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. 2019 Jun;25(6):1226–1227. doi: 10.3201/eid2506.181431

Absence of Neospora caninum DNA in Human Clinical Samples, Spain

Rafael Calero-Bernal 1,2,, Pilar Horcajo 1,2, Marta Hernández 1,2, Luis Miguel Ortega-Mora 1,2, Isabel Fuentes 1,2
PMCID: PMC6537714  PMID: 31107232

Abstract

Low antibody titers to Neospora caninum have been reported in humans, but infection has not been confirmed. We used N. caninum–specific PCR to test 600 clinical samples from patients with toxoplasmosis signs but Toxoplasma gondii–negative PCR results. We did not detect N. caninum DNA, demonstrating it is an unlikely opportunistic zoonotic agent.

Keywords: Neospora caninum, toxoplasmosis, neosporosis, parasites, PCR, Spain


The coccidian parasite Neospora caninum (Apicomplexa: Sarcocystidae) is a major abortifacient agent in ruminants, especially cattle. It is phylogenetically close to Toxoplasma gondii (1), a parasite of high prevalence in humans, but biologically different. N. caninum parasites have a restricted host range but can infect primates (2,3).

N. caninum infection causes neuromuscular disease in dogs and reproductive disorders in ruminants, causing fetal loss due to vertical transfer of parasites during acute infections or reactivation of chronic infections. Clinical neosporosis in animals resembles the disease outcome of toxoplasmosis (1).

N. caninum parasites have been successfully cultured in human cell lines, but low antibody titers of unconfirmed specificity against N. caninum have been reported in human serum samples (1,4,5). The significance of these findings is uncertain because neither parasite DNA nor viable parasites have been demonstrated in human tissues. Unconfirmed reports of N. caninum–specific antibodies in the human population (4,5) prompted us to test specifically for Neospora DNA in human clinical specimens and assess its possible role in human illness.

We obtained 600 DNA samples from a collection of anonymized human clinical samples from the National Registry of Biobanks (no. C.0004715) in Spain that were deemed exempt from a second ethics approval. Our criteria for selection included any pregnancy-related disorder affecting women or fetuses, toxoplasmosis-like clinical signs or suspicion of toxoplasmosis, and negative results for T. gondii–specific real-time PCR (6) and nested PCR (7) (Table).

Table. Types of samples analyzed and demographic and clinical data for 600 patients tested for Neospora caninum parasites, Spain*.

Characteristics
No. (%)
Sample type
Amniotic fluid 267 (44.5)
Cerebrospinal fluid 113 (18.8)
Blood 100 (16.7)
Placental tissue 51 (8.5)
Bronchoalveolar lavage 25 (4.2)
Urine 17 (2.8)
Brain biopsy 12 (2.0)
Aqueous humor 4 (0.7)
Fetal tissues and fluids 4 (0.7)
Lymph node aspirate 3 (0.5)
Vitreous humor 2 (0.3)
Bone marrow aspirate 1 (0.2)
Hepatic abscess aspirate 1 (0.2)
Patient demographic information
Sex
Unknown 6 (1.0)
M 135 (22.5)
F 459 (76.5)
Of childbearing age, 17–42 y 333 (55.5)
Age, y
>1, average 36.1 481 (80.2)
<1 116 (19.3)
Native country
Spain 382 (63.7)
Other† 36 (6.0)
Unknown
182 (30.3)
Patient clinical information
Immune status
Immunocompetent 458 (76.3)
Immunodepressed or 
 immunosuppressed 83 (13.8)
HIV/AIDS 19 (22.9)
Chemotherapy 29 (34.9)
Organ transplant 35 (42.2)
Unknown 59 (9.8)
Pregnancy-related disorders 454 (75.7)
Seroconversion–infection suspicion 
 and lymphadenopathy 418 (92.1)
Spontaneous abortion 27 (5.9)
Ophthalmic 4 (0.9)
Other fetal signs‡ 5 (1.1)
Neurologic and ocular symptoms and 
 conditions§ 108 (18.0)
Neurologic condition with ocular signs 8 (7.4)
Ophthalmic only 3 (2.7)
General signs, n = 38 38 (6.3)
Pneumonia 24 (63.2)
Lymphadenopathy 2 (5.3)
Hematologic or oncologic 12 (31.6)

*Patients were from 12 regions: Andalusia, Aragon, Asturias, Balearic Islands, Cantabria, Castile-La Mancha, Castile and Leon, Extremadura, Galicia, Madrid, Navarre, Valencia. 
†Africa, 8; Asia, 1; Europe, 8; Latin America, 19.
‡Anencephaly, malformations, and microcephaly.
§Neurologic symptoms and conditions include ataxia, disorientation, sudden blindness, encephalitis, calcifications, and intracranial space occupying lesions; ophthalmic symptoms and conditions include chorioretinitis, panuveitis, posterior uveitis, and vitritis.

We isolated total DNA using a QIAamp DNA Mini Kit (QIAGEN, https://www.qiagen.com) and used a single-tube nested PCR to amplify the N. caninum internal transcribed spacer 1 region using external primers NN1–NN2 and internal primers NP1–NP2, as previously described (8,9). We expected a diagnostic 249-bp fragment. In each batch of amplifications, positive PCR controls included genomic DNA of 10, 1, and 0.1 N. caninum tachyzoites. Using these PCR methods, we found that the analytical sensitivity was <1 tachyzoite of Neospora spp. or T. gondii.

We did not detect N. caninum–specific DNA in the samples analyzed. Previously, transplacental neosporosis was experimentally demonstrated in rhesus macaques (Macaca mulatta) in the United States (2,3). A literature review summarized reports of unconfirmed presence of antibodies against N. caninum in patients with neurologic disorders, pregnant women, and healthy people, including blood donors (1). Findings of N. caninum IgG in HIV-infected patients from Brazil and France (4,5) are of special interest because of possible association with T. gondii infections.

We believe N. caninum parasites are an unlikely opportunistic zoonotic agent. Application of direct methods for parasite detection in a greater number of samples from HIV-positive patients should complement unclear serologic findings to fully dispel suspicion of human neosporosis.

Acknowledgments

This work was supported by National Health Research Funds Project P13/01106. Carlos III Health Institute Spanish Ministry of Science and Innovation. R.C-B. is funded by Complutense University of Madrid, Madrid, Spain (grant no. CT65/16).

Biography

Dr. Calero-Bernal is a postdoctoral researcher at the Saluvet Research Group of the Complutense University, Madrid. His major research interests are Apicomplexan parasites of zoonotic interest, epidemiology of foodborne parasites, and molecular pathways in virulence and drug susceptibility in protozoans.

Footnotes

Suggested citation for this article: Calero-Bernal R, Horcajo P, Hernández M, Ortega-Mora LM, Fuentes I. Absence of Neospora caninum DNA in human clinical samples, Spain. Emerg Infect Dis. 2019 Jun [date cited]. https://doi.org/10.3201/eid2506.181431

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