Transmission-Blocking Vaccines for Canine Visceral Leishmaniasis: New Progress and Yet New Challenges.

Dogs with visceral leishmaniasis play a key role in the transmission cycle of Leishmania infantum to humans in the urban environment. There is a consensus regarding the importance of developing a vaccine to control this disease. Despite many efforts to develop a protective vaccine against CVL, the ones currently available, Leish-tec® and LetiFend®, have limited effectiveness. This is due, in part, to the complexity of the immune response of the naturally infected dogs against the parasite and the complexity of the parasite transmission cycle. Thus, strategies, such as the development of a transmission-blocking vaccines (TBVs) already being applied to other vector-borne diseases like malaria and dengue, would be an attractive alternative to control leishmaniasis. TBVs induce the production of antibodies in the vertebrate host, which can inhibit parasite development in the vector and/or interfere with aspects of vector biology, leading to an interruption of parasite transmission. To date, there are few TBV studies for CVL and other leishmaniasis forms. However, the few studies that exist show promising results, thus justifying the further development of this approach.

Vaccination with Formulation of Nanoparticles Loaded with Leishmania amazonensis Antigens Confers Protection against Experimental Visceral Leishmaniasis in Hamster

Visceral leishmaniasis (VL) is a fatal disease caused by the protozoa Leishmania infantum for which dogs are the main reservoirs. A vaccine against canine visceral leishmaniasis (CVL) could be an important tool in the control of human and CVL by reducing the infection pressure of L. infantum. Despite the CVL vaccine available on the market, the Brazilian Ministry of Health did not implement the use of it in their control programs. In this sense, there is an urgent need to develop more efficient vaccines. In this study, the association between two polymeric nanoformulations, (poly (D, L-lactic) acid (PLA) polymer) loading Leishmania amazonensis antigens, was evaluated as a potential immunobiological agent against VL using golden hamsters as an experimental model. The results indicated that no significant adverse reactions were observed in animals vaccinated with LAPSmP. LAPSmP presented similar levels of total anti-Leishmania IgG as compared to LAPSmG. The LAPSmP and LAPSmG groups showed an intense reduction in liver and spleen parasitic load by qPCR. The LAPSmP and LAPSmG vaccines showed exceptional results, indicating that they may be promising candidates as a VL vaccine.

Nanoformulations with Leishmania braziliensis Antigens Triggered Controlled Parasite Burden in Vaccinated Golden Hamster (Mesocricetus auratus) against Visceral Leishmaniasis.

Leishmaniasis is a widespread vector-borne disease in Brazil, with Leishmania (Leishmania) infantum as the primary etiological agent of visceral leishmaniasis (VL). Dogs are considered the main reservoir of this parasite, whose treatment in Brazil is restricted to the use of veterinary medicines, which do not promote a parasitological cure. Therefore, efficient vaccine development is the best approach to Canine Visceral Leishmaniasis (CVL) control. With this in mind, this study used hamsters (Mesocricetus auratus) as an experimental model in an anti-Leishmania preclinical vaccine trial to evaluate the safety, antigenicity, humoral response, and effects on tissue parasite load. Two novel formulations of nanoparticles made from poly(D, L-lactic) acid (PLA) polymer loading Leishmania braziliensis crude antigen (LB) exhibiting two different particle sizes were utilized: LBPSmG (570 nm) and LBPSmP (388 nm). The results showed that the nanoparticles were safe and harmless to hamsters and were antigenic with the induction in LBSap, LBPSmG, and LBPSmG groups of total anti-Leishmania IgG antibodies 30 days after challenge, which persists 200 days in LBSap and LBPSmP. At the same time, a less pronounced hepatosplenomegaly in LBSap, LBPSmG, and LBPSmP was found when compared to control groups, as well as a less pronounced inflammatory infiltrate and granuloma formation in the spleen. Furthermore, significant reductions of 84%, 81%, and 90% were observed in spleen parasite burden accessed by qPCR in the LBSap, LBPSmG, and LBPSmP groups, respectively. In this way, LBSap, LBPSmG, and LBPSmP formulations showed better results in vaccinated and L. infantum-challenged animals in further reducing parasitic load in the spleen and attenuating lesions in liver and splenic tissues. This results in safe, harmless nanoformulation vaccines with significant immunogenic and infection control potential. In addition, animals vaccinated with LBPSmP had an overall reduction in parasite burden in the spleen, indicating that a smaller nanoparticle could be more efficient in targeting antigen-presenting cells.

Rhipicephalus microplus: An overview of vaccine antigens against the cattle tick.

