Dr Rhayza D. C. Maingon

Research group

Current research projects

I have been investigating the leishmaniases during the past 18 years, working alongside colleagues from endemic countries, on a number of largely European Union sponsored projects of varied objectives towards solutions of scientific and practical problems in molecular epidemiology and vector control. My current main focus is on American visceral leishmaniasis caused by Leishmania chagasi/infantum and transmitted by Lutzomyia longipalpis, a complex of sibling species.

Within CAEP, my group is part of the Leishmania & Sandflies group, an informal association of CAEP members which meets to share and discuss relevant journal and laboratory information, joint grant applications, publications or supervision of research students, and to represent the subject area within CAEP/ISTM and outside Keele.

Our group shares state of the art facilities for molecular and cellular techniques housed in the Huxley Building with other members of the Centre, and a new Proteomics Mass Spectrometry set up housed at the Robert Jones & Agnes Hunt Orthopaedic Hospital, Oswestry, with members of the Institute for Science and Technology in Medicine.

The Lutzomyia longipalpis species complex: does population sub-structure matter?

(Maingon, Ward, Hamilton in collaboration with Alexander Peixoto, Instituto Oswaldo Cruz, Rio de Janeiro, Brazil, Stephen Kemp and Phill Watts, Liverpool University; supported by the Wellcome Trust and the Brazilian CNPq)

Lutzomyia longipalpis is the main sandfly vector of Leishmania chagasi/infantum, the cause of visceral and atypical cutaneous leishmaniasis in Latin America. There is now good evidence for Lu. longipalpis being a complex of incipient, sibling species, and also for the sexual isolation barriers between siblings. Lu. longipalpis siblings may differ in their micro-habitats and/or in their vectorial capacities, as is the case in An. gambiae. We are applying post-genomic strategies to define speciation determinants relevant to sandfly-Leishmania co-evolution aiming to identify novel sandfly molecules important for Leishmania transmission, and adaptation to changing eco-climates.

	Liberia: The white sanded coastal ACL foci of Liberia where Lu. longipalpis transmits Le. chagasi/infantum, is characterised by large extended families living under the same roof, in one-two rooms with an outside open fire stove, (Photo: RDCM, August 1994).
	San Juan Bautista (a): The agricultural settlement of San Juan Bautista in Southern Honduras, where Le. chagasi/infantum causes visceral leishmaniasis. Photo: RDCM, May 1993.
	San Juan Bautista (b): Close proximity to livestock (chickens, dogs, donkeys and pigs) is observed. Photo: RDCM, May 1993.
Microsatellite-based un-rooted nearest-neighbour tree for Brazilian and Venezuelan Lutzomyia longipalpis populations. Genetic differentiation values (theta) estimated from microsatellite allele frequencies were used to construct the tree. Dashed line separates Brazilian and Venezuelan samples. Male sex pheromone structures for each population are shown when known. Bootstrap values above 50% are displayed. Note the cembrene cluster that maps to the Northeast of Brazil, the region contributing more than 90% of visceral leishmaniasis cases from Latin America.
	The main entrance to the Charles Nicolle laboratory, at the Institute Pasteur, Tunis (Photo: RDCM, May 1992). Charles Jules Henry Nicolle (1866-1936) was a French bacteriologist who won the Nobel Prize in Medicine in 1928 for showing that lice transmits typhus fever. He named Leishmania infantum Nicolle in 1908.

Characterisation of salivary proteins from sibling species of the Lutzomyia longipalpis species complex

(Maingon, Taha, Ward in collaboration with Heidi Fuller, Mass Spectrometry Facility, Oswestry RJAH Orthopaedic Hospital , and Harry Noyes, Genomics Laboratory, Liverpool University)

Insect vectors for pathogens are more than mere 'flying syringes'. Experimental animal models and epidemiological studies have demonstrated that sandflies influence infection outcome, aiding initial pathogen establishment in vertebrate hosts, by regurgitating Leishmania, at the biting site, along with a battery of salivary components that down-regulate the mammalian immune response. A number of salivary proteins are currently the object of intense research elsewhere aiming to develop a sandfly spit-vaccine and one of the most studied sandflies is Lu. longipalpis since it is the main vector for visceral leishmaniasis in the Americas. This research however has focused on just one of the sibling species of the Lu. longipalpis species complex and one vaccine for all 'longipalpis' might not be a practical option.

