Comparative Repellent Activities of Some Plant Extracts Against Simulium damnosum Complex

Abstract

The root and leaf extracts of four plants, Occimum gratissimum, Azadirachta indica, Pterocarpus santalinoides, and Pistia hyptis, were studied for repellent activities against the adults of Simulium damnosum sensu lato. The leaves and roots were extracted with 95% ethanol and the stocks were diluted with paraffin. The repellent activities of the extracts were investigated using human baits along the banks of River Oyan and River Ogun in southwestern Nigeria. The results showed that the root extract of O. grattissium and leaf extract of P. hyptis had highest repellent potentials with 78% and 78.1% protection against S. damnosum sensu lato, respectively, whereas the root and leaf of P. santalinoides recorded the least. Although there were significant differences in the percentage of protection of the extracts of the plants (p < 0.05), the variations in the percentage of protection of the leaf and root extracts were not statistically significant (p > 0.05). The study concludes that there exist some repellent efficacies in the extracts of the plants, most importantly O. grattissimum and P. hyptis. The plant extracts can further be developed in the prevention of man–vector contact in onchocerciasis endemic communities.

Introduction

O nchocerciasis is the disease resulting from infection with the parasitic worm, Onchocerca volvulus, of the family Filariidae, which lives in the human body for up to 14 years or more. Man is the natural host and the vectors are species of the blackfly Simulium spp. The six main West African members of the Simulium damnosum complex can be separated into three pairs. The pairs are S. damnosum sensu stricto and S. sirbanum, S. sanctipauli/S. soubrense, and S. yahense/S. squamosum. The first two are known as savannah species and the other four are forest species. The geographical distribution of the species is considerably influenced by local climatic and ecological characteristics (WHO 1995). The parasite strain differences are reflected in their different pathogenicities and antigenic peculiarities. The savannah form of O. volvulus constitutes the blinding type, with less blinding and more skin disease from the forest form (Oyibo and Fagbenro-Beyioku 2003).

Control methods against onchocerciasis vectors have been directed almost entirely against the larval stage of the Simulium fly (larviciding). The adult population is difficult to control because of their broad dispersal and wide variety of resting sites (WHO 1995). The emergence of resistance to certain organophosphorus insecticides by various blackfly species led to the strategy of rotation of various operational insecticides in the onchocerciasis control program area. Therefore, the formulation of insecticides to be used for large-scale campaigns must be highly effective against the vector and be safe for the rest of the environment (Hougard et al. 1997).

There exist some information on the use of environment-friendly substances for the treatment and control of various pest and vectors of disease agents (Green et al. 1985, Usip et al. 2006, Adeleke et al. 2009, Oparaocha et al. 2010). Green et al. (1985) observed that Chromonalia odorata and Parkia biglobosa were effective larvicides for most insect vectors of man. Moreover, some volatile oils of Citrus sinensis, Ageratum conyzoides, Cymbopogon citratus, Callistemon rigidus, and Occimum gratissimum have been tested as repellents against the blackfly S. damnosum sensu lato (s.l.) and have shown to be very effective. C. sinensis, A. conyzoides, and C. citratus oils repelled the blackflies for up to 2 h, whereas Callistemon and Occimum oils were effective for 3 h.

Crude extracts of plant materials have been used by farmers in Africa, Asia, and Latin America to control insects of medical and agricultural importance (Crosskey 1992). This research aims at evaluating the repellent potency of some plants from Nigeria for the prevention of man–blackfly contact.

Materials and Methods

Study areas

The study was conducted from August to September 2009, corresponding to the peak of the biting months of S. damnosum s.l., along the banks of River Oyan and River Ogun at Lisa and Idiata villages, respectively, in southwestern Nigeria. The two rivers are among the designated catching sites for WHO/APOC cross-border blackfly migration project between Nigerian/Benin Republic research projects.

Ethical clearance

The study was approved by the Ministries of Health in the two states. Informed consent was obtained from persons who acted as fly catchers and the communities involved. The fly catchers were treated with ivermectin after the study.

Selection of plants

Occimum gratissimum (Labiaceae), Pistia hyptis (Araceae), Pterocarpus santalinoides (Fabaceae), and Azadirachta indica (Meliaceae) were selected based on their reported toxicity to insect vectors (Ansari et al. 2005, Usip et al. 2006, Adeleke et al. 2009).

