Little fleas have lesser fleas

Hugh Pennington

The announcement on 26 October that the Wellcome Trust, the Gates Foundation and the UK, US and Brazilian governments will spend $21.7 million over the next two years releasing Aedes aegypti mosquitoes infected with Wolbachia in Rio de Janeiro and Medellín is excellent news.

Wolbachia, a bacterium that lives in the reproductive systems of insects and worms, is one of the commonest parasites in the world. In some of its invertebrate hosts it either kills males or feminises them. For others, infection with it is essential for fertility. Discovered in 1923 in the ovaries and testes of mosquitoes from Boston and Minneapolis, it remained an entomological curiosity for half a century before its importance began to be realised. Now it has its own website, and the Anti-Wolbachia Consortium, A-WOL, is funded by the Gates Foundation.

Wolbachia plays a crucial role in the causation of river blindness. When a person is infected by the parasitic worm Onchocerca volvus, which is in turn infected by Wolbachia, their immune system focuses (ineffectually but with bad side-effects) on the bacterium rather than the worm. Attacking it with antibiotics might be the best curative approach. In mosquitos, however, Wolbachia blocks the replication of Zika, dengue and chikungunya viruses.

S. Burt Wolbach was born in 1880. In his youth he rode with cowboys in Nebraska. He was a crack shot, and although being called a pathologist – and sometimes a morbid anatomist – was a naturalist of the best and most useful variety. He was joint head of the Red Cross Typhus Research Commission to Poland in 1920. It ran wards at the St Stanislaus Typhus Hospital in Warsaw, studied 181 cases, and conducted 39 post mortems. The Commission Report says:

The lice employed in this study were taken to Warsaw from areas in North America and in Great Britain, where typhus is not endemic, and were fed upon members of the Commission during the entire periods of the research.

Studies using the lice showed unequivocally that they transmitted the causative agent, Rickettsia prowazekii. Wolbach received the Order of Polonia Restituta. His work had not been without risk. The Battle of Warsaw, the climax of the Polish-Soviet War, started on 12 August. The commission was still recording the results of experiments on 25 July. And the commissioners dedicated their report to the memory of the seven typhus investigators who had died as a consequence of their researches, including Stanislaus von Prowazek and Howard Ricketts. Wolbach’s focus on insect bacteria continued after his typhus work. It led directly to his discovery, with an entomological colleague, of Wolbachia.