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Biomedical subjects

L D Jones

Publications and source records attributed to L D Jones.

At least 55 records · Page 3Linked to original sources
PubMed1989

Viral interference in the tick, Rhipicephalus appendiculatus. I. Interference to oral superinfection by Thogoto virus.

Interference between arboviruses in a naturally infected tick vector is reported for the first time. Rhipicephalus appendiculatus nymphs were dually infected with Thogoto (THO) virus, a tick-borne virus, similar to members of the family Orthomyxoviridae. In the first series of experiments examining 'inter-stadial' interference, larvae were orally infected with a temperature-sensitive (ts) mutant, and after moulting the nymphs were superinfected with the wild-type (wt) virus. In the second series of experiments examining 'intra-stadial' interference, nymphs were dually infected by interrupted feeding; the time interval between infective feeds was either shorter than 24 h or lasted for 10 days. Interference was demonstrated by the inability of wt virus to replicate in ticks previously infected with ts virus. Both inter- and intra-stadial interference were observed and complete interference was detected in 78% of dually infected nymphs. A pool of dually infected ticks, in which intra-stadial interference had been detected, failed to transmit the superinfecting virus after moulting.

Animals↗
PubMed1989

Viral interference in the tick, Rhipicephalus appendiculatus. II. Absence of interference with Thogoto virus when the tick gut is by-passed by parenteral inoculation.

Genetic reassortment of Thogoto (THO) virus has been demonstrated in dually infected Rhipicephalus appendiculatus ticks. However previous results showed that oral superinfection is inhibited by interference. To ascertain the site of THO viral interference, ticks were infected parenterally or orally with a temperature-sensitive (ts) mutant of THO virus. Infected ticks were then challenged with wild-type (wt) THO virus via parenteral inoculation. Intra-stadial superinfection was carried out by parenteral inoculation of newly infected engorged ticks whereas inter-stadial superinfection involved inoculation of engorged ticks infected at the previous stage. In both instances viral interference was not observed, i.e. the challenge virus replicated and was delivered by bite to susceptible hosts. Therefore when the gut is bypassed, R. appendiculatus ticks are apparently permissive to dual infection even when there is a delay in the presentation of the superinfecting virus. These results demonstrate that interference following superinfection per os does not occur in the salivary glands, but may occur in the gut and possibly in a secondary site of viral replication such as the synganglion.

Animals↗
PubMed1989

Vector capacity of Rhipicephalus appendiculatus and Amblyomma variegatum for Thogoto and Dhori viruses.

Experimental studies were undertaken to ascertain the vector potential of Rhipicephalus appendiculatus Neumann and Amblyomma variegatum Fabricius for Thogoto (THO) and Dhori (DHO) viruses, candidate members of the Orthomyxoviridae. In the first set of experiments, ticks were infected orally by feeding on viraemic hamsters. THO virus replicated in R. appendiculatus and A. variegatum, persisted trans-stadially in both tick species, and was transmitted to susceptible hosts during feeding. In contrast, both R. appendiculatus and A. variegatum were refractory to per os infection by DHO virus. In the second set of experiments, engorged R. appendiculatus and A. variegatum nymphs were parenterally inoculated with DHO virus. The virus persisted trans-stadially in both tick species and was transmitted by bite to susceptible hosts. These results indicate that the midgut acts as a barrier to per os infection of R. appendiculatus and A. variegatum by DHO virus. However, when this barrier is bypassed, i.e. by parenteral inoculation, both R. appendiculatus and A. variegatum can serve as efficient vectors of DHO virus.

Animals↗
PubMed1987

A novel mode of arbovirus transmission involving a nonviremic host.

In nature, infected and uninfected arthropod vectors often feed together on an animal. In mimicking this scenario in the laboratory, uninfected vectors were found to acquire virus while cofeeding on the same host as infected vectors. However, the vertebrate host on which they fed did not develop detectable levels of virus in its blood. These observations were made with Thogoto virus, an influenza-like virus of medical and veterinary significance. Rhipicephalus appendiculatus ticks were used as the vector and guinea pigs as the vertebrate host. The results demonstrate that a vertebrate that is apparently refractory to infection by an arthropod-borne virus can still play an important role in the epidemiology of the virus, and they suggest a novel mode of arthropod-borne virus transmission.

