Mechanisms of Pathogenesis, Infective Dose and Virulence in Human Parasites

Abstract

The number of pathogens that are required to infect a host, termed infective dose, varies dramatically across pathogen species. It has recently been predicted that infective dose will depend upon the mode of action of the molecules that pathogens use to facilitate their infection. Specifically, pathogens which use locally acting molecules will require a lower infective dose than pathogens that use distantly acting molecules. Furthermore, it has also been predicted that pathogens with distantly acting immune modulators may be more virulent because they have a large number of cells in the inoculums, which will cause more harm to host cells. We formally test these predictions for the first time using data on 43 different human pathogens from a range of taxonomic groups with diverse life-histories. We found that pathogens using local action do have lower infective doses, but are not less virulent than those using distant action. Instead, we found that virulence was negatively correlated with infective dose, and higher in pathogens infecting wounded skin, compared with those ingested or inhaled. More generally, our results show that broad-scale comparative analyses can explain variation in parasite traits such as infective dose and virulence, whilst highlighting the importance of mechanistic details.

Functional, Phylogenetic and Host-Geographic Signatures of Labyrinthula spp. Provide for Putative Species Delimitation and a Global-Scale View of Seagrass Wasting Disease

“…As such, putatively pathogenic Labyrinthula types might exist as relatively quiescent biotrophs until they reach a certain density, or a threshold-level of damage is reached, thereby triggering host cell death in advance of more aggressive growth as necrotrophs (e.g., Schmid-Hempel and Frank 2007;Leggett et al 2012). In addition, the fact that Labyrinthula can also be cultured on a variety of media including bacteria and various eukaryotic microbes (Porter 1990), with some ability to infect via waterborne transmission (this study), suggests that they have the ability to dwell on other substrates in nature, at least temporarily.…”

Comparison of the Detection Limits of the Culture and PCR Methods for the Detection of Clostridium difficile, Clostridium perfringens, Campylobacter jejuni, and Yersinia enterocolitica in Human Stool

“…Although usage of an effective culture medium will improve the isolation rate of the bacterium, the need to provide microaerophilic conditions for its growth and supplements to prevent the growth of fecal microbiota are considered the main limitations of this method. Alcohol pretreatment of stool specimens together with appropriate incubation time (up to 1 week) seems to be an effective method for the detection of C. difficile spores in the stool samples (7,8); however, usage of other sensitive and rapid tests is preferable. In our experiment, the PCR detection limit for this bacterium was 100 CFU/g.…”

“…Clostridium difficile is also considered the most frequently identified enteric Copyright pathogen in hospitalized patients with a recent history of medication (7). The infectious dose of these pathogens varies depending on their virulence potency and level of resistance to the harsh conditions of the gut environment (8). In some cases, gastrointestinal infectious diseases are acquired by the consumption of contaminated foods or water that are infected with fewer than 10 microorganisms (9).…”

Wastewater use in urban agriculture: an exposure and risk assessment in Accra, Ghana

“…This study did not isolate specific strains of E. coli, or other pathogens, and therefore is unable to determine whether this exposure could potentially result in an adverse health effect as big differences exist in the infective dose for different E. coli strains, though a recent study reported the infective dose of Enterohaemorrhagic Escherichia coli (EHEC) serotype O157 to be 10 CFU [120]. Again, the presence of E. coli only indicates the presence of faecal pollution and does not necessarily guarantee the presence of pathogens that can cause diseases to humans.…”