Host Modification Research Articles

A Petalless Flower Caused by aMicrobotryum violaceumMutant

The anther-smut fungus, Microbotryum violaceum, is a biotrophic plant pathogen that causes unique host modifications. In flowers infected by M. violaceum, fungal spores replace pollen in the anthers. In addition, infection of female (XX) Silene latifolia host plants results in the promotion of stamens, which is otherwise controlled by the plant’s genetic basis of sex determination (XY). This host plant manipulation represents an excellent example where fitness of the fungus is strongly correlated with the host’s floral development. In this study, we report that Mv537, the first M. violaceum mutant, altered the manipulation of S. latifolia flower development, causing a petalless flower. The petalless symptom can be caused by failure in the three main pathogenic stages: promotion of stamens, suppression of the gynoecium, and replacement of pollen with spores. This M. violaceum mutant is thought to exhibit a failure in the “timing” of spore production, in which the process of replacing pollen with spores occurs earlier than in the wild-type pathogen and/or there is “oversuppression” of floral development, resulting in the suppression of all floral primordia except the anthers. This M. violaceum mutant can be used as a tool for the study not only of pathogenesis but also of dioecy.

Neoplastic transformation of T lymphocytes through transgenic expression of a virus host modification protein.

Virus host evasion genes are ready-made tools for gene manipulation and therapy. In this work we have assessed the impact in vivo of the evasion gene A238L of the African Swine Fever Virus, a gene which inhibits transcription mediated by both NF-κB and NFAT. The A238L gene has been selectively expressed in mouse T lymphocytes using tissue specific promoter, enhancer and locus control region sequences for CD2. The resulting two independently derived transgenic mice expressed the transgene and developed a metastasic, angiogenic and transplantable CD4+CD8+CD69– lymphoma. The CD4+CD8+CD69– cells also grew vigorously in vitro. The absence of CD69 from the tumour cells suggests that they were derived from T cells at a stage prior to positive selection. In contrast, transgenic mice similarly expressing a mutant A238L, solely inhibiting transcription mediated by NF-κB, were indistinguishable from wild type mice. Expression of Rag1, Rag2, TCRβ-V8.2, CD25, FoxP3, Bcl3, Bcl2 l14, Myc, IL-2, NFAT1 and Itk, by purified CD4+CD8+CD69– thymocytes from A238L transgenic mice was consistent with the phenotype. Similarly evaluated expression profiles of CD4+CD8+ CD69– thymocytes from the mutant A238L transgenic mice were comparable to those of wild type mice. These features, together with the demonstration of (mono-)oligoclonality, suggest a transgene-NFAT-dependent transformation yielding a lymphoma with a phenotype reminiscent of some acute lymphoblastic lymphomas.

Chronic Toxoplasma Infection Modifies the Structure and the Risk of Host Behavior

The intracellular parasite Toxoplasma has an indirect life cycle, in which felids are the definitive host. It has been suggested that this parasite developed mechanisms for enhancing its transmission rate to felids by inducing behavioral modifications in the intermediate rodent host. For example, Toxoplasma-infected rodents display a reduction in the innate fear of predator odor. However, animals with Toxoplasma infection acquired in the wild are more often caught in traps, suggesting that there are manipulations of intermediate host behavior beyond those that increase predation by felids. We investigated the behavioral modifications of Toxoplasma-infected mice in environments with exposed versus non-exposed areas, and found that chronically infected mice with brain cysts display a plethora of behavioral alterations. Using principal component analysis, we discovered that most of the behavioral differences observed in cyst-containing animals reflected changes in the microstructure of exploratory behavior and risk/unconditioned fear. We next examined whether these behavioral changes were related to the presence and distribution of parasitic cysts in the brain of chronically infected mice. We found no strong cyst tropism for any particular brain area but found that the distribution of Toxoplasma cysts in the brain of infected animals was not random, and that particular combinations of cyst localizations changed risk/unconditioned fear in the host. These results suggest that brain cysts in animals chronically infected with Toxoplasma alter the fine structure of exploratory behavior and risk/unconditioned fear, which may result in greater capture probability of infected rodents. These data also raise the possibility that selective pressures acted on Toxoplasma to broaden its transmission between intermediate predator hosts, in addition to felid definitive hosts.

