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PubMed2002

Natural and induced dyskinetoplastic trypanosomatids: how to live without mitochondrial DNA.

Salivarian trypanosomes are the causative agents of several diseases of major social and economic impact. The most infamous parasites of this group are the African subspecies of the Trypanosoma brucei group, which cause sleeping sickness in humans and nagana in cattle. In terms of geographical distribution, however, Trypanosoma equiperdum and Trypanosoma evansi have been far more successful, causing disease in livestock in Africa, Asia, and South America. In these latter forms the mitochondrial DNA network, the kinetoplast, is altered or even completely lost. These natural dyskinetoplastic forms can be mimicked in bloodstream form T. brucei by inducing the loss of kinetoplast DNA (kDNA) with intercalating dyes. Dyskinetoplastic T. brucei are incapable of completing their usual developmental cycle in the insect vector, due to their inability to perform oxidative phosphorylation. Nevertheless, they are usually as virulent for their mammalian hosts as parasites with intact kDNA, thus questioning the therapeutic value of attempts to target mitochondrial gene expression with specific drugs. Recent experiments, however, have challenged this view. This review summarises the data available on dyskinetoplasty in trypanosomes and revisits the roles the mitochondrion and its genome play during the life cycle of T. brucei.

Animals↗
PubMed2002

Expression of calreticulin P-domain results in impairment of secretory pathway in Leishmania donovani and reduced parasite survival in macrophages.

The secretory proteins of Leishmania are thought to be involved in the parasite survival inside the insect vector or mammalian host. It is clear from studies in higher eukaryotes that proper folding in the endoplasmic reticulum and targeting out of the endoplasmic reticulum is critical for the function of secretory proteins. The endoplasmic reticulum chaperones such as calreticulin play an important role in the quality control of secretory proteins. However, very little is known about the secretory pathway of trypanosomatid parasites such as Leishmania. In the present study, we show that overexpression of the P-domain of Leishmania donovani calreticulin in transfected L. donovani resulted in a significant reduction in the secretion of the parasite secretory acid phosphatases. This effect is associated with an intracellular accumulation of active enzyme in these transfected parasites. In addition, parasites expressing the P-domain calreticulin showed a significant decrease in survival inside human macrophages. This study suggests that altering the function of an endoplasmic reticulum chaperone such as calreticulin in Leishmania may affect the targeting of proteins that are associated with the virulence of the parasite during their trafficking through the parasite secretory pathway.

Acid Phosphatase↗
PubMed2003

Cowpea mosaic virus-based chimaeras. Effects of inserted peptides on the phenotype, host range, and transmissibility of the modified viruses.

Expression of foreign peptides on the surface of cowpea mosaic virus particles leads to the creation of chimaeras with a variety of phenotypes and yields. Two factors were shown to be particularly significant in determining the properties of a given chimaera: the length of the inserted sequence and its isoelectric point. The deleterious effect of high isoelectric point on the ability of chimeras to produce a systemic infection occurs irrespective of the site of insertion of the peptide. Ultrastructural analysis of tissue infected with chimaeras with different phenotypes showed that all produced particles with a tendency to aggregate, irrespective of the size or isoelectric point of the insert. Host range and transmission studies revealed that the expression of a foreign peptide did not (1) alter the virus host range, (2) increase the rate of transmission by beetles or through seed, or (3) change the insect vector specificity. These findings have implications for both the utility and the biosafety of Cowpea mosaic virus-based chimaeras.

Amino Acid Sequence↗
PubMed1983

Cell-mediated killing of protozoa.

