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

Abstract

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.

Global Distribution of Canine Visceral Leishmaniasis and the Role of the Dog in the Epidemiology of the Disease

“…Thus, in addition to the control measures recommended by the Ministry of Health, a vaccine for prophylactic purposes was commercially available until 2015 [276]. The sale of LeishTec ® , the only vaccine available in Brazil, was suspended in 2023.…”

“…The sale of LeishTec ® , the only vaccine available in Brazil, was suspended in 2023. The effectiveness of currently marketed vaccines sold on the European market, CaniLeish ® and LetiFend ® , is from 68,4% and 72%, respectively [277,278], and the levels of protection provided by immunization are not sufficient to prevent infection by L. infantum [17,276,279]. Furthermore, even when vaccinated, dogs can be a source of parasites for sandflies and, consequently, for other dogs and humans [280].…”

New Approaches to the Prevention of Visceral Leishmaniasis: A Review of Recent Patents of Potential Candidates for a Chimeric Protein Vaccine

“…However, these control measures have limitations and present a challenge to reducing the number of canine and human cases [ 19 , 20 , 21 ]. In this context, the search for the development of effective vaccines against leishmaniasis becomes essential to improving disease control measures worldwide [ 22 , 23 ].…”

“…Some of these trials are in progress to characterize the protective immunity of candidates for use in a canine vaccine against L. infantum infection, including live or dead Leishmania parasites, purified Leishmania antigens, live recombinant bacteria expressing Leishmania antigens, and antigen-encoding DNA plasmid [ 26 , 27 , 28 , 29 , 30 ]. Recently, sandfly antigens have been considered as an important approach to blocking the transmission of VL from infected dogs [ 23 , 31 , 32 , 33 ].…”

“…The study of susceptibility and resistance biomarkers in CVL could guide the search for a vaccine capable of inducing a protective response. According to this logic, an ideal vaccine against CVL should have immunological features that include the elicitation of a long-lasting cell-mediated immune response that contributes to controlling the infection [ 21 , 23 , 31 , 42 ].…”