Rhipicephalus microplus, popularly known as the cattle tick, is the most important tick of livestock as it is responsible for significant economic losses. The use of chemical acaricides is still the most widely used control method despite its known disadvantages. Vaccination would be a safe alternative for the control of R. microplus and holds advantages over the use of chemical acaricides as it is environmental-friendly and leaves no residues in meat or milk. Two vaccines based on the Bm86 protein were commercialized, TickGARD® and Gavac®, with varying reported efficacies in different countries. The use of other vaccines, such as Tick Vac®, Go-Tick®, and Bovimune Ixovac® have been restricted to some countries. Several other proteins have been analyzed as possible antigens for more effective vaccines against R. microplus, including peptidases, serine proteinase inhibitors, glutathione S-transferases, metalloproteases, and ribosomal proteins, with efficacies ranging from 14% to 96%. Nonetheless, more research is needed to develop safe and efficient tick vaccines, such as the evaluation of the efficacy of antigens against other tick species to verify cross-reactivity and inclusion of additional antigens to promote the blocking of the infection and spreading of tick-borne diseases. This review summarizes the discoveries of candidate antigens for R. microplus tick vaccines as well as the methods used to test their efficacy.

Vaccine approaches applied to controlling dog ticks.

Ticks are considered the most important vectors in veterinary medicine with a profound impact on animal health worldwide, as well as being key vectors of diseases affecting household pets. The leading strategy applied to dog tick control is the continued use of acaricides. However, this approach is not sustainable due to surging tick resistance, growing public concern over pesticide residues in food and in the environment, and the rising costs associated with their development. In contrast, tick vaccines are a cost-effective and environmentally friendly alternative against tick-borne diseases by controlling vector infestations and reducing pathogen transmission. These premises have encouraged researchers to develop an effective vaccine against ticks, with several proteins having been characterized and used in native, synthetic, and recombinant forms as antigens in immunizations. The growing interaction between domestic pets and people underscores the importance of developing new tick control measures that require effective screening platforms applied to vaccine development. However, as reviewed in this paper, very little progress has been made in controlling ectoparasite infestations in pets using the vaccine approach. The control of tick infestations and pathogen transmission could be obtained through immunization programs aimed at reducing the tick population and interfering in the pathogenic transmission that affects human and animal health on a global scale.

Synovial fluid as an auxiliary diagnostic tool for different stages of canine visceral leishmaniasis / Líquido sinovial como ferramenta diagnóstica auxiliar da leishmaniose visceral canina em diferentes estádios

ABSTRACT: Leishmaniasis represents a complex of chronic diseases with a broad geographic distribution and a high significance in public health worldwide. The varied clinical signs in conjunction with the low sensitivity and specificity of canine visceral leishmaniasis (CVL) detection methods make diagnosis of the disease complex. Among the several available laboratory tests, studies have suggested that the detection of parasites in synovial fluid (SF) is a good auxiliary tool in the diagnosis of CVL. However, no study has evaluated the influence of the clinical stage of CVL in the detection of Leishmania sp. in SF. This study aimed to evaluate the detection of Leishmania sp. amastigotes in the SF of dogs at different stages of the disease. The negative control group (G1) comprised 12 dogs that tested negative for CVL. Thirty-six other dogs, tested serologically positive for CVL, were divided into two groups: Group 2 (G2), which included animals at stage II of the disease (moderate; n=18), and Group 3 (G3) included animals at stage III of the disease (severe; n=18). The analysis of SF revealed the presence of parasites in six (33.3%) dogs from G2 and in 16 (88.9%) dogs from G3 (p=0.0437). The present research suggested that SF analysis is of high value as a supplementary tool in the diagnosis of CVL. As a new finding, the present study also indicated that this test has a higher sensitivity in animals presenting with more severe stage of the disease.

RESUMO: As leishmanioses representam um complexo de doenças de caráter crônico de alta importância na saúde pública mundial e com distribuição geográfica ampla. A apresentação clínica variada e a baixa sensibilidade e especificidade de alguns métodos para a detecção da doença tornam complexo o diagnóstico da leishmainiose visceral canina (LVC). Entre os diversos testes laboratóriais disponíveis, estudos tem sugerido que a pesquisa de parasitos no líquido sinovial (LS) pode ser uma ferramenta auxiliar no diagnóstico da LVC. Apesar disso, inexistem estudos avaliando a relação entre o estágio clínico da doença e a detecção de Leishmania sp. no LS. Dessa forma, o presente trabalho teve como objetivo avaliar a detecção de amastigotas de Leishmania sp. no LS de cães acometidos por diferentes estádios da doença. Foram avaliados 48 cães, sendo 12 negativos para LVC (grupo controle negativo, G1) e 36 soropositivos. O grupo 2 (doença moderada, G2) incluiu animais classificados no estádio II da doença, enquanto o grupo 3 (doença grave, G3) abrangeu animais classificados em estádio III. Na análise do líquido sinovial dos cães, o parasito foi visualizado em seis (33,3%) cães do G2 e 16 (88,9)% dos cães de G3 (p=0.0437). O presente trabalho sugere que a análise do LS apresenta alto valor como ferramenta suplementar no diagnóstico da LVC. Em adição, o presente estudo indica, pela primeira vez, que o teste apresenta uma sensibilidade maior em animais que apresentam a forma grave da doença.