VECTOR-BORNE INFECTIOUS DISEASE RESEARCH GROUP
Below is a description of our recent research projects:
An infectious bite marker for sensitive malaria detection and population level surveillance
As international efforts towards malaria elimination increase, accurate data on transmission intensity will be crucial for directing control efforts, developing and testing new interventions, as well as predicting the effects of these interventions under various conditions.
However, current tools; the entomological inoculation rate, parasite infection and serological measures have limitations in either sensitivity at low-level transmission or lack the inherent ability to track short-term changes at different geographical scales. Again changes measured by these traditional tools reflect either parasite or vector exposure but not both. The ideal tool for tracking malaria transmission intensity should reflect both exposure to the vector, parasite infection and human immunity as well as detect short-term changes and also be applicable at both individual and population level. Furthermore, the role of infectious bite markers in identifying areas of higher transmission (‘hotspots’) and ‘and highly exposed sub-populations have not been fully elucidated. Other questions such as how long do these antibodies last in absence of exposure? Thus, the ability of these biomarkers to detect short-term changes in malaria transmission has not been thoroughly studied.
Our previous findings have identified sporozoite and ookinete peptides/proteins which human immune response correlates with seasonal vector and parasite exposure and thus a promising ideal marker for an infectious bite. Using longitudinal community cohorts under varying levels of malaria transmission, we are currently conducting kinetic studies to evaluate the dynamics of antibody response to candidate biomarkers in comparison to other salivary proteins to validate infectious-bite markers. It is hoped that these biomarkers will prove to be sensitive tools for the identification of micro geographical hotspots, vulnerable populations and thus inform focused interventions to speed up malaria elimination.
Molecular epidemiology of malaria in Ghana
Plasmodium falciparum causes the most severe form of malaria and is the predominant malaria parasite in sub-Saharan Africa. Most commercially available rapid diagnostic tests target the Histidine-Rich Protein-2 (HRP-2) gene which is expressed by P. falciparum for malaria diagnosis. However, there have been multiple reports of deletion of this gene in Peru and other parts of the world. As such, we are conducting a nationwide molecular epidemiology of the deletion of this gene in targeted communities within Ghana and assess the implication of these gene deletions on the use of HRP-2 based RDTs for malaria diagnosis in Ghana.
Distribution and incidence of trypanosome infection in tsetse fly, pig and cattle populations in the Ayensuano and Suhum/Kraboa/Coaltar Districts in the Eastern region.
African animal trypanosomiasis (AAT) also known as ‘nagana’ is a life-threatening disease transmitted to livestock by tsetse fly of the Glossina genus. The disease is a severe constraint for people that are indigenous to sub-Saharan Africa and with agriculture as their main occupation. Ghana is one of the countries within the Sub-Saharan region where agriculture is an important sector which does not only help in alleviating poverty but also help in achieving the Sustainable Development Goals. However, AAT causes huge loss of livestock and agricultural productivity with some socio-economic consequences (Chanie et al., 2013; Mattioli et al., 2004). It is estimated that about 4 billion dollars is spent on agricultural losses yearly due to nagana (Francis, 2014). AAT causes huge loss in animal productivity and this obstructs the economic development in tsetse endemic areas in Africa. Most importantly, the cause of morbidity and mortality is estimated between US$ 1.0 -1.2 billion in cattle alone in sub-Saharan Africa. In an attempt to reduce the incidence of the disease, many measures including Regional Tsetse and Trypanosomiasis Control Programme (RTTCP) and the use of trypanotolerant livestock breeds, have been deployed. However, recent studies have observed the occurrence of ‘nagana’ with a high infection rate of trypanosomes in certain areas in Ghana (Bauer et al., 2011; Ebhodaghe et al., 2016). This underscores the necessity to investigate the incidence and the distribution of the trypanosome parasite in both the insect vector and the mammalian host with a more sensitive and specific molecular tools to be able to ascertain the current nagana status in Ghana.
