Macro & Vector Control Strategy

Dr Enyong, Cameroon's foremost Entomologist in the field, South West Region - Cameroon

Therefore, an urgent need exists to validate and implement alternative strategies for the control and elimination of onchocerciasis, as well as to fully understand potential reasons for sub-optimal success of the CDTi strategy so that these may be avoided in the future.

Social science approaches will be used to help identify risk factors for the poor efficacy of the current CDTi strategy, alongside the capture of societal and health economic data to assess the acceptability and feasibility of the test and treat strategy.

Integrated Control Strategies 1: Macro & Vector

Work in both countries will look at how targeted vector control can be used to increase the impact of drug delivery to affected populations. In Ghana, integrated delivery of Long Lasting Insecticidal Nets (LLIN) targeting mosquitos alongside MDA in hotspot areas of continued lymphatic filariasis transmission will be explored. In Cameroon, targeted ground larviciding against blackflies will be used synergistically alongside delivery of doxycycline to infected individuals.

The overall aim of the Cameroonian onchocerciasis community trial is to implement a test-and-treat strategy for onchocerciasis control using the WHO-endorsed macrofilaricidal drug, doxycycline. This is being carried out in tandem with targeted larvicidal treatment of riverine vector breeding sites in South West Cameroon. Doxycycline differs from ivermectin, the drug current control strategies rely on, as it targets symbiotic bacteria, Wolbachia, living within both adult worms and microfilariae. Depleting the symbionts sterilises adult worms residing in human tissues, preventing the production of skin infecting microfilariae, and significantly reduces adult lifespan. Biological monitoring will be undertaken to determine the impact of this alternative strategy on the prevalence of onchocerciasis microfilariae in the skin, using traditional parasitological techniques.

Onchocerciasis is a vector-borne disease caused by the parasite Onchocerca volvulus. It manifests as troublesome itching, skin rash, visual impairment and irreversible blindness. It is common and widespread in Cameroon, and is estimated to effect 18 million people in sub-Saharan Africa. The current strategy for control is using mass drug administration with ivermectin, a drug that kills the immature form of the parasite found in the skin. Ivermectin does not have significant effects on adult worms, so the treatment needs to be repeated for the entire lifespan of the worm; therefore MDA for 15-17 years is recommended by the WHO.MDA has been conducted in South West Cameroon for more than twelve years in a strategy known as Community-Directed Treatment with ivermectin (CDTi), yet higher than expected prevalence and intensity of onchocerciasis remains. The persistence of onchocerciasis highlights that control of this disease in Cameroon is complicated by several factors, including geographical overlap with Loa loa, hampering CDTi due to adverse effects; poor perception and uptake of CDTi due to fear of adverse effects, even in areas free from Loa loa; and high prevalence of skin microfilariae even after prolonged MDA.

Understanding the Characteristics of Lymphatic Filariasis 'Hotspots' to Accelerate Disease Elimination through integrated MDA and Vector Control Strategies in Ghana

Lymphatic filariasis (LF) is a mosquito-borne infection caused by the parasitic worm Wuchereria bancrofti. It causes significant illness, disability and disfigurement in affected individuals, and is endemic in Ghana. Currently, the national Lymphatic Filariasis Elimination Programme is distributing MDA using a combination of ivermectin and albendazole to interrupt the transmission of the disease. The WHO recommends distribution of drugs annually for 5-7 years, which is the estimated life span of adult worms.

The LF elimination programme in Ghana has achieved tremendous success through the MDA campaign and many regions have met the criteria to scale down distribution. In these regions, it will be crucial to sustain the gains made by the programme and prevent resurgence. However, although MDA for LF has been conducted in an increasing number of communities for over 10 years in Ghana, the infection prevalence is highly heterogeneous and hotspots (areas with ongoing parasite transmission) persist in some parts of the country. It is likely that these heterogeneities are driven by differences in access to drugs, drug uptake, vector characteristics such as biting density, vector competence, host-seeking behaviours and possibly host and vector genetic factors. To achieve effective elimination of LF, it is pivotal to address the underlying social, epidemiological, parasitological and entomological causes allowing the disease to persist despite long periods of intervention.  There is evidence that integration of vector control and MDA can accelerate elimination, but long lasting insecticide treated nets (LLINs) are not distributed along with MDA and there is no coordination between National Malaria Control Programme and LF elimination programmes to ensure LLIN coverage can meet elimination targets. Although vector control is a part of many national malaria control programmes, coverage and compliance are sub-optimal.

The overall aim of the research in Ghana is to provide evidence to support rapid and sustainable scale-up of complementary intervention strategies to eliminate LF in the country. This will be achieved through evaluating the social, entomological and epidemiological characteristics of hotspot communities to identify the causes of persistent transmission, alongside evaluating the impacts of an integrated MDA and vector control programme on service delivery, community participation and LF transmission.

Outputs will deliver evidence on social acceptance and cost-effectiveness of alternative strategies for implementation in these “hotspot” areas or in post-MDA endgame scenarios, where test and treat strategies become more cost effective and deliverable. It is likely that better coordination Long Lasting Insecticidal Net (LLIN) distribution can accelerate and bolster progress towards the interruption of LF transmission. In addition, the feasibility and cost of integrating LLIN distribution with MDA will be assessed and evaluated on how vector characteristics might influence the impacts of LLIN.

 

GH_Agyan_CM_Mosquito Collectors Training

The collected information will be then used to identify opportunities for better planning and co-implementation of the interventions at the district and community level, to help developing tools and methods to inform scale-down of interventions, including the application of disease transmission models to predict the impacts of interventions on LF to help setting locally relevant targets for elimination, and to guide the optimisation of available and emerging tools for the sensitive detection of the parasite in the mosquito vectors for post-MDA surveillance.