A Half-Century of Inspiration: An Interview with Hamilton Smith

In 1962, Hamilton Smith abandoned a career in medicine to follow his passion for the emerging field of molecular biology; within six years, he had made the discovery of a lifetime. As a new Johns Hopkins faculty member, Smith, together with his first graduate student, Kent Wilcox, geared up to study recombination in vitro but instead discovered the restriction enzyme “R” in Haemophilus influenzae. By cobbling together crude techniques, Smith, along with Wilcox and later Tom Kelly, showed that R cleaves DNA at a specific recognition sequence, a palindromic site, yielding blunt-ended DNA fragments. Now known as HindII, R proved to be the first of an enormous class of Type II restriction enzymes, and as such, presaged gene cloning, allowed DNA to be reproducibly fragmented and then sequenced, and enabled physical mapping of genomes. Smith went on to discover DNA methylases that constitute the other half of the bacterial host restriction and modification systems, as hypothesized by Werner Arber of Switzerland. Together with Arber and his Hopkins colleague Daniel Nathans, who first used the enzyme on SV40 DNA and demonstrated discrete bands on a tube gel, Smith shared the Nobel Prize for Physiology or Medicine in 1978.

Electronic structure, molecular electrostatic potential and spectral characteristics of pillar[6]arene hosts and their complexes with n-octyltriethylammonium ions

Electronic structure, charge distribution and (1)H NMR in pillar[6]arene (P6) conformers, their diisobutoxy derivatives and their host-guest complexes have been investigated by employing the density functional theory. It has been shown that a P6 conformer obtained by flipping of alternate hydroquinone units turns out to be of lowest energy, owing to the hydrogen bonded network at both rims of the host. As opposed to this, a conformer void of hydrogen bonding interactions has largely been destabilized. The O-HO interactions are analyzed using molecular electrostatic potential topography as a tool. Modification of a P6 host by substituting a diisobutoxy group at reactive phenols (DIBP6) renders rigid pillar-shape architecture to the host in which electron-rich regions are localized within the cavity and near portals. Complexation of n-octyltriethylammonium ions (n-OTEA) with P6 and DIBP6 reveals qualitatively different binding patterns. It has been shown that the conformer in which n-OTEA penetrates from the lower rim of the host and partially encapsulates within the P6 cavity turns out to be 1.4 kJ mol(-1) lower in energy than the complex showing complete guest encapsulation. Host-guest binding patterns, viz. encapsulation or portal interactions, can be distinguished from (1)H NMR chemical shifts. The shielding of ethyl and n-octyl chain protons in an n-OTEA⊂DIBP6 complex points to encapsulation of the guest which has been rationalized from natural bond orbital analyses. These inferences are in consonance with (1)H NMR experiments.

Embryonic Stem Cell Incorporation in Gastric Wall is Enhanced by Modified Proinflammatory Stem Cells and Enhanced Proliferative Host Compartment

BACKGROUND We showed previously that modified embryonic stem cells (ESCs) can be transplanted into and constitute mouse gastric wall for local delivery of particular gene products. We wished to assess differences in transplant efficiency depending on host and stem cell modifications. As a model, we looked at wild type (WT) and ITF-deficient (ITF) mice, since the latter are known to have an expanded proliferative compartment and are susceptible to epithelial injury factors presumed preferential for ESC incorporation. ESCs were compared to modified ESCs over-expressing inducible nitric oxide synthase (NOSCs). METHODS ESCs were derived from blastocysts of male B6;129S-Gt(ROSA)26Sor mice constitutively expressing β-gal activity. ESCs and NOSCs (5*106) were injected into the gastric wall of 10-12 week old female B6129F1 (Jackson Lab, WT) and ITF-/mice. Stomachs were harvested 7 or 10 days after transplantation. BrdU (50μg per gram of body weight) was injected i.p. in mice 2 hours before sacrificing. Tissues were fixed in 10% buffered formalin. ESCs and NOSCs were identified by X-gal staining and confirmed as male genotype by Y chromosome FISH (Starfish). Frozen or paraffin sections were stained with Sheep antiBrdU antibody conjugated with biotin (Abcam) and detected by DAB substrate kit (Vector). RESULTS Scattered clusters of ESCs and NOSCs were observed in gastric mucosa of both ITF-/and WT mice, but some injected cells were found densely at the base of gastric mucosa after 7 days. There was greater presence of NOSCs in ITF-/compared to WT mice. X-gal positive cells were situated higher along the crypt axis at day 10 compared to day 7. In contrast, ESCs showed similar pattern of residence in both ITF-/mice and WT mice. In WT mice, NOSCs and ESCs had similar density and distribution in the gastric wall 7 days after transplantation. However, in ITF-/mice, there was greater presence of NOSCs than ESCs at 7 days. Transplanted stem cells were confirmed by Y chromosome FISH. Proliferative capacity of tissues transplanted with stem cells was evaluated by BrdU uptake. In WT mice, there is no significant difference in number or distribution of BrdU-uptaking cells between ES and NOSC injected stomachs. However, in ITF-/mice, there was greater number of BrdU-uptaking cells when injected with NOSCs than ESCs, similar to their greater presence by X-gal stains. Overall, ITF-/mice had greater number of BrdU-uptaking cells than WT mice. CONCLUSION Both host and ES factors appear to influence the distribution and possible incorporation of injected cells. ITF-/mice, with an expanded proliferative compartment, may be capable of greater incorporation of ESCs. iNOS delivery in these mice, co-acting with their decreased toleration of inflammation, may explain the enhanced transplant efficiency.

