Molecular approaches to DNA diagnosis

Enzymatic amplification of mini-exon-derived RNA gene spacers of Leishmania donovani: primers and probes for DNA diagnosis

The multicopy mini-exon-derived RNA (med RNA) locus of Leishmania donovani was enzymatically amplified by the polymerase chain reaction (PCR). The major 180 bp PCR product contained conserved med RNA gene sequences flanking the variable intergenic spacer from the med RNA gene tandem repeat. The oligonucleotide primers cross-reacted with other Leishmania species. In serial dilution experiments, positivity in the PCR assay was observed down to the genomic DNA equivalent of less than a single Leishmania cell. When the major PCR products from Indian L. donovani isolates were cloned and used as probes in dot hybridization analyses, they discriminated between L. donovani and L. amazonensis, L. major and L. infantum under high stringency conditions. DNA from spleen biopsies and blood samples of confirmed kala azar patients was positive, as were two skin biopsies from patients with post-kala azar dermal leishmaniasis (PKDL). These observations demonstrate that PCR amplification of med RNA intergenic spacers is sufficiently sensitive for clinical diagnosis of kala azar and PKDL, and furthermore, that cloned intergenic spacer probes may be useful for identification and classification of L. donovani.

Tubo-ovarian abscess containing tapeworm proglottids and ova: a case report

We report a case of pelvic inflammatory disease complicated by a tubo-ovarian abscess containing Taenia spp. proglottids and ova which migrated through a fistula with the sigmoid colon.

Leishmaniases of the New World: current concepts and implications for future research

Recent epidemiologic studies indicate that leishmaniasis in the Americas is far more abundant and of greater public health importance than was previously recognized. The disease in the New World is caused by a number of different parasite species that are capable of producing a wide variety of clinical manifestations. The outcome of leishmanial infection in humans is largely dependent on the immune responsiveness of the host and the virulence of the infecting parasite strain. This article reviews current concepts of the clinical forms, immunology, pathology, laboratory diagnosis, and treatment of the disease as well as aspects of its epidemiology and control. Recommendations for future research on the disease and its control are made.

[Molecular biological techniques in the diagnosis of tropical parasitic diseases]

Recent advances in the development of molecular biological techniques have resulted in their supplementary application for improved diagnosis of tropical parasitic diseases. The main areas of interest are the production of recombinant antigens for immunodiagnosis, and the detection of parasites by hybridization of nucleic acids and by DNA amplification (PCR) in vitro.

Diagnosis of New World leishmaniasis: Specific detection of species of the Leishmania braziliensis complex by amplification of kinetoplast DNA

We have sequenced single kinetoplast DNA minicircles from three species and part of a minicircle from the fourth major species within the Leishmania braziliensis complex. Alignment of these sequences with each other and with those of other kinetoplastids allowed the selection of a pair of oligonucleotides suitable as primers in a polymerase chain reaction which is highly specific for the Leishmania braziliensis complex. The reaction is capable of detecting less than one femtogramme of kinetoplast DNA. It has been tested with crude specimens from South American leishmaniasis patients, potential wild animal reservoirs and sandfly vectors. The tests indicate that these primers are suitable for diagnosis of leishmaniasis and potentially useful in epidemiological surveys.

Implications of rDNA technology in the microbiology laboratory

The present and potential future roles in service and research microbiological laboratories of recombinant DNA (rDNA) techniques (nucleic acid hybridization, nucleic acid amplification, in situ hybridization, pulsed field gel electrophoresis) are described. Applications rDNA technology include the detection of micro-organisms; an approach to the understanding of their role in disease pathogenesis and provision of alternative strategies for studying the epidemiology of infectious diseases.

DNA fingerprints: a tool for identification and determination of the relationships between species and strains of Leishmania

Using nonradioactive hybridization, the multilocal probes 33.15, F10 and (CAC)5 were shown to recognize multiple minisatellite regions in nuclear DNA of Leishmania, producing on Southern blots complex banding patterns typical of DNA fingerprints. We used the 33.15 probe to study 14 different strains belonging to 6 different species from both the sub-genus Viannia and the Leishmania mexicana complex of the sub-genus Leishmania. Distinct DNA fingerprints were obtained for each strain, permitting their identification. On the other hand, each strain showed little or no clonal variation. The information from the fingerprinting maps could be used for constructing phenograms and cladograms of the species and strains of Leishmania.

Adaptation of a radioactive L. donovani complex DNA probe to a chemiluminescent detection system gives enhanced sensitivity for diagnostic and epidemiological applications

The cDNA probe, Lmet2, was labelled with digoxigenin and used in a chemiluminescent system to detect fewer than 100 membrane-immobilized Leishmania parasites. The probe was found to hybridize primarily with members of the L. donovani complex but a slight cross-reaction was also observed with greater than 5 x 10(4) L. major. This cross-reaction was reduced by hybridizations in 50% formamide at 37 degrees C. Formamide also significantly reduced non-specific binding of the digoxigenin-labelled probe to the membrane support which, in hybridizations without formamide, masked the specific hybridization signal. This background was not observed with the corresponding radio-isotope labelled probe. With hybridizations in formamide the sensitivity achieved by the chemiluminescent system after exposure to film for 3 h was greater than that achieved by the isotopic system even after autoradiography for 24 h.

