Everlasting pea

Lathyrus latifolius

Other names

Perennial pea. Often called sweet pea, but should not be confused with the true sweet pea, L. odoratus, which is only found in gardens (although probably toxic too).

Description

Scrambling perennial twining plant producing very showy pink or purple flowers. Blooms from late spring through late summer.

Similar plants

There are nine species of Lathyrus or vetchlings in NZ. All are probably poisonous.

Distribution

A relatively common plant seen throughout the country on waste ground. Prefers sunny areas and well drained soils - the photos were taken on a north facing railway embankment.

Toxin

Seeds/peas contain the amino acid b (g L glutamyl) aminopropionitrile. This compound is converted after ingestion to b aminopropionitrile which causes the toxic effects.

Species affected

Horses are particularly sensitive. Cattle, sheep, dogs.

Clinical signs acute

Two forms are recognised:

Neurolathyrism: manifests as an irreversible paralysis of the legs. Includes transient laryngeal paralysis in horses associated with degenerative changes in the vagus and recurrent laryngeal nerves. Also seen as a slow, weak pulse, depressed, weakened respiration and convulsions.
Osteolathyrism: manifested by a variety of skeletal changes due to inhibition of cross linking during the formation of collagen. Vascular wall development can also be affected by the inhibition of elastic fibre formation; this will limit vascular wall stretching and will thus predispose to aneurysm.
Cattle: generally affected by osteolathyrism, with lameness manifesting between the third and fifth days after consumption. Lameness is rarely severe.
Horses: generally affected with neurolathyrism. Weight is shifted to front legs, hind legs are held forward, and locomotion is a hopping, painful gait. Seem normal in recumbency, and there may be paralysis of the recurrent laryngeal nerve (dyspnoea and roaring).

Clinical signs chronic

May see skeletal deformities - reported in experimental animals.

Post mortem signs

A dissecting aneurysm of the aorta and a direct neurotoxic effect results in the degeneration of the spinal cord and nerves to the hind limbs.

Diagnosis

Post mortem lesions, presence of plant in paddock and in the stomach, limb paralysis, painful gait (lameness) and roaring (in horses).

Differential diagnosis

Colic (horses), osteoarthritis, copper deficiency (defective collagen formation), Lower motor neuron disease, aortic thrombosis (acute cases), strychnine, spinal trauma, cytotoxic oedema.

Treatment

Essentially supportive therapies, if a large amount of seed has been ingested induce emesis where possible, and perform a gastric lavage. Dose with activated charcoal and a saline cathartic. Remove plant from paddocks.

Prognosis

Recovery can be complete, however some animals may be chronically affected. Death is possible in extreme acute cases.

Prevention

References

Beasley V.R. (1993) A systems Approach to Small Animal Toxicology [vol 1 & 2]

Connor, HE, The Poisonous plants in New Zealand, 2nd ed.,1977, Government Publications Ltd., Wellington

Parton K, Bruere A.N. and Chambers J.P. Veterinary Clinical Toxicology, 3rd ed. 2006. Veterinary Continuing Education Publication No. 249