On this day in medical history: Sir Ronald Ross’ game-changing discovery about malaria gives rise to World Mosquito Day

By Liz Meszaros, MDLinx
Published August 20, 2018

Key Takeaways

Born in Almora, India, in 1857, Ronald Ross had no early inclinations toward medicine. But at 17, he followed the wishes of his father and joined the Indian Medical Service. In 1874, he began to study medicine at St. Bartholomew’s Hospital Medical College in London. Upon receiving his medical degree from the Royal College of Surgeons of England in 1879, he accepted the post of ship’s surgeon on a transatlantic steamship.

Ross entered the Indian Medical Service in 1881 and continued his studies with a course in bacteriology. He married Rosa Bloxam, with whom he had four children, and returned to Bangalore to serve as a staff surgeon.

At the time, Alphonse Laveran and Sir Patrick Manson—considered the father of tropical medicine—hypothesized that mosquitoes were involved in the spread of malaria. Ross developed an interest in the disease, and despite being an early skeptic, came to believe that malaria parasites could exist in the bloodstream. In 1895, he returned to India and set out to prove this and corresponded with Laveran and Sir Manson regularly on his findings.

On August 20, 1897, while dissecting the stomach of a mosquito, Ross discovered a malaria parasite. He continued his research using malaria in birds as a model. Working with mosquitoes that fed on malaria-infected birds, he observed that malaria parasites developed within the mosquitoes, migrated to the infected bird’s salivary glands, and were thus transmitted to any healthy birds the mosquito subsequently fed upon. In this way, Ross proved that the Anopheles mosquito was involved in the transmission of malaria parasites to humans.

Not one for false modesty, Ross declared that each year, on August 20, an annual observance be held to commemorate this discovery. This became World Mosquito Day, still celebrated each year.

Ross went on to become a professor of tropical medicine at the Liverpool School of Tropical Medicine, and personal chair of tropical sanitation at Liverpool University, where he studied implementing antimalaria efforts in West Africa.

Thus he began far-reaching expeditions—to Ismailia, Egypt; the Republic of Panama in Central America; Greece; and the Republic of Mauritius, off the southeast coast of Africa—in a quest to develop and implement malaria control measures.

After being elected a Fellow of both the Royal College of Surgeons of England and the Royal Society, Ross was awarded the Nobel Prize for Physiology or Medicine in 1902 for his discovery that the malarial parasite Plasmodium relictuma could be transmitted to humans in the bite of infected mosquitoes.

In the same year, Ross was appointed Companion of the Most Honorable Order of Bath by the King of Great Britain, and in 1911, he was knighted and elevated to the rank of Knight Commander of the same Order. In 1910, the Karolinska Institute, Stockholm, conferred an honorary MD degree on Ross. He also became an honorary member of many medical societies throughout the world.

In 1926, the Ross Institute and Hospital for Tropical Diseases was opened in Putney Heath, London, by the Prince of Wales to commemorate Sir Ross’ work. He was named Director in Chief and served at the institute until his death in 1932 after a protracted illness.

In addition to his work on malaria, Sir Ross was also a mathematician, epidemiologist, sanitarian, editor, novelist, dramatist, poet, amateur musician, composer, and artist.


World Mosquito Day

Since the 1930s, the London School of Hygiene & Tropical Medicine has held World Mosquito Day celebrations on August 20th, with the goal of raising awareness about malaria and its prevention and treatment. Many other organizations throughout the world also host events and activities.

For World Mosquito Day 2018, and in honor of Sir Ross and his discovery, here’s a list of the top five deadly diseases that mosquitoes transmit to humans.

  1. Malaria. Malaria is a widespread, potentially fatal disease that causes acute symptoms, including fever, headache, vomiting, and fatigue. Experts estimate that 300-600 million people contract malaria every year, and more than 1 million die. Most cases occur in sub-Saharan Africa, and most fatalities are in children less than 5 years old. Quinine and other anti-malarial agents are available, but patients who are not treated can have disease recurrence months later.
  2. Dengue fever. This viral illness is spread by the Aedes mosquito in areas with tropical and subtropical climates. Symptoms are acute, and include fever, headaches, joint pain, rashes, and eye pain. Some patients can progress to dengue hemorrhagic fever. An estimated 390 million people contract dengue fever annually, for which there is no vaccine and no specific treatment.
  3. West Nile virus. The West Nile virus is spread by Culex mosquitoes worldwide. Most people who are infected do not manifest symptoms, but in those who do, symptoms are usually mild, and can include fever, headache, muscle pain, nausea, vomiting, rash, and fatigue. Rarely, West Nile virus can affect the central nervous system. In the United States, the first case of West Nile virus was discovered in 1999. Since then, about 42,000 cases have occurred, including 19,000 cases of neurological disease and 1,700 deaths.
  4. Yellow fever. Like dengue fever, this virus is spread by the Aedes mosquito. Symptoms include severe fever, headache, and nausea. The mortality rate is 50% and although there is no specific treatment for yellow fever, a vaccine does exist. According to the World Health Organization, between 84,000 and 170,000 cases of yellow fever occur annually worldwide, resulting in as many as 60,000 deaths.
  5. Zika virus. Also transmitted by the Aedes mosquito, this illness was discovered in 1947, and since then few cases have occurred. In 2015, however, Brazil was the site of a Zika virus outbreak. Symptoms are minor, and can include fever, joint pain, rash, and redness of the eyes. Although Zika virus is rarely fatal, it has been linked to microcephaly in infants born to mothers who contracted it during their pregnancy. According to the Centers for Disease Control and Prevention, 5,716 persons were infected with Zika virus as of August 1, 2018, and 37,262 were infected in all US territories.

Other illnesses transmitted by mosquitos include Chikungunya fever, Rift Valley fever, Murray Valley encephalitis, and Japanese encephalitis.  


“Ross and the Discovery that Mosquitoes Transmit Malaria Parasites.” Centers for Disease Control & Prevention. https://www.cdc.gov/malaria/about/history/ross.html. Accessed August 8, 2018.

“Ronald Ross—Biographical.” The Nobel Prize. https://www.nobelprize.org/nobel_prizes/medicine/laureates/1902/ross-bio.html. Accessed August 8, 2018.

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