The Threat of Vector-Borne Diseases in Sierra Leone

ABSTRACT. Sierra Leone is vulnerable to a wide range of vector-borne diseases transmitted by mosquitoes, tsetse flies, black flies, and other vectors. Malaria, lymphatic filariasis, and onchocerciasis have posed the greatest threat and have received the most attention in terms of vector control and capacity for diagnosis. However, malaria infection rates remain high, and there is evidence of circulation of other vector-borne diseases, such as chikungunya and dengue, which may go undiagnosed and unreported. The limited understanding of the prevalence and transmission of these diseases restricts the capacity for predicting outbreaks, and impedes the planning of appropriate responses. We review the available literature and gather expert opinions from those working in the country to report on the status of vector-borne disease transmission and control in Sierra Leone, and present an assessment of the threats of these diseases. Our discussions highlight an absence of entomological testing for disease agents and the need for more investment in surveillance and capacity strengthening.

Dr. Mary Hodges provides technical support to the NTDP implemented by the MoHS. This programme was initiated with financial support from the United States Agency for International Development (USAID) and other partners to eliminate onchocerciasis, and lymphatic filariasis and control schistosomiasis and STHs. It uses the integrated preventive chemotherapy strategy according to WHO guidelines HKI train teams of young graduates who support the government in implementing the programme, and independent monitors to evaluate activities.
There are 44 staff at HKI, of which nine are working with the NTDP. HKI supported the Ebola outbreak in the Western Area with the quarantine process and contact tracing. HKI introduced GPS and mobile reporting for case tracking which could be rapidly scaled-up and adapted again to meet new challenges of another VBD outbreak. The six-week Aedes project was led by Mr. Sandi from June-August 2017, and examined sites in Bo and Bombali districts for prevalence, abundance and density of Aedes. Larval habitats were identified to calculate larval indices and eggs and adults were collected and sent to the US for insecticide resistance and arbovirus testing, The results were reported to the MoHS, and will allow them to make decisions on which types of insecticides could be used effectively in the future should there be a need, and which types of habitats to target for larval source reduction. The input of CDC has therefore added an element of Aedes research to that conducted on Anopheles for the NMCP. Dr. Levine said that while entomology in Sierra Leone has become more robust under the CDC and PMI activities, resource-constraints made it a previously overlooked field and little laboratory capacity currently exists in-country for pathogen-testing from entomological samples.
Project Sierra Leone became a PMI focus country in 2017. The initiative supports key malaria interventions that are aligned with the NMCP national strategic plan to achieve access to malaria control interventions for all and reduce malaria morbidity and mortality. For prompt diagnosis and effective treatment using the "test-treat-and-track" practice, PMI procures diagnostic tests, anti-malarials, and injectable artesunate for severe disease. PMI also supports health worker training and mentoring, entomological surveillance, social and behavioural change strategies, and routine health information systems at the chiefdom level. 1 PMI works through the VectorLink project in Sierra Leone to analyse the suitability of insecticides for use in bed nets, and determine which vector control strategies will be most effective given the results. They try to strengthen the country's capacity, and trained 12 people in entomology (including Whilst the laboratory therefore has the capability to detect a range of viruses transmitted by arthropods, it cannot specifically detect RVFv and is employed for the detection of infectious agents in human samples, rather than in vectors. Dr. Ansumana stated that, in his research projects, there is often funding for the study of a particular disease, but this does not allow for further analysis of other pathogens, and he sees a significant gap in the identification of pathogens in vectors. Further, without the weight of evidence it is difficult for his team to apply for grants that would allow them to specifically look for less well-known VBDs in human or mosquito samples. Funding for his work often comes from outside Sierra Leone, and is obtained in partnerships with other institutions such as George Mason University in Virginia. When diagnoses are made from patient samples at Mercy Hospital, reports are sent to the District Health Management Team (DHMT). The hospital has sent two people to the CDC facility in Fort Collins, Colorado, for training in diagnostic methodology for Yersinia pestis. They also intend to purchase a MinION portable real-time device for DNA and RNA sequencing, which will enhance their ability to diagnose VBDs in patients.

University of Sierra Leone
Prof. Sahr, Vice Chancellor and Principal of the University of Sierra Leone, is a professor of medical microbiology who collaborates with other scientists in Sierra Leone on work related to Ebola, Lassa, malaria, HIV and tuberculosis. The University of Sierra Leone contributes to capacity building through offering courses in public health in the College of Medicine and Allied Health Sciences. It has colleges in Freetown and Njala, and offers courses in pure and applied sciences, including community health services and social sciences. Their Masters in Public Health programme includes core modules in epidemiology, health promotion, and disease detection, prevention and control. Students also have the opportunity to take a module in communicable diseases, which includes content on vector-borne diseases, but he noted that there has been very little taught content on vector-borne diseases so far.
The King's College London King's Sierra Leone Partnership is working with all faculties to provide support across medicine and nursing, but has little involvement with education around vector-borne diseases.
Prof. Sahr feels that entomology training is lacking in the College of Medicine and University of Sierra Leone, and is not currently seen as important as diagnostics. Prof. Sahr said that the Ebola outbreak has encouraged capacity building and the country is now better able to respond because of the possibility of Ebola returning. However, the mainstream hospitals are not adequate and require outbreak centres instead.

Hospital
The Lassa fever program at the Kenema Government Hospital in eastern Sierra Leone provides diagnostic services and clinical care for more than 500 suspected Lassa fever cases per year. The hospital has also been involved in surveillance of other viral infections to better define the nature and extent of viral pathogens infecting the Sierra Leonean population, the results of which suggest that unrecognized outbreaks of viral infection have occurred.
The Lassa ward has a triage structure for febrile illness or viral haemorrhagic fever with an ambulance system, and receives referrals from other hospitals. Dr. Samuels, Senior Clinician at Kenema Government Hospital, explained that they have RDTs for Lassa IgG and IgM, and local teams are being trained in their use, but they are not confirmatory; ELISA or RT PCR are used for confirmation of diagnosis. The PCR RDTs panel contains primers for other filoviruses so can provide differential diagnoses, and if the results are negative they have access to an Illumina MiSeq for sequencing. However, due to budgets not all samples are sequenced.
A surveillance team, from the Lassa ward and DHMT, partners with an outreach team to go out into communities for community mobilisation and education about disease prevention and to identify disease transmission routes. The Lassa hospital also has strong links with Tulane University School of Medicine. Virologists from Tulane have been researching Lassa fever in West Africa for more than 15 years, and with local partners have built research facilities.

Dr. K. Jacobsen
George Mason University Dr. Jacobsen, a professor specializing in global health epidemiology, has held a long-running partnership with Njala University (Dr. Rashid Ansumana), Mercy Hospital, and the U.S. Naval Research Lab (NRL) testing new methods for infectious disease surveillance. She told us that the US Department of Defense (DoD) was supporting development and testing of diagnostic test kits tests for pathogens such as Ebola, yellow fever, and various adenoviruses and flaviviruses in several countries, including Sierra Leone. 2 Ongoing work by Dr. Jacobsen and her collaborators should provide further insight into current situation of VBDs in Sierra Leone, and by partnering with Mercy Hospital it is hoped that there will be both a transfer of skills and further investment in the facilities managed by Dr. Ansumana.