We have been studying the single SDS-PAGE dimension and Mass Spectra salivary gland proteomes for three of the Lu. longipalpis siblings as well as their Western blot recognition by sera from hamsters separately challenged with each of the siblings. A number of surprising and exciting observations stemming from these investigations are currently being prepared for dissemination. We would like to pursue salivary candidates for pheromone reception, Al/Si binding and sandfly-Leishmania co-speciation factors that might influence Leishmania virulence in the vertebrate host.

Determinants of Leishmania tropism: Leishmania chagasi/infantum infection in Central America

(Maingon, Ward, in collaboration with Chris Exley, EPSAM)

Leishmania infection in humans results in a wide spectrum of outcomes ranging from asymptomatic infection, single or multiple non-ulcerated or ulcerated dermal lesions, mucosal destruction, to visceral involvement. Parasite tissue tropism and disease severity appear to depend upon an as yet not fully understood interplay between the genetic susceptibility and immune status of the host, the Leishmania species, genetic variability of the sandfly vector, and possibly environmental factors.

Since 1992, we have been studying Leishmania chagasi/infantum infection in Central America where patients display varied infection outcomes: either relatively benign non-ulcerated lesions (atypical cutaneous leishmaniasis, ACL), or full blown visceral leishmaniasis.

We found that Le. chagasi/infantum genetic heterogeneity and polymorphisms of specific candidate virulence factors were not associated with clinical pleiotropism. However, recently it has been demonstrated elsewhere that ACL lesions also harbour solid inorganic particles rich in Si and Al. Al might be boosting the immune response in ACL compared to VL patients or/and induce apoptosis in Leishmania-infected macrophages is possible.

We have been investigating this further and are currently preparing the first promising results for dissemination.

Atypical cutaneous leishmaniasis: Non-ulcerated lesions harbouring Le. chagasi/infantum parasites, on the back shoulder of a young man from Liberia, Costa Rica. (Photo: RDCM, August 1994).
Cutaneous leishmaniasis: A single large crater-bordered ulcer harbouring Le. braziliensis on the left hand dorsal area of a young woman from Lomas Bajas, in the Andean coffee-growing Táchira State , Venezuela , (Photo: RDCM, November 1990).
Visceral leishmaniasis: A child with enlarged spleen and liver, in the State of Bihar , North Eastern India (Photo: RDCM, April 2003).

Leishmania transmission and Leishmania load in sandflies

(Maingon, Ranasinghe, Hamilton, Ward in collaboration with Matt Rogers and Paul Bates, Liverpool School of Tropical Medicine)

Accurate determination of pathogen load within its cognate vector is important for studies on the vector-pathogen interactions involved in transmission, where infection rates, infectivity and vectorial capacity need to be estimated. It is also useful for assessing the impact of transmission blocking vaccines.

We have developed an accurate, sensitive and robust QRT-PCR method for the detection, identification, and quantification of Leishmania chagasi/infantum within Lutzomyia longipalpis, its main natural vector in Central and South America. The assay is based upon amplifications and TaqMan probes of the DNA polymerase gene of Le. infantum and the periodicity gene of Lu. longipalpis. Relative and absolute quantification methods estimated a sensitivity of ~25-100 parasites, a specificity of ~100%, and excellent inter-assay CV (6.5%<CV<8%), when used to quantify Leishmania within experimentally infected sandflies.

We are currently interested in applying this and other methods to molecular epidemiology field investigations in Sri Lanka where Phlebotomus argentipes and Le. donovani and only the cutaneous form of this disease occur.

UV-induced apoptosis in Anopheles gambiae: roles of bcl-2 like proteins

(Maingon, Mills, Williams, Deaville)

Programmed cell death is as important as life sustaining active processes for differentiation and development, as well as for avoiding spread of uncontrolled proliferating cells and inheritance of damaged DNA. Controlling PCD is therefore important for any organism. This is partly achieved by the balance between apoptotic and anti-apoptotic bcl-2.

We have developed an Anopheles gambiae Sua 4.0 cell line system amenable to the study of UV-induced apoptosis, and used it to study the expression of a number of bcl-2 genes. Using RT-PCR, we found diminished expression of Dad-1, an essential N-glycosyl transferase and an anti-apoptotic bcl-2 type protein, soon after UV induction of apoptosis. This supports a p53-mediated mitochondrial intrinsic apoptotic pathway for this system. The expression of other bcl-2 genes (Bax, Bok, Bag, Morgue and others) is currently being investigated. It is hoped that understanding apoptosis in An. gambiae will help to define new avenues for the control of malaria.

e-mail: caep@keele.ac.uk
Last updated: 27 June 2007 09:20