Animals↗
PubMed1987

Reassortment of Thogoto virus (a tick-borne influenza-like virus) in a vertebrate host.

Reassortment is an important factor in the evolution of segmented genome viruses. For arthropod-borne viruses it is important to determine whether the vertebrate host acts as a site of reassortant virus formation since vertebrates often act as amplifying hosts. Mutants of Thogoto virus, a tick-borne orthomyxo-like virus, were shown to produce wild-type progeny in a dually infected permissive host (hamster), when hamsters were infected with two mutant viruses either by direct inoculation or by oral transmission from infected ticks. Viral dose and time of co-infection of the host affected the incidence of reassortment. This is the first report of reassortment of an arbovirus following infection of a vertebrate host via an arthropod vector.

Animals↗
PubMed1987

In vivo reassortment of Thogoto virus (a tick-borne influenza-like virus) following oral infection of Rhipicephalus appendiculatus ticks.

Arboviruses with segmented genomes have the potential to reassort in both their vertebrate hosts and arthropod vectors. Reassortment of Thogoto virus, a tick-borne orthomyxo-like virus, has been demonstrated following dual infection of hamsters by temperature-sensitive mutants. To investigate whether similar events can occur in ticks, Rhipicephalus appendiculatus larvae and nymphs were dually infected by interrupted feeding on viraemic hamsters. Wild-type reassortant virus was isolated from the ticks 12 to 15 days after engorgement. Following moulting, nymphs and adults transmitted reassortant virus to uninfected hamsters. This is the first reported evidence that a tick-borne arbovirus can reassort in vivo in a naturally infected arthropod vector. The relative roles of vector and vertebrate host in generating and perpetuating reassortant viruses in nature are discussed.

Animals↗
PubMed1986

Experimental studies on the transmission cycle of Thogoto virus, a candidate orthomyxovirus, in Rhipicephalus appendiculatus.

Thogoto (THO) virus, a candidate orthomyxovirus, replicated in and was transmitted by larvae, nymphs, and adults of the brown ear tick, Rhipicephalus appendiculatus. Larvae fed on viremic hamsters (10(7-8) PFU/ml blood) acquired an average of 10(2.5) PFU per tick. Following engorgement the titer dropped to 10(1.9) PFU on day 2 but increased by day 6 to 10(3.3) PFU. Virus survived transstadially in these ticks as demonstrated by the fact that, on day 10, newly moulted nymphs contained, on average, 10(3.5) PFU/tick. When 10 such infected nymphs were placed on a hamster a fatal infection of the animal developed involving a viremia of 10(6.7) PFU/ml blood. Another group of 6 infected nymphs did not elicit a detectable viremia in a hamster, or cause death. However the animal seroconverted to THO, virus indicating that virus transmission had occurred. Following acquisition of THO virus at the larval stage, virus was detected in adult ticks 138 days later. Uninfected nymphs fed on viremic hamsters acquired an average of 10(4) PFU/nymph. No virus was detected in the nymphs 4 days post-engorgement. Virus was, however, recovered by 6 days post-engorgement (10(4.7) PFU/nymph). Virus persisted transstadially as shown by the presence of an average of 10(3.4) PFU in newly moulted adults. Three groups of these infected adults (5-6 ticks/group) induced viremia in hamsters with blood titers of the order 10(2.8-3.5) PFU/ml. Virus persisted in engorged adults for up to 66 days following nymphal engorgement.(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗
PubMed1984

Comparison of mice and cell cultures for the isolation of tick-borne viruses.

Three methods of isolating viruses from 10 tick pools were compared; none of the methods produced all 13 of the viruses isolated (7 viruses of the bunyaviridae and 6 orbiviruses). Inoculation of homogenised ticks into various cell lines was the most successful, yielding 11 virus isolations. Only 2 tick homogenates induced overt signs of infection following intra-cerebral inoculation of 2-day-old mice. However, when inoculated mouse brain was passaged in various cell lines, 8 of 12 isolations were made. The rates of success of the 3 methods of virus isolation appeared to vary according to the type and titre of the virus in the tick pool.