Cell-mediated immunity represents an important host defence mechanism against protozoal infections. The effector cells directly involved are neutrophils, macrophages and, ultimately, activated macrophages. Within this simple scheme there are, however, considerable variations in activity. Effector cells from different animal species, and even from different strains of the same species, may be more or less effective in controlling a certain protozoal infection. Different protozoa differ in their susceptibility to cell-mediated killing according to genus, species, strain and morphological form. The most susceptible morphological form is that which occurs in the insect vector, and which has not yet adapted to protect itself from the vertebrate host. Epimastigotes of Trypanosoma and promastigotes of Leishmania are readily killed by phagocytic cells, while the corresponding trypomastigote and amastigote forms are considerably more resistant. Protozoa which live in macrophages, such as amastigotes of Leishmania, endozoites (tachyzoites) of Toxoplasma and amastigotes of reticulotropic strains of T. cruzi, have developed a remarkable resistance to the microbicidal activity of the host cell. Conversely, amastigotes of myotropic strains of T. cruzi, which live in muscle cells, have not developed this resistance to cell-mediated killing by macrophages. Readily accessible protozoa, such as T. brucei trypomastigotes and Plasmodium merozoites in the bloodstream, while they lack the marked resistance developed by reticulotropic protozoa, have a partial protection since they are attacked by phagocytic cells only when specific antibody is present. Granulocyte-mediated killing can be largely attributed to neutrophils. Eosinophils appear to play only a minor role and compete ineffectually when neutrophils are also present. The only group of protozoal species which may be significantly controlled by eosinophils are the stercorarian species of Trypanosoma. In vitro experiments show that antibody-coated trypomastigotes of T. cruzi can be killed by eosinophils, although there is little evidence that this occurs in vivo. Interestingly, this is the only species that has been reported to be susceptible to the major basic protein of eosinophils, a toxic component of the lysosomal granules which is very active against helminths. Neutrophils are not very active against endozoites of Toxoplasma gondii, Trypanosoma, trypomastigotes of salivarian Trypanosoma, free merozoites of Plasmodium, and promastigotes and amastigotes of Leishmania.(ABSTRACT TRUNCATED AT 400 WORDS)

Animals↗
PubMed1983

Changes in malaria incidence after mass drug administration in Nicaragua.

Mass drug administration (MDA) in 1981 reduced the incidence rates of both Plasmodium vivax and P falciparum infection in Nicaragua. Impact on P vivax cases lasted for four months and on P falciparum for seven. Subtherapeutic primaquine doses, the shorter extrinsic cycle of P vivax in the insect vector, and the timing of MDA at a high-transmission period of the year may explain the limited effects of the campaign. Positive results of the anti-malaria campaign included improvements in case-finding and routine surveillance, the apparent prevention of at least 9200 malaria cases, the training of some 70 000 antimalaria volunteers, and the participation of about 70% of the population in anti-malarial activities.

Adolescent↗
PubMed1985

Slim disease: a new disease in Uganda and its association with HTLV-III infection.

A new disease has recently been recognised in rural Uganda. Because the major symptoms are weight loss and diarrhoea, it is known locally as slim disease. It is strongly associated with HTLV-III infection (63 out of 71 patients) and affects females nearly as frequently as males. The clinical features are similar to those of enteropathic acquired immunodeficiency syndrome as seen in neighbouring Zaire. However, the syndrome is rarely associated with Kaposi's sarcoma (KS), although KS is endemic in this area of Uganda. Slim disease occurs predominantly in the heterosexually promiscuous population and there is no clear evidence to implicate other possible means of transmission, such as by insect vectors or re-used injection needles. The site and timing of the first reported cases suggest that the disease arose in Tanzania.

Acquired Immunodeficiency Syndrome↗
PubMed1999

The evolution of two Trypanosoma cruzi subgroups inferred from rRNA genes can be correlated with the interchange of American mammalian faunas in the Cenozoic and has implications to pathogenicity and host specificity.

