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Am. J. Trop. Med. Hyg., 80(2), 2009, pp. 263-267
Copyright © 2009 by The American Society of Tropical Medicine and Hygiene

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SHORT REPORT


Prevalence of Neospora caninum and Toxoplasma gondii Antibodies in Northern Egypt

Hany M. Ibrahim, Penglong Huang, Tarek A. Salem, Roba M. Talaat, Mahmoud I. Nasr, Xuenan Xuan, AND Yoshifumi Nishikawa*
National Research Center for Protozoan Diseases, Obihiro University of Agriculture and Veterinary Medicine, Inada-cho, Obihiro, Hokkaido, Japan; Genetic Engineering and Biotechnology Institute, Minufiya University, Sadat City, Egypt

 

ABSTRACT

In view of the worldwide importance of Toxoplasma gondii and Neospora caninum and the limited data on the seroprevalence of these parasites in Egypt, this study aimed to estimate the prevalence of anti-T. gondii and anti-N. caninum antibodies in rabbits, cattle, and humans. We used ELISA methods based on surface antigen 2 of T. gondii (TgSAG2t) and surface antigen 1 of N. caninum (NcSAG1t). High seroprevalence of T. gondii (51.49%) was detected in pregnant women, and antibodies to N. caninum were also detected in human samples (7.92%). Anti-T. gondii or N. caninum antibodies were detected in cattle (TgSAG2t: 10.75%; NcSAG1t: 20.43%). In rabbits, only one sample was N. caninum positive (1.85%). The high prevalence of toxoplasmosis and neosporosis in cattle affects the development of the livestock industry and is also an important infective source for human infection in Egypt.

Toxoplasma gondii and Neospora caninum are two closely related protozoan parasites distributed worldwide. Both organisms have an indirect life cycle with carnivores as the definitive hosts and can infect a wide range of animal species. In the host, T. gondii can cause abortion or neonatal mortalities.1 The organism is estimated to infect 4–77% of the human population.2 Although it is not normally a significant problem for healthy individuals, T. gondii infection can be life threatening for infants infected congenitally and immunocompromised and immunodeficient patients (e.g., AIDS patients, cancer patients, and organ transplant recipients), as a result of either acute infectionor reactivation of infection.3–6 Toxoplasmic encephalitis is a life-threatening central nervous system infection observed in the later stages of HIV infection.7 In animals, T. gondii infection not only results in significant reproductive losses, and hence economic losses, but also has implications for public health because consumption of infected meat or milk can facilitate zoonotic transmission.8 Neosporosis, caused by the protozoan Neospora caninum, is an important cause of bovine abortion9 and neurologic alterations in dogs. 10 It can also cause abortion or neonatal mortality in other animal species, such as sheep, goats, horses, and deer. 11 Moreover, antibodies against N. caninum were detected in humans. 12,13 However, there are no reports about the clinical implications of N. caninum in humans because the parasites have not been detected or isolated from human tissues.

Serologic testing is an important method for detecting these parasitic infections, and includes immunofluorescent antibody test (IFAT), enzyme-linked immunosorbent assay (ELISA), competitive-inhibition ELISA, Western blotting, and direct agglutination test (DAT) using intact tachyzoite or tachyzoite-derived antigens. 14,15 However, the use of whole tachyzoites or tachyzoite-derived antigens may result in false positives because of cross-reaction with other closely related parasites. 16 Therefore, it is necessary to develop a reliable, sensitive, and specific diagnostic test using parasite-specific antigens. The molecular search for diagnostic antigens for T. gondii and N. caninum infection has been focused on the identification of immunodominant antigens that are recognized by sera from animals infected with geographically distant isolates and from both acute and chronically infected animals. Surface antigen 2 of T. gondii (TgSAG2), expressed either in Escherichia coli or insect cells, was validated as a useful antigen and promises a highly sensitive and specific ELISA. 17,18 Surface antigen 1 of N. caninum (NcSAG1) is an important candidate for developing a diagnostic reagent for neosporosis. 19,20

In previous surveys from Egypt, T. gondii antibodies were found in 27.3% of sera from 600 asymptomatic pregnant women, 21 47% of 108 chickens, 22 15.7% of 19 ducks, 23 and 65.6% of 121 donkeys. 24 Anti-T. gondii and N. caninum antibodies were detected in 17.4% and 3.6% of 166 camels, respectively. 25 A total of 51 of 75 (68%) water buffalo sera had antibodies to N. caninum.26

Economically, toxoplasmosis and neosporosis are considered important diseases in animals, and toxoplasmosis causes a variety of clinical manifestations in humans. Hence, our objective was to estimate the prevalence of anti-T. gondii and anti-N. caninum antibodies in rabbits, cattle, and humans by ELISA. We studied the serum of 101 human samples from Dakahlia province, Mansoura City (northeast of Delta), and 93 cattle samples and 54 rabbit samples from Sharkia Province (east of Delta).