Therefore, a cross-sectional survey was carried out in February, 2019 to investigate the distribution and incidence of nagana in both the tsetse fly vector and the mammalian host in the Eastern region of Ghana. Cytochrome c (cox1) and internal transcribed spacer (ITS1) dependent PCR assays were performed to detect and identify tsetse fly species as well as trypanosome species. Sequence analysis reveals that all tsetse flies collected during the survey belong to Glossina palpalis palpalis. There was high trypanosome infection rate in tsetse flies and pigs in the study area; with the majority of the infections due to T. congolense. There was molecular evidence of concurrent colonization of T. congolense and T. simiae, T. congolense and T. vivax, and T. congolense and T. b. brucei in the tsetse midgut.
Atypical Human Trypanosomiasis (a-HAT); An emerging zoonosis in Ghana?
It is well established that human infection by trypanosomes is caused by two protozoan parasites, Trypanosoma brucei gambiense and Trypanosoma brucei rhodesiense that have acquired the innate ability to infect man by escaping the effect of the trypanolytic factor, ‘Apolipoprotein’ in human serum. Other Trypanosoma parasites considered to be animal species like Trypanosoma brucei brucei, Trypanosoma congolense, Trypanosoma vivax and Trypanosoma evansi that cause ‘Nagana’ in livestock lack such ability to infect human. However, Atypical human trypanosomiasis caused by animal species of trypanosomes is on the rise and has become a public health issue to the human society as the parasites continuously seem to be changing their geographical distribution and host specificity. Already, 19 cases of atypical human trypanosomiasis have been reported worldwide with Ghana on the list with 2 cases. Generally, human African trypanosomiasis is fatal when left untreated. From the 19 reported cases, some were fatal, some disappeared after treatment whilst others were not showing symptoms at all. According to WHO reports, Africa accounts for close to 90% of all the patients reported to have contracted HAT. As a result, it is estimated that Africa loses up to US$1.5 billion annually. Animal pathogens are also known by their activities to be a major constraint to livestock production in tsetse fly endemic areas. In Suhum, there have been some deaths of livestock due to Trypanosoma infections according to Mr Agbevor Hanson, the veterinary officer in charge of the area as farmers have made losses. Findings from previous studies conducted by two members of our team, Yana Rossau and Austine Tweneboah showed the presence of atypical parasites in tsetse flies and pigs. Moreover, over the last 10 years, Ghana has not made any report on HAT.
This study is therefore based on the hypothesis that the human population at the selected study sites may be under comparatively higher exposure to these animal species of trypanosomes which may, in turn, increase the probabilities of the parasites undergoing evolutionary pressure to mutate and eventually cause atypical human trypanosomiasis. My study seeks to find the occurrence of these potentially zoonotic parasites in the selected study areas at Suhum Municipality and the effect of these parasites on human health. Under the aim of the study, clarification will be made to whether new strains of animal pathogens have evolved and also identify risk populations among study participants for intervention. So far, 214 blood and urine samples have been collected from study participants and DNAs already extracted for Polymerase chain reaction (PCR) tests. Ten (10) out of the 214 blood samples are positive for trypanosome parasite DNA, although PCR tests are still ongoing. Enzyme-linked immunosorbent assay is also ongoing to check the immune profiles of the study participants.
Transmission of Cutaneous Leishmaniasis in an endemic district in Ghana
Neglected Tropical Diseases (NTDs) inflict physical and psychological damage on populations putting poor families in a vicious cycle of poverty. NTDs affect over one billion of the poorest of the poor worldwide, and have been recognized as important for control and elimination in order to achieve the sustainable development goals. Leishmaniasis, a typical NTD caused by different species of the protozoan parasite of the genus Leishmania, is transmitted through the bites of infected female sand flies of varying species. Leishmaniasis in its various forms thus the visceral, cutaneous and mucocutaneous forms, afflicts 12 million of the world’s poorest people in 98 countries, with up to 350 million at risk of the disease. In Ghana the cutaneous leishmaniasis has been identified which manifests as a papule that enlarges into a nodule and then ulcerates. This causes morbidity due to the continued presence of a skin ulcer and disfigurement. It was first observed in 1999 in the Ho, Volta Region of Ghana. The outbreak worsened during 2003/2004 with up to 8,533 cases involving some 116 villages being reported [MoH Annual Report, 2003]. However, there is re-emergence of CL recently in the Nkwanta South District of the Oti Region. This can be as a result of lack of management of CL in endemic communities and prospective leishmaniasis patients in Ghana. The biggest problem is that the protozoa and insect vectors that transmit them are made up of several species and currently, it is unclear which vector-parasite species system is driving the transmission. This therefore justifies the need for further studies to identify all circulating parasites to identify the predominant species responsible for ongoing infections and further determine the vector or vectors responsible for the transmission of Leishmania within communities.
