Route Of Exposure

Blue vetch is found in Eurasia, North America, temperate South America and East Africa. But the geographical origin of Lathyrus sativus is unknown.

Blue vetch is a many-branched straggling or climbing herbaceous winter annual with stems up to 90 cm tall. It produces a drought-resistant, high-yielding, nitrogen-rich pulse with high-quality protein and carbohydrate. The seeds are used for food (which may be an exclusive food during times of drought or famine) and livestock feed, and the plant as green manure and a cold-weather forage crop, and for erosion control.

Lathyrus sativus is a high-yielding, drought-resistant legume consumed as a food in northern India and neighbouring countries, as well as in Ethiopia. Its development into an important food legume, however, has been hindered by the presence of the neurotoxin beta-N-oxalyl-L-alpha,beta-diaminopropionic acid (beta-ODAP), which, if consumed in large quantities for prolonged periods, can cause irreversible paralysis. The flour is used in cattle feeding and industrial processing in some countries.

The plant is found in cultivated beds or as a relict of cultivation; no truly wild stands exist. The immature seed can be eaten like Green peas. The mature seed is eaten roasted or boiled, after soaking or parching, and the young shoots can also be cooked. The seed is often used in making dhal, paste balls for curry, or beverages. It can also be ground into a powder and mixed with Wheat to make protein-enhanced bread. The seeds are used locally in homeopathic medicine.

Clinical Relevance

Allergen decription

No allergens from this plant have yet been characterised.

More than 60% of the seed comprises globulin proteins, and 30% albumins. A single 24 kDa polypeptide comprises more than half of the protein present in the albumin fraction. The globulins may be fractionated into 3 main components, which are named alpha-lathyrin (the major globulin), beta-lathyrin, and gamma-lathyrin.

Blue vetch flour shows a complex allergenicity. Most allergens are said to be thermostable, but researchers in other studies suggest that some or all allergens in Blue vetch may be heat-labile, resulting in Blue vetch-allergic individuals being able to ingest cooked Blue vetch products.

In a study of sera from 38 Spanish legume-sensitised patients, 77% were shown to have skin reactivity to Blue vetch flour; 4 of whom had developed clinical symptoms to Blue vetch, and 2 of whom, in addition, to other legumes. No protein bands were identified by IgE antibodies to extracts boiled for 15 minutes, whereas 20 protein bands were identified to raw Blue vetch extracts. Serum IgE bound most frequently to protein bands of 50.9 and 27.7 kDa. Only 2 allergens of molecular weights 27.7 and 12.9 kDa were identified by sera from the subjects who were sensitive only to Blue vetch. Other studies have indicated the presence of allergens of 46, 32 and 28 kDa.

A 24 kDa protein was purified from the seeds of Lathyrus sativus. The N-terminal amino-acid sequence showed significant homology with the 2S albumin class of seed storage proteins. The protein showed 85% sequence homology with the seed albumin of Pisum sativum. However, its allergenicity was not evaluated.

Potential Cross Reactivity

An extensive cross-reactivity among the different individual species of the genus could be expected but in fact is not seen frequently. In an in vitro study, the specific IgE binding by protein extracts of 11 food legumes was examined by IgE antibody determination and RAST inhibition. Cross-allergenicity was demonstrated to be most marked among the extracts of Peanut, Garden pea, Chick pea, and Soybean. However, clinical studies have found that there is little cross-reactivity among members of the Fabaceae (Leguminosae).

Cross-reactivity and/or co-sensitivity have been reported among Blue vetch, Chick pea, and Lentil.

Clinical Experience

IgE-mediated reactions

Blue vetch may uncommonly induce symptoms of food allergy and occupational allergy in sensitised individuals.

Sera from 38 Spanish legume-sensitised patients were used to assess the allergenic composition of Blue vetch. Seventy-seven percent of patients showed a positive skin test to Blue vetch flour; 4 of these patients had developed clinical symptoms in relation to Blue vetch, and 2 of them, in addition, to other legumes.

