Project Topic {Seasonal Variations In Human Onchocerciasis Transmission By Black Flies}

Project Topic {Seasonal Variations In Human Onchocerciasis Transmission By Black Flies}

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Seasonal variations in human onchocerciasis transmission by black flies (Simulium Damnosum s. I.) In a forest area of cross river state, Nigeria is now available.

Seasonal Variations In Human Onchocerciasis Transmission By Black Flies

 

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Seasonal Variations In Human Onchocerciasis Transmission By Black Flies

Abstract On Seasonal Variations In Human Onchocerciasis Transmission By Black Flies

Observations on seasonal variations in onchocerciasis transmission by Simulium damnosum sensu lato were made in a study carried out in Kwa Falls, Aningeje in Akamkpa LGA (a typical forest area) of Cross River State, Nigeria. The study was carried out for three months of the rainy season (August, September and.October, 1999) and three months in the dry season (November, December, 1999 and January, 2000). Black flies were caught on five consecutive days of each month by two flycatchers working alternate hours for a total of eleven hours in a day (07 hr. — 1800 hr.).

 

The black flies caught were dissected fresh in the field to determine the physiological age (parity). Parous flies were stained with Mayer’s Haemalum and dissected to determine -the infectionrates (percentages) due to Onchocerca volvulus. During 30 days of black flies catching, a total of 7,403 S. damnosum s. |. vectors were attracted io man. Out of this figure, 230 (3.1%) black flies were parous. More black flies were caught in the rainy season than in the dry season. This was also true of the parous black flies identified. The infectionrates (percentages) averaged 9.4.7. The problem of onchocerciasis in the study area is more of a biting nuisance by the vector.

Keywords: Simulium damnosum, Black flies, Human onchocerciasis, Dry Season, Rainy Season, Forest

INTRODUCTION

Humen onchocerciasis (River blindness) is a parasitic disease of immense public health importance in view of the medical and socioeconomic oroblems associated with ithe disease. A parasitic nematode worm, Onchocerca volvulus that causes itching and disfiguring skin disease, serious eye lesions and blindness in countries wnere the disease is endemic, causes oenchocerciasis. It also causes abandonment andprevention of cultivation of fertile lands in endemic communities (Taylor et al., 1990, Edungbola & Parakoyi, 1991, Wigg, 1993, Bassanaz et al., 1994, WHO, 1995a, WHO, 1995b, WHO, 1995c).

 

In addition, onchocerciasis could result in such important complications as onchocercomata, hanging groins, hernia and elephantiasis (Edungbola et al., 1991, Botto et al., 1997).

 

Onchocerciasis is transmitted from an infected human to a no-infected one by the bite of the infected black fly known to naturalists as Simulium damnosum (Tsalikis, 1993). In West Africa and East Africa, the predominant species is Simulium damnosum complex, which coexist with other species such as S. sirbanum, S. sanctipauli and S. soubrense (Braide, 1996).

 

In Nigeria, Simulium species are responsible for the prevalence of onchocerciasis. The disease varies in endemicity in the endemic States including the Federal Capital Territory with sporadic infections in others (WHO, 1995a). In Cross River State, Nigeria, S. damnosum complex was incriminated as the main vector of onchocerciasis. This complex was made up of the following Simulium species: S. damnosum, §S. alcocki, S. cervicornutum, _ S. unicornutum and S. impukne (lboh & Braide, 1987).

 

Cytotaxonomic studies of the S. damnosum complex from different parts of Nigeria have revealed the presence of the five cytospecies, these include: S. damnosum sensu stricto, S. sirbanum, S. squamosum, S. yahense and S. soubrense (including the Beffa form). In these studies, the biogeographical distribution of the sibling species was mostly similar to that observed further west of the Onchocerciasis Control 15 Atting, Ejezie, Braide, Opara, and Ekwe

Programme (OCP) area, although geographic variation was recorded in S. sgamosum s. str. and S. sirbanum (Mafuyai et al., 1996). Biting by these black flies occurs out-doors at almost any daylight hour, but each species of black fly may have its preferred times of biting (Awolola and Ogunrinade, 4996, Adewale et al., 1996). A study conducted in Obubra LGA, Cross River State, Nigeria revealed that the biting density of Simulium vary with the time of the day (lboh & Braide, 1987). In addition, researchers working in different countries of the world have observed that irrespective of the posture of the catchers, the legs and any exposed part of the body nearest to the ground are the preferred biting sites of Simulium. Variations have also been observed in the monthly proportions of S. damnosum s. |. biting various body regions (Iboh & Braide, 1987, Adebote, 1990).

