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PubMedDate not supplied

Trypanosoma rangeli (Tejera, 1920): observations upon pleomorphism.

Meta-trypomastigotes of Trypanosoma rangeli Tejera, 1920, harvested from LIT medium, were inoculated i.p. or s.c. into 6, 16, and 26 g NMRI mice, these representing increasing degrees of immunological maturity. In all cases, similar pleomorphic patterns were observed. Four morphobiometrically differentiable types of trypanosome were encountered in an overlapping temporal sequence. These observations, taken in comparison with those on pleomorphism in this and other species of Trypanosoma by other workers, are consistent with the hypothesis that the pleomorphic types represent the natural development of the parasite, rather than the result of the immune response of the mammal host. Small, slender trypanosomes prevalent at the onset of the parasitemia either reinvade the tissue cells for relatively limited subsequent generations of tissue reproduction, or else differentiate toward the forms that are only capable of colonizing the insect vector.

Age Factors↗

PubMed1975

Epizootiology of bluetongue: the situation in the United States of America.

Bluetongue was first reported in the United States in 1948 in sheep in Texas. The virus has now been isolated from sheep in 19 States. When the disease first occurs in a flock, the morbidity may reach 50 to 75% and mortality 20 to 50%. In subsequent years, the morbidity may be only 1 to 2% with very few deaths. Difference in breed susceptibility has not been observed. Natural bluetongue infection has not been observed in Angora or dairy goats. Bluetongue virus was first isolated from cattle, in Oregon, in 1959. The virus has now been isolated from cattle in 13 States. In cattle, the disease is usually inapparent but can cause mild to severe clinical disease and neonatal losses. Natural clinical bluetongue has also been reported in bighorn sheep, exotic ruminants in a zoo, mule deer, and white-tailed deer. Serological evidence of exposure to the virus has also been found in other species of ruminants in the wild. Inoculation of virulent bluetongue virus, vaccine virus, or natural disease can cause congenital deformities and neonatal losses in calves, lambs, and white-tailed deer fawns. Culicoides is considered the important insect vector of bluetongue. The virus has also been isolated from sheep keds and cattle lice. U.S. field strains of the virus fit into four serologic groups. No cross reactions were found between bluetongue and epizootic haemorrhagic disease of deer viruses. Cattle are considered significant virus reservoirs. It is necessary to use washed erythrocytes, rather than whole blood, and to inoculate susceptible sheep, rather than embryonated chicken eggs, to detect longer-term viraemia in cattle.

Animals↗

PubMed1992

Insect-mediated transmission of mixed and reassorted cucumovirus genomic RNAs.

Transmissions of virus using the aphid Myzus persicae were performed using plants co-infected with two cucumoviruses, tomato aspermy virus (V-TAV) and cucumber mosaic virus (M-CMV). Five of the aphid-transmitted progeny viruses (3.7%) induced symptoms distinct from those induced by either parental virus. Northern blot hybridization analysis of encapsidated RNAs from these novel progeny demonstrated that all of the RNA profiles were characteristic of pseudo-recombinants, i.e. viruses with reassorted genomic RNAs. The two larger RNAs, 1 and 2, originated from V-TAV, whereas RNA 3 was derived from M-CMV. A more sensitive RNase protection assay analysis of both unencapsidated and encapsidated RNAs revealed the presence of minor populations of V-TAV-derived RNA 3 in all of these novel progeny, and of M-CMV-derived RNA 1 (and presumably RNA 2) in one of the progeny. A bias against the encapsidation of the minor populations of RNAs by the M-CMV coat protein was observed, suggesting that there is specificity or competition with regard to the encapsidation of cucumoviral RNAs in vivo. This study demonstrates that insect vectors can mediate the establishment of pseudorecombinants with mixed populations of RNA 3.

Animals↗

PubMed1992

Molecular biological approaches to the study of vectors in relation to malaria control.

To a large extent, control of malaria vectors relies on the elimination of breeding sites and the application of chemical agents. There are increasing problems associated with the use of synthetic insecticides for vector control, including the evolution of resistance, the high cost of developing and registering new insecticides and an awareness of pollution from insecticide residues. These factors have stimulated interest in the application of molecular biology to the study of mosquito vectors of malaria; focussing primarily on two aspects. First, the improvement of existing control measures through the development of simplified DNA probe systems suitable for identification of vectors of malaria. The development of synthetic, non-radioactive DNA probes suitable for the identification of species in the Anopheles gambiae complex is described with the aim of defining a simplified methodology which is suitable for entomologist in the field. The second aspect to be considered is the development of completely novel strategies through the genetic manipulation of insect vectors of malaria in order to alter their ability to transmit the disease. The major requirements for producing transgenic mosquitoes are outlined together with the progress which has been made to date and discussed in relation to the prospects which this type of approach has for the future control of malaria.

