Failure of a multi-subunit recombinant leishmanial vaccine (MML) to protect dogs from Leishmania infantum infection and to prevent disease progression in infected animals

We report results of a Phase III trial of the multi-subunit recombinant Leishmania polyprotein MML for the protection of dogs against infection by Leishmania infantum. The antigen, also known as Leish-111f, is the first antileishmanial human vaccine entered Phase I clinical testing. The study was performed in a leishmaniasis endemic area of southern Italy. Three groups of 15 Leishmania-free beagle dogs each, received 3 monthly injections with vaccines A (MML+MPL-SE adjuvant), B (sterile saline = control) and C (MML+Adjuprime adjuvant), respectively, before transmission season 2002. The surviving dogs received a second three-dose vaccine course 1 year later. The dogs were naturally exposed to sandfly bites for 2.5 months in 2002, and for 5 months in 2003. Every 2 months post vaccination, dogs were examined by clinical and immunological evaluation, and by specific serology, microscopy, culture and PCR. A weak lymphoproliferative response to MML was seen in A and C groups throughout the study period. One year after the first vaccine course, the cumulative incidence of leishmanial infections was 40% in group A, 43% in group B and 36% in group C. Two-year post-vaccination (1 year after the second vaccine course) the cumulative incidence was 87% in group A (with three symptomatic cases), 100% in group B (with no symptomatic cases) and 100% in group C (with two symptomatic cases). The efficacy of the MML vaccine as an immunotherapeutic agent for the prevention of disease progression (subpatent infection-->asymptomatic patent infection-->symptomatic patent infection) was evaluated through follow-up of dogs found infected prior to the second vaccination. Among 15 infected animals, progression to a subsequent stage of infection was found in 5/6 dogs of group A, 3/6 of group B and 2/3 of group C. We conclude that vaccination with MML is not effective to prevent leishmaniasis infection and disease progression in dogs under field conditions.

Deltamethrin-impregnated collars for the control of canine leishmaniasis: Evaluation of the protective effect and influence on the clinical outcome of Leishmania infection in kennelled stray dogs

A 2-year field study on kennelled stray dogs living in a highly endemic area of leishmaniasis was designed to evaluate whether deltamethrin-impregnated collars (Scalibor) Protector Band) could confer protection against leishmaniasis in this peculiar setting, and to assess differences in clinical outcomes between collared and uncollared dogs. A cohort of 120 clinically healthy and Leishmania-seronegative dogs was enrolled, 50% of which were collared before the 2003 transmission season, and then re-collared before the subsequent season. Collared and uncollared animals were allowed to live with infected dogs in same groups within the kennel. Follow-up included serological (IFAT) assessment twice a year with parasitological Leishmania confirmation, and clinical evaluation performed every 3 months on seroconverted dogs from both groups. Collar losses during the two seasons were high (35%). About 50% of enrolled dogs were lost at follow-up because of death or they were moved to other locations. After the 2003 season, cross-sectional serological examinations tested positive in 5 out of 44 collared animals (11.4%) and in 14 out of 34 controls (41.2%), with 72.3% estimated protection (P<0.005). After the 2004 season, 7/31 seronegative collared dogs seroconverted (22.6%) compared with 7/17 seronegative controls (41.2%), with 45.1% protection (P=0.15). At the end of the study, the cumulative rate of protection was 50.8% (P=0.005). At the clinical evaluation of 21 seroconverted dogs from both groups, canine leishmaniasis signs were significantly more frequent (90% versus 36%, P=0.017) and rapidly progressive in uncollared than in collared dogs. Reasons for such partial clinical protection in collared dogs may be found in the vector anti-feeding effect of protector bands, resulting in a lower number of infectious bites and, probably, in the reduction of antigenic stimuli necessary to shift toward a non-protective immune response.

Pathological changes in the bone marrow of dogs with leishmaniosis

Bone marrow aspiration smears from 15 dogs naturally infected with leishmania were evaluated. Three of the dogs showed no clinical signs, six had up to three clinical signs and six had more than three. The most common pathological features of the bone marrow were megakaryocytic dysplasia in 10 of the dogs, erythrophagocytosis in eight, erythroid dysplasia in two and emperipolesis in two. The megakaryocytic and erythroid dysplasia were probably related to an increased number of marrow macrophages producing high levels of tumour necrosis factor alpha and interferon gamma. Six of the dogs with clinical signs showed bone marrow dysplastic features and erythrophagocytosis, suggesting that leishmaniosis could be the unique cause of both conditions.

