7.0 LECTURE SYNOPSES:
7.1 Dr. Clive Bennett : double lectures Back
Plasmodium ultrastructure, Pathogenesis,
Introduction to vaccination and diagnosis .
The malaria (Plasmodium) genome project
MAJOR REFERENCE FOR MALARIA SERIES:
Molecular approaches to malaria: Special Issue of
Parasitology Today Vol 16 (No 10) pp 407-454
(Electronic Access from Library resources)
For this lecture
Pathogenesis of malaria Ref: Parasitology Today (Special Issue of Parasitology Today Vol 16 (No 10)
Vol 16 (No 10) p451 I.A. Clarke and L. Schofield
There is a real prospect of untreatable malaria spreading round the world. The more benign malarias are seasonal but in tropical areas the lethal form Plasmodium falciparum is more common.
Children that survive early childhood malaria develop some form of immunity but some parasites remain in the bloodstream.
Black water fever hampered colonisation of Africa until the discovery of quinine.
Resistance to drugs like the synthetic form of quinine: chloroquine is spreading and malaria as a result is returning to areas where the disease was eradicated in the 1960's
The Walter Reed Institute has produced evidence of the best protective immunity
with a vaccine containing parts of the parasites acts as a protective vaccine against the infective stage of the parasite.
Concern revolves around the strain of the parasite used experimentally as compared with the variety of strains which present in the world at large.
Penetration of the Red Blood cell by Plasmodium: structure and cell biology of Plasmodium.
Parasitology Today Vol 16 (No 10) p 410 Parasite rupture and drug combinations
Parasitology Today Vol 16 (No 10) p 411 Host Cell Invasion by malaria parasites
i) to demonstrate penetration and survival mechanisms of the genus Plasmodium both inside and outside of host cells:
The invasion of host red blood cells by Plasmodium falciparum merozoites is a complex process requiring multiple receptor-ligand interactions. Glycophorin A, a sialic acid-rich integral membrane protein, is an important RBC receptor for merozoites.
Naitza et al 1998 The thrombospondin-related protein family of apicomplexan parasites: The gears of the cell invasion machinery. Parasitology Today 14 (2) 479-484
ii) To provide a parasite perspective of survival mechanisms including deployment of repetitive epitopes.
The mature human erythrocyte has no internal organelles, no protein synthesis machinery and no infrastructure for protein trafficking. The malaria parasite invades this empty shell and effectively converts the erythrocyte back into a fully functional eukaryotic cell.
Parasitology Today, 1995, Vol.11, (11), 436-439
Merozoite Erythrocyte Surface antigen (MESA) binding to protein 4.1 plays a major role in intraerythrocytic parasite viability.
Magowan et al (1995). Role of the Plasmodium-falciparum Mature-Parasite Infected Erythrocyte Surface-Antigen (Mesa/Pfemp-2) In Malarial Infection of Erythrocytes. Blood,.86, No.8, pp.3196-3204
iii) To provide an understanding of other functional surface molecules.
Parasitology Today Vol 16 (No 10) p 416 falciparum malaria Sticking up standing out and out standing Cooke et al.
e.g. antigens affecting sequestration. Adhesive ligands on the infected erythrocyte are less well characterised. but there is evidence from cloned parasites that there is antigenic variation of erythrocyte surface antigens:
VESA (Variant Erythrocyte Surface Antigens) These have been proved to be involved in Sequestration
Host antigens recognised: CD36 endothelial membrane glycoprotein
Sequestration is: withdrawal of erythrocytes containing mature forms of the parasites from the peripheral circulation . The advantages are :
avoidance of the spleen, allows completion of maturation of the infection 48-72 hours, allows completion of the differentiation to gametes (7 days)
iv ) to introduce the concept of host immune response affecting parasite populations. The var multigene family which encodes the PfEMP1 variants and the 'strain' hypothesis.
Parasitology Toay Vol 16 (10) p 427 A brief Illustrated guide to the ultrastructure of Plasmodium falciparum van Doren et al.