Animals↗

PubMed1978

Epidemiology and ecology of leishmaniasis in Latin-America.

Of the diseases caused by protozoal parasites, leishmaniasis is probably second in importance only to malaria. Chemotherapeutic drugs are toxic, expensive and not 100% effective. This, and the absence of any non-living vaccine against the disease, means that control depends on eliminating either reservoirs or insect vectors, or both. Recently, a greatly increased knowledge of the Leishmania species involved, and of their natural hosts, has helped to define the nature and extent of the problem.

Animals↗

PubMed1975

The epizootiology of bluetongue: the African situation.

Bluetongue virus is transmitted biologically by various species of Culicoides, notably C. pallidipennis and C. variipennis. Factors such as rainfall, temperature and relative altitude, which influence the breeding of the insect vectors also govern the incidence and distribution of the disease. The host range of bluetongue virus includes sheep, cattle, goats and various antelopes. Many other, as yet unidentified hosts could perhaps harbour the virus and influence the epizootiology of the disease. The close relationship between C. pallidipennis and cattle is indicated and the efficient mechanism for virus maintenance which this relationship constitutes is emphasised. It is further postulated that sheep are not essential for the continued survival of bluetongue virus, but merely function as accidental or indicator hosts.

Africa, Southern↗

PubMed1975

The control of bluetongue in an enzootic situation.

On account of the wide host range of bluetongue virus and its biological transmission by insects, control of the disease in an enzootic situation is based primarily on the active immunisation of susceptible animals as well as on the prevention of contact between the insect vectors and the susceptible hosts. In spite of their unquestionable value, the egg attenuated vaccines which are currently employed for prophylactic immunisation, have certain shortcomings. The existence of 16 known serotypes of bluetongue virus makes it difficult to achieve a very wide spectrum of immunity in sheep vaccinated once or twice only. The problems which are experienced with the immunisation of lambs born in spring are indicated. The present vaccine can also present problems when used in breeding animals. Furthermore, the costs involved in the annual vaccination of large numbers of animals are considerable. The need for a vaccine for cattle is indicated. Work is also being conducted at present on the development of an inactivated vaccine for use in sheep. The use of novel virological techniques may aid in the future development of absolutely safe and highly efficient vaccines against bluetongue.

Animals↗

PubMed1992

Surface-associated antigens of Brugia malayi L2 and L3 parasites during vector-stage development.

Surface and metabolic labeling procedures were used to characterize the composition and the time of expression of Brugia malayi L2 and L3 surface-associated molecules as the larvae develop within the mosquito vector. Larvae were harvested from mosquito tissues at 5 (early L2), 8 (late L2) and 11 (L3) days post-infection and labeled with 125I-Iodo-Gen. The results of one-dimensional analysis showed that there is a progressive increase in the complexity of peptides associated with the surface of developing larvae, culminating in the expression of 7 major labeled components on L3s. Both L2 and L3 parasites have surface-associated components of 42, 35, 33, 19 and 17 kDa. Between days 8 and 11 of development in the insect vector, Brugia malayi undergoes the L2 to L3 molt and acquires additional major immunogenic peptides of 40 and 22 kDa. Two-dimensional analyses of extracts from 125I-labeled L2s and L3s revealed that the major 35-, 33-, 19- and 17-kDa molecules are part of a peptide complex that forms a 'ladder' between 17 and 150 kDa. To gain information on the times during which the major surface-associated molecules are produced by the parasite, larvae were labeled with [35S]methionine either in situ as they developed within the mosquito or during culture after exiting the vector. For in situ labeling, [35S]methionine was introduced into the hemolymph of infected mosquitoes by micro-injection at days 2, 5 and 8 post-infection and the larvae were allowed to develop for an additional 3 days. The results of 1- and 2-dimensional analyses of [35S]methionine-labeled extracts from vector-stage or post-vector-stage larvae indicate that the molecules associated with the surface of B. malayi L3s are synthesized between day 5 and day 11 of development in the insect host. Immediately after the larvae exit the vector, the synthesis of the 40 and 22-kDa peptides is drastically reduced or terminated.

Animals↗

PubMed1976

Entomopathogens: ecological manipulation of natural associations.

