"We do not have any evidence to determine any broader contaminated game meat, or that there is a risk to public health, however I would encourage anyone who is hunting or handling game meat to follow guidelines as set out by the Ministry for Primary Industries [MPI]," he said.
National Poisons Centre director and medical toxicologist Dr Adam Pomerleau said the sudden onset of the illness in all three adults suggested a toxin rather than an infection, although he had not seen the patients' clinical details.
Botulism poisoning is one possible cause of the reported symptoms. The rare and potentially fatal illness is caused by the bacteria Clostridium botulinum. Symptoms can include vomiting, muscle weakness and paralysis.
However there is usually a lag of several hours or days between ingesting the bacteria and symptoms appearing, Pomerleau said - not 30 minutes after eating.
"But it's all about dose. If the dose is very high, the symptoms could be seen more rapidly - the incubation period could be the day of consumption."
An antitoxin for botulism does exist but it can be hard to find and must be used quickly, Pomerleau said.
"If it does turn out to be botulism, the faster the antitoxin is given, the better their improvement."
Recovery would take weeks or months, he said, and there could be residual symptoms.
Paralytic shellfish poisoning, or a range of anticholinergic poisons - some of which are found in plants - could also cause similar symptoms, he said.
There has been speculation online that the pig may have eaten 1080, which is used in New Zealand to control predators that threaten native bird populations.
Pomerleau said he had never heard of a case of 1080 poisoning where the person had not directly ingested the bait.
The NZ Deerstalkers' Association president Bill O'Leary he had never heard of anyone being poisoned from game meat - but it was not that uncommon for wild animals to be dropped off at a game butcher and then be deemed unfit for human consumption.
"From a hunter's point of view, this is the first incident I've heard of a number of people going down," he said.
O'Leary questioned how the meat was treated, including whether it was gutted quickly and safely and how long it had been left out before or after cooking.
He also said it was important for hunters to get their kill somewhere cool quickly especially as temperatures rise.
MPI's food safety recommendations for hunters
• Remove organs as soon as possible to avoid contamination with faecal matter and to help cool the animal down
• Take precautions to avoid puncturing the gut, including shooting the animal in the head or forequarter and using a specialised knife for gutting
• Checking for signs of illness in the animal including unusual smells, swollen organs or being underweight
• Cleaning gear and hands before and during bleeding and gutting the animal
• Chill the carcass as soon as possible
• Avoiding hunting in areas where poisons have been laid
