Onchocerciasis as a risk factor for night blindness

Area of Science:

• Ophthalmology
• Infectious Diseases
• Public Health

Background:

• Reported night blindness (RNB) prevalence in the Kaduna State, Nigeria Onchocerciasis focus was 12.9%, significantly higher than the national average (1%) and a control non-onchocercal community (0.83%).
• Vitamin A deficiency was not identified as a cause for the elevated RNB rates in this population.

Purpose of the Study:

• To investigate the risk factors associated with reported night blindness (RNB) in an onchocerciasis-endemic area of Kaduna State, Nigeria.
• To determine the contribution of onchocerciasis infection and its ocular manifestations to the prevalence of RNB.

Main Methods:

• Analysis of baseline data from phase three ivermectin trials (1988-1995) involving 6831 subjects in the onchocercal zone and 1563 in a control zone.
• Ordinal logistic regression was employed to assess the relationship between microfilaria load and the likelihood of RNB.
• Evaluation of ocular onchocerciasis lesions, including optic nerve disease (OND), sclerosing keratitis, and chorioretinitis, in relation to RNB.

Main Results:

• The prevalence of RNB and its associated odds ratio increased with higher microfilaria loads.
• Subjects with onchocerciasis-related ocular lesions were significantly more likely to report night blindness.
• Optic nerve disease (OND), often onchocerciasis-related, was the single most common associated pathology, accounting for 30% of RNB cases.

Conclusions:

• Onchocercal infection is likely responsible for the excess reported night blindness observed in this Nigerian focus.
• Ocular manifestations of onchocerciasis, particularly optic nerve disease, are significant contributors to night blindness in endemic regions.