The N. caninum (NC-1 strain) and T. gondii (RH strain) tachyzoites were maintained on monkey kidney adherent fibroblasts (Vero cells) cultured in Eagle minimum essential medium (EMEM; Sigma, St. Louis, MO) supplemented with 8% heat-inactivated fetal bovine serum. For the purification of tachyzoites, parasites and host-cell debris were washed in cold phosphate-buffered saline (PBS), and the final pellet was resuspended in cold PBS and passed through a 27-gauge needle and a 5.0-µm-pore filter (Millipore, Bedford, MA).

Blood samples were collected from the brachial vein of 101 pregnant women, (20–35 years of age, 6–18 weeks of gestation) at private clinical laboratories in Dakahlia Province, Mansoura City (northeast of Delta). Blood samples were collected from the jugular or caudal vein by local veterinary practitioners from 93 cattle at a cattle veterinary station and 54 albino rabbits samples at San El-hagr rabbit farm, Sharkia Province (east of Delta). See Figure 1Go for a map of the sampling area. Blood samples were centrifuged at 1,000 g for 10 minutes, and the serum was collected and stored at –20°C.


Figure 1
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  		FIGURE 1. Map of sampling area. Serum samples were collected from 101 pregnant women at private clinical laboratories in Dakahlia Province, Mansoura City (northeast of Delta). Animal samples were collected from 93 cattle at a cattle veterinary station and 54 albino rabbits at San El-hagr rabbit farm, Sharkia Province (east of Delta).

 
The template DNA for polymerase chain reaction (PCR) was extracted from tachyzoites of the T. gondii RH strain and N. caninum Nc-1 strain. 11,14,16,27 Two oligonucleotide primers, 5'-ACGAATTCGTCCACCACCGAGACG-3' and 5'-ACG-AATTCTTACTTGCCCGTGAGA-3', which correspond to amino acids 75 to 221, were used to amplify the truncated SAG2 (TgSAG2t) gene, without sequences encoding a highly hydrophobic signal peptide and C terminus by PCR. 14,28 The truncated NcSAG1 (NcSAG1t) gene, without sequence encoding a hydrophobic signal peptide and a C ter-minus, was amplified by PCR with two primers 5'-ACGAA-TTCATCAGAAAAATCACCT-3' and 5'-ACGAATTC-GA-CCAACATTTTC AGC-3', which correspond to amino acids 65 to 333. 16 The TgSAG2t gene or NcSAG1t gene was inserted into EcoRI site of the bacterial expression vector, pGEX-4T-3 (Promega, Madison, WI). Each resulting plasmid was designated as either pGEX/TgSAG2t or pGEX/NcSAG1t. pGEX/ TgSAG2t or pGEX/NcSAG1t was expressed as glutathione S-transferase (GST) fusion protein (GST-TgSAG2t or GST-NcSAG1t) in E. coli (DH5{alpha} strain), and the proteins were purified by glutathione Sepharose 4B according to the method of Chahan and others. 16

ELISA was performed according to modified procedures described previously. 14,16,17 The plates were coated using the recombinant antigens (GST-TgSAG2t, GST-NcSAG1t, or GST, 5 µg/mL), produced as described earlier, in a coating buffer (50 mmol/L carbonate) and incubated overnight at 4°C. After washing once with washing buffer (PBS containing 0.05% Tween 20), the plates were blocked with blocking solution (PBS containing 3% skim milk) at 37°C for 2 hours. After washing once with washing buffer, 50 µL of serum diluted (1:100) in blocking solution was added to duplicate wells for each sample and incubated at 37°C for 1 hour. After washing six times with washing buffer, the plates were incubated with 50 µL of horseradish peroxidase (HRPO)-conjugated goat anti-bovine immunoglobulin G plus IgA and IgM (Bethyl Laboratories, Montgomery, TX), HRPO-conjugated goat anti-rabbit immunoglobulin G (Bethyl Laboratories), and HRPO-conjugated goat anti-human immunoglobulin G (Sigma) diluted in blocking solution (1:4,000) per well at 37°C for 1 hour. After washing six times with washing buffer, the plates were incubated with 100 µL substrate 2,2'-azino-bis(3-ethylbenzthiazoline-6-sulphonic acid) (ABTS) in an ABTS buffer (0.1 mol/L citric acid, 0.2 mol/L sodium phosphate) per well at room temperature for 1 hour. The absorbance at 405 nm was measured using a microplate reader (TECAN Sunrise, Grödig, Austria). The ELISA result was determined by the difference in mean optical densities at a value of 405 nm (OD405) between the recombinant antigen (TgSAG2t or NcSAG1t) and the GST protein. The cut-off values were determined as the OD405 value for T. gondii– or N. caninum–negative sera plus 3 SD—TgSAG2t: 0.039 and NcSAG1t: 0.211 in humans (N = 13), TgSAG2t: 0.02 and NcSAG1t: 0.042 in cattle (N = 15), and TgSAG2t: 0.041 and NcSAG1t: 0.031 in rabbits (N = 10). The negative sera from our sera stock were tested and confirmed negative by ELISA, DAT, and IFAT.

