The Epidemiological Implications of Deer Fly Nuisance Biting and Transmission of Loiasis in an Endemic Area in Southeastern Nigeria

This work was aimed at determining the epidemiological implications of deer fly biting in Southeastern Nigeria and ascertaining the circadian and monthly biting pattern and the transmission potential of Chrysops in the area. Human-landing catches were carried out for 52 weeks by a catching team of four. A total of 930 female Chrysops sp. was caught; biting peaked during the months of June through August. The highest monthly biting rate (MBR) was 353 bites per person per month in July 2006. The annual biting rate (ABR) was 3,317 bites per person per year. The overall infective rate was 3.8%. A total of 314 L3s was recorded with a mean of 9.8 L3s per infective Chrysops. The highest monthly transmission potential (MTP) was 389 infective bites per month observed in July 2006. The annual transmission potential (ATP) was 1,265 infective bites per person per year. Parous rate was 29.3% and was higher during dry months of October through February. The circadian biting activities showed two peaks: between 07:00 and 10:00 hours and between 15:00 and 17:00 hours. The epidemiological implications of deer fly biting in the area are multifaceted. Resources must not be spared in bringing an end to their menace. 1. Introduction Loiasis is a globally important human filarial infection found in tropical rainforest Africa afflicting about 13 million persons [1]. It is caused by a Nematode Loa loa and transmitted by Chrysops. Visitors to Loiasis endemic areas tend to be symptomatic, with a predominance of “allergic symptoms,” including pruritus, urticaria, and transient, migratory angioedema, or Calabar swellings, whereas majority of infected people from endemic areas are asymptomatic despite high levels of microfilariae detectable in the peripheral blood. However, migration of the adult worm across the conjunctiva, eye worm, occurs with equal frequency in natives and visitors to endemic areas. Although this migration is often associated with a transient intense edematous conjunctivitis, most episodes resolve without sequelae. Other human filarial parasites found in Nigeria and Africa are Wuchereria bancrofti, Onchocerca volvulus, Mansonella perstans, and M. streptocerca [2, 3]. L. loa infection has been recorded in Nigeria since, at least, four decades ago [4] and has persisted in various parts of the country, especially in the rural areas. In the western part of Nigeria, L. loa microfilaraemia is prevalent and well distributed especially in the vegetational zones [5–8]. In the savannah zone the prevalence is relatively lower [9]. Prevalence of L. loa microfilaraemia