[Canine leishmaniasis: evolution of the chemotherapeutic protocols]

Dogs are the domestic reservoir for Leishmania infantum (syn.: L. chagasi), the parasite causing zoonotic visceral leishmaniasis (ZVL) in both the Old and New Worlds. In foci of canine leishmaniasis (CanL), symptomatic disease occurs in less than 50% of infected dogs, and is characterized by chronic evolution of viscero-cutaneous signs. Among strategies recommended to control ZVL, detection and drug treatment of infected dogs are usually employed in the endemic countries of southern Europe. However, the conventional antileishmanial drugs successfully used in human therapy, such as pentavalent antimonials, amphotericin B, pentamidine or miltefosine, have low efficacy in the treatment of CanL. In dogs, these drugs induce only temporary remission of clinical signs, do not prevent occurrence of relapses, and often cause severe side effects. Leishmaniotic dogs may be classified into 4 groups: 1) Asymptomatic resistant dogs ("contacted dogs"), 2) Asymptomatic dogs (preclinical), 3) Dogs with minimal signs of leishmaniasis (oligosymptomatic dogs? Chronic form of leishmaniasis?), 4) Dogs suffering from different forms of clinical leishmaniasis (symptomatic dogs). The dog's immunological status and the associated clinical signs may influence the efficacy of antileishmanial drugs. Subjects belonging to groups 2, 3 and 4 should be always treated, in order to reduce their parasite load. Parameters that must be considered before starting the antileishmanial treatment are hemogram, renal and hepatic functions, electrophoretic protein pattern, antileishmania antibody titres, and bone marrow and lymph node parasite load. The most common antileishmanial drugs currently used in Italy to treat CanL are pentavalent antimonials (meglumine antimoniate) and allopurinol, alone or in combination. Other used drugs are aminosidine (syn.: paromomycin), pentamidine, metronidazole and spyramicin. Each drug regimen has different duration, from a few weeks (aminosidine), to a few months (meglumine antimoniate) or several months (allopurinol). One of the most recent drug used in human VL is liposomal amphotericin B (AmBisome--L-AMB), a powerful antileishmanial drug in both experimental murine models and in VL patients. In Italy, L-AMB is now considered the drug of choice for the treatment of human cases. However, in HIV co-infected patients high doses of L-AMB are ineffective in obtaining a radical cure. In dogs, L-AMB treatment rapidly leads to clinical recovery but is uneffective to eliminate the parasites. Drugs containing amphotericin B should not be used in veterinary practice in order to avoid selection of parasites resistant to the drug, as it already occurred for the pentavalent antimonials. Currently, there is not a standard protocol for CanL treatment in Italy, as there is an extreme variability of proposed dosages. Clinical studies on immunotherapeutics and new antileishmanial drugs, such as miltefosine and its derivates, are in progress.

Laboratory evidence that dinotefuran, pyriproxyfen and permethrin combination abrogates Leishmania infantum transmissibility by sick dogs

Dogs are reservoir hosts of leishmaniasis caused by Leishmania infantum and transmitted by phlebotomine vectors. The effect of dinotefuran, pyriproxyfen and permethrin spot-on solution (Vectra®3D, Ceva Santé Animale, Libourne, France) on Leishmania transmissibility by naturally infected dogs via reared Phlebotomus perniciosus, was assessed. Dogs affected by leishmaniasis were submitted to xenodiagnosis and 6 infecting >10% of insects were treated topically on day 0. Antifeeding, insecticidal and anti-transmissibility effects were evaluated through xenodiagnoses performed on days 1, 7 and 28, using individual pre-treatment parameters as control. Feeding and mortality rates were assessed at 24 h, whereas promastigote infection, maturation and burden were assessed up to 96 h post blood meal (potentially infectious rate). On day 1, the anti-feeding efficacy was >95% in 4 dogs, insecticidal efficacy 100% in 4 dogs, and anti-transmissibility effect 100% in 6 dogs. Efficacy rates recorded on day 7 were very similar to day 1. On day 28, anti-feeding and insecticidal efficacy values were much broader, ranging 32.6-100% and 7.7-94.4%, respectively. Potentially infectious insects were recorded from two dogs, with sharp decrease in transmissibility rate as compared with pre-treatment condition. Altogether, Vectra®3D abrogated by >98% the potential Leishmania transmissibility by the examined pool of infected dogs over 1 month.

Tick-transmitted diseases in dogs: clinicopathological findings

In this article we describe the main clinicopathological findings of some tick-transmitted diseases observed in Italy, due to Ehrlichia canis and Babesia canis, and most rarely Anaplasma phagocytophilum and Anaplasma platys. Canine monocytic ehrlichiosis (CME) is a multisystemic disorder that is characterized by various clinical signs. Acutely-infected dogs show various clinical and haematological abnormalities including fever, lymphadenopathy, anorexia, lethargy, depression and thrombocytopenia. Many dogs with CME evolve in to an asymptomatic or chronically symptomatic carrier states. In Italy there are very few cases of Canine Granulocytic Ehrlichiosis (CGE) and all are attributed to A. phagocytophilum. The early manifestations of CGE are usually mild and consist in acute onset of fever and depression with or without thrombocytopenia. Lameness due to polyarthritys is also possible. Other clinical manifestations most rarely described are very similar to those reported in chronic form of E. canis infections. There are very few studies about clinicopathological findings of canine babesiosis in Italy. In our country this infection is caused by Babesia canis (large form of parasite) subspecies B. canis canis and B. canis vogeli. These two subspecies are morphologically indistinguishable. Clinical signs reflect the intravascular and extravascular haemolysis due to the life cycle of the parasite. The most common haematological abnormalities found in canine babesiosis are anaemia and thrombocytopenia. It is important to point out that co-infection between two or more agents is possible. In this case it is very difficult to attribute the clinical signs and haematological and/or biochemical abnormalities to a single specific agent.