Evidence of soft-mode quantum phase transitions in electron double layers

Inelastic light scattering by low-energy spin-excitations reveals three distinct configurations of spin of electron double layers in gallium arsenide quantum wells at even-integer quantum Hall states. The transformations among these spin states appear as quantum phase transitions driven by the interplay between Coulomb interactions and Zeeman splittings. One of the transformations correlates with the emergence of a spin-flip intersubband excitation at vanishingly low energy and provides direct evidence of a link between quantum phase transitions and soft collective excitations in a two-dimensional electron system.     

Quantitation of canine distemper virus and antibodies by enzyme-linked immunosorbent assays using protein A and monoclonal antibody capture

Monoclonal antibodies produced from 19 cloned hybridomas were selected for this study. Specific canine distemper virus (CDV) antibodies in medium from cloned hybridomas were detected by direct enzyme-linked immunosorbent assays (ELISA) and by indirect immunofluorescence. Three different sandwich ELISA systems were developed either to detect CDV in cell cultures and clinical specimens or to detect specific antibody in canine sera. Protein A and monoclonal antibodies attached in sequence to a solid phase constituted the capture system in the assays. Viral antigens were detected by sandwiching extracts of clinical specimens (or infected cell cultures), monoclonal antibody, and peroxidase-labeled protein A in sequence onto the capture layer. In 1 procedure, biotin-labeled antibody and peroxidase-labeled avidin were used as the last 2 layers in the assay. The CDV antibodies in dog sera were quantitated in a similar manner, but the sequential sandwiching levels consisted of partially purified CDV, serum specimen, and peroxidase-labeled protein A, respectively. The procedures were specific and highly sensitive.     

Freeze-drying of Aegyptianella pullorum

Heparinized whole blood, parasitized with Aegyptianella pullorum, was collected from 2 fowls. Buffered lactose peptone (BLP) was added v/v as a stabilizer and the mixture lyophilized in 2 ml aliquots after rapid or slow freezing. At different stages during the freeze-drying process, as well as after lyophilization and reconstitution with 1.8 ml of sterile water, samples were taken and injected into pullets. Infectivity was maintained throughout. However, the prepatent period was lengthened after freezing and particularly after lyophilization when there was some loss of viability.     

The influence of complement on the neutralization of infectious bovine rhinotracheitis virus by globulins derived from early and late bovine antisera.

Calves were inoculated at four week intervals with infectious bovine rhinotracheitis virus (IBRV). Sera were obtained at eight days (early sample) and 21 days (late sample) after each inoculation. Kinetic neutralization was carried out with 7S and 19S globulins derived from these sera, both in the presence and in the absence of guinea pig complement (C). In all instances the 19S neutralizing antibody (AB) was dependent on C for neutralization of IBVR. However, C dependency was not observed with any of the 7S preparations. Neutralizing activity was readily detected in 19S globulins from the early sera after primary and subsequent inoculations but not in any of the late sera. Early sera collected after primary inoculation did not contain any 7S neutralizing AB but it was present in all the other sera tested. The 7S AB when present was always at a considerably higher concentration than 19S AB. Thus it may be possible to determine whether cattle have recently been exposed to IBRV when paired serum samples are not available by determining the presence of C-dependent 19S globulins. In addition, by comparing 19S and 7S levels, a distinction may be made between primary and secondary responses to IBRV.     

The isolation and transmission of an unidentified Babesia sp. to cattle by Hyalomma truncatum Koch 1844

An unidentified Babesia sp. which causes a mild disease in cattle was isolated in a splenectomized ox that received pooled blood from field cattle. That this organism is pleomorphic and resembles Babesia occultans makes it difficult to differentiate between these organisms microscopically. Initially, it was suspected that this Babesia could be B. occultans. Several attempts to transmit this parasite transovarially with Hyalomma marginatum rufipes, the vector of B. occultans, failed. Continued efforts to identify possible vectors, using Boophilus microplus, Rhipicephalus evertsi evertsi and Rhipicephalus appendiculatus, all failed. The only tick thus far identified that could have transmitted the infection transovarially in the adult stage was the two-host tick Hyalomma truncatum.     

Experimental parvovirus infection in dogs.