The persistent congestion problem of FAST‐TCP: analysis and solutions

AbstractFAST‐TCP achieves better performance than traditional TCP‐Reno schemes, but unfortunately it is inherently unfair to older connections due to wrong estimations of the round‐trip propagation delay.This paper presents a model for this anomalous behaviour of FAST flows, known as the persistent congestion problem. We first develop an elementary analysis for a scenario with just two flows, and then build up the general case with an arbitrary number of flows. The model correctly quantifies how much unfairness shows up among the different connections, confirming experimental observations made by several previous studies.We built on this model to develop an algorithm to obtain a good estimate of the propagation delay for FAST‐TCP that enables to achieve fairness between aged and new connections while preserving the high throughput and low buffer occupancy of the original protocol. Furthermore, our proposal only requires a modification of the sender host, avoiding the need to upgrade the intermediate routers in any way. Copyright © 2010 John Wiley & Sons, Ltd.

Analysis of Host-Mediated Repair Mechanisms after Human CNS-Stem Cell Transplantation for Spinal Cord Injury: Correlation of Engraftment with Recovery

BackgroundHuman central nervous system-stem cells grown as neurospheres (hCNS-SCns) self-renew, are multipotent, and have potential therapeutic applications following trauma to the spinal cord. We have previously shown locomotor recovery in immunodeficient mice that received a moderate contusion spinal cord injury (SCI) and hCNS-SCns transplantation 9 days post-injury (dpi). Engrafted hCNS-SCns exhibited terminal differentiation to myelinating oligodendrocytes and synapse-forming neurons. Further, selective ablation of human cells using Diphtheria toxin (DT) abolished locomotor recovery in this paradigm, suggesting integration of human cells within the mouse host as a possible mechanism for the locomotor improvement. However, the hypothesis that hCNS-SCns could alter the host microenvironment as an additional or alternative mechanism of recovery remained unexplored; we tested that hypothesis in the present study.Methods and FindingsStereological quantification of human cells using a human-specific cytoplasmic marker demonstrated successful cell engraftment, survival, migration and limited proliferation in all hCNS-SCns transplanted animals. DT administration at 16 weeks post-transplant ablated 80.5% of hCNS-SCns. Stereological quantification for lesion volume, tissue sparing, descending serotonergic host fiber sprouting, chondroitin sulfate proteoglycan deposition, glial scarring, and angiogenesis demonstrated no evidence of host modification within the mouse spinal cord as a result of hCNS-SCns transplantation. Biochemical analyses supplemented stereological data supporting the absence of neural stem-cell mediated host repair. However, linear regression analysis of the number of engrafted hCNS-SCns vs. the number of errors on a horizontal ladder beam task revealed a strong correlation between these variables (r = −0.78, p<0.05), suggesting that survival and engraftment were directly related to a quantitative measure of recovery.ConclusionsAltogether, the data suggest that the locomotor improvements associated with hCNS-SCns transplantation were not due to modifications within the host microenvironment, supporting the hypothesis that human cell integration within the host circuitry mediates functional recovery following a 9 day delayed transplant.

