The rise of modern medicine, alongside economic and infrastructure development, is often credited for the reduction of infectious diseases and the subsequent raise in life expectancy across many nations. Since individuals live longer and have more readily access to high-caloric foods, chronic diseases associated with obesity and age are becoming more prevalent. Yet, for many societies worldwide infectious diseases have not abated and continue to be the top causes of quality of life reduction and death. In 2013, infectious diseases killed 9.2 million people worldwide, the vast majority of them in Africa, South Asia, and Central and South America. This year’s Nobel Prize in Physiology or Medicine is a stark reminder of the importance of continuing to fight such diseases, as the prize acknowledged developments to treat them and the need to continue to towards their eradication. The 2015 Nobel Prize in Physiology or Medicine was awarded to Dr. William C. Campbell and Professor Satoshi Ōmura for their joint discovery of a therapy against roundworm parasites, and to Professor Youyou Tu for her discovery of treatment for Malaria.
Treating roundworm parasites
Parasitic roundworms, invertebrates with long, round bodies that range from several centimeters long to microscopic lengths, are much more common than most people would realize. While they are more prevalent in Sub-Saharan Africa, Asia, and Central and South America, they are present worldwide. However, their ability to cause infection and disease is aggravated by a lack of clear water supply, lack of access to healthcare services, and a lack of education and availability of sanitation measures. Thus, these diseases disproportionally affect the poorest populations.
African River Blindness (Onchocerciasis) is caused by the filarial larvae of the worm Onchocerca volvulus through the bite of a female blackfly, commonly found near rivers. The larvae penetrate into the subcutaneous tissue where they can mature to adult worms, which can measure up to 50 cm and live for 18 years. Inside the host’s body, the mature worms can mate and release thousands of eggs every day. These eggs migrate through the body to cause several skin conditions, but if they reach the eyes they can cause blindness through chronical inflammation of the cornea. It is estimated that about 25 million people are currently infected from this parasite. On the other hand, Lymphatic Filariasis is generally caused by three parasitic worms: Wuchereria bancrofti, Brugia malayi, and Brugia timori. These are transmitted into the human body through the bite of infected mosquitoes, inside their new host they can infect the lymph nodes and damage lymphatic vessels blocking the flow of lymph and causing edemas, often in the lower part of the body. Lymphatic Filariasis, also known as Elephantiasis tropica, has affected bout 120 million people worldwide and around one billion more are at risk of contracting the disease.
Satoshi Ōmura isolated a strain of the bacteria Streptomyces commonly from soil samples, later called Streptomyces avermectinius. Afterwards William C. Campbell acquired the strain and discovered that it contained a compound that was effective against parasites in animals. This compound was isolated and named Avermectin, which was later modified into the more active compound Ivermectin and used to treat roundworm parasitic infections in humans. This drug is now listed by the WHO as one of the most important medications in a basic healthcare system. At this point Ivermectin, alongside other efforts, is making the complete elimination of Lymphatic Filariasis and Onchocerciasis worldwide a feasible goal for 2020 and 2025, respectively.
The oldest reports of malaria date to more than 4,000 years ago. It receives its name from the Medieval Italian for “mal aria” meaning bad air. According to the WHO, Malaria is one of the most severe public health problems in the entire world. In 2014, the organization estimated that 3.3 billion people are at risk of contracting the disease, while for many developing countries, mainly in Africa, it is the main cause of death. It is estimated that there are 198 million cases of Malaria and hundreds of thousands of deaths every year. This disease impacts most heavily children and pregnant women in developing countries. The Lancet once reported that direct costs of this disease can represent about US$12 billion a year.
The disease is caused by parasitic protozoans from the genus Plasmodioum falciparium, which is transmitted by the female Anopheles mosquito. Once inside the body, the parasites travel through the blood into the liver were they can grow and reproduce into thousands of merozoites. The liver cells rupture and release the merozoites into the blood stream where they infect and destroy blood cells releasing even more merozoites to continue the cycle. Malaria causes fever, vomiting, fatigue, and in extreme causes seizures, coma, and death. Early treatments against malaria include quinine and chloroquinine. These were extremely useful until the emergence of resistant strains of Plasmodioum falciparium, which contributed the increase in the infection and death from the disease in the 1960s.
Youyou Tu and her team analyzed more than 2,000 traditional Chinese herbal medicines until they observed that an ether extract of the plant Artemesia annua was highly effective in killing the parasites of infected mice and monkeys. The active compound was isolated and named Artemisinin, this medication was the first of a new class of antimalarial agent which kill the parasite in the early stages of its development. Artemisinin is now used alongside other antimalarian drugs and, alongside vector control of mosquitoes through nets and insecticides, has helped to reduce the mortality rate of malaria worldwide.