Background Nowadays, Ehrlichia canis receives increasing attention because of its great morbidity and mortality in animals. Dogs in the subclinical and chronic phases can be asymptomatic, and serological tests show cross-reactivity and fail to differentiate between current and past infections. Moreover, there could be low parasitaemia, and E. canis might be found only in target organs, hence causing results to be negative by polymerase chain reaction (PCR) on blood samples. Methods We evaluated by PCR the prevalence of E. canis in blood, liver, spleen, lymph node and bone marrow samples of 59 recently euthanised dogs that had ticks but were clinically healthy. Results In total, 52.55% of the blood PCRs for E. canis were negative, yet 61.30% yielded positive results from tissue biopsies and were as follows: 63.15% from bone marrow; 52.63% from liver; 47.36% from spleen; and 15.78% from lymph node. In addition, 33% had infection in three tissues (spleen, liver and bone marrow). Conclusions Our results show the prevalence of E. canis from tissues of dogs that were negative by blood PCR. Ehrlichia canis DNA in tissue was 30% lower in dogs that tested negative in PCR of blood samples compared to those that were positive. However, it must be taken into account that some dogs with negative results were positive for E. canis in other tissues.

Background: Nowadays, Ehrlichia canis receives more attention because of its great morbidity and mortality in animals. Dogs in the subclinical and chronic phases can be asymptomatic, and serologic tests show cross-reactivity and fail to differentiate between current and past infections. Moreover, there could be low parasitaemia, and E. canis might be found only in target organs, hence negative by PCR in blood. Methods: We evaluated by PCR the prevalence of E. canis in blood, liver, spleen, lymphatic nodules, and bone marrow in 59 recently euthanized dogs that had ticks but were clinically healthy. Results: In total, 52.55% of the blood PCRs for E. canis were negative, yet 61.30% yield positive results in tissue biopsies as follows: 63.15% from bone marrow, 52.63% from liver, 47.36% from spleen and 15.78% from lymphatic nodules. In addition, 33% had infection in three tissues (spleen, liver and bone marrow). Conclusions: Our results show prevalence of E. canis in tissue from dogs that were negative by PCR in blood. E. canis DNA in tissue was 30% lower in dogs that tested negative in blood samples by PCR, compared to those that were positive. However, it must be taken into account that some dogs with negative results were positive for E. canis in others tissues.

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Palabras clave: Detección, leucocitos, Neospora caninum, PCRABSTRACT. Seropositivity to Neospora caninum was evaluated by Enzyme-Linked ImmunoSorbent Assay (ELISA) and the DNA was detected by PCR nested with external initiators Np 21-4 and internal Np 9-10 in cow leukocytes from the small-scale milk production system in Amecameca, State of México. A herd with 34 adult females was studied, performing follow-up with blood sampling for ve months. Also, two brain samples from aborted fetuses were analyzed and the sequence of the amplicons in the Genbank was veried. Consistency between techniques was compared using the Kappa test. ELISA seroprevalence was 85.3 %; and DNA of the parasite was detected in 89.4 % of the cows. A brain sample was positive. The similarity of the amplicons ranged from 91 to 96 %, the Kappa index was 0.41. The use of leukocytes increases the likelihood of amplifying N. caninum DNA.