Animals↗
PubMed1983

Organ preferences in metastatic colony formation by spontaneous mammary carcinomas after intra-arterial inoculation.

We have demonstrated earlier that cells from some spontaneous murine mammary tumours heavily colonise the lungs of every inoculated animal when injected intravenously, whereas those from others do so weakly or not at all. Extrapulmonary deposits are rare when cells are inoculated by this route. In the current experiments, we have found that if the cells are inoculated retrograde along the subclavian artery into the arch of the aorta, or directly into the abdominal aorta, they are capable of colonising organs other than the lungs and that individual tumours have reproducible preferences for establishing colonies in certain sites. The combination of organs favoured vary from tumour to tumour but most still showed a predilection for forming pulmonary deposits. Several organs are not colonised by any tumour in any recipient. It is concluded that the distribution of metastatic colonies formed by these spontaneous mammary tumours is influenced by interplay between intrinsic properties of tumour cells, microenvironmental influences in the organs in which the cells arrest, and rheological considerations.

Animals↗
PubMed1982

Experimental analysis of factors affecting metastatic spread using naturally occurring tumours.

This paper describes the applications and latest results of recently developed techniques in metastasis research using naturally occurring animal and human tumours. Intravenous inoculation of cells from murine mammary tumours into syngeneic recipients has shown that some are consistently capable of heavy pulmonary colonisation (HCP) while others have low colonisation potential (LCP). These distinct characteristics are stable over wide cell-dose ranges. Autopsies on a sample of 100 consecutive tumour-bearing C3H/Avy mice revealed that the incidence of spontaneous metastasis is 26%. When inoculated intravenously, cells from some of the spontaneously metastatic primary tumours had HCP and others LCP. We now report that, knowing the degree of pulmonary colonisation of a particular tumour after intravenous inoculation, the degree of its spontaneous metastasis in the original host, and the dose-response relationships mentioned above, it is possible to back-titrate the degree of cell shedding from the tumour into the blood stream. Other experiments reported here demonstrate that separate mammary tumours on the same animal have independent colonisation potentials and growth rates, that tumours appearing later on an animal are not necessarily more capable of metastatic spread than the earlier ones, and that tumour weight and length of presence on the host do not show any strong correlation with spontaneous metastatic spread. A moderately significant association between pulmonary colonisation potential and tumour growth rate is reported and evidence corroborating our earlier observations that ability to colonise the lungs is possessed only by neoplastic mammary cells is also presented. Similar investigation are, of course, much more difficult to organise on tumour spread in man because of ethical and logistic considerations but it is possible to circumvent some of these difficulties and we refer to some of our ongoing studies.

Adipose Tissue↗
PubMed1977

Metabolic responses to prolonged fasting and subsequent refeeding in the pig.

Metabolic responses associated with prolonged fasting and subsequent refeeding of pigs were investigated. Fasting for 14 or 28 days produced significant increases in serum levels of alanine, aspartic and glutamic acid in the three branched-chain amino acids. Glycine, serine and lysine levels were elevated after 28 days of fasting while the levels of histidine, methionine, threonine and phenylalanine were reduced. Fasting markedly stimulated hepatic and renal gluconeogenesis and the activity of the urea cycle enzymes. Fatty acid synthesis and glucose oxidation were virtually abolished in hepatic and adipose tissue in pigs subjected to a 14- or 28-day fast. After the first day of refeeding, the levels of amino acids returned to the control values. The activity of the hepatic urea cycle enzymes, fructose-1,6-diphosphatase and phosphoenolpyruvate carboxykinase remained elevated after the first day of refeeding but returned to the control levels thereafter. The activity of hepatic glucose-6-phosphate dehydrogenase, malic dehydrogenase and acetyl CoA carboxylase were slightly enhanced in pigs refed for 4 and 8 days. The activity of these enzymes in adipose tissue was enhanced 8 days after refeeding. Hepatic synthesis of fatty acids from glucose was slightly stimulated in refed pigs on days 4 and 8 but returned to control values on day 16. Refeeding did not enhance glucose incorporation into fatty acids in adipose tissue above the values observed in fed controls.

Amino Acids↗