The control of insect pests with entomopathogens is unique, in that naturally occurring host-pathogen relations are manipulated to the benefit of man: protecting agricultural crops and forests or controlling insect vectors of disease. The isolation and identification of a virulent pathogen is the initial step in the development of a potential control agent. Production of the pathogen in adequate quantities must be possible either in vivo (insects) or in vitro (artificial medium). To insure usefulness, the pathogen must remain viable in the formulated form and after application in the field. Since inactivation rather than persistence is a problem, the pathogens must be formulated, protected, and applied to insure satisfactory pest control action. Studying the natural host--pathogen interactions will be necessary in order to manipulate the pathogen effectively, by introducing it at the most opportune time in the life cycle of the target pest. Generally, insect pathogens are more selective than conventional pesticides; this will limit their use and industrial development. Development, at least in part, by the public sector may be necessary and desirable. The most promising areas for the use of pathogens are in integrated pest management and in situations where pests have developed resistance to chemical control.

Animals↗

PubMed1976

Human sleeping sickness in the Gboko endemic area of Nigeria.

Human infection with Trypanosoma gambiense in the Gboko endemic area was first reported in May, 1974 although T. gambiense sleeping sickness had been present there since the turn of the century. The disease is associated with the presence of the tsetse Glossina tachinoides and Glossina palpalis which is plentiful and widespread throughout the division as well as in thickets along the streams in the area. No successful attempt has been made to control the tsetse vector in the Division. The incidence and geographical distribution of cases of T. gambiense sleeping sickness in the Gboko area are described in this report. Cases were treated with Antrypol Tryparsamide mixture and Mel B. The highest number of cases of infection is usually picked up just before the start of the rains in early April. It is suggested that, for meaningful control of the disease a quick method should be devised to rid the area of the insect vector.

Humans↗

PubMed1992

Trypanosoma brucei mitochondrial ribosomal RNA synthesis, processing and developmentally regulated expression.

The steady-state levels of the mitochondrial ribosomal RNAs of Trypanosoma brucei are repressed in the early bloodstream developmental stage of the parasite and accumulate approximately 30-fold during differentiation to the stage found in the midgut of the insect vector. In order to determine the mechanism regulating this developmental process, we have examined the transcription and processing of the 9S and 12S mitochondrial rRNAs of T. brucei. A short-lived RNA was detected in pulse labeling experiments which contains the mature 12S and 9S rRNAs and at least 1200 nucleotides of RNA transcribed from upstream of the 12S rRNA gene. This putative processing precursor RNA was identified in both intact cells and in run-on experiments using isolated mitochondria. The transcripts containing the upstream sequences are unstable and reach isotopic equilibrium within 15 min. Mature rRNAs in the insect developmental stage are stable and show no detectable turnover during a 36-h chase. Comparison of rRNA synthesis in bloodstream and insect life-stages indicates that mitochondrial rRNA levels are controlled not at the transcriptional level, but rather by a mechanism which likely modulates the stability of the mature rRNAs. These results suggest that a short-lived rRNA precursor is synthesized and processed at comparable rates in both bloodstream and insect stages of the parasite. Thus, it appears that differential stability of the mature 9S and 12S rRNAs plays a major role in modulating mitochondrial gene expression during the developmental cycle of T. brucei.

Animals↗

PubMed1992

Leishmania major: differential regulation of the surface metalloprotease in amastigote and promastigote stages.

During its life cycle, the protozoan parasite Leishmania major alternates from an intracellular amastigote form in the mammalian host to a flagellated promastigote form in the insect vector. The expression of the surface metalloprotease (PSP) during differentiation in vitro was investigated by Western and Northern blots, by immunoprecipitation of cells metabolically labeled with [35S]methionine or labeled at the surface with radioactive iodine, and by quantification of the proteolytic activity in substrate-containing polyacrylamide gels. We report that the surface metalloprotease is down-regulated at both the mRNA and the protein level in amastigotes, where it represents less than 1% of the equivalent proteolytic activity detected in promastigotes. A significant amount of mRNA is detected 4 hr after the onset of differentiation. The expression of the protease begins at that time and reaches steady state 8 hr later. The synthesis of PSP precedes the complete morphological differentiation to the promastigote stage and the appearance of the lipophosphoglycan, another major promastigote surface component. In contrast to PSP, a family of mercaptoethanol-activated proteases present in the amastigote exists only at a reduced level in the promastigote. The confinement of the surface metalloprotease to the insect stage of the parasite suggests that it has no physiological function in the parasitism maintenance of mammalian host macrophages.

Animals↗

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↗

PubMed1979

[Tertian malaria in children and adults from an epidemic region in southern Turkey (author's transl)].