An improved in vitro and in vivo Sindbis virus expression system through host and virus engineering

The Sindbis viral expression system enables the rapid production of high levels of recombinant protein in mammalian cells; however, this expression is typically limited to transient production due to the cytotoxicity of the virus. Limiting the lethality inherent in the Sindbis virus vector in order to enable long term, sustained expression of recombinant proteins may be possible. In this study, modifications to virus and host have been combined in order to reduce the cytopathic effects. Non-cytopathic replication competent viruses of two Sindbis viral strains, TE and 633, were developed using a non-structural protein (nsP) P726S point mutation in order to obtain persistent heterologous gene expression in infected Baby Hamster Kidney (BHK) cells and Chinese Hamster Ovary (CHO) cells. Cells infected with the P726S variant viruses were able to recover after infection, while cells infected with normal virus died within 3 days. The P726S mutation did not reduce the susceptibility of 5- and 14-day-old mice to 633 and TE viruses in vivo. In addition, animal survival with the P726S variant viruses was increased and GFP expression was sustained for at least 14 days while the 633 and TE infection resulted in short-term GFP expression or an earlier mortality. Modifications to the host BHK and CHO cells themselves were subsequently undertaken by including the anti-apoptotic gene Bcl-2 and a deletion mutant of Bcl-2 (Bcl-2Δ) as another method for limiting the cytopathic effects of the Sindbis virus. The inclusion of anti-apoptotic genes permitted higher production of heterologous GFP protein following Sindbis virus infection, and the combination of the TE-P726S virus and the CHO-Bcl-2Δ cell line showed the greatest improvement in cell survival. Sindbis virus infection also induced ER stress in mammalian cells as detected by increased PERK phosphorylation and ATF4 translation. Overexpression of Parkin, an E3 ubiquitin ligase that can protect cells against agents that induce ER stress, suppressed Sindbis virus-induced cell death in both BHK cells and in vivo studies in mice . Such findings show that viral and host modifications can improve cell survival and production of heterologous proteins, change viral behavior in vitro and in vivo, and assist in the development of new expression or gene delivery vehicles.

Encapsulation of Small Ionic Molecules within α-Cyclodextrins

Results from molecular dynamics experiments pertaining to the encapsulation of ClO4- within the hydrophobic cavity of an aqueous alpha-cyclodextrin (alpha-CD) are presented. Using a biased sampling procedure, we constructed the Gibbs free energy profile associated with the complexation process. The profile presents a global minimum at the vicinity of the primary hydroxyl groups, where the ion remains tightly coordinated to four water molecules via hydrogen bonds. Our estimate for the global free energy of encapsulation yields DeltaGenc approximately -2.5 kBT. The decomposition of the average forces acting on the trapped ion reveals that the encapsulation is controlled by Coulomb interactions between the ion and OH groups in the CD, with a much smaller contribution from the solvent molecules. Changes in the previous results, arising from the partial methylation of the host CD and modifications in the charge distribution of the guest molecule are also discussed. The global picture that emerges from our results suggests that the stability of the ClO4- encapsulation involves not only the individual ion but also its first solvation shell.

Exploiting host compensatory responses: the ‘must’ of manipulation?

Parasite-induced alterations of the host phenotype have been reported in many systems. These changes are traditionally categorized into three kinds of phenomena: secondary outcomes of infection with no adaptive value, host adaptations that reduce the detrimental consequences of infection and parasitic adaptations that facilitate transmission. However, this categorization is a simple view, and host modifications should be considered as co-evolved traits, rather than a total takeover. Here, we present a novel scenario of manipulation, which has considerable potential to resolve issues that are specific to the evolution of behavioural alterations induced by parasites. It is proposed that certain parasites affect fitness-related traits in their hosts to trigger host compensatory responses because these responses can meet the transmission objectives of parasites.

