The article mentions the toxicity of dogs' liver, which is excessively rich in vitamin A. "...may have hastened Mertz's death ..."
An educated guess?

The ill-fated Franklin Expedition to the Arctic suffered from lead poisoning from the solder used in the canned (tinned) food they ate. Autopsies on the frozen corpses of crewmen, preserved in their permanently frozen graves, suggested their deaths were due to this rather than starvation or cold.

I could cite the scientific articles and books that posit this conclusion, but I thought this school paper does a good job of summarizing the data.
Franklin