 

The focus of this present study was to observe the biting behavior of S. damnosum s. |. and also to measure some entomological indicesof human onchocerciasis transmission in the forest area of Cross River State, Nigeria during two distinct seasons (that is, rainy and dry seasons). The findings of this study will definitely contribute to improved planning, effective monitoring and evaluation of the progress of control programmes.

 

MATERIALS AND METHODS

STUDY AREA/SITE

The study areais located in the Cross River State which is situated within the Cross River Basin, between latitude 5° 32′ and 4° 27′ north and longitude 7° 50′ and 2° 20′ east. The study was carried out in Kwa Falls, Aningeje in Akamkpa LGA. This study area is a typical forest area with numerous plantations including palm, rubber, cocoa etc. The area is about 68 km eastward from the State Capital, Calabar. Cross River State experiences two climatic seasons, the rainy season from May to October and the dry season from November to April.

 

In this State, there is an all year round rainfall of about 350 mm along the coastal area. Rainfall in the hinterland is between 120 mm and 200 mm annually with maximum precipitate occurring from July to September. The State’s ambient temperature remains high throughout the year (22.4°C — 33.2°C). Its relative humidity is high (60% – 93%). The right and left bank tributaries of the Cross River drain the State.

 

ADULT BLACK FLIES COLLECTION

  • Two trained flycatchers drawn from the study area

working alternate hour from 0700 hr. ~ 1800 hr. caught adult black flies. The study was conducted in three months of the rainy season (August to October, 1999) and three months in the dry season (November, 1999 to January, 2000). A total of 30 days (that is, five days a month) were used for black flies catching spread over the six months period of field studies. Flies were captured before they settled to feed by flycatchers dressed in knickers or with trousers folded up to the knee level using glass-catching tubes.

 

DISSECTION AND IDENTIFICATION OF ADULT BLACK FLIES

The black flies captured were immediately dissected fresh in the field to determine their physiological age (parity) according to Mokry (1980). Each fly dissected was first anaesthetized with chloroform and placed on a glass slide in a normal saline solution. Where it was not possible to dissect all the flies caught, they were brought back to the laboratory alive, in perforated collecting tubes with a piece of cotton wool soaked in 1% glucose solution (Iboh & Braide, 1987, Mafuyai et al., 1997, Okon et al., 2002).

 

RESULTS

During the study, a total number of 7,403 black flies were caughtfor parity. Out of this number, 5,411 flies were for the rainy season while 1,992 flies were for the dry season (Tables 1 and 2). The parous flies were 53(2.7%) in the rainy season and 30 (4.7%) in the dry season. The biting densities, infectionrates and transmission potentials of O. volvulus by black flies for rainy and dry seasons are also shown on Tables 1 and 2.

 

The infection rate was 7.5% during the rainy season and 6.2% in the dry season. The infectivity rates were 5.7% and 3.3% in the rainy and dry seasons, respectively. The totaltransmission potentials were 16 and 3 for the rainy and dry seasons respectively.  16 Atting, Ejezie, Braide, Opara, and Ekwe Afr. J. of Appl. Zool. & Environ. Biol. 2005. Vol. 7

 

Table 1: BITING DENSITIES AND TRANSMISSION POTENTIALS OF Onchocerca volvulus by Simullum damnosum s. |. AT KWA FALLS, ANINGEJE (A FOREST AREA) DURING 30 MANOF COLLECTION FROM AUGUST — OCTOBER 1999 (RAINY SEASON)
Data on Months of collection Total/ August | September | October | Average 1999 1999 1999
No. of black Flies
  1. Caught1,943 1,906 1,562 5,411
  2. Parous 53 53 77 183
  • With 1* or 2™ or 3™ stage larvae in the thorax 4 6 5 15
  • With infective larvae* of 3 (2.0) 4 (1.4) 2 (2.1) 9 (5.5) O. volvulus (3 stage larvae in the head)

 

 

Rate (Percent):

  • Parous 2.7 2.8 4.9 3.4
  • With 1™ or 2™ or 3″ stage larvae in the thorax 7.5 113 6.5 8.2
  • With infective larvae of O. volvulus (3″ stage 5.7 7.5 2.6 4.9 larvae in the head) Transmission potential + 6 6 4 16/5
  • Average number of infective larvae per infective black fly in parentheses.
  • Total number of infective larvae available for transmission rounded off (that is, product of infective biting density and average number of infective larvae per infective black fly).

