In vitro culture of the strobilar stage of Echinococcus granulosus from protoscoleces of human, camel, cattle, sheep and goat origin from Kenya and buffalo origin from India

Protoscoleces from human, camel, cattle, sheep, goat (all from Kenya) and buffalo (from India) hydatid cysts were cultured under identical conditions in vitro using the diphasic culture system of Smyth (1979b). Organisms from all sources grew and segmented in culture. Genital anlagen developed in all cultured worms but further genital differentiation occurred only in cultures of cattle (testes) and camel (testes and genital pore) material. The possible significance of these results is discussed in relation to the general epidemiology of hydatid disease and the potential infectivity of the different strains to man.     

Dose dependent responses of cattle to Theileria parva stabilate

Dolan T. T., Young A.S., Losos G.J., McMillan I., Minder Ch.E. and Soulsby K. 1984. Dose dependent responses of Theileria parva stabilate. International Journal for Parasitology14: 89–95. A tick derived stabilate of Theileria parva (Maguga) was titrated in a large group of Boran (Bos indicus) cattle of the same age, sex and origin. The infectivity data was analysed using the independent action model. The cattle were identified as heterogeneous in their response to infection with 75% showing one ID₅₀ (0.0014) and 25% showing another (0.01). The disease responses of the cattle given different dose levels were compared for a variety of parameters. The results obtained showed these parameters to be dose dependent including the time to onset of piroplasm parasitaemia. The stabilate is of large volume and can be used for controlled challenge in immunity studies and for comparison of susceptibility between cattle of different breeds and from different epidemiological backgrounds.     

Chronobiological aspects of the host-parasite relationships between Biomphalaria glabrata and Schistosoma mansoni: cercarial production and infectivity, and growth kinetics of the host

In the Biomphalaria glabrata-Schistosoma mansoni association, variations in cercarial production, in cercarial infectivity, and in the growth of infected snails are rhythmic. These chronobiological aspects are correlated with the dynamics of the intramolluscan larval stages of the parasite during the course of the infection. Rhythmic variations in the growth kinetics of infected snails are interpreted in terms of host-parasite metabolic exchanges.     

Thermal stability and conformational transitions of scrapie amyloid (prion) protein correlate with infectivity.

The scrapie amyloid (prion) protein (PrP27-30) is the protease-resistant core of a larger precursor (PrPSc) and a component of the infectious scrapie agent; the potential to form amyloid is a result of posttranslational event or conformational abnormality. The conformation, heat stability, and solvent-induced conformational transitions of PrP27-30 were studied in the solid state in films by CD spectroscopy and correlated with the infectivity of rehydrated and equilibrated films. The exposure of PrP27-30 in films to 60 degrees C, 100 degrees C, and 132 degrees C for 30 min did not change the beta-sheet secondary structure; the infectivity slightly diminished at 132 degrees C and correlated with a decreased solubility of PrP27-30 in sodium dodecyl sulfate (SDS), probably due to cross-linking. Exposing PrP27-30 films to formic acid (FA), trifluoroacetic acid (TFA), trifluoroethanol (TFE), hexafluoro-2-propanol (HFIP), and SDS transformed the amide CD band, diminished the mean residue ellipticity of aromatic bands, and inactivated scrapie infectivity. The convex constraint algorithm (CAA) deconvolution of the CD spectra of the solvent-exposed and rehydrated solid state PrP27-30 identified five common spectral components. The loss of infectivity quantitatively correlated with a decreasing proportion of native, beta-pleated sheet-like secondary structure component, an increasing amount of alpha-helical component, and an increasingly disordered tertiary structure. The results demonstrate the unusual thermal stability of the beta-sheet secondary structure of PrP27-30 protein in the solid state. The conformational perturbations of PrP27-30 parallel the changes in infectivity and suggest that the beta-sheet structure plays a key role in the physical stability of scrapie amyloid and in the ability to propagate and replicate scrapie.     

Differences in the infectivity of Babesia incubated in plasma and serum and the role of glucose in prolonging viability

Babesia rodhaini was less infective to mice after incubation in rat serum than in rat plasma. This was explained by lower levels of glucose in serum than in plasma. Both serum and plasma were found to become metabolically depleted of glucose following prolonged contact with clotted and unclotted blood cells, respectively. When glucose concentrations in depleted samples were restored to those in freshly separated samples, infectivities of parasites were similar. This was shown for both B. rodhaini and B. argentina. Products of blood cell metabolism, produced when separation of plasma or serum was delayed for 24 h, were not shown to have any detrimental effects on the parasites. Average glucose values for plasma from rats and cattle were 153 mg/100 ml and 63 mg/100 ml, respectively, whereas serum and plasma remaining in contact with blood cells contained as little as 2 mg glucose/100 ml. Lactate values were correspondingly low in plasma and high in serum. Fibrinogen and platelets, factors involved in clotting, did not affect infectivity of B. rodhaini or B. argentina. The relevance of these findings to living babesial vaccines in which plasma- and serum-based diluents may be used is discussed.     

Papaya Leaf Curl Guangdong Virus and Ageratum Yellow Vein Virus Associated with Leaf Curl Disease of Tobacco in China

Two samples (YC7, YC27) of Nicotiana tabacum showing leaf curling, vein swelling and enations on undersides of leaves were collected in the Fujian Province of China in 2007. Virus isolates YC7‐1 and YC7‐2 (associated with betasatellite, YC7‐2β) were detected in both samples. The complete DNA‐A sequence of YC7‐1 (FJ869907) comprised 2741 nucleotides (nt). The complete DNA‐A (FJ869908) and betasatellite (FJ869909) sequence of YC7‐2 consisted of 2754 and 1344 nt, respectively. YC7‐1 had the highest nucleotide sequence identity (97.3%) with Papaya leaf curl Guangdong virus (PaLCuGuV‐[CN:Gd2:02], AJ558122). YC7‐2 had the highest sequence identity (90.1%) with Ageratum yellow vein virus (AYVV‐TW[TW:Tai:99], AF307861) and its betasatellite (96.5%) with Ageratum yellow vein betasatellite (AYVB‐[TW:CHu:02], AJ542495). These indicate that YC7‐1 and YC7‐2 are isolates of PaLCuGuV and AYVV, respectively. Symptoms including leaf curling, vein swelling and enations on undersides of leaves were observed in N. tabacum and N. glutinosa when infected by whiteflies with sample YC7 as the viral source under greenhouse conditions. PCR results showed that these infected plants contained both YC7‐1 and YC7‐2/YC7‐2β. To our knowledge, this is the first report of PaLCuGuV and AYVV/AYVB co‐infecting N. tabacum in China.     

Eco‐evolutionary dynamics in a coevolving host–virus system

Eco‐evolutionary dynamics have been shown to be important for understanding population and community stability and their adaptive potential. However, coevolution in the framework of eco‐evolutionary theory has not been addressed directly. Combining experiments with an algal host and its viral parasite, and mathematical model analyses we show eco‐evolutionary dynamics in antagonistic coevolving populations. The interaction between antagonists initially resulted in arms race dynamics (ARD) with selective sweeps, causing oscillating host–virus population dynamics. However, ARD ended and populations stabilised after the evolution of a general resistant host, whereas a trade‐off between host resistance and growth then maintained host diversity over time (trade‐off driven dynamics). Most importantly, our study shows that the interaction between ecology and evolution had important consequences for the predictability of the mode and tempo of adaptive change and for the stability and adaptive potential of populations.