Control of Leishmania infantum infection is dependent upon Th1 CD4+ T cells to promote macrophage intracellular clearance of parasites. Deficient CD4+ T cell effector responses during clinical visceral leishmaniasis (VL) are associated with elevated production of IL-10. In the primary domestic reservoir of VL, dogs, we define occurrence of both CD4+ and CD8+ T cell exhaustion as a significant stepwise loss of antigen-specific proliferation and IFNγ production, corresponding to increasing VL symptomatology. Exhaustion was associated with a fourfold increase in the population of T cells with surface expression of Programmed Death 1 (PD-1) between control and symptomatic populations. Importantly, exhausted populations of CD8+ T cells and to a lesser extent CD4+ T cells were present prior to onset of clinical VL. VL exhausted T cells did not undergo significant apoptosis ex vivo after antigen stimulation. Antibody block of PD-1 ligand, B7.H1, promoted return of CD4+ and CD8+ T cell function and dramatically increased reactive oxygen species production in co-cultured monocyte-derived phagocytes. As a result, these phagocytes had decreased parasite load. We demonstrate for the first time that pan-T cell, PD-1-mediated, exhaustion during VL influenced macrophage reactive oxygen intermediate production. Blockade of the PD-1 pathway improved the ability of phagocytes isolated from dogs presenting with clinical VL to clear intracellular parasites. T cell exhaustion during symptomatic canine leishmaniasis has implications for the response to vaccination and therapeutic strategies for control of Leishmania infantum in this important reservoir species.

Canine leishmaniosis (CanL) is caused by Leishmania infantum, an obligate intracellular protozoan parasite, endemic in U.S. hunting dog populations. CanL has been found in dogs in 28 states and two Canadian provinces. Previous studies by our group, (Boggiatto, 2011), demonstrated that vertical transmission of Leishmania was the predominant means of transmission within U.S. dogs. Very little is known regarding how this alternative means of transmission, alters the long-term immunity and clinical presentation of leishmaniosis in dogs born to a positive bitch. This study follows the immunological progression of CanL in three pups after birth to an infected bitch. During the course of the study, these dogs were tested every six months over the course of six years. Both immunologic (IFN-γ, T cell proliferation, antibody production) and parasitological parameters (qPCR) of vertically-infected dogs were measured. Within the six years after birth to an L. infantum-infected, oligosymptomatic bitch, all dogs had at least one L. infantum PCR-positive test. Interestingly, despite living in the same location for their entire lives and being full siblings, these pups demonstrate three different disease progression patterns of L. infantum infection. One dog progressed to oligosymptomatic disease, maintaining a positive titer and had intermittent positive PCR results. One asymptomatic dog had positive serological titers and demonstrated a robust CD4+ immune response to infection. The third dog had a negligible response to L. infantum antigen and was healthy. This work demonstrates the biologic variability associated with vertically-transmitted infection similar to the variety of presentations observed during vector-borne leishmaniosis.

Leishmaniasis is a zoonotic disease caused by predominantly vectorborne Leishmania spp. In the United States, canine visceral leishmaniasis is common among hounds, and L. infantum vertical transmission among hounds has been confirmed. We found that L. infantum from hounds remains infective in sandflies, underscoring the risk for human exposure by vectorborne transmission.

Dirofilaria immitis is the causative agent of heartworm disease in North America. The adult nematodes are typically found in the pulmonary arteries leading to respiratory, cardiac and systemic illness. In this report, the authors describe an aberrant migration of adult D immitis associated with fibrinous lesions in the peritoneum of a dog. The nematode was recovered during routine ovariohysterectomy. Examination of the organism revealed that the anterior end of the nematode contained several insignificant cranial papillae and no lips while the caudal region contained two rows of papillae. Histological examination demonstrated coelomyarian musculature and prominent lateral internal cuticular ridges. Subsequent amplification of a region of the 16S rRNA gene confirmed the authors’ diagnosis of D immitis. Diagnosis of nematode parasites often heavily relies on the location of the worm and the identity of the host. This case highlights the use of integrating morphological, histopathological and molecular data in order to identify an aberrantly migrating nematode which is important for diagnostic, public health and epidemiological purposes.