The agent of Chagas disease, Trypanosoma cruzi, is divided into two highly divergent genetic subgroups, lineages 1 and 2, which include all typed strains isolated from humans, insect vectors, and sylvatic mammals. The evolutionary origin of these two T. cruzi lineages and the clinical importance of their identification, have been the subject of intense debate. Here, using molecular phylogenetic analysis, we found that the distance between the two T. cruzi lineages is equivalent to the distance between genera Leishmania and Endotrypanum. Also, we confirmed that T. rangeli is more closely related to T. cruzi than to T. brucei using the rDNA sequence from a human strain of T. rangeli. Phylogenetic trees based on small subunit rDNA sequences further suggest that the two T. cruzi lineages diverged between 88 and 37 million years (Myr) ago. We hypothesize that lineage 2 is indigenous to South America while lineage 1 has been introduced to South America recently, along with North American placental mammals, after the connection of the Americas in the Pliocene (5 Myr ago) or with caviomorph rodents and primates in the Oligocene (38 Myr ago). This would explain the preferential association of T. cruzi lineage 2 with marsupials and of lineage 1 with human disease. These two T. cruzi lineages are likely to be distinct species, or at least subspecies, because of their different ecological and epidemiological traits and estimated long period of independent evolution.

Animals↗
PubMed1997

Heteroduplex analysis in medical entomology: A rapid and sensitive sequence-based tool for population and phylogenetic studies.

Classical studies on the insect vectors of parasitic diseases have relied on morphological, biochemical and cytological characters to classify vector species. These are often inadequate for a detailed dissection of the dynamics of the parasite-vector relationship. Molecular techniques have the potential to provide more reliable data on various aspects of vector biology, including population genetics, molecular phylogenetics, and molecular differentiation and classification of closely related species. However, most molecular techniques are expensive, cumbersome or difficult to apply to the analysis of a large number of samples. Here, Jianming Tang and Tom Unnasch discuss the practical advantages of heteroduplex analysis for the study of medically important vectors, using the black flies that serve as vectors for the filarial parasite Onchocerca volvulus as an example. This technique is simple, rapid, inexpensive and capable of detecting minor differences among DNA sequences.

Journal Article↗
PubMed2003

Canine visceral leishmaniasis and its emergence in the United States.

Leishmaniasis is an important zoonotic disease that accounts for approximately 57,000 deaths among people each year. Dogs are reservoirs for the disease, and dog ownership is a risk factor in endemic areas. This article discusses insect vectors for this disease, as well as diagnosis and treatment for dogs.

Animals↗
PubMed2002

A plasmid from a non-insect-transmissible line of a phytoplasma lacks two open reading frames that exist in the plasmid from the wild-type line.

Two novel rolling circle replication (RCR) plasmids, pOYM (3932 nt) and pOYNIM (3062 nt), were isolated from a mildly pathogenic variant line (OY-M) and a mildly pathogenic plus non-insect-transmissible line (OY-NIM), respectively, of onion yellows (OY) phytoplasma, a plant and insect endocellular mollicute. OY-M was isolated from an original wild-type line (OY-W) after regular maintenance using alternate plant/insect infections, while OY-NIM was further isolated from OY-M after maintenance by plant grafting without insect vectors. The RCR-initiator proteins (Rep) of both plasmids, which have a characteristic structure with both plasmid- and virus-like domains, were highly homologous to that of a previously described OY-W plasmid, pOYW (3933 nt), and were expressed in OY-M- and OY-NIM-infected plants, indicating that this replicon is stably maintained in the phytoplasma. Interestingly, pOYNIM lacked two ORFs that exist in both pOYW and pOYM, which encode a single-stranded DNA binding protein (SSB) and an uncharacterized putative membrane protein, indicating that these two proteins are not necessary for the phytoplasma to live in plant cells. These are the first candidates as phytoplasma proteins possibly related to host specificity.

Animals↗
PubMed2002

Invasion of skin by Schistosoma cercariae.

Schistosomiasis caused by Schistosoma spp. remains a major global health problem affecting >200 million people. The success of these parasites is a result of their adaptation to several different environments, including snail tissue, fresh water and mammalian blood; and their ability to switch between these environments rapidly. The initial step in infection of the human host involves penetration of the human skin by the aquatic form of Schistosoma, the cercaria. This aspect of host invasion is remarkable because no wounds or insect vectors are required and cercariae can penetrate through intact skin rapidly. The mechanisms of host finding and invasion represent fascinating and complex biological phenomenon, which are discussed here.

