Efficacy of local essential oils against Amblyomma variegatum tick from Burkina Faso

The native tick Amblyomma variegatum remains one of the most important tick species affecting cattle in West Africa. This hinders animal production by negatively impacting the health and reproduction of animals infested with the tick. Given the negative consequences on production quality and environmental health, the use of chemical products for tick control is increasingly being discouraged. Therefore, this study aimed to assess the acaricidal activity of essential oils such as Ageratum conyzoïdes, Cymbopogon citratus, Cymbopogon giganteus, Lippia multiflora and Ocimum gratissimum against specimens of A. variegatum from Burkina Faso. A larval immersion test was performed to investigate the larvicidal activities of these essential oils. Gas chromatography-mass spectrometry was used to determine the chemical compositions of essential oils. The chemical composition was predominantly oxygenated monoterpenes in A. conyzoïdes (48.71 %), C. citratus (99.9 %) and C. giganteus (73.63 %), while hydrocarbon monoterpenes were the most abundant in O. gratissimum (63.7 %) and hydrocarbon sesquiterpenes in L. multiflora (71.719 %). The recorded larvicidal activity, varied according to the species of plants and the dose applied. At a dose of 12.5 mg/mL, all essential oils studied, except L. multiflora (7.54 %), induced 100 % larval mortality. In this study, we highlight the promising larvicidal effects of local essential oils against A. variegatum. These essential oils can be used as bio-acaricides, which are effective and environmentally-friendly alternatives to chemical products. However, further investigations are required to determine the mechanisms of action of these essential oils for in vivo experimentation and their practical application in the control of A. variegatum ticks.

Evaluation of synergism in essential oils against the cattle tick Rhipicephalus microplus in Burkina Faso

The cattle tick Rhipicephalus microplus affects animal production economically by reducing weight gain and milk production and causing diseases, such as babesiosis and anaplasmosis. Using synthetic acaricides to reduce their incidence has caused the emergence of resistant tick populations. The present study aimed to assess the in vitro acaricidal activity of combinations of essential oils (EOs) from Ocimum americanum, Ocimum gratissimum, and Lippia multiflora against R. microplus larvae. In fact, numerous biological properties have been reported on EOs from these three plants, including acaricidal properties. Hence, a larval immersion test was performed using a population of R. microplus resistant to synthetic acaricides used in Burkina Faso. Results revealed that EO from O. gratissimum was the most effective on R. microplus larvae with LC50 and LC90 values at 10.36 and 15.51 mg/mL, respectively. For EO combinations, the most significant synergistic effect was obtained by combination 6 (1/3 O. americanum + 2/3 O. gratissimum +1/6 L. multiflora), with a combination index value of 0.44. All combinations presented dose reduction index >1, indicating a favorable dose reduction. According to the literature, this is the first study to determine the combination effect of EOs from the abovementioned plants in controlling R. microplus activity in vitro. Thus, the combination of these EOs is an alternative to control the resistant populations of invasive cattle ticks.

Alternatives to Pyrethroid Resistance: Combinations of Cymbopogon nardus and Ocimum americanum Essential Oils Improve the Bioefficiency Control Against the Adults' Populations of Aedes aegypti (Diptera: Culicidae)

Dengue vector control strategies are mostly based on chemicals use against Aedes aegypti populations. The current study aimed at investigating the insecticidal effects of essential oils (EOs) obtained from five plant species, Cymbopogon citrates (D. C.) Stapf. (Poaceae), Cymbopogon nardus (Linn.) Rendle (Poaceae), Eucalyptus camaldulensis Linn. (Myrtaceae), Lippia multiflora Moldenke (Verbenaceae), and Ocimum americanum Linn. Lamiaceae, and combinations of Cymbopogon nardus and Ocimum americanum on Ae. aegypti populations from Bobo-Dioulasso. For this purpose, adults of the susceptible and field strains of Ae. aegypti were tested in WHO tubes with EO alone and binary combinations of O. americanum (OA) and C. nardus (CN; scored from C1 to C9). The extraction of the essential oils was done by hydrodistillation, and their components were determined by GC/MS. Among the 5 EOs tested, L. multiflora essential oil was the most efficient, with KDT50 values below 60 min on all Ae. aegypti strains tested, and also with a rate of mortality up to 100 and 85% for Bora Bora and Bobo-Dioulasso strains, respectively. This efficacy may be due to its major compounds which are with major compounds as β-caryophyllene, p-cymene, thymol acetate, and 1.8 cineol. Interestingly, on all strains, C8 combination showed a synergistic effect, while C2 showed an additive effect. These combinations exhibit a rate of mortality varying from 80 to 100%. Their toxicity would be due to the major compounds and the putative combined effects of some major and minor compounds. More importanly, L. multiflora EO and combinations of C. nardus and O. americanum EO, may be used as alternatives against pyrethroid resistant of Ae. aegypti.