Route to a Malaria Vaccine (see Blackboard for additional details and references)
MHC and candidate antigens for vaccination
Parasitology Today 16 (10) p 444 'Malaria Vaccines' Andres and Saul
Sutherland (1998) Parasitology Today 14 (8) 329-332
Anti-gametocyte / gamete transmission blocking antibodies (e.g. anti Pfs230)
Inhibitors or antibodies against mid-gut proteases
Antizygote-ookinete transmission blocking antibodies (e.g. anti Pfs25/Pbs21)
Anti-chitinase antibodies or drugs (e.g. allosamidin).
Antibodies directed against mosquito structures and molecules
Receptor - ligand interactive molecules
Immune or chemotherapeutic inhibitors of sporozoite maturation/migration or salivary gland invasion
MHC responses malaria vaccines and vaccination technology
An up to the minute review of the various candidate antigens for vaccination against malaria. Current trial results and the way forward.References:
Methods in Microbiology Volume 25 459-469 Chapter 5 : Art and Science of DNA vaccines
Methods in Microbiology Volume 25 470- 502 Chapter 6 : Prepararation and Use of Adjuvants
Molecular Genomic and data-mining approaches
The Bill Gates Foundation research on Malaria lead by Prof Dominic Kwiatkowski, University of Oxford addresses how new genomic approaches are tackling old questions - how does protective immunity against malaria work via an impressive international malaria research consortium.
The recent developments in DNA profiling techniques automation and testing for single nucleotide polymorphisms to discover novel genetic factors underlying the nuts and bolts of malaria parasitism.
Information stored in electronic databases for both people and parasites allow important statistical data-mining. Armed with all of data, we can be in a position close enough even to make major a hypotheses for malaria.
The haemoflagellates: Trypanosoma and Leishmania
Lecture 7 Antigenic variation and Genetic variability in trypanosomes
To explain the problems with vaccines against protozoa which have a mechanism of antigenic variation: specifically in African sleeping sickness caused by Trypanososoma brucei gambiense and T.b. rhodesiense.
General web site:
A Brief Introduction to Antigenic Variation
F.E.G.Cox (2nd Edn) Modern Parasitology. A Textbook of Parasitology
Elsayed, et al. (1995) Trypanosoma-brucei-rhodesiense provide new insights into the biology of the parasite. Molecular And Biochemical Parasitology 73, (1-2) 75-90
Chagas disease caused by another trypanosome T. cruzi uses a completely different set of strategies for survival. It also appears to produce a range of clinical effects that may be governed by both the genetics of the host and the parasite.
Implications for the pathogenesis of Chagas Disease: Macedo and Pena (1998) Parasitology Today 14 (3) 119-124
Leishmaniosis : a spectrum of disease causing species
To introduce the life cycle and zoonotic aspects of the range of Leishmania infections
There are three groups
1. Cutaneous types from two areas of the world:
Old world Leishmaniasis: L. tropica, L major , L. aethioipica
New world cutaneous Leishmaniasis L. braziliensis etc
2. Mucocutaneous leishmaniasis
3. Visceral leishmaniais 'Kala - azar' caused by L. donovani
J.D. Smyth Introduction to Animal Parasitology pp68-87
To introduce the intra-cellular habitat of Leishmania in a host cell and specifically in the host parasitophorous vacuole.
This fluid filled vesicle that contains many individual parasites can swell to occupy the bulk of the host cell. PV intersects readily with the endocytic pathway of the macrophage
( Alexander J. and Vickerman K. 1975 J. Protozool. 22 502-508.)
This interaction between the parasite and the macrophage causes little overt alteration in macrophage function and appears to be an extremely enduring relationship. Protective immunity to Leishmanial infection is mediated through activation of the macrophage by interferon gamma (IFN ) and tumour necrosis factor (TNF) . The activated macrophage, using the inducible nitric oxide synthase, produces nitric oxide (NO) which is toxic to the parasites. It also absorbs the dead parasites, and recovers its normal morphology and function.
It is thought that the PV behaves as a functional, acidic, hydrolase-rich lysosomal compartment within the continuum of the host cell's endocytic pathway.
