not statistically related to T. gondii infection or were within normal ranges for this species⁽³⁴⁾.

Due to the lack of scientific studies on hematological parameters of males experimentally infected with T. gondii, this study aimed to compare the parameters of the experimental animals with the parameters considered to be normal for this domestic species, as well as the parameters collected in the control group and on -2^nd DAI for all experimental groups.

The oscillation in average red blood count could be observed in the three groups throughout the experiment, including in the non-inoculated group (control group). Therefore, experimental infection with T. gondii could not be deemed responsible for any change in this parameter. According to Elitok,⁽³⁷⁾ the reference value for red blood cell count in adult male goats is 23.09 ± 3.63 x 10¹²/L. Although, it was noticed that on some experiment dates this highest value exceeded, it was not statistically different (P>0.05) from the other experimental groups.

Considering the adopted reference values of hemoglobin concentration,⁽³⁵⁾13.34 ± 0.14 g/dL, in this study, average values of hemoglobin concentration (g/dL) in groups GII and GIII were similar to those found in group GI (control group) on the same dates throughout the study. There were no statistically significant differences (P>0.05) among the observed values.

A gradual reduction in the mean values of hematocrit was noticed in the three groups from the 35^th DAI to the end of the experiment. Such reduction was also observed in the group of non-inoculated animals with T. gondii,which rules out the hypothesis of change due to protozoa infection in the remaining experimental groups. Another extremely relevant datum is that there was no statistically significant difference (P>0.05) in the mean values of hematocrit (%) among the groups throughout the experiment on any of the dates. Furthermore, such values were within the normality range (22%-38%) of the species being studied⁽³⁵⁾.

Reduction in total value count of leukocytes (x 10³/UI) in the three groups was observed from the 3^rd to the 11^th DAI. Nevertheless, besides being within the normality range, 13.84 ± 0.21 x 10³/UI⁽³⁵⁾, these mean values did not have statistically significant differences (P>0.05) when comparing the groups on the same experiment dates, thus, they cannot be considered episodes of leukopenia.

According to Egbe-Nwiyi et al.⁽³⁵⁾, the mean values of eosinophil and monocytes count were within the normality limits for this species (452.2 ± 56.53 cells/µL and 442.0 ± 88.74, respectively) throughout the experiment. Moreover, these values did not differ statistically (P>0.05) among the groups on any date after the infection.

Values of banded neutrophil count in this study were rare, which was also within the normality values for this parameter in goats⁽³⁵⁾. Normal reference parameters of segmented neutrophil should range from 30 to 48% of total leukocyte count, that is 5715.9 ± 165.2/µµL⁽³⁵⁾. In this study, a variation in the absolute mean values of the three groups could be noticed, yet, without exceeding the normality limit for this parameter.

Episodes of lymphopenia in animals inoculated with oocysts (3^rd DAI) and with tachyzoites (3^rd and 42^nd DAI) were observed; moreover, lymphocyte count was lower on these dates, being statistically different (P<0.05) from the values found in animals in the control group . However, in spite of this difference, such values were within the normality range for this parameter in goats, 7203 ± 264/ µL⁽³⁵⁾. On other experiment dates, such as on the 63^rd and 70^th DAI, we noticed low mean count of lymphocytes, mainly regarding the animals inoculated with oocysts. Nonetheless, these values were still within the normality range although they did not differ statistically from the means of the other experimental groups (P>0.05).

Parasite presence in the blood of the male goats infected with tachyzoites (GII) was verified on 11^th, 14^th, 28^th, 49^th, 56^th, 63^rd and 70^th DAIs, and on 14^th, 21^st, 56^th, 70^th DAIs for the male goats infected with oocysts (GIII). The high frequency of parasitic outbreaks observed in the male goats could be related to the susceptibility of the host to T. gondii, as also shown by Nishi et al.,⁽¹⁸⁾ Chhabra et al.⁽²⁰⁾ and Dubey et al.⁽³³⁾.

Although statistical differences (P<0.05) were observed for spermatic concentration and pathologies (Tables 2 and 3, respectively) in the goats throughout the experiment, these could not be directly related to toxoplasmic infection; thus, these could be dependent on other factors, such as the collection technique, semen manipulation and scrotal temperature, among others.

Moura et al.⁽³⁶⁾affirmed that a direct effect of T. gondii on spermatogenesis should be accompanied by a significant increase in the frequency of primary pathologies, as well as relevant alterations in semen variables. However, some factors like temperature were difficult to control and could influence these results. No significant differences (P >0.05) were observed between the control and infected animals concerning motility, vigor and volume obtained.

Conclusion

Despite having found hyperthermia in the group of animals inoculated with Toxoplasma gondii oocysts just on one experimental date, the infection was asymptomatic, without clinical or hematological changes in the inoculated goats. Thus, recognition and posterior treatment of animals infected by this parasite is hindered. Furthermore, despite the absence of changes in the evaluated clinical parameters, attention should be paid to this parasitosis, not only because of the economic losses it leads to but also because of its relevance to public health.