Many wildlife populations are declining at a much higher rate than can be explained by known threats to biodiversity, such as habitat loss and climate change. Furthermore, local outbreaks of disease are observed to an unprecedented extent in many feral species today. The incidence rate is so high that immunosuppression is strongly suspected to be involved. We investigate thiamine (vitamin B1) deficiency as a possible contributing cause to these problems. Thiamine diphosphate is required as a cofactor in at least five life-sustaining enzymes in the basic cellular metabolism. Many of the sick and/or dying animals have turned out to be more or less thiamine deficient, as determined by analysis of different phosphorylated forms of thiamine, as well as the holoenzyme and apoenzyme forms of thiamine-dependent enzymes. It has also been possible to cure sick animals by thiamine treatment. The observed thiamine deficiency is also linked to secondary effects on other health status variables, such as growth, condition, liver size, blood physiology, histopathology, swimming behaviour and endurance, reproduction, population size, and parasite infestation. So far, we have published data on severe thiamine deficiency in several species of fish and birds. To the best of our knowledge, thiamine deficiency is the only currently known phenomenon that can explain a large part of the population declines and outbreaks of disease reported worldwide today, and our work so far indicates that the cause must be searched for at the chemical and biochemical levels.
Figure legend: Karin Ström, Lennart Balk, Tomas Hansson, Lisa Sigg, Hanna Gustavsson, Yolanda Ruiz Muñoz, Per-Åke Hägerroth, (Birgitta Liewenborg missing)