The paradox remains as to how Leishmania can resist degradation by the host cell enzymes and survive the low pH of the vacuole, while exploiting the rich supply of nutrients delivered by the host cell.
Methods in Microbiology Volume 25 (Reserve Collection)
Chapter 4.2 The leishmaniasis Model
Kropf and Muller Benson and Etges (1998)
To introduce the drug treatments
The drugs of choice for visceral leishmaniosis and mucocutaneous leishmaniosis are pentavalant antimonial compounds, such as sodium stibogloconate which is given daily by intramuscular or intravenous injection. In adults the dose is 10mg/Kg body weight for up to 30 days.
This is usually a mild condition which can be treated by infiltration of the ulcerated area by sodium stiboglucoate or mepacrin. A daily dose of pyrimethamine consisting of 0.5mg/Kg body weight for 21 days also appears to be effective. An alternative is oral memetronidazole.
The Leishmaniosis web site is:
Papadopoulou_G, et al. (1998) ISCOMs vaccine against experimental leishmaniasis Vaccine, 16, 885-892
Veterinary Parasite Ecology
(see Blackboard for all references and details : these are new lectures).
II Forecasting of disease in sheep and cattle
Veterinary parasitology new technology
(see Blackboard for all references and details : these are new lectures).
I Nematode vaccines and treatments : Toxocara canis
II Fleas and tick control. Tapeworms Taenia species and vaccine development. Dog tapeworm Echinococcus (hydatid). Control of a zoonosis.
LECTURES OF Dr. Lindy Holden-Dye occur here
Treatment and Drug resistance in metazoan parasites
(both Endo and Ecto Parasites) Examples :Schistosomiosis and Scabies
i) to provide a general introduction to resistance to treatments in metazoan parasites and current methods of detecting resistance..
See Library Electronic resources for the following reference:
Anthelmintic resistance detection methods, Pages 183-194
M. A. Taylor, K. R. Hunt and K. L. Goodyear
Summary Plus Full Text + Links PDF (65 K)
'Genetically transmitted loss of sensitivity in a parasite population that was previously sensitive to a given drug' Redman 1996 Parasitology Today 12, 14-20
Resistance to drug treatments in Schistosomes:
Rogers and Bueding reported the first genuine cases of resistance in 1971 They observed that S. mansoni infected mice treated with low doses of hycanthone after an initial period of apparent cure resumed faecal egg excretion if observed for a further 6-12 months. Schistosomes originating from these eggs were highly reistant to Hycanthone, Lucanthone and Oxamniquine. In humans this patter re-occurred and Hycanthone was withdrawn even though the number of cases was small. Oxamniquine however is still widely used.
N.B. Oxamniquine is a treatment which is restricted in its use to S. mansoni.
There is a much greater controversy over whether problems with Praziquantel the most widely used drug are due to true resistance or tolerance. This drug is effective against all major species including S.haematobium.
In Northern Senegal low cure rates have been reported over the past decade Danso-Appiah & De Vlas (2002) as low as 18-38%. Increasing the dose did not significantly improve the results.This finding alarmed the scientific community!
Rogers and Bueding (1971) Hycanthone resistance : Development in Schistosoma mansoni Science 172 1057-1058
Cioli D Pica-Mattococcia L & Archer S. (1995) Drug resistance in schistosomes Parasitology Today 9, 162-166
Cioli D (1998) Chemotherapy of Schistosomiasis an update Parasitology Today 14 418-422
Piereira C. Fallon P. Cornette J, Capron, A Doenhoff M & pierce R (1998) Alterations in Cytochrome-c oxidase expression between praziquantel resistant and susceptible strains of Schistosoma mansoni. Parasitology 117, 63-73.