Cellulose nano whiskers from grass of Korea

Polymer composites form a fascinating interdisciplinary area by bringing together biology and material science for wide verity of applications ranging from construction to biomedical technology. A deliberate interest in the development of eco-friendly material motivated the efforts toward research on cellulose composites due to its cheap, sustainable, recyclable, degradable nature and remarkable reinforcing properties at 167.5 GPa of Young’s modulus along the chain axis per theoretical estimations. The use of natural fiber for technical applications like automobile industry is restricted due to its incompatibility with generally hydrophobic host matrix and increase in weight of resulting products which provide a poor cost performance ratio. After resolving the incompatibility issues up to a satisfactory extent by adequate modification either in host or filler, it was assumed that dispersion and material properties may be enhanced with reduction in the size and increase in surface area by introducing nano fillers. Nano size (5-20 nm cross sections with length to several μm depending on source) rod like cellulose crystallites particles, known as cellulose nano whiskers (CNW), can be extracted from laterally stabilized fibrils bundle by removing amorphous region through controlled acid hydrolysis. These whiskers have been employed in reinforcing several polymers, which result in comparatively better mechanical properties. Nevertheless, such fibers have conquered many obstacles against industrial practices due to time consuming preparation procedure with very low yield, commercial unavailability, and most importantly, comparative higher cost through expensive source such as tunicate, bacterial, algal (valonia), brown algae (Oomycota) and commercially available microcrystalline cellulose. The low yield and availability of raw materials of these sources generally inhibit the penetration of this tremendous reinforcer for the development of daily use biodegradable products. The current attempt was made to obtain the cellulose nano whiskers from the cheapest source, grass of Koera for the first time, which may further broaden the use of these bio fillers ranging from commodity to constructive applications.

Progress towards clinical xenotransplantation

Xenotransplantation has progressed from early heroic experiments on the path to meet the ever increasing demands of tissue and organ transplantation in patients with end-stage organ failure. The pig species is regarded as the most promising donor species. However, due to the evolutionary distance, innovative approaches are to be developed to permit life-supporting function in humans. Transplantation of organs from non-human primates has increased our knowledge on rejection mechanisms and provided opportunities for testing modified immunosuppression of the host and genetic modification of the donor. The development of transgenic animals expressing human complement-regulatory factors, and of animals lacking the target for naturally occurring anti-pig antibodies, has essentially eradicated hyperacute rejection of solid organs. However, there is still a need for tolerable immunosuppression or immune-tolerance regimens to provide broadly available procedures in the clinical setting. Safety concerns especially cross-species transmission of infectious pathogens, in particular of porcine endogenous retrovirus. Many studies have indicated that this is highly unlikely. At present, cell and tissue transplantation of islets of Langerhans to diabetic patients is close to being tested in well-designed clinical trials. Further research is required before other porcine xenografts can offer a broadly available therapeutic option in clinical medicine.

The influence of intercalation on the phonon spectrum of titanium dichalcogenides

A systematic investigation of the inelastic neutron scattering spectra is carried out for intercalation titanium diselenide compounds of the general formula M x TiSe2 (M = Cr, Fe, Ni, Ag). It is shown that the effect of intercalation on the phonon spectrum of the material is determined primarily by the modification of the host lattice due to the formation of Ti-M-Ti covalent centers. It is established that the lattice can undergo a substantial softening when the impurity band coincides with the Fermi level.

Defense suppression by virulence effectors of bacterial phytopathogens

Phytopathogenic bacteria and plants are locked in molecular struggles that determine the outcome of an infection. Bacteria make effector molecules that can induce defenses if recognized by specific host resistance (R) proteins. In susceptible hosts, however, effectors frequently promote virulence by suppressing host defenses. Defense-inducing and defense-suppressing activities are often related, as virulence-associated host modifications can elicit R protein activation. Thus, understanding of how an effector elicits defenses can translate into understanding of how it promotes virulence and vice versa. To control host cell functions, such as defense gene expression and vesicle trafficking, effectors use various biochemical activities, including protein modification, transcriptional regulation, and hormone mimicry. Progress with individual effectors will lead to an integrated view of how the activities of a collection of effectors intersect with genetically variable host plants to regulate susceptibility and resistance.

Energy transfer between rhodamine 3B and oxazine 4 in synthetic-saponite dispersions and films

The objective of this study was the investigation of energy transfer between the laser dyes rhodamine 3B (R3B) and oxazine 4 (Ox4) adsorbed on the surface of synthetic Sumecton saponite (Sum). The process of energy transfer was studied for both saponite dispersions and oriented solid films. The electronic properties, luminescence, and the energy transfer process were described by UV–vis absorption and fluorescence spectroscopy. For the efficiency of the energy transfer process, the concentrations of energy donor and acceptor components on a clay mineral surface were found to be essential. A side reaction of the molecular assembly formation reduced both the luminescence and energy-transfer yields, mainly due to fluorescence quenching. The quenching was more problematic for the solid film specimens, where an appropriate modification of the inorganic host with hydrophobic alkylammonium cations was used to achieve a higher luminescence. Due to the higher tendency of Ox4 to form nonluminescent aggregates at higher concentrations, the lowering of the Ox4 concentration further improved the luminescent properties of the films. In this case, the energy transfer occurring in the solid film from R3B to Ox4 was clearly proven.