Slides were spotted with whole N. caninum (NC-1 strain) tachyzoites. The purified tachyzoites were washed three times in PBS (25 mmol/L NaPO4–150 mmol/L NaCl; pH 7.2) and diluted to 106/mL. One drop of the solution was placed in each of the 12 wells per slide and allowed to dry at 37°C. The cells were fixed with 80% acetone–20% methanol.

Sera used in the IFAT were diluted 1:100 in PBS, and 20 µL of each sample was added to a well containing tachyzoites and incubated in a humidified chamber at 37°C for 30 minutes. The sera were removed, and each well was rinsed and washed for 10 minutes with rinse buffer (25 mmol/L Na2CO3 , 100 mmol/L NaHCO3 , 36 mmol/L NaCl; pH 7.4). Alexa Fluor 488 goat anti-human immunoglobulin G (IgG) and Alexa Fluor 488 goat anti-mouse immunoglobulin G (IgG) (Invitrogen; Molecular Probes, Eugene, OR) diluted 1:100 in PBS were placed in each well. The slides were incubated and washed as described above, overlaid with mounting medium (50% glycerol–50% rinse buffer) and a coverslip, and viewed at x63 magnification by confocal fluorescence microscopy. For controls, one well on each slide was tested with N. caninum–negative control serum. Moreover, another well was tested with N. caninum–positive mice control serum to confirm reactivity.

The prevalence of T. gondii and N. caninum in humans (pregnant women), cattle, and rabbits from the northeastern and eastern Delta regions is summarized in Tables 1Go and 2Go, respectively. The results of the ELISA for detecting the antibodies against the recombinant TgSAG2t showed high seroprevalence (51.49%) in pregnant women, 10.75% in cattle, and 0% in rabbit samples. Antibodies against the recombinant NcSAG1t were detected in pregnant women (7.92%), cattle (20.43%), and rabbits (1.85%). Mixed infection of both T. gondii and N. caninum was detected in human sera (5.94%, N = 6). On the other hand, the mixed infection was not observed in either cattle or rabbit sera. Because human neosporosis is controversial, we minutely confirmed the seroreactivity of N. caninum–positive human samples examined by ELISA. The IFAT showed that all human samples (N = 8) reacted with the N. caninum tachyzoite. The positive human sera showed obvious tachyzoite staining like the staining with positive mouse serum (Figure 2Go).


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TABLE 1
Seroprevalence of T. gondii infection in humans, cattle, and rabbits

 

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TABLE 2
Seroprevalence of N. caninum infection in humans, cattle, and rabbits

 

Figure 2
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  		FIGURE 2. IFAT of human sera for reactivity against N. caninum. Slides were prepared with N. caninum tachyzoites as described and treated with a 1:100 human sera. A, Positive reactivity of serum from a mouse infected with N. caninum tachyzoites. B, Positive reactivity of human serum against N. caninum tachyzoites. C, Negative reactivity of human serum against N. caninum tachyzoites.

 
The proportion of women at risk of acquiring the Toxoplasma infection during pregnancy in many countries, including Egypt, is not well known. Primary infection with Toxoplasma during pregnancy may lead to severe complications and may result in the death of the fetus. 29,30 Our study showed that there was a high seroprevalence of T. gondii (Table 1Go; seroprevalence was 51.49%) in pregnant women in Dakahlia Province, Mansoura City, Egypt. High percentages of T. gondii infection were reported in Jordan 29,31 (54% and 58.2%) and in Mexico 32 (44.9%). Also, Zuber and Jacquier 33 reported that serologic evidence indicated that human infections are common in many parts of the world. Human neosporosis is a controversial question now because N. caninum was not detected or isolated from human tissues. In our study, N. caninum–specific antibodies were detected in pregnant women (Table 2Go; Figure 2Go; seroprevalence was 7.92%). These results are consistent with previous studies conducted in the United States 12 and Brazil. 13 This seroprevalence suggests human exposure to N. caninum, but further study is needed to determine the extent and significance of exposure. Because dogs are definitive hosts and excrete oocysts in their feces, the potential for human exposure to N. caninum is high. 34 The infection of healthy individuals by N. caninum may follow a course similar to that of T. gondii, where the vast majority of infections are asymptomatic. 35 Testing tissues and fluids from immunocompromised individuals and fetuses with suspected toxoplasmosis for N. caninum may show that sub-populations of these patients are infected with N. caninum. Mixed infection of both T. gondii and N. caninum was detected in 5.94% (N = 6) of the human sera tested, indicating concomitant infection of T. gondii and N. caninum in those women.

