Leishmaniasis is a group of parasitic diseases that takes its name from William Leishman, a British Army physician who first reported the parasite in 1903. Researchers have since identified more than 20 species of Leishmania but have struggled in the many decades since then to find effective treatments, safe diagnostic tests and, above all, a vaccine to prevent a disease that causes considerable morbidity and mortality. Recently, though, determined scientists, funders, manufacturers and others around the world are seeing more light at the end of the tunnel in battling this very difficult target.
Leishmaniasis is transmitted by sand flies and causes 59,000 deaths annually—mostly in children. An estimated two million new cases occur each year. Twelve million people are currently infected, and 350 million are at risk.
In the last decade, the number of recorded cases has risen sharply, attributed to rising HIV/AIDS co-infections, climate change that has expanded sand fly habitats, and increasing numbers of people who travel with their pets, since dogs act as a reservoir in some areas.
Leishmaniasis takes three main forms: cutaneous, which causes skin lesions; mucosal, which attacks mucous tissues; and visceral leishmaniasis (VL), a systemic disease that is fatal if untreated. Most of the 500,000 annual cases of VL occur in India, Nepal and Bangladesh, but the disease is also important in East Africa, South America, and the Mediterranean region.
Current treatments are expensive, toxic, impractical, or ineffective in some geographical regions. Efforts at vector control have largely proven to be impractical, limited in efficacy, and risky to public health in the case of repeated insecticide applications.
The rise in cases of leishmaniasis and emergence of drug resistance has brought new urgency to research for a vaccine, for better treatments, and for even better diagnostic tests.
New Hope for a Vaccine
The search for an effective leishmaniasis vaccine goes back some 70 years, and WHO has declared development of a leishmaniasis vaccine to be a priority. To effectively prevent the fatal form of the disease globally, vaccines are needed for both humans and dogs.
IDRI developed the world’s first defined vaccine candidate for leishmaniasis and the first recombinant vaccine for canine leishmaniasis. Recently, with funding from the Bill & Melinda Gates Foundation and the National Institutes of Health (NIH), IDRI has tested newer, recombinant proteins together with advanced adjuvants (developed by IDRI) and identified effective vaccines in mouse models. Separate vaccine candidates have been developed for humans and dogs. In collaboration with teams in the United States, Brazil, Europe and India, these vaccines are being evaluated in humans and dogs for prophylactic efficacy.
In South America and the Mediterranean coast, human VL and canine VL co-exist, and canine VL epidemics tend to precede human epidemics.
“We must control the dog disease to control the human disease,” says Antonio Campos-Neto, MD, PhD, head of the Department of Cytokine Biology at the Forsyth Institute. Campos-Neto is coordinating a two-part canine vaccine trial with IDRI and research institutions in Brazil. “In Brazil, if we control only the human disease, it will come back because dogs are the reservoir.”
Globally, current practices have included ignoring VL infection in dogs, treating the dogs with drugs, or culling infected dogs. A VL vaccine administered as part of dogs’ standard vaccinations would provide a potentially more effective and more humane solution than culling and avoid the potential for resistance arising from using the same drugs in dogs and humans.
IDRI and its partners are optimistic that their vaccine candidate will offer improved efficacy over existing options. Two canine VL vaccines have already been licensed in Brazil and one in Europe by other organizations.
Results from the testing of IDRI’s vaccine in a kennel setting are expected in mid- to late 2012. To date, the study has shown that the vaccine is safe, well tolerated, immunogenic and potentially efficacious in prevention and treatment of diverse forms of leishmaniasis. Dr. Ricardo Fujiwara of the Universidade Federal de Minas Gerais is overseeing the study in Belo Horizonte, Brazil.
Campos-Neto cautions, though, that “in the canine vaccine field, for reasons we don’t understand, for most diseases transmitted by micro-organisms, we may be able to induce good immunity in kennels, but, moving to field trials, the vaccine doesn’t protect.”
For that reason, the next phase of the trial will be field tests, vaccinating pet dogs who are at risk of naturally acquired VL infection. Sponsored by Brazil’s Instituto Butantan, and led by Butantan’s Prof. Isaias Raw, this two-year study is beginning in 2012 in three northeastern cities in Brazil where VL is most endemic. The vaccinated dogs will be monitored for signs of VL.
According to IDRI, the ideal human vaccine for leishmaniasis would be safe and cost-effective, lend itself to a reproducible transferable manufacturing process, produce long-term immunity, provide prophylactic and therapeutic benefits, and protect against more than one form of the disease.
Randall F. Howard, PhD, leishmaniasis project manager for IDRI, says “A human leishmaniasis vaccine should really be effective for more than just the visceral form, which is relatively uncommon. Ideally it should also work for the cutaneous form, which is the most common.”
Franco M. Piazza, MD, MPH, medical director for IDRI, says, “Phase 1 testing began in the United States in January 2012, evaluating the new vaccine candidate in healthy adults. A subsequent phase 1 trial in India is likely to begin later in 2012, working with Dr. Shyam Sundar of Banaras Hindu University and others.” The vaccine for this and future trials in India will be manufactured by Gennova Biopharmaceuticals Ltd., a biotechnology subsidiary of Emcure Pharmaceuticals Ltd., in Pune, India.