Five eight week old dogs were inoculated orally and intranasally with cell culture origin canine parvovirus. Three dogs became depressed and anorectic and developed a mild (one dog) to severe diarrhea five days postinfection. The remaining dogs had subclinical infections but developed a lymphopenia followed by a transient lymphocytosis. The ill dogs developed mild (one dog) to severe neutropenia and a moderate lymphopenia. One died nine days postinfection. Recovery was associated with cessation of viral excretion and with lymphocytosis and antibody production. Two of three dogs challenged intragastrically developed mild clinical signs and a moderate panleukopenia four to eight days postinfection. The pathological changes of the experimental disease were very similar to that of spontaneous disease. Bone marrow changes included a severe granulocytic and mild erythroid depletion. The pathogenesis of canine parvovirus infection is discussed.     

An apparatus for collecting blood samples by radiotelemetry from horses during exercise

An apparatus was designed to collect four consecutive blood samples from exercising horses. The collection of each sample was controlled by valves activated by radiotelemetry signals transmitted by an observer. Using the device, venous blood samples were collected from ten thoroughbred racehorses before, during and after a 400 m training gallop. Blood glucose increased markedly post-exercise. Both phosphorus and potassium concentrations increased during exercise, decreased post-exercise and recovered to pre-exercise levels within 120 minutes. The system was modified to collect anaerobic samples of arterial and venous blood, and the efficiency of the modified system was investigated in a standing conscious horse. Blood gas values of samples collected by means of the apparatus were compared with those collected manually and simultaneously, directly from the neck of the intravascular catheter. For eight pairs of arterial and venous samples, the coefficients "r" were 0.998 and 0.997 for PO2 and PCO2 respectively. It was concluded that the system worked efficiently and that the anaerobic sealing of the modified version was adequate.     

Four p67 alleles identified in South African Theileria parva field samples

Previous studies characterizing the Theileria parva p67 gene in East Africa revealed two alleles. Cattle-derived isolates associated with East Coast fever (ECF) have a 129 bp deletion in the central region of the p67 gene (allele 1), compared to buffalo-derived isolates with no deletion (allele 2). In South Africa, Corridor disease outbreaks occur if there is contact between infected buffalo and susceptible cattle in the presence of vector ticks. Although ECF was introduced into South Africa in the early 20th century, it has been eradicated and it is thought that there has been no cattle to cattle transmission of T. parva since. The variable region of the p67 gene was amplified and the gene sequences analyzed to characterize South African T. parva parasites that occur in buffalo, in cattle from farms where Corridor disease outbreaks were diagnosed and in experimentally infected cattle. Four p67 alleles were identified, including alleles 1 and 2 previously detected in East African cattle and buffalo, respectively, as well as two novel alleles, one with a different 174 bp deletion (allele 3), the other with a similar sequence to allele 3 but with no deletion (allele 4). Sequence variants of allele 1 were obtained from field samples originating from both cattle and buffalo. Allele 1 was also obtained from a bovine that tested T. parva positive from a farm near Ladysmith in the KwaZulu-Natal Province. East Coast fever was not diagnosed on this farm, but the p67 sequence was identical to that of T. parva Muguga, an isolate that causes ECF in Kenya. Variants of allele 2 were obtained from all T. parva samples from both buffalo and cattle, except Lad 10 and Zam 5. Phylogenetic analysis revealed that alleles 3 and 4 are monophyletic and diverged early from the other alleles. These novel alleles were not identified from South African field samples collected from cattle; however allele 3, with a p67 sequence identical to those obtained in South African field samples from buffalo, was obtained from a Zambian field isolate of a naturally infected bovine diagnosed with ECF. The p67 genetic profiles appear to be more complex than previously thought and cannot be used to distinguish between cattle- and buffalo-derived T. parva isolates in South Africa. The significance of the different p67 alleles, particularly the novel variants, in the epidemiology of theileriosis in South Africa still needs to be determined.     

Population structure of South African and Australian Pyrenophora teres isolates

There are two recognized forms of the disease net blotch of barley: the net form caused by Pyrenophora teres f. teres (PTT) and the spot form caused by P. teres f. maculata (PTM). In this study, amplified fragment length polymorphism analysis was used to investigate the genetic diversity and population structure of 60 PTT and 64 PTM isolates collected across Australia (66 isolates) and in the south‐western Cape of South Africa (58 isolates). For comparison, P. tritici‐repentis, Exserohilum rostratum and Bipolaris sorokiniana samples were also included in the analyses. Both distance‐ and model‐based cluster analyses separated the PTT and PTM isolates into two strongly divergent genetic groups. Significant variation was observed both among the South African and Australian populations of PTT and PTM and among sampling locations for the PTT samples. Results suggest that sexual reproduction between the two forms is unlikely and that reproduction within the PTT and PTM groups occurs mainly asexually.