 

 

Table 2: BITING DENSITIES AND TRANSMISSION POTENTIALS OF Onchocerca volvulus by Simulium damnosum s. |. AT KWA FALLS (A FOREST AREA) DURING 30 MANOF COLLECTION FROM NOVEMBER 199 ~— JANUARY 2000 (DRY SEASON)
Data on Months of collection Total/ November | December | January | Average 1999 1999 2000
No. of black Flies
  • Caught638 655 699 1,992
  • Parous . 30 9 8 47
  • With 1* or 2™ or 3” stage larvae in the thorax 2 1 2 5
  • With infective larvae* of O. volvulus (3™ stage 1 (1.0) 1 (1.8) ) 2(2.8)
larvae in the head)

 

Rate (Percent):

  • Parous 4.7 1.3 1.1 2.4
  • With 1″ or 2™ or 3° stage larvae in the thorax 6.7 11.1 25.0 10.6
  • With infective larvae of O. volvulus (3™ stage 3.3 11.1 0 4.3

larvae in the head) _

Transmission potential + 1 2 0 3/1

  • Average number of infective larvae per infective black fly in parentheses.
  • Total number of infective larvae available for transmission rounded off (that is, product of infective biting density and average number of infective larvae per infective black fly).

 

DISCUSSION

The results from this study significantly confirm seasonal variations in human onchocerciasis transmission by the vector, S. damnosum s. I. in the forest area of Cross River State, Nigeria. In this forest area, the black flies show serious biting nuisance. This biting nuisance was greater in the rainy season than in the dry season. The bites of these blood sucking adult female flies are not only a source of discomfort to the villagers who regularly bathe, fetch water and wash their waresin the stream around the Kwa Falls, but also to the oil palm farmers and fishermen who engage in their chosen occupations in and around the Falls.

 

The Daily Biting Rate (DBR) and the Monthly Biting Rate (MBR) were higher in the rainy season than in the dry season. This finding agrees with that of (Cheke et al., 1997) working in Bioko island of Equatorial Guinea. This led to the conclusion that, due to restricted distribution of S. damnosum complex in dry season, vector eradication may be feasible. The Monthly Transmission Potentials (MTP) had mix distribution, oscillating between low 17 Atting, Ejezie, Braide, Opara, and Ekwe and high in the study site. These potentials were higher during the rainy season than during the dry season. The overall proportion of parous flies caught was higher in the rainy season than in the dry season.
In Kwa Falls, the lower transmission potentials compared to the high number of female adult black flies caught strengthens the argument for high degree of biting nuisance by the black flies. This proportion differs from what was obtained in the study carried out at five sites across the Guinea Savanna and Montane areas of Nigeria (Mafuyai et al., 1997). However, the overall infection and infectivity amongst parous flies were higher in the dry season than in the rainy season. These later findings are in consonant with that made by Mafuyai et al. (1997) studying in Nigeria. The results from the study site will be better appreciated when one considers the fact that Kwa Falls was completely flooded in the month of October 1999. This incident brought about a reduced productivity of existing breeding sites during the rainy season.
The seasonal changes in the rates of infected and infective flies in the study site are indication of changes in the flies’ contact rates with infected people. Such changes could be mediated by variations in human behavior, such.as a higher proportion of people visiting the riverside in the dry season or by increased anthropophily of the flies (Cheke et al., 1992). In the study area, there was less human activity during the rainy season, especially in the month of October 1999 when the rains were very heavy. Intensive human activity was however recorded in November and part of December 1999 when the rains had gone down drastically. These months happen to fall within the farming season and oil palm harvesting period.

 

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