Adaptation, Physiological↗
PubMed1979

Incidence of bluetongue virus precipitating antibodies in sera of some domestic animals in the Sudan.

To determine the presence and prevalence of bluetongue (BT) infection in a variety of domestic animal species in different geographical regions of the Sudan, a serological study using the agar gel precipitation technique was initiated. A total of 2142 serum samples were examined. Of the numbers tested approximately 28% of sheep, 11.2% of goats, 8% of cattle and 4.9% of camels were positive for group-specific antibodies to BT virus antigen, indicating previous exposure to BT infection. None of the samples tested from horses or donkeys were positive. The findings suggest that the disease is widely distributed in most parts of the Sudan where possible insect vectors prevail and may be endemic in sheep in Juba District, Equatoria Province, Southern Region. Goats appeared to have some degree of resistance to infection compared with sheep, and there seemed to be no significant differences in positive rates between farm and free-range cattle. It is concluded that BT infection may cause clinical disease in sheep, while it is probably subclinical or inapparent in goats, cattle and camels of the Sudan.

Animals↗
PubMed1981

An improved technique for the cryopreservation of Onchocerca microfilariae.

Experimental describe the use of ethanediol to store Onchocerca microfilariae in liquid nitrogen. The technique involves a 2-stage incubation of the parasites at 37 degrees C and 0 degrees C in ethanediol, before rapid cooling to -196 degrees C. Viability has been assessed by motility, by migration in a proxy host and by development to the infective stage in the insect vector. A total of 71-79% of the cryopreserved microfilariae was shown to be viable compared to unfrozen controls. The technique is simple, inexpensive and very effective when compared to previous cryopreservation procedures for microfilariae and should be particularly suited for use under field conditions.

Animals↗
PubMed1989

Detection of Trypanosoma congolense and Trypanosoma brucei subspecies by DNA amplification using the polymerase chain reaction.

The nuclear DNA of Trypanosoma congolense contains a family of highly conserved 369 base pair (bp) repeats. The sequences of three cloned copies of these repeats were determined. An unrelated family of 177 bp repeats has previously been shown to occur in the nuclear DNA of Trypanosoma brucei brucei (Sloof et al. 1983a). Oligonucleotides were synthesized which prime the specific amplification of each of these repetitive DNAs by the polymerase chain reaction (PCR). Amplification of 10% of the DNA in a single parasite of T. congolense or T. brucei spp. produced sufficient amplified product to be visible as a band in an agarose gel stained with ethidium bromide. This level of detection, which does not depend on the use of radioactivity, is about 100 times more sensitive than previous detection methods based on radioactive DNA probes. The oligonucleotides did not prime the amplification of DNA sequences in other trypanosome species nor in Leishmania, mouse or human DNAs. Amplification of DNA from the blood of animals infected with T. congolense and/or T. brucei spp. permitted the identification of parasite levels far below that detectable by microscopic inspection. Since PCR amplification can be conducted on a large number of samples simultaneously, it is ideally suited for large-scale studies on the prevalence of African trypanosomes in both mammalian blood and insect vectors.

Animals↗
PubMed1993

The mini-exon gene: a molecular marker for Endotrypanum schaudinni.

The mini-exon gene repeats from three different strains of Endotrypanum schaudinni have been amplified by the polymerase chain reaction (PCR). Sequence analysis of the cloned products shows the gene and intergenic region to be identical in two of the strains (LV86 and M6159); the intergenic region from the mini-exon gene of the third strain (LV59) is significantly different. The LV86 gene and an intergenic probe from the LV59 mini-exon gene do not cross-hybridize with the mini-exon gene from New World Leishmania species. These data provide the basis of a PCR assay to detect E. schaudinni and distinguish it from New World Leishmania species, and which should be applicable to epidemiological studies in insect vectors and mammalian reservoirs. The identification of two different mini-exon gene repeats in E. schaudinni isolates is indicative of further strain variation within this species.

Animals↗