This review considers available evidence for mechanisms of conferred adaptive advantages in the face of specific infectious diseases. In short, we explore a number of genetic conditions, which carry some benefits in adverse circumstances including exposure to infectious agents. The examples discussed are conditions known to result in resistance to a specific infectious disease, or have been proposed as being associated with resistance to various infectious diseases. These infectious disease—genetic disorder pairings include malaria and hemoglobinopathies, cholera and cystic fibrosis, tuberculosis and Tay-Sachs disease, mycotic abortions and phenylketonuria, infection by enveloped viruses and disorders of glycosylation, infection by filoviruses and Niemann–Pick C1 disease, as well as rabies and myasthenia gravis. We also discuss two genetic conditions that lead to infectious disease hypersusceptibility, although we did not cover the large number of immunologic defects leading to infectious disease hypersusceptibilities. Four of the resistance-associated pairings (malaria/hemogloginopathies, cholera/cystic fibrosis, tuberculosis/Tay-Sachs, and mycotic abortions/phenylketonuria) appear to be a result of selection pressures in geographic regions in which the specific infectious agent is endemic. The other pairings do not appear to be based on selection pressure and instead may be serendipitous. Nonetheless, research investigating these relationships may lead to treatment options for the aforementioned diseases by exploiting established mechanisms between genetically affected cells and infectious organisms. This may prove invaluable as a starting point for research in the case of diseases that currently have no reliably curative treatments, e.g., HIV, rabies, and Ebola.

The dairy industry is faced with the challenge of euthanizing unwanted male offspring in addition to other sick or injured neonates. Carbon dioxide (CO2) may be a potential alternative to current methods. The goat kid served as a model in approachavoidance and conditioned place aversion paradigms. A preference test box was custommade with two connected chambers; one chamber held an ambient atmosphere (control) and one maintained a static CO2 concentration (treatment). Kids were allotted 5-minutes in the control chamber before a sliding door was opened, after which kids were given 10minutes access to the treatment chamber. The objective of the first study was to determine the ability of kids to move from the control to the treatment chamber to access a milk reward, and the effect of an olfactory or visual stimulus on learning. All kids (n=24) exhibited learning, and latencies to enter, touch the milk bottle, and suckle decreased over day (P<0.0001). Milk consumption increased over days (P<0.0001), and startle, bottle engagement, and lying behavior did not differ between days (P>0.05). The presence of an olfactory stimulus (peppermint oil) did not affect learning, and the visual stimulus (plastic curtain) did not prevent learning. The second study examined kids' tolerance of 10%, 20%, and 30% CO2. Kids (n=12) were randomly assigned 10% or 20% as the first treatment, and were systematically tested with all kids receiving 30% as the last treatment. A 2-day washout (ambient CO2) period occurred between each gas treatment. 10 kids tolerated 10% CO2, while one kid exited the treatment chamber after consuming his full ration, and 1 kid lost posture at 289s. At 20% and 30%, posture loss ranged from 83s to 271s. One kid exited before losing posture at 20%, then re-entered the chamber and became recumbent. Kids did not show avoidance behavior to any CO2 ix concentration, and did not appear to develop a conditioned aversion. The results of this study show promising results for CO2 as a euthanasia method in goat kids. Further research is required to confirm its suitability, and determine its potential for other ruminant species.

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