Essential oils of plants and their combinations as an alternative adulticides against Anopheles gambiae (Diptera: Culicidae) populations

The persistence of malaria and the increasing of resistance of Anopheles gambiae species to chemicals remain major public health concerns in sub-Saharan Africa. Faced to these concerns, the search for alternative vector control strategies as use of essential oils (EOs) need to be implemented. Here, the five EOs from Cymbopogon citratus, Cymbopogon nardus, Eucalyptus camaldulensis, Lippia multiflora, Ocimum americanum obtained by hydro distillation were tested according to World Health Organization procedures on An. gambiae "Kisumu" and field strains collected in "Vallée du Kou". Also, the binary combinations of C. nardus (Cn) and O. americanum (Oa) were examined. As results, among the EOs tested, L. multiflora was the most efficient on both An. gambiae strains regarding KDT₅₀ (50% of mosquitoes knock down time) and KDT₉₅ and rate of morality values. Our current study showed that C8 (Cn 80%: Oa 20%) and C9 (Cn 90%: Oa 10%), were the most toxic to An. gambiae strain "Vallée de Kou" (VK) with the mortality rates reaching 80.7 and 100% at 1% concentration, respectively. These two binary combinations shown a synergistic effect on the susceptible population. However, only C9 gave a synergistic effect on VK population. The bioactivity of the two EOs, C. nardus and O. americanum, was improved by the combinations at certain proportions. The resistance ratios of all EOs and of the combinations were low (< 5). The combinations of C. nardus and O. americanum EOs at 90: 10 ratio and to a lesser extent L. multiflora EO, could be used as alternative bio-insecticides against malaria vectors resistant to pyrethroids in vector control programmes.

Mycobacterium tuberculosis drug-resistance in previously treated patients in Ouagadougou, Burkina Faso

BACKGROUND

Tuberculosis drug-resistance becomes common in sub-Saharan Africa; however, very few data are available in Burkina Faso. The aim of this study is to assess the acquired resistance of Mycobacterium tuberculosis complex strains identified in TB patients to four first-line drugs in Ouagadougou.

METHODS

One hundred and ten (110) pulmonary tuberculosis patients with acid-fast bacilli-positive sputum and in situation of failure, relapse, or treatment abandonment were included in the study. Ninety six strains, including 92 (95.8%) M. tuberculosis and 4 (4.2%) M. africanum, were isolated from the sputum samples of these patients. Their drug susceptibility testing was performed using the proportion method. The first-line drugs tested were isoniazid (INH), streptomycin (STR), ethambutol (EMB), and rifampicin (RIF).

RESULTS

The overall drug-resistance rate of M. tuberculosis was 67.4% (n=60), including 3.4% to one drug, 18% to two, 10.1% to three, and 35.9% to four drugs. The resistance to INH, RIF, EMB, and STR were 67.4%, 51.7%, 50.6%, and 44.9%, respectively. Two strains of M. africanum were resistant to all drugs. Forty-six (51.7%) strains were multidrug-resistant (resistant to at least INH and RIF).

CONCLUSIONS

In previously treated patients, the level of resistance of M. tuberculosis complex to commonly used anti-tuberculosis drugs is very high in Ouagadougou. Our results showed that multidrug-resistant tuberculosis could be a public health problem in Burkina Faso.

[Description and survey of a measles epidemic in Burkina Faso]

Measles remains a major cause of child and infant mortality in Africa. Burkina Faso was the first country in Africa to run mass measles vaccination campaigns. The "Commando" vaccination program in 1984 immunized children aged between 9 months and 6 years old. The EPI was then implemented across the whole country; and with particular emphasis on the North Central region (with the help of two Non Governmental Organizations). Coverage cluster surveys were conducted in 1987 and 1989. In addition, a community-based evaluation of the immunization program and a serological survey were run in January 1989. A measles epidemic started in March 1989 in the Eastern province (Namentenga) of the North Central region and lasted until the rainy season. A survey reported 230 cases of which a large proportion were adults. Vaccine efficacy (85%) was normal. Index cases were from a neighbouring province. Epidemiological and serological surveys in 1989 indicated that the circulation of the wild type virus had been low since the 1984 "Commando" vaccination program. The epidemic was due to unsatisfactory vaccinal coverage (53%) which had further declined (35%). Consequently the primary health care system is being mobilized to improve vaccinal coverage.