The severity of this disease depends on the number of heartworms present. (drsfostersmith.com)
The test detects adult heartworms if there are more than 5 female adult heartworms present (the test doesn't recognize a pure male heartworm population). (dogsnaturallymagazine.com)
Other than with an overwhelming, sudden exposure to mosquitoes, the number of heartworms present in your pet likely to be most related to the number of months or years that the pet lived without monthly heartworm preventatives. (2ndchance.info)