A study reports on a 10-year-old child with asthmatic attacks related to Lathyrus sativus flour inhalation. This child had a history of perennial rhinitis, and bronchial asthma was reported. In the previous year, shortly after exposure to Blue vetch flour in the family store, he had experienced sneezing, rhinorrhoea, wheezing and dyspnoea attacks. Avoiding exposure resulted in a marked reduction of symptoms, and he became asymptomatic. He tolerated the ingestion of foodstuffs prepared from this legume, as well as exposure to other types of flours. Skin test with the raw extract was positive, and negative for the heated extract. Specific bronchial provocation challenge was markedly and immediately positive. IgE antibodies to Lathyrus sativus flour were demonstrated by indirect enzyme immunoassay. The authors suggest that the loss of allergenic sensitivity observed in the cutaneous test with heated Blue vetch may indicate the reason this patient was able to ingest cooked foodstuffs prepared with this flour without reacting.

Two young women experienced symptoms after eating Blue vetch. They reported previous hypersensitivity to other legumes.

Generalised urticaria and facial oedema in a 5-year-old, occurring a few minutes after ingestion, have been reported.

Occupational asthma has been reported following exposure to flour made from Blue vetch. This flour is used in the industrial processing of parquet (wood flooring). A 55 years old man is described, who reported a one year long history of rhinorrhoea, paroxysmal sneezing, eyes and nasal pruritus, and wheezing dyspnea with coughing and chest tightness, symptoms which were related to his working with Blue vetch flour. Symptoms abated during holidays and weekends. He had worked in direct contact with Blue vetch flour for 15 years, which involved the production of a sealant for wooden floor panels. He had never eaten Blue vetch and did not experience adverse effects ingesting other legumes. Skin prick test with the extract showed a positive immediate response. IgE antibody level to grass pea was 9.57 kUA/l. Specific bronchial challenge test elicited an immediate response, both clinically (rhinitis, cough, dyspnoea, chest tightness) and with a 20% decrease in FEV1 at 5 minutes.

A 42-year-old man was described who had worked as a carpenter for 6 years and who reported a history of rhinorrhoea, paroxysmal sneezing, nasocular pruritus, lacrimation, wheezing and dyspnoea attacks while preparing a mixture to seal the junctures between wooden panels. Skin prick tests with Blue vetch and Lentil extracts were positive. IgE antibody level to Blue vetch was 0.62 kUA/l. Histamine release tests were positive. Bronchial challenge with Blue vetch was positive within 5 minutes, with a decrease in FEV1 of 20%. He also developed rhinoconjunctivis. The authors point out that in cases of occupational asthma to Blue vetch flour, patients tolerate the cooked food. As suggest by other authors as well, some or all allergens in Blue vetch are heat-labile, resulting in Blue vetch-allergic individuals being able to ingest cooked Blue vetch products.

Occupational asthma to a close relative, Sweet pea (Lathyrus odoratus), has also been described.

Other reactions

Neurolathyrism is a neurological condition seen among people who eat the seeds of Lathyrus sativus as a principal source of food energy for 2 months or more. It is characterised by severe muscular rigidity and irreversible spastic paralysis of the lower limbs, spinal hyperreflexia, and structural changes of the skeleton and connective tissue. Once prevalent throughout Europe, N. Africa, the Middle East and parts of the Far East, the disease is presently restricted to India, Bangladesh and Ethiopia. The biochemical mechanism involves beta-N-Oxalyl amino-L-alanine (L-BOAA); a synonym is beta-N-oxalyl-alpha,beta-diaminopropionic acid (beta-ODAP). This is a naturally occurring non-protein amino acid present in Blue vetch. Ingestion of L-BOAA in a staple diet results in a progressive neurodegenerative condition, a form of motor neuron disease that affects the upper motor neurons and anterior horn cells of the lumbar spinal cord. L-BOAA is an excitatory acid and acts as an agonist at the AMPA receptor.

The oil from the seeds is a powerful and dangerous cathartic that contains a poisonous principle, probably an acid salt of phytic acid.