From 2000 to 2017 the Sabin Vaccine Institute partnered with the Texas Children’s Hospital Center for Vaccine Development at Baylor College of Medicine in Houston, Texas to develop safe, effective and low-cost vaccines for infectious and neglected tropical diseases. Baylor College of Medicine and Texas Children’s Hospital Center for Vaccine Development continue this research as of May 2017.

Organism: Onchocerca volvulus
Vaccine Candidate: Ov-103 and Ov-RAL-2
Stage of Development: Preclinical
Years Sabin conducted research: 2015-2017

Onchocerciasis, also known as river blindness, is the world’s fourth leading cause of preventable blindness and infects 26 million people, 99 percent of whom live in sub-Saharan Africa.

About the Vaccine

From 2015 to 2017, the Sabin Vaccine Institute Product Development Partnership (Sabin PDP) was part of The Onchocerciasis Vaccine for Africa (TOVA) Initiative, a global partnership of onchocerciasis researchers in the United States, Europe and Africa established in 2015. The Initiative traces its origins to initial support during the 1980s and 1990s from the Edna McConnell Clark Foundation. As of May 2017, Baylor College of Medicine and the Texas Children’s Hospital’s Center for Vaccine Development continue this research.

The project aims for the development and global accessibility of a low-cost, safe and effective vaccine for onchocerciasis in Africa. The TOVA Initiative is exploring two candidate antigens for a preventive vaccine for use in young children and a therapeutic vaccine for children and adults with Onchocerca volvulus infection. 

Baylor College of Medicine researchers are investigating two promising candidate antigens, Ov-RAL-2 and Ov-103. These antigens were selected from a total of eight candidates based on their ability to induce protective immune responses in small animal models of infection. Importantly, both antigens were recognized by antibodies from individuals that are believed to be protected from onchocerciasis. This indicates that the immune response generated by these two antigens may be associated with protection from infection.

About Onchocerciasis

Onchocerciasis, also known as river blindness, is a disease caused by the parasite Onchocerca volvulus and transmitted by infected blackflies living near rivers or fast-moving streams in Africa. Onchocerciasis is the world’s fourth leading cause of preventable blindness and infects 26 million people, 99 percent of whom live in sub-Saharan Africa. 500,000 of those infected with onchocerciasis are severely visually impaired, and another 270,000 have been rendered permanently blind by the disease.

Following a bite from an infected blackfly, O. volvulus larvae enter the skin at the bite site and form nodules. There, the larvae mature to adults and release millions of microscopic larvae – called microfilariae – into the surrounding human tissue. The larvae move throughout the body and ultimately die, contributing to a variety of health conditions including skin rashes and depigmentation, debilitating itching, visual impairment and blindness. 

Why We Need a Vaccine

An effective vaccine would represent an important tool in the treatment and prevention of onchocerciasis in Africa, and may contribute to the control and elimination of the disease.

The World Health Organization has set a goal of eliminating onchocerciasis by 2025. However, the growing consensus is that onchocerciasis in Africa will not be eliminated within proposed timeframes using MDA alone In 2012, The London Declaration on Neglected Tropical Diseases called for sustained efforts to expand and extend programs to ensure the necessary supply of drugs and other interventions to help control human onchocerciasis in order to meet the elimination goal. Development of new tools such as a vaccine may be needed to ensure onchocerciasis elimination and remove the risk of reintroduction of the infection to areas where elimination may have been achieved.

The current drug treatment for onchocerciasis, ivermectin, primarily targets O. volvulus larvae and has minimal effect on the adult worms. As a result, ivermectin must be administered annually to 65 percent of the population until the adult worm finishes its natural lifespan in the human host – approximately 17 years – in order to eliminate onchocerciasis in an endemic area. This renders elimination through drug treatment infeasible in many endemic areas. For example, elimination in endemic areas of Central Africa would take 1.15 billion treatments over the next 30 or more years.

Additionally, ivermectin cannot be given to individuals living in areas endemic for loaisis, as it can cause severe side effects in a patient with a heavy loa loa infection. An estimated 12 million Africans live in areas co-endemic for onchocerciasis and loaisis; thus, an onchocerciasis vaccine might be especially important for use in these areas. A recent modeling study revealed that a preventive vaccine administered to preschool-aged children as part of the Expanded Program on Immunization (EPI) could reduce onchocerciasis disease burdens in loiasis-endemic areas, and simultaneously prevent the re-emergence of onchocerciasis in areas where drug treatment had been halted. 

 

Photo courtesy of the National School of Tropical Medicine