Summary

The domestic pig is the most common domesticated animal around the world. They prefer various natural habitats, ranging from semi-desert to tropical rain forests, and survive on household waste and garden crops. Different mammalian meat products including beef and pork may trigger allergic reactions. Delayed type 1 reaction to red meat, especially towards α-Gal allergen is majorly reported from Europe. The main route of exposure to pork meat allergen is ingestion. The secondary route includes skin contact and inhalation of aerosols among pork processing industry workers and pig farmers. The major allergens identified in pork are Sus s 1 (serum albumin) and α- Gal. Consumption of pork meat in allergic individuals can lead to anaphylactic reactions, skin symptoms (urticaria), and gastrointestinal symptoms. Moreover, occupational exposure among the workers can lead to airway diseases (such as rhinitis, occupational asthma) and dermatitis. Cross-reactivity between Fel d 2 (cat serum albumin) and Sus s 1 (pork serum albumin) is known as Pork-cat syndrome. Avoidance of mammalian meat products is the most important method to prevent meat allergy. Occupational exposure can be reduced by timely diagnosis and identification of specific allergen, which helps to avoid contact and prevent allergic symptoms in sensitized individuals.

Epidemiology

Worldwide distribution

Pork meat intake has shown an increase worldwide, especially in Southeast Asia. In Korea, pork meat is popular and recently the consumption of pork meat has been increased there. In one survey on urban school children in Korea, pork was found to be one of the ten foods related to allergy and the incidence of pork allergy was 1.9% among the children. A double-blind, placebo-controlled food challenge was conducted on 2,417 patients of different age groups (including infants, toddlers, children, adolescents, adults and elderly) with repeated eczema and aggravation of atopic dermatitis (AD) in Korea. The results showed a pork allergy prevalence of 8.9% and the minimum and maximum onset time of pork allergic reactions were 3 hrs. to 24 hrs. respectively.

A cross-sectional retrospective study among 365 Honduran children (age range: 1-18 years) found that pork meat allergy was one of the common food allergies among the study participants with a prevalence of 4.4%. In Spain, a study evaluated in-vitro response to different IgE antibody extracts including beef, lamb, pork, venison, chicken, and turkey in 57 meat allergic patients. Results showed that 58% of patients (33/57) had IgE reactivity to pork meat (both raw and cooked) and among them, 17 showed a reaction to raw pork, 1 showed a reaction to cooked pork, while 15 were reactive to both raw and cooked pork meat.

Delayed type I reaction to red meat occurs usually in α-Gal sensitized patients. The worldwide prevalence of α-Gal allergy has shown a drastic increase. In the US about 10% of some population are anticipated to have higher IgE titers against α-Gal. In Europe, α-Gal allergy associated delayed type I reaction is majorly reported.

Risk factors

There are some risk factors known to be associated with red meat allergy (pork meat and kidney) including physical exercise within 4 hours after meals, along with intake of alcohol, aspirin, or Non-steroidal anti-inflammatory drugs (NSAID).

Route Of Exposure

Main

The main route of exposure to pork meat allergen is ingestion.

Secondary

Other routes of exposure include skin contact and inhalation, which occur during the processing of raw pork meat (cutting and handling) among the workers in the pork processing industry and among pig farmers.

Clinical Relevance

Oral food allergy symptoms and anaphylaxis

Different mammalian meat products may trigger allergic reactions. Worldwide patients have reported delayed urticarial or anaphylactic reactions, which occurred 2 - 6 hrs after ingestion of red meat such as beef, pork, lamb, rabbit, horse, and kangaroo. In sensitized individual consumption of porks kidney lead to severe allergic symptoms within a short time after ingestion in comparison to skeletal muscle meat of mammals. Also, 100% sensitivity was reported in a prick to prick test using raw or cooked pork kidney in comparison to raw pork (42-63%). The galactose- α -1,3-galactose (α -Gal) is found to be responsible for delayed-type I anaphylactic reactions after eating red meat especially pork.

