Sorghum genes responsive to purple witchweed parasitism were isolated, and their expression was analyzed. Using the suppression-subtractive hybridization strategy, 30 genes that were up-regulated in response to purple witchweed parasitism were isolated from the roots of a susceptible sorghum cultivar ‘Abu 70’. The changes in the expression of each gene were investigated in the roots and leaves of the sorghum cultivars ‘Wad Ahmed’ and ‘Tabat’ were parasitized by purple witchweed. Tabat is more susceptible and Wad Ahmed is less susceptible to purple witchweed than Abu 70. Further, the changes in the gene expression and host susceptibility to purple witchweed were studied in the roots of the three sorghum cultivars after treatment with salicylic acid (SA) or methyl jasmonate (MeJA). Purple witchweed parasitism induced jasmonic acid (JA)-responsive genes and suppressed SA-responsive genes in the roots of the cultivars Abu 70 and Tabat. In contrast, purple witchweed parasitism in the less-susceptible cultivar Wad Ahmed induced SA-responsive genes and induced JA-responsive genes to a small extent. SA, but not MeJA, decreased the susceptibility of all the sorghum cultivars to purple witchweed. Systemic expression of a few genes was observed in the leaves of the purple witchweed–parasitized sorghum cultivars.

The pathogenesis of bovine respiratory disease (BRD) is determined by a complex interaction of environmental, infectious, and host factors. Environment trends could impact feedlot cattle by increasing their level of stress. The polymicrobial nature of BRD produces synergies between infectious agents that can alter pathogenesis. However, the nature of the host response to these environmental and infectious challenges largely determines the characteristics of the progression and outcome of BRD.

Mycoplasma pneumoniae is a frequent cause of community-acquired pneumonia. Three subtypes and three variants of M. pneumoniae have been described showing sequence differences in the main P1 adhesin. Between 2003 and 2006 we collected respiratory tract samples of adult outpatients with symptoms of pneumonia in a German nationwide network and detected M. pneumoniae by real-time PCR in 140 specimens. The strains were typed by sequencing and demonstrated the circulation of subtypes 1 and 2 and variants 2a and 2b. The overall number of isolates belonging to the two variant genotypes increased during the investigation period but the relationship of subtypes and variants within the participating local centres varied strongly. ELISA experiments using sera of acute-phase patients with a known M. pneumoniae type in the respiratory tract resulted in no correlation of IgA and IgG antibodies to subtype- and variant-specific regions of the P1 gene with the genotype of the M. pneumoniae strain causing the actual infection.

The application of genome-scale approaches to study Trypanosoma cruzi–host interactions at different stages of the infective process is becoming possible with sequencing and assembly of the T. cruzi genome nearing completion and sequence information available for both human and mouse genomes. Investigators have recently begun to exploit DNA microarray technology to analyze host transcriptional responses to T. cruzi infection and dissect developmental processes in the complex T. cruzi life-cycle. Collectively, information generated from these and future studies will provide valuable insights into the molecular requirements for establishment of T. cruzi infection in the host and highlight the molecular events coinciding with disease progression. While the field is in its infancy, the availability of genomic information and increased accessibility to relatively high-throughput technologies represents a significant advancement toward identification of novel drug targets and vaccine candidates for the treatment and prevention of Chagas' disease.

Factors affecting ‘invasion efficiency’ of steinernematid entomopathogenic nematodes into hosts were elucidated. The phenomenon that only part (10–40%) of the nematode population invades the target host has been recorded in many studies. It has been mainly ascribed to differences in the ability of individual nematodes to infect. In the present study the effect of an infected host, the wax moth Galleria mellonella, on subsequent infection of the entomopathogenic nematodes Steinernema carpocapsae Mexican, S. riobravus and S. feltiae was evaluated. The invasion rate of the 3 nematode species to a non-infected host was reduced by 40–60% after pre-exposure to infected hosts. These nematodes regained their full invasion potential after they were rinsed with water. Invasion into insects which were previously injected with nematodes was significantly reduced by 60–80% 6–9 h after injection. The reduction in subsequent invasion due to the initial infection was nematode species specific. This phenomenon was also observed with other lepidopteran pests (Helicoverpa armigera and Spodoptera littoralis). The data indicate that the initial infection by entomopathogenic nematodes induced the release of a substance which reduced the subsequent invasion. The chemical and biological characteristics of this substance are currently under investigation.

To study the infection dynamics of metacercariae of the digenean Cryptocotyle lingua, wild living Atlantic cod, Gadus morhua, were caged for 18 months close to the shore. Here they were exposed to naturally occurring transmission stages of the parasite. First, both the abundance and the variance to mean ratio of metacercariae increased, but during the second half of the study the abundance levelled out, and the variance to mean ratio showed a significant decrease. Host mortality was negligible throughout the study. Based on the relationship between pigment spots and metacercariae observed by skin digestion, there was no indication of density-dependent parasite mortality. We conclude that the infrapopulations of metacercariae on the caged cod probably were regulated by density-dependent host responses acting against the cercariae.