Environmental Toxins

by Dr. Linda Sorensen





Algae (cyanobacteria) can produce compounds that cause illness and even death in dogs. Algae "blooms" - or high reproductive bursts - occur when the weather is warm and a lack of rainfall allows streams to drop to low flows. Blooms are more likely to occur in rivers and lakes that have an excess of nutrients present, as is seen in some agricultural run-off.


The most common problematic species in rivers is Cyanobacteria Phormidium, which forms thick dark brown or black mats on rocks. These mats may break off and form floating rafts of algae as well. This algae occurs throughout Canterbury, and dogs have died in the past after licking the mats. While the algae does not always produce toxins, it is best to not let your dog swim in the river if you see large quantities of these algae mats in the area. Please note that the commonly seen brightly coloured long green algae is not toxic.


Wandering Dew


In lakes, there is phytoplankton Cyanobacteria Nodularia. This algae will commonly turn the lake water blue-green, but can also result in yellow or red discoloration of the water. There may be thick scum on the water surface, or foam at the waters edge when this algae is blooming.


Signs of exposure in dogs include lethargy, tremors, panting, twitching, paralysis, and convulsions. Death can occur as quickly as 30 minutes after exposure. Human exposure can result in rashes or blisters, eye irritation, allergic reactions, and gastrointestinal upset. Because of the rapid progression of symptoms and the potential for death in dogs, we advise that you avoid letting your pet swim in or drink from any suspect water source. There are some great internet pages for more information (including pictures of the algae mats).


Useful Weblinks



Wandering Jew


Wandering jew (Tradescantia fluminensis) is an introduced South American weed commonly found here in New Zealand. While ingestion of the plant does not seem to be problematic, it can cause itching and skin eruptions in dogs that come into contact with it. Typical lesions will be redness (with or without blisters) on less haired areas of the body (belly, feet). This can be intensely itchy for the dog, and often times their self-chewing will progress to a full-blown skin infection.


This plant is a perennial (lives year after year), and is quite happy in shaded, damp areas. The leaves are dark green, shiny, smooth, and elliptical, measuring 3-6 cm. It produces white triangular flowers with 3 petals in December and January. Pictures may be found via the links from our website.


RNZIA lists this plant as an unwanted organism in New Zealand. It propagates from cuttings, so you need to remove the entire plant and dispose of the bits and pieces away from any soil where it could regenerate itself. It does not seed here, so removal should be curative.


Useful weblinks



Insect Stings


Insect stings (bees, hornets, wasps) can be quite painful for our pets, and sometimes can progress to severe allergic reactions (anaphylaxis) in some individuals. This can be life-threatening. Severe reactions typically occur within 10-20 minutes of the sting. Signs include vomiting, breathing difficulty, generalized hives, facial swelling and collapse. If you should note any of these signs in your pet following a sting, please bring them into the clinic ASAP for treatment.


For more mild stings (without all the severe signs listed previously!), you should institute the following home care:

  • If you can find the stinger, scrape it off the skin with an EFTPOS card or other stiff material. If you are trying to remove a stinger with tweezers, do not put any pressure on the venom sac as this will squeeze additional venom into your pet! Grasp the stinger below the sac.
  • Apply cool compresses.
  • Apply a baking soda and water paste to the sting area to neutralize the acid in the venom.


It is always best for us to see any pet that has received multiple stings so we can minimize any reaction and pain for them.



Spider Bites


Spider bites (White-tail spiders) can result in necrosis (cell death) in the area of the bite. This necrosis may spread to adjacent tissues, thus resulting in an ever-growing ulcer or defect in the skin and surrounding muscles. Typically there will be a small blister or ulceration at the site of the bite, which does not heal (or continues to enlarge). Removal of all the damaged tissue, as well as some of the surrounding healthy tissue, may be required to allow these wounds to heal. If you suspect a spider bite as a cause of a lesion on your pet, please do not hesitate to tell us so we may monitor the lesion appropriately.



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