Plant extracts

The leaves and roots of the plants were extracted by first cutting each of the leaves and roots into shreds and allowing to dry at room temperature. After drying, 100 g of the dry leaves and roots were added to 200 mL of 95% ethanol in conical flasks and allowed to stand for 48 h. After 48 h, the solution was sieved. The extracts were stored in refrigerator until use.

Catching method and repellent test procedure

Five male fly collectors aged between 25 and 40 years were used to test the repellent activity of each of the selected plants in each site. The study was independent of the ongoing fly migration project and different fly collectors were used for the study. All the fly collectors were dark in complexion. Four fly collectors served as experimental subjects, and the remaining one acted as control. Each of the extract was diluted with paraffin at 90 mL of the extract to 10 mL of paraffin. Three milliliters of the diluted extract was applied topically on both legs and forearms by the fly collectors. Each collector rubbed each extract. The control fly collector applied only paraffin on his skin and sat with the test individuals who have applied the plant extracts for the duration of the experiment. The fly collectors were 5 m apart and sat exposing their lower legs at the bank of the river from 8 am to 6 pm daily for 2 days. Any fly that came to the exposed legs was caught before it sucked blood by inverting a small glass tube over it. The caps of the tubes were then immediately replaced. All tubes containing flies were labeled to indicate time, date, and place of capture.

Data analysis

The percentage of protection of the extracts was calculated as percentage of experimental catch minus control catch over the control catch as previously described by Ansari et al. (2005). Data were analyzed using t-test to determine the difference in percentage of protection of the extracts.

Results

The results of the repellent activities of the root extracts of plants are presented in Table 1 and Figure 1. The root extract of O. grattissmium had the highest percentage of protection (78%) over S. damnosum s.l., followed by P. hyptis (69.2), whereas P. santalinoides had the least (29.67%). On average, O. grattisimum and P. hyptis root extracts had an absolute protection time of 2 h, whereas the rest had 1.2 h except P. santalinoides, which had 0.4 h of protection time. The differences in percentage of protection of the root extracts were statistically significant (t = 5.15, p < 0.05).

FIG. 1.

Hourly repellent activities of the root extracts of the plant species.

Table 1.

Percentage of Protection of the Root Extracts of the Plant Species

	No. of flies collected
Plant species	CB	EB	% Protection
Occimum grattissimum	91	20	78.0
Pistis hyptis	91	28	69.2
Pterocarpus santalinoides	91	64	29.7
Azadiratha indica	91	46	49.5

p < 0.05.

CB, control bait; EB, experimental bait.

Also, the leaf extract of P. hyptis had the highest percentage of protection time (78.1%), followed by O. grattissimum (73.4%), whereas the lowest was obtained for P. santalinoides (28.1%). All the leaf extract had less than 1 h of protection time except O. grattissimum and P. hyptis, which had 1.9 and 2.2 h of absolute protection time. There were significant differences in percentage of protection of the leaf extracts (t = 4.172, p < 0.05) (Table 2 and Fig. 2).

FIG. 2.

Hourly repellent activities of the leaf extracts of the plant species.

Table 2.

Percentage of Protection of the Leaf Extracts of the Plant Species

	No. of flies collected
Plant species	CB	EB	% Protection
Occimum grattissium	128	34	73.4
Pistis hyptis	128	28	78.1
Pterocarpus santalinoides	128	92	28.1
Azadiratha indica	128	82	35.9

p < 0.05.

Comparatively, the root extracts of the plants exhibited higher percentage of protection against S. damnosum s.l. relative to the leaf extracts with the exception of P. hyptis, whose leaf had higher protection (78.1%) than the root extract (69.2%). However, both chi-square test and t-test showed that the differences in percentage of protection of the leaves and roots of the plants were not significant (p > 0.05).

Discussion

The results from this study had shown that the leaf and root extracts of O. gratissimum, P. hyptis, A. indica, and P. santalinoides had repellant activities against the adults of S. damnosum. The relatively high percentage of protection and protection time of the root and leaf extracts of P. hyptis and O. gratissimum showed that the two plants exhibit substantial repellent activities against S. damnosum s.l. This observation was similar to the earlier reports on toxicity of these plants against insect vectors (Usip et al. 2006, Oparaocha et al. 2010). The appreciable protection and protection time of the extracts of the two plants could serve as great relief to the people living in onchocerciasis endemic areas, where black flies constitute both nuisance and vector of the disease and the people's daily activities usually along the river courses predisposed them to insect bites. The topical application of these plant extracts would further reduce the vector access to the already reduced load of microfilaria achieved through ivermectin treatment, thereby reducing disease transmission and biting nuisance.