Plasmodium rhoptries: how things went pear-shaped

Plasmodium parasites have three sets of specialised secretory organelles at the apical end of their invasive forms--rhoptries, micronemes and dense granules. The contents of these organelles are responsible for or contribute to host cell invasion and modification, and at least four apical proteins are leading vaccine candidates. Given the unusual nature of Plasmodium invasion, it is not surprising that unique proteins are involved in this process. Nowhere is this more evident than in rhoptries. We have collated data from several recent studies to compile a rhoptry proteome. Discussion is focussed here on rhoptry content and function.

Improved Production of Enzymes, Which Are Expressed under the Pho Regulon Promoter, in thermfGene (encoding ribosome modulation factor) Disruptant ofEscherichia coli

Using a DNA macroarray, we investigated the effects of rmf gene (encoding ribosome modulation factor) disruption on gene expression profiles in Escherichia coli. This strain showed a phosphate-starvation-like response in gene expression even under phosphate sufficient conditions; significant upregulation of the Pho regulon genes was observed. Further, the production of alkaline phosphatase, a product of the Pho regulon gene, phoA, increased in the rmf disruptant under a Pi sufficient condition. Furthermore, production of PhoC acid phosphatase/nucleoside pyrophosphate phosphotransferase derived from Morganella morganii also increased significantly in the rmf disruptant. We concluded that host modification by the rmf gene disruption has potential benefit in industrial enzyme production using Escherichia coli.

Maintaining rapid growth in moderate‐density Escherichia coli fermentations

A novel feeding strategy that prolongs rapid growth rates for Escherichia coli fermentations to moderately high cell density is presented. High-density fermentations are a common and successful means of producing biological products. However, acetate accumulation can be a substantial problem in these procedures. To avoid this problem, many feeding strategies and host modifications have been developed, but all result in relatively low growth rates. If a faster growth rate could be maintained, the growth phase of the process would be shortened, leading to increased productivity. It is also possible that the subsequent specific production rate could be enhanced by growing the early culture at a faster rate. We have developed a procedure to enable rapid growth to a cell density of 20 g/L and have used cell-free protein synthesis to evaluate the relative potential of the resulting cells for producing recombinant proteins. The method uses glucose pulses and the duration of the dissolved oxygen response to calculate the appropriate glucose feed rate based on the glucose demand of the culture. Amino acids and vitamins were supplied in the medium to increase the growth rate. We were able to sustain a growth rate of 0.8/h up to 20 g/L dry cell weight without significant acetate accumulation. Analysis of amino acid consumption indicates that cell composition is an accurate predictor of amino acid demand for most amino acids. Cell-free protein synthesis was used to compare the protein production potential of the high-density cultures with that of cells grown in complex medium and harvested at low cell density and maximum growth rate. Protein production for the extract from the controlled, high-density fermentations was 950 mg/L compared with 860 mg/L for the low-density control. Therefore, the new control procedure has promising potential for developing rapid and productive industrial fermentations.

Intra-specific host sharing in the manipulative parasite Acanthocephalus dirus: does conflict occur over host modification?

The acanthocephalan parasite Acanthocephalus dirus induces a colour change in the intermediate host, the aquatic isopod Caecidotea intermedius, which increases transmission to definitive hosts (creek chub, sunfish). We examined the potential for conflict to occur between infective (cystacanth) and non-infective (acanthor, acanthella) stages of A. dirus over the level of colour modification that should be induced when these stages share a host. Using a field survey, we showed that host sharing by infective and non-infective stages was relatively common and that infective and non-infective stages differed in their effects on colour modification. Non-infective stages induced a colour change over 40% of the body, whereas infective stages induced a colour change over 80%. Thus, conflict could occur between stages over the level of modification that should be induced. We then showed that mixed-stage infections induced a colour change in the host that was consistent with the level of modification induced by the infective stage. We discuss the potential significance of these results to patterns of host modification and their effects on stage-related survival in nature.