Danso-Appiah, A & De Vlas S (2002) Interpreting low praziquantel cure rates of Schistosoma mansoni infections in Senegal. Trends in Parasitology 18, 125-129
Treatment of ectoparasites including Scabies and head lice: Resistance to treatment
caused by Sarcoptes scabiei f.scabiei (var. humanis) is common worldwide
(Mellanby 1972). And is a major human health problem in many less
developed countries. Where long term data exist, the disease appears to show
cyclical epidemiology with a periodicity of 10-15 years (Rook, Wilkinson, and
Ebling 1998). In the U.K., in common with many European Countries,
scabies is not a reportable disease but is considered by some to be a
major health issue, which has been ignored. Infection occurs primarlily through
close personal contact (Mellanby 1941). Typically only a few
adult female mites, which tend to remain in their burrows, provoke an
intense allergic reaction with lesions and pruritis *(Falke 1988). Delayed type
hypersensitivity has been suggested from the histology and predominance of
T-lymphocytes in the inflammatory papules and nodules (Rook, Wilkinson, and
past treatments for scabies in the U.K. have included gamma benzene hexachloride,
withdrawn because of resistance and Quellada
(lindane) withdrawn 1997 because of
toxicity. Currently treatments include malathion (Derbac M), permethrin
(Lyclear Dermal Cream) and benzyl benzoate. Additionally there is some
unlicensed use of oral ivermectin.
all treatments there can be problems which lead to failure. These include
non-compliance with instructions and the need to treat all contacts of affected
patients. In the case of benzyl benzoate there is also the need for repeat
application and problems with compliance result from a transient burning
sensation with itching in some cases. Non-controlled studies with benzyl
benzoate have indicated a cure rate of 50% with resistance implicated.
There is now a rising and urgent need for assessment of efficacy of the available treatments, however there have been few randomised controlled trials on treatments of scabies and none published which compare malathion, permethrin and benzyl benzoate.
In 1999 no resistance had been reported to malathion or permethrin treatments. Most treatment failures were attributed to inadequate application.
By 2000 a survey of British dermatology consultants indicated resistance to permethrin 'Lyclear Dermal Cream 5%'
Bennett C.E. et al. Perceptions of the incidence of scabies and efficacy of treatment in U.K. hospitals. British Journal of Dermatology 143, 1337-8
Results of a GP survey in 2002 indicate likewise:
1 Christopherson J. Epidemiology of Scabies. Parasitol
Today 1986; 2:
Harvey I, Kennedy CTC. The epidemiology of head lice and scabies in the UK. Epidemiol
and Infect 1999; 122: 471-477.
and Johnstone PW. Interventions for
treating scabies. Cochrane review. In the Cochrane Library (ISSN 1464-780X)
Issue 2000; 1: http://www.update-software.com/abstracts/ab000320.htm
4. Champion RH, Burton JL, Burns DA, Breathnach SM, (editors) Rook/Wilkinson/Ebling: Textbook of Dermatology. Oxford: Blackwell Science: 1998.
5. Head Lice Resistance statement by Pfizer on resistance of head lice to Pyrethrin/piperonyl butoxide, the active ingredients in RID Shampoo.
Travel medicine and alternative control measures Debate on vaccination against malaria: prospects for vaccination, diagnosis and treatments,
Reference 1. Disease control leaflet
(CDR) Communicable Disease Report
Review Volume 7 Review No 10 19 Sept 1997
Reference 2 Poster outside my office Practice Nurse Sept 2002. This is the same material as is available only to doctors and nurses from TRAVAX
Gametocidal drugs (e.g. primaquine, and possibly artemisin and its derivatives
Sporonticidal drugs (e.g. pyrimethamine and atovaquone)Parasitology Today 16 (10) p 438 Anti-malarial drug development and new targets Macreadie et al.
Low Technology approaches to parasite control: WHO Bed nets and spraying comparisons The rationale used by the WHO World bank in selecting beneficial projects and to review the products of the Tropical Disease Research (TDR) projects (WHO perspectives).
DEBATE: High Technology Vaccination development and theory.
The demands to keep the vaccine up to date due to variation in the parasite with time.
The risks to a parasitologically naive population. Would vaccination have to continue for life?
Drugs and Vaccines Is Complimentarity is crucial?
Tanner and Evans Parasitology Today October 1994 10, 406-407
Curtis C.F. et al. (1998). A comparison of use of a pyrethroid either for house spraying or for bednet treatment against malaria vectors Tropical Medicine & International Health, 3,.619- 631
(Biol3002 Reserve Collection)
© Dr. Clive Bennett 2006