However, the low protection and protection time observed for A. indica and P. santalinoides showed that these two plants had poor repellent activities against the adults of S. damnosum s.l. This observation dissented from previous reports that stated that the leaf and seed extracts of A. indica and P. santalinoides had been known to be toxic to the larvae of mosquitoes and has high protection against the adults (Sharma et al. 1993, Ansari et al. 2005, Adeleke et al. 2009). The variation observed (though not statistically significant) in the repellent activities of the leaf and root extracts could plausibly be a reflection of differences in phytochemical constituents of different parts of the plants as earlier posited by Osuagwu et al. (2007) and Oparaocha et al. (2010). The plant extracts were relatively safe using the model of Buck (1974) as none of the experimental collectors complained of adverse skin reactions during the period of the study.

In conclusion, the study had shown that there exists some level of repellent activities of O. gratissimum, A. indica, P. santalinoides, and P. hyptis against biting adult S. damnosum and the potentials of these plant extracts can be further developed. The results obtained most importantly on O. gratissimum and P. hyptis are very promising in formulating a potent and affordable natural product in the prevention of man–blackfly contact in onchocerciasis endemic communities. The phytochemical analysis of the active constituents responsible for the repellent activities and the long-term impacts of the plants will be subjects of future studies.

Footnotes

Acknowledgments

The authors appreciate the management of WHO/APOC and Multi-Disease Surveillance Centre (MDSC), Ouagadougou, for stimulating the need for the study, and residents of the study communities and the fly captures for their assistance during the study.

Disclosure Statement

No competing financial interests exist.

References

Adeleke

, Popoola

, Agbaje

, Adewale

, Adeoye

, Jimoh

. Larvicidal efficacy of seed oils of Pterocarpus santalinoides and Tropical Manihot Species against Aedes aegypti and effects on aquatic fauna. Tanzan J Health Res, 2009; 11:150–152.

Ansari

, Mittal

, Razdan

, Sreehari

. Larvicidal and mosquito repellent of Pine (Pinus longifolia, Family: Pinaceae) oil. J Vector Borne Dis, 2005; 42:95–99.

Buck

. Onchocerciasis, Symptomatology, Pathology, Diagnostic. Geneva: World Health Organization, 1974; 80.

Crosskey

. Blackflies Simuliidae. Lane

, Crosskey

. Medical Insects and Arachinids. Chapman and Hall, 1992; 241–287.

Green

, Taylor

, Cupp

, Murphy

, White

, Aziz

, Schulzkeys

, D'Anna

, Newland

, Goldsmith

, Auer

, Hanson

, Freeman

, Reber

, Williams

. Comparison of ivermectin and diethylcabamizine in the treatment of onchocerciasis. N Engl J Med, 1985; 313:133–138.

Hougard

, Yameogo

, Seketeli

, Boatin

, Dadzie

. Twenty-two years of blackfly control in the onchocerciasis control programme in West Africa. Parasitol Today, 1997; 13:425–431.

Oparaocha

, Iwu

, Ahanaku

. Preliminary study on mosquito repellent and mosquitocidal activities of Occimum gratissimum (L) grown in Eastern Nigeria. J Vector Borne Dis, 2010; 47:45–50.

Osuagwu

CGE

, Okwuelehie

, Emenike

. Phytochemical and mineral content of the leaves of four Nigerian Pterocarpus (JACO) species. Int J Mol Med Adv Sci, 2007; 3:6–11.

Oyibo

, Fagbenro-Beyioku

. Effect of repeated community based ivermectin treatment on the intensity of onchocerciasis in Nigeria. Rural Remote Health, 2003; 3:211.

10.

Sharma

, Nagpal

, Srivastava

. Effectiveness of neem oil mats in repelling mosquitoes. Trans R Soc Trop Med Hyg, 1993; 87:626–628.

11.

Usip

LPE

, Opara

, Ibanga

, Atting

. Longitudinal evaluation of repellent activity of Ocimium gratissimum (Labiatae) volatile oil against Simulium damnosum. Mem Inst Oswaldo Cruz, 2006; 101:201–205.

12.

[WHO] World Health Organization. Onchocerciasis and its control. Report of a WHO expert committee on onchocerciasis control. Tech Rep ser, 1995; 852:1–104.