A study was then conducted in the Nkwanta South District in the Oti Region to identify the vector species transmitting the disease as well as the parasite species causing the disease. The study confirmed the persistent spread of CL in the endemic communities in the country with the discovery of new vector species in Ghana. Phlebotomus chinensis and Lutzyomia anduzei haplotype were the vector species identified through PCR with Phlebotomus chinensis being the most abundant. However, Leishmania parasites were not detected in these vectors but L. major and L. tropica parasites were detected in tissue fluids of cutaneous lesions on filter papers.
A novel paper-based mass spectrometry immunoassay for malaria diagnosis
Malaria remains a major global health problem particularly in sub-Saharan Africa and Asia where it continues to be an active killer of children less than 5 years and among expectant mothers. Increased international commitment to control malaria over the past two decades have resulted in 18% and 48% decrease in morbidity and mortality respectively. Despite this progress, 228 million malaria cases were reported worldwide in 2018 with 405,000 associated deaths.
Microscopy is considered as the ‘gold standard’ for malaria diagnosis. However, the accuracy of this method largely depends on the experience and expertise of the microscopist. Current field tests based on rapid diagnostic tests (RDTs) are also limited by poor sensitivity, low specificity and even more worrying is yielding false positive and negative results making it unsuitable for active case detection and treatment. Serological and molecular methods such as ELISA and PCR, though providing high sensitivity and superior specificity, is not optimal for routine/surveillance purposes in resource-limited endemic settings since the process is laborious, time-consuming and requires sophisticated equipment. A simple, rapid, affordable and ultrasensitive diagnostic tool is therefore needed to support disease elimination efforts.
Here, we evaluate the accuracy of a promising novel paper-based immunoassay for malaria diagnosis. The proposed platform employs the use of synthetic novel ionic probes to facilitate ultrasensitive detection of PfHRP-2 antigen using a handheld mass spectrometer. Preliminary studies in a lab setting have shown the proposed platform to be sensitive and stable however, it is yet to be tested in the field. This study therefore aims to assess the diagnostic accuracy of the novel platform based on performance metrics such as sensitivity, specificity, stability and limit of detection in comparison to traditional methods. In addition, we expect this technology to provide three unique levels of malaria testing: (1) point-of-care (POC) application, (2) community-based surveillance detection – to identify people with latent infection (i.e., asymptomatic patients) that serve as reservoirs for continuous transmission of the disease, and (3) field analysis in the case of an outbreak (occurring every rainy season in endemic regions).This will enable policy makers to make well-informed decisions on the suitability of the novel platform for routine and/or population-level surveillance.
Assessing the accuracy of a novel automated device for malaria diagnosis
Accurate and prompt diagnosis of malaria is important in the renewed interest to eliminate and eradicate malaria. This project is in collaboration with Noul Inc., an AI-based blood cell diagnosis device developer which has its headquarters in Yong-in, Gyeonggi-do, South Korea. The equipment (MiLab) is a fully automated device that employs artificial intelligence (AI) to detect and quantify the various malaria parasites. A successful implementation of this project might yield a better sensitivity than light microscopy and also eliminate the human error due to diagnosis. Malaria is known to be endemic in sub-Saharan Africa, as such, it is appropriate to assess the sensitivity and specificity of such an automated device in this part of the world. The Vector-Borne Infectious Diseases Research Group (VBID-RG) is partnering with Noul Inc. to assess the accuracy of the automated device for malaria diagnosis. VBID-RG has been studying malaria transmission at the community/hospital level in Ghana across all the transmission settings. The results obtained from the automated device will be compared with the traditional methods (microscopy and RDT) used in malaria diagnosis.
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