A study by Morisset et al. (2012) evaluated the association of anaphylaxis to α-Gal allergen-specific IgE in 14 patients who showed anaphylactic reactions after consumption of pork or beef kidney. The result showed that allergic reactivity to kidney is higher than mammalian meat. Anaphylaxis was usually severe (12 anaphylactic shocks) and four patients reported a loss of consciousness. Anaphylaxis occurred within 10 min to 5 h of eating pork kidney with immediate anaphylaxis observed in nine patients and semi-delayed anaphylaxis in four patients.

A study analyzed 25 German patients (median age 56 years) with a history of allergy to pork kidney (at least 1 allergic reaction) and reported that consumption of pork kidney led to anaphylactic reactions in 72% of patients (among them 56% belonged to grade II and 44% to grade III) and 28% patients showed urticaria/angioedema but no extracutaneous symptoms. The type I allergic reactions to α-Gal was categorized into two subtypes according to the time between pork kidney consumption and the beginning of the symptoms. They were immediate type I reaction occurring within 3 hours and delayed-type I reaction occurring within 3 to 6 hours. The majority of the patients (67%; 21 out of 25) in this study showed immediate type I reaction.

A case study of a 79-year-old female with no history of meat allergy reported severe anaphylaxis within 3 hours of eating pork. Allergen identified was α-Gal. Also, the patient had reported tick bite and tick is known to carry α-Gal.

Another case study reported about a 16-year-old girl with allergic symptoms such as repeated episodes of itching, angioedema of lips and oral mucosa occurring few minutes after consumption of pork meat (salami, both raw and cooked ham and bacon). However, she tolerated cooked pork (chops and sausages). She had a history of moderate rhino-conjunctivitis and gastrointestinal (GI) symptoms on exposure to horse dander and after drinking fresh milk respectively. The patient had shown oral allergy syndrome (OAS) and the skin prick tests (SPT) were strongly positive for pork and horse dander.

Asthma

Cutting and handling pork meat can release aeroallergen into the breathing zone and may also expose the skin to the fluid. This may cause occupational rhinitis, occupational asthma, contact urticaria, and protein contact dermatitis in workers, butchers, cooks, and industry workers. A study by Jungewelter et al. (2018) assessed four slaughterhouse workers who were allergic to raw pork allergens and detected occupational rhinitis in two patients, occupational asthma in one patient and contact urticaria in one patient.

A case study by Donnay et al. (2006) showed that vapors of pig gut soaking water consisting of pig albumin, gamma globulin, and a 26- kDa protein are responsible for causing occupational asthma in a woman working in a pork-processing unit.

Animal farmers are at high risk to get exposed to organic dust (aeroallergens), which may trigger occupational airway disease. A study by Radon et al. (2001) found that among 6,156 animal (cattle, pig, poultry, sheep) farmers from four European countries, pig farmers had a maximum risk of developing occupational airway disease and symptoms related to asthma and allergies. Also, chronic phlegm was found in a higher percentage among these farmers. Another questionnaire-based study by Kimbell-Dunn et al. (1999) evaluated the prevalence of asthma and allergic symptoms in 2,500 farmers from New Zealand. The study found out that asthma prevalence was high; about 18.2% among pig farmers and also females were more prone to report asthma compared to males.

Prevention And Therapy

Prevention strategies

Avoidance

Avoidance of mammalian meat products is the most important method to prevent allergy due to α- Gal. At the workplace, timely diagnosis and identification of allergen help to avoid contact and prevent allergic symptoms in sensitized individuals.

Cross-Reactivity

Pork-cat syndrome occurs due to cross-reactivity between cat serum albumin (Fel d 2) and pork serum albumin Sus s 1. Pork-cat syndrome is reported in children and adults; however, less frequent in infants and toddlers since cat allergy is quite uncommon among these age groups. A sensitized individual has been found