The single film that composes the Prentice Collection, Similium Damnosum – Vector of Onchoceriasis, details a 1959 attempt by the Ugandan Ministry of Health to control the spread of the disease onchocerciasis. Also known as ‘river blindness’, onchocerciasis is caused by the presence in the body of a nematode worm, Onchocerca volvulus, the females of which release thousands of tiny offspring per day into the host body. Though the adult worms live within the skin, the microscopic worm larvae (‘microfilariae’) travel through the body and eventually die, at which time they cause itching, depigmentation, lymphatic problems, and blindness (www.who.int). Attempts to control the disease focussed on the aquatic larval stage of the eponymous Similium damnosum fly (commonly known as the ‘Mbwa [dog] fly’, on account of its painful bites), a blood-eating fly that is the major vector of the disease. In Uganda, the fly was found to breed in ‘astronomical numbers in the many rapids which characterise the course of the Nile between Lake Victoria and Lake Kyoga’ and the affected areas suffered onchocerciasis infection rates of close to 100% (Prentice: shot list in BECM accession notes).

The particular control programme shown in the film was initiated during 1959, in order to protect the workers that would be constructing a planned hydro-electric power station at Karuma Falls, on the Victoria Nile. Control of the fly would protect labourers from both the irritation of the fly-bites (tests in the area suggested a bite-rate of 300 bites per hour) and the danger of onchocerciasis infection. Mr. Prentice, then the Senior Entomologist (Vector Control) in the Ugandan Ministry of Health, was in charge of the project. It was found that the 85km stretch of the Nile near the projected power-station – the ‘Kabalega’ Nile below the Murchison Falls, ‘simply a canal characterised by rapids interspersed with long quiet pools’ – was also the sole breeding point for the fly in the area, making effective control a real possibility (Prentice: papers in accession notes).

Figures given by Mr. Prentice in a paper on river blindness that was submitted to the BECM with the film (‘Onchoceriasis Control Programme in Uganda’: undated, henceforth OCPU) suggest that applications of DDT earlier in the 1950s had significantly reduced fly numbers in some areas, and a note in the May 1974 issue of the British Medical Journal credits Prentice’s colleague, G. R. Barnley, with having largely controlled the disease on the Ugandan Nile (Prentice, OCPU, 8; BMJ,1974, 401-2). The method of control was release DDT dissolved in fuel oil into the rivers above areas where the filter-feeding fly larvae were concentrated. Earlier trials had established that relatively low concentrations – between 0.2 to 0.5 parts per million – were enough to eradicate Similium larvae, apparently without causing serious ecological damage to the river, though he does note that after the treatments shown in the film algal blooms covered rocks and vegetation (Prentice, op.cit., 6); Holden (1984), in her account of Barnley’s earlier attempt at Similium control, reports that there was ‘no time for ecological investigation’ (Holden, 1984, 163). According to the figures supplied by Mr. Prentice, over 10,000kg of DDT, mixed with fuel oil, was released into the Victoria Nile between 1952 and 1961; despite this, and despite Barnley’s earlier success, he in fact indicates that the control programme shown in the film was rather unsuccessful, and was in any case abandoned when the Government chose not to press ahead with the dam and power plant (ibid., 5-6, 8).

It seems from Mr. Prentice’s notes that the film was intended for lay (probably African) audiences, in order to disseminate information about Government measures to control the fly; a letter in the accession notes mentions ‘unsophisticated audiences’, and the film was screened at 16fps in order to allow time for explanatory commentary. It is also possible that the films were used for training purposes. An earlier film on the same subject was also made by Mr Prentice; shot in 1957, in a different area, it was titled ‘Onchoceriasis and the Control of the Mbwa Fly’, and detailed an earlier fly control scheme, this time centred on protecting the staff of a ‘projected Coffee Research Station’ near Mount Elgon. It is noteworthy that both the control projects he was part of did not have the welfare of local people as a primary concern, and rather were focussed on protecting the staff and workers on projects relating to the colonial presence. A shot list is held at the BECM, though there is no copy of the film; it apparently featured scenes of the Entomology team explaining the disease and its vectors to local people and representatives of the Local African Government, and various sequences of the control programme itself.