The prevalence of T. gondii and N. caninum in cattle and rabbits in Sharkia Province, Egypt, was detected by ELISA with TgSAG2t and NcSAG1t as coated recombinant antigens. Anti-T. gondii or -N. caninum antibodies were detected in cattle (TgSAG2t: 10.75% in Table 1Go; NcSAG1t: 20.43% in Table 2Go), whereas only one sample was N. caninum positive in rabbits (Tg SAG2t: 0% in Table 1Go ; NcSAG1t: 1.85% in Table 2Go). No mixed infection of both T. gondii and N. caninum was detected in the animal sera tested. These results suggest that the identification of recombinant Tg SAG2t and recombinant Nc SAG1t could distinguish between toxoplasmosis and neosporosis. The high prevalence of toxoplasmosis and neosporosis in cattle not only affects the development of the livestock industry but is also an important infective source for human toxoplasmosis.

There are three possible routes by which the host could become infected with T. gondii or N. caninum: ingestion of sporulated oocysts, ingestion of bradyzoite cysts in the tissues of intermediate hosts, or vertical transmission.1 Many risk factors need to be studied to understand the high percentage of parasitic infection. In Egypt, consumption of grilled lamb (undercooked) is very high. Sheep are reared outdoors, which puts them at greater risk of environmental exposure than animals reared indoors. 36 It is these trends that may increase the exposure to parasites because lamb has a greater potential as an infection source than beef or poultry. Another risk factor associated with seropositivity is contact with soil-harboring oocysts from wild homeless cats and dogs, which also may be responsible for the high infection rates. If the infections of these parasites increase and spread among domestic animals, contamination of the water and soil will also increase. In Egypt, T. gondii has been reported in chickens and ducks, 22,23 in horses, 37 and in donkeys, 24 and both T. gondii and N. caninum have been reported in water buffalo and camels. 25,26

In conclusion, our study indicated that these diseases may be widely distributed and present the threat of an epidemic in Delta, Egypt, with high seropositivity in humans and cattle. Recombinant TgSAG2t and NcSAG1t are good diagnostic candidates and were able to distinguish between T. gondii and N. caninum infection. More studies are needed to understand the high rates of these parasitic infections in Egypt. This study provides additional information of the prevalence of T. gondii and N. caninum infection in Delta, Egypt, and will assist in developing strategies for controlling the disease.

Received May 18, 2008. Accepted for publication September 25, 2008.

Acknowledgments: The authors thank J. P. Dubey (US Department of Agriculture, Agriculture Research Service, Livestock and Poultry Sciences Institute, and Parasite Biology and Epidemiology Laboratory) for supplying the N. caninum NC-1 isolate, local veterinary practitioners for collecting blood samples, and researchers at the Genetic Engineering and Biotechnology Institute (Minufiya University) who helped us during this work. This study was supported by the Egyptian Ministry of High Education and scientific research.

* Address correspondence to Yoshifumi Nishikawa, National Research Center for Protozoan Diseases, Obihiro University of Agriculture and Veterinary Medicine, Inada-cho, Obihiro, Hokkaido 080-8555, Japan. E-mail: nisikawa{at}obihiro.ac.jp Back

Authors’ addresses: Hany M. Ibrahim, Penglong Huang, Xuenan Xuan, and Yoshifumi Nishikawa, Genetic Biochemistry Lab, National Research Center for Protozoan Diseases, Obihiro University of Agriculture and Veterinary Medicine, Inada-cho, Obihiro, Hokkaido 080-8555, Japan, Tel: 81-155-49-5886, Fax: 81-155-49-5643, E-mail: nisikawa{at}obihiro.ac.jp. Tarek A. Salem, Roba M. Talaat, and Mahmoud I. Nasr, Genetic Engineering and Biotechnology Institute, Minufiya University, Sadat City, PO Box 79, Egypt, Tel: 2-048-2601262, Fax: 2-048-2601268, E-mail: salem_tarek{at}yahoo.com.

 

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