Time to visual symptoms

The average time between a larva being fed spores and starting to exhibit clinical AFB disease symptoms is about 12.5 days. This is therefore the earliest that an infection can be detected visually. However, most colonies need considerably longer periods of time before they develop observable disease symptoms. The following table shows the length of time it took for honey bee colonies in one study to develop AFB disease symptoms after they were fed spores.

 Months after spores were fed Percent of colonies developing AFB symptoms
1 19
2 30
3 11
4 14
5 11
6 6
>6 9

Table 1: Length of time taken for honey bee colonies to develop AFB symptoms after being fed AFB spores

Symptoms of AFB can often take time to show

Just under half of the colonies developed disease symptoms within two months of being fed spores. However, approximately one-third of the colonies did not show any symptoms until three months or longer.

If the infections had come from spores in contaminated honey supers that were unknowingly removed from infected hives in the autumn and placed on clean hives the next spring, then the most a full brood check the following autumn would reveal would be about 85% of the infections that were created. The remainder would hopefully be identified the following spring, one and a half years after the honey supers were removed from the original AFB hives.

If AFB spores are introduced to a beehive in the spring, the disease may not be evident until the following spring.