Locoweed Poisoning in Dogs

The locoweed got its name from the Spanish word for crazy which is loco, because it causes animals to act crazy. It is the neurological damage that produces the symptoms of what people describe as craziness. All the parts of the locoweed have the toxic alkaloid, swainsonine, including the flowers, foliage, stems, seeds, and even the pollen. Swainsonine is actually used to create chemotherapy drugs to treat cancer in humans. Although your dog would have to eat locoweed continually over a week or more for these symptoms are evident, there are other symptoms you may see right away, such as vomiting and diarrhea. Found in the western United States, locoweed is approximately four to twelve inches tall, with flowers that look similar to sweet peas. The petals can be white, yellow, purple, or blue and is commonly found on hills growing in groups. If you believe your dog has consumed locoweed, you should call your veterinarian right away to make an appointment.

Locoweed poisoning is the most common poisonous plant problem in the western United States. While this refers mainly to livestock, it is also very common for dogs get sick from locoweed. The most toxic property in the locoweed is swainsonine, which is an indolizidine alkaloid (phytotoxin) that can cause severe neurological damage by changing the way the body processes proteins. Like many toxic plants, the locoweed is not very palatable to dogs, so most will not eat a lethal amount, but it does not take very much. In fact, it only takes .3 milligrams per kilogram of body weight to cause symptoms. If your dog continues to eat locoweed, no matter what the amount, chronic locoism will result because it accumulates. Chronic locoism creates dangerous neurological damage, congestive heart failure, lysosomal storage disease, and eventually death.

If your dog has eaten just a small portion of locoweed, the signs may just mimic an upset stomach, with vomiting and diarrhea. However, if your dog continues to eat locoweed on a regular basis, you will start seeing symptoms gradually. These signs will develop over several weeks until they just collapse. The most common symptoms are:

• Appetite loss
• Birth defects/sterilization
• Congestive heart failure (blue or gray tongue and gums, fainting, fluid retention - swollen abdomen)  
• Death
• Depression
• Head bobbing
• Locoism (aggression, blindness, excessive drooling, hyperactivity, increasing incoordination, weakness, and death)
• Seizures
• Stiff and clumsy walking
• Loss of body control
• Lysosomal storage disease (delayed development, dementia, enlarged liver and spleen, hearing loss, seizures)
• Nervousness
• Slow growth
• Subtle tremors
• Weight loss

 Types

In North America, Locoweed is a common name given to all plants that make swainsonine. These plants are part of the Fabaceae, Oxytropis, and Astragalus family. This includes cannabis, or more commonly known as marijuana. Many of the 2000 types of locoweed do not produce swainsonine, but they are so similar to toxic astragalus that they should be avoided as well. These are some of the most common types of locoweed in North America:

•  A. earlei, Big Bend locoweed
• A. humistratus, groundcover milkvetch
• A. lentiginosis, spotted locoweed, freckled milkvetch
• A. mollissimus, purple woolly locoweed
• A. nothoxys, sheep milkvetch
• A. tephrodes, ashen milkvetch
• Astragalus canadensis, Canada locoweed
• Astragalus didymocarpus, white dwarf locoweed
• Astragalus gambelianus, dwarf locoweed
• Astragalus oxyphysus, Diablo locoweed
• Astragalus trichopodus, coast locoweed, Southern California locoweed
• Astragalus whitneyii, Whitney's locoweed
• Cannabis, loco weed, when used as a recreational drug
• Datura stramonium, loco weed, when used as a hallucinogen
• Oxytropis campestris, Fassett's locoweed, field locoweed, northern yellow locoweed
• Oxytropis lambertii, Colorado locoweed, Lambert locoweed, locoweed, purple locoweed, stemless locoweed, woolly locoweed
• Oxytropis nana, Wyoming locoweed
• Oxytropis riparia, Ruby Valley locoweed
• Oxytropis sericea, early yellow locoweed, locoweed, Rocky Mountain locoweed, silky locoweed, white locoweed, white point locoweed

The cause of locoweed poisoning is swainsonine, an indolizidine alkaloid (phytotoxin). Continuous consumption of locoweed causes locoism, which produces neurological, cardiovascular, muscular damage, and without treatment it can be fatal.

If possible, take a portion of the locoweed with you to the veterinarian to help in getting a definitive diagnosis.  The veterinarian will give your dog a thorough physical examination, including coat condition, oxygen levels, weight, reflexes, heart rate, body temperature, breath sounds, blood pressure, and respiration rate. Tell them all the details about the incident, such as how much and how long you believe your dog was eating the locoweed. The veterinarian will also need to know your dog’s medical history, vaccination records, unusual behavior, or appetite changes.

Some laboratory tests are needed which include a urinalysis, chemical profile, complete blood count, blood urea nitrogen (BUN), glucose and electrolyte levels. The results of the chemical profile of your dog would have detectable levels of swainsonine, decreased α-D-mannosidase activity, and increased aspartate aminotransferase (AST). A packed cell volume (PCV) is helpful in determining if your dog is dehydrated. Sometimes, an electrocardiogram (ECG) is performed to measure the electrical performance of your dog’s heart. Imaging done with x-ray, MRI, ultrasound, and a CT scan may also be necessary.

The treatment depends on how much locoweed your dog has eaten and how long he has been eating it. Once your dog is unable to consume locoweed, the damage to most of the body diminishes slowly, although the brain and nervous system damage are permanent. There are no treatments that are proven effective for locoism. Any complications caused by locoweed, such as congestive heart failure, will be treated as well. The treatment for congestive heart failure depends on the amount of damage. Most often, the veterinarian will prescribe an ACE inhibitor, such as enalapril, and diuretics to help decrease fluid buildup.

Your dog’s chances of recovery depend on how much locoweed was consumed and for how long. If there is not a severe amount of neurological damage, prognosis is good. If your dog has congestive heart failure, prognosis is guarded, but with treatment, the chance of survival for more than one year is good. Be sure to keep your dog away from locoweed to prevent further damage and call your veterinarian if you have any questions or concerns.