Dr. Sanjay Singh, Gennova’s CEO and former head of malaria vaccine antigen research for NIH, says, while this vaccine will be Gennova’s first foray into leishmaniasis, the company is already collaborating with IDRI and many other partners to formulate vaccines for malaria, TB and HIV. In this partnership for leishmaniasis, Singh says, “Gennova’s strength is in recombinant vaccine production, and IDRI’s strength is in adjuvant research and formulation development, so combining these diverse strengths gives a powerful platform to produce vaccines.”
He adds, “India has played a very important role in delivering vaccines at an affordable price in India and in developing countries through WHO and UNICEF. We hope our joint efforts will bring a major breakthrough for the eradication of leishmaniasis.”
A Second-Generation Rapid Diagnostic Test
“One difficulty in managing people with visceral leishmaniasis is that the diagnosis isn’t straightforward,” says Piazza. “It can be confused with other diseases. For instance, it may be clinically difficult to distinguish malaria and leishmaniasis.”
Drawing fluid from the spleen, bone marrow or lymph nodes is the classic way to confirm visceral leishmaniasis—invasive, expensive, painful, potentially dangerous procedures that require expertise and facilities for patient monitoring, potential blood transfusions and surgery. A safe, fast, accurate, low-cost test had long been needed, one that could be administered by field workers at the village level.
The first such rapid diagnostic test (RDT) was based on early research funded by NIH and developed by IDRI with Seattle manufacturer InBios International. Based on a recombinant antigen (rK39), the test can diagnose more than 98 percent of human VL cases with a single blood drop. The introduction of these tests in the last two decades was a game-changing development. “It’s had an immense impact on how to manage these individuals,” says Piazza.
The rK39-based RDTs for human and canine VL are now commercially available worldwide. However, they have proven less sensitive to African VL, so a better test is still needed.
A Rapid Test That Works in East Africa
Drawing on more recent NIH discoveries, IDRI searched for and tested additional antigens under a grant from the Bill & Melinda Gates Foundation. IDRI then began working with manufacturers to create and evaluate second-generation RDT prototypes based on a new VL-specific detection antigen (rK28). To achieve a low-cost RDT despite the small market for an eventual African VL test, some development funds were used to minimize manufacturers’ internal R&D costs.
Laboratory testing with banked sera showed the superiority—greater than 95 percent accuracy—of an rK28 test for African VL in the platforms of several manufacturers, including InBios and ChemBio Diagnostics Systems, Inc. In early 2012, comparative testing to further validate platforms began at endemic sites in Africa. Collaborations with Drs. Roque Almeida (Universidade Federal de Sergipe, Brazil), Dinesh Mondal (International Centre for Diarrhoeal Diseases Research, Bangladesh), and Maowia Mukhtar (University of Khartoum, Sudan), and their staff and partners provided sera for test development. Mukhtar and Drs. Hashim Ghalib (University of Lausanne, Switzerland) and Asrat Hailu (Addis Ababa University, Ethiopia) are validating the new RDT in Africa.
“We are currently developing a protocol for Phase 3 trials of the best rK28 format for detection of active VL in Africa,” he adds. If Phase 3 results are as expected, he says, “This will be a major advance in the application of biotechnology to the control of killer VL.”
Mukhtar and his colleagues in Sudan have worked with IDRI on a new RDT since 2008, contributing scientific knowledge and field experience. He says, “The preliminary evaluation of the rK28 antigens showed very high sensitivity and specificity. The current rK28 tests overcome the difficulties facing accurate and rapid diagnosis of VL in remote endemic areas.”
“Sudan is one of five countries where 90 percent of the annual cases of VL occur,” Mukhtar adds. “The endemic areas of Africa usually are very remote with very weak medical services. The family of VL patients, usually children, has to seek diagnosis and treatment at a far distance that requires traveling for days. The developed rK28 RDT is very simple and can be done in the village, saving cost and time and allowing early diagnosis of VL.”
Among challenges Ghalib has observed are gaps in state-of-the art technologies between north and south, plus dealing with IRB committees in the developing world which have little capacity to handle legal and ethical issues.
The Keys to Cracking a Neglected Killer
The efforts of IDRI and its many collaborators have the potential to advance leishmaniasis research substantially, putting important progress on the horizon for a disease that has plagued humans for centuries but was still not defined 100 years or so ago.
The high caliber of the partnership is one key to the great promise this work holds. Campos-Neto says, “Research like this has to be done with strong collaborations. You have components and a bridge to link them. In the Brazilian studies, it’s a very good match between IDRI, Butantan and Forsyth—a very productive collaboration.” The other partners likewise praise the quality of the partnership.
A deep commitment to fighting neglected diseases is also essential. Ghalib notes, “IDRI, its founder Steve Reed and its collaborators have committed more than 30 years to applying modern technology for the development of cost-effective diagnostics and a vaccine for VL.”
If the results of this research collaboration continue to be positive, that 30-year commitment may soon bring good news to millions worldwide.
By Heather Jameson