Since 1974 an epidemic of tertian malaria has been spreading around the Adana and Tarsus townships in southern Turkey, with a peak incidence of 115 500 cases in 1977. A further increase is to be expected because the insect vectors have become resistant to insecticides. Since 1975 eleven children and three adults have been treated for P. vivax malaria. They had all stayed in the epidemic area during the transmission season which lasts from July to October. Because of a long primary latent period seven patients only developed first manifestations of the disease six to nine months after leaving Turkey. The classical malarial paroxysms were missing during the first weeks of the primary attack. Several children had a febrile illness over weeks with headache, vomiting, abdominal pain, hepatosplenomegaly, high blood-sedimentation rate and severe haemolytic anaemia, so that appendicitis or septicaemia had been suspected. Tetracyclines and trimethroprimsulphamethoxazole were able to suppress the disease without preventing relapses.

Adolescent↗

PubMed1992

Genetically engineered rice resistant to rice stripe virus, an insect-transmitted virus.

The coat protein (CP) gene of rice stripe virus was introduced into two japonica varieties of rice by electroporation of protoplasts. The resultant transgenic plants expressed the CP at high levels (up to 0.5% of total soluble protein) and exhibited a significant level of resistance to virus infection. Plants derived from selfed progeny of the primary transformants also expressed the CP and showed viral resistance, indicating stable transmission of the CP gene and the trait of resistance to the next generation. Moreover, the virally encoded strip disease-specific protein was not detected in transgenic plants expressing CP 8 weeks after inoculation, indicating protection before viral multiplication. These studies demonstrated that CP-mediated resistance to virus infection can be extended to cereals and to the viruses transmitted by an insect vector (planthopper).

Base Sequence↗

PubMed1975

Cutaneous infection due to a rough variant of Mycobacterium marinum.

Spreading lesions clinically resembling lymphangitic sporotrichosis developed on the right arm and chest of a 60-year-old man with chronic lymphocytic leukemia. Acid-fast bacilli were seen in exudates from lesions and in biopsies, and were cultured from them. The isolant grew initially as a yellowish-orange scotochromogen on Lowenstein-Jensen medium at room temperature and at 35 C., but failed to grow at 37 C. It failed to grow on 7-H-10 medium. On repeated subculturing over a 2-year period it gradually converted to a photochromogen. Histologically, there was ulceration with extensive acute and chronic inflammation with fibrosis. Organisms occurred intracellularly as dense, compact, cigar-like packets resembling lepara bacilli. The appeared to have a predilection for the nucleus. The patient was anergic to PPD S, B, Y and G, and lacked antibodies to BCG phosphoglycolipids. The mycobacteriosis was alleviated by combined INH and ethambutol therapy. The isolant was identified as a rough variant of Mycobacterium marinum. It may have been transmitted by an insect vector.

Antibodies, Bacterial↗

PubMed1992

Molecular biology of African trypanosomes: development of new strategies to combat an old disease.

African trypanosomes are protozoan parasites that cause a number of diseases of man and domesticated animals in large regions of sub-Saharan Africa. The diseases have proven to be particularly difficult to prevent or to effectively treat due to features of both the trypanosome and the insect vector, the tsetse fly. The habitat of the tsetse and its resistance to insecticides have rendered vector control efforts ineffective. Attempts to develop a vaccine against the African trypanosomes has been dwarfed by the parasite's ability to change the composition of its exposed surface antigens. This process of antigenic variation allows the parasite to avoid the host's immune response and presents the host with a seemingly endless antigenic repertoire. Since conventional approaches to the control of African trypanosomiasis have largely met with failure, there has been a renewed interest in identifying novel aspects of the biology, biochemistry, and molecular biology of trypanosomes that might be exploited to develop new targets for vaccines or chemotherapy. Importantly, this research has opened a virtual Pandora's box of exciting biochemical and molecular surprises, which makes the African trypanosomes not only important medical pathogens but also an exciting experimental system for the basic scientist. In this review, the authors will describe some of the most recent and intriguing developments in the field of molecular parasitology.

Animals↗

PubMed1992

Characterization of a new picorna-like virus, himetobi P virus, in planthoppers.

Picorna-like virus particles, 29 nm in diameter, were purified from apparently healthy Laodelphax striatellus Fallen. The virus particles had a buoyant density of 1.352 g/ml in CsCl and a sedimentation coefficient of 161 s. The virus capsid proteins consisted of three major polypeptides of M(r)s 36,500, 33,000 and 28,000, and three minor polypeptides. The virus contained a major ssRNA of M(r) 2.8 x 10(6) and was also frequently associated with a minor dsRNA of M(r) 4 x 10(6). The 3' end of the ssRNA had a poly(A) tract of about 60 adenine residues. The virus has been provisionally named himetobi P virus.

Animals↗