Leishmaniasis epidemiology: all down to the DNA

Application of quantitative methods to the study of leishmaniasis epidemiology has allowed Dye (1992) to pinpoint important biological parameters which, if they could be accurately measured in the field, would contribute most to our knowledge of the spread of disease and key targets for control. Three areas in which laboratory-based research could impact most on leishmaniasis epidemiology were highlighted by Dye (1992): (i) the development of accurate diagnostic tools which can distinguish between current and past infection; (ii) to determine the underlying molecular/genetic basis to virulence polymorphisms in the parasite and study these in the context of field epidemiological studies; and (iii) to provide the molecular tools to measure genetic variation in resistance to infection in humans and in reservoir hosts of disease. This paper describes current progress in attaining these goals, highlighting first the work on isolation and field application of genomic and kDNA probes for species-specific diagnosis, and the development of PCR-based assays which can be performed under field conditions. At a more preliminary stage, studies are described in which variability in the major molecular determinants of virulence (lipophosphoglycan, GP63, and members of the HSP70 family of stress proteins) identified through studies of laboratory models of infection, is being measured in primary field isolates of Leishmania peruviana. To complete the picture, current progress in identifying and cloning the genes which control host resistance to leishmanial infection is described, along with field studies of multicase families of human disease in which linkage analysis using marker genes from the chromosomal regions bearing these genes can be used to find evidence for their role in determining disease phenotypes in man. The projected view from these studies is that the future of leishmaniasis epidemiology will be all down to the DNA.

A species-specific oligonucleotide DNA probe for the identification of Meloidogyne incognita

A genomic library of Meloidogyne incognita Race 1 has been prepared in the bacteriophage lambda gt10 and screened for specific DNA sequences by hybridization with radio-isotope labelled total genomic DNA from a number of Meloidogyne species. One clone isolated (MR1 #15), although not totally species specific, clearly showed preferential hybridization to M. incognita. Following subcloning and sequencing of the 255 bp insert, four stretches of the sequence corresponding to oligonucleotides of approximately equal length (approximately 70 bp) were synthesized and examined for specificity. One of them, MR1 #15.2, showed the necessary specificity to be used as a diagnostic tool.

A family of repeated DNA sequences in Toxoplasma gondii: cloning, sequence analysis, and use in strain characterization

A Toxoplasma gondii genomic library was constructed in lambda EMBL3. Repeated fragments were detected by hybridization with radiolabeled total DNA from the parasite and one recombinant was chosen due to its strong hybridization signal. By using electrophoretic and hybridization analysis, four cross-hybridizating restriction fragments were selected and sequenced. The determined nucleotide sequence of these fragments (TGR1A, TGR1E, TGR2, and TGR4) has shown a complex system of conserved and degenerated repeats in which TGR1E corresponds to the most conserved element. This last sequence was used to investigate restriction fragment length polymorphisms among several T. gondii strains by Southern blotting.

Detection of Babesia equi in infected horses and carrier animals using a DNA probe

The ability of the Babesia equi repetitive probes, pSE2 and pSB20, to detect parasites in blood from experimentally infected, naturally infected and carrier animals was tested using a spot hybridization assay. The clinical course of the experimentally infected horses was monitored using microscopy, indirect fluorescent antibody tests, packed cell volume, temperature and the probe assay. The probes sensitively monitored the parasite level during the development of the disease and correlated well with the other parameters tested. The sensitivity of the probe assay was superior to that of light microscopy, and a parasitaemia equivalent to less than 0.0025% could be detected. Detection of B. equi DNA was possible in all natural cases tested and 20 of the 119 randomly selected horses were identified as carriers of B. equi parasites. Microscopy could identify parasites in only 8 of these carrier animals. These results show that the probes can detect B. equi parasites in carrier animals and that they are suitable for use in a laboratory-based assay for B. equi.

Nucleic acid techniques and the detection of parasitic diseases

The detection of infectious disease-causing organisms is important for the initiation of effective treatment, in monitoring response to therapy and in epidemiological studies of disease of human or animal hosts. In this article Stuart Wilson primarily considers parasitic diseases, but much can be applied to infectious diseases in general.

DNA polymorphisms within Spanish Trichinella isolates

A total of 13 Spanish Trichinella isolates were characterised by DNA analysis. Genomic DNA cross-hybridisation tests revealed two distinct groups that exhibited weak cross-reactions. Further diagnostic subdivision was attempted according to restriction-fragment polymorphism using a cloned T. spiralis DNA repetitive fragment as a probe, but no major difference between the two Trichinella groups was observed.

Differential diagnosis of Taenia saginata and Taenia solium with DNA probes

A size selected genomic DNA library was constructed using DNA extracted from Taenia saginata. The DNA was digested using the restriction enzyme EcoR1 under star conditions and the 2-4 kbase fraction, selected following sucrose density-gradient separation, was cloned in the bacteriophage lambda gt 10. A panel of cestode DNAs including Taenia saginata, Taenia solium, Taenia taeniaeformis, Taenia crassiceps, Echinococcus granulosus and DNAs of bovine, porcine and human origin were used in conjunction with hybridization analysis to identify two recombinant bacteriophages. The first probe, designated HDP1, reacted specifically with T. saginata DNA. The second, designated HDP2, reacted with DNA from both T. saginata and T. solium but not the other DNA samples and thus provided a general reagent for positive identification of fragments of Taenia spp. proglottides of human faecal origin. If used in conjunction the two DNA probes allow positive identification of T. saginata. In the clinical situation it is important to be able to distinguish T. saginata and T. solium infections and DNA probes such as these may be useful in such differentiation.

Variation and polymorphism in parasite phenotype--implications for the selection of potential intervention strategies

Work reported at this meeting has described the exploitation of variation in parasite phenotype in disciplines ranging from molecular taxonomy and drug development, through the understanding of host-parasite interaction, to the evolution of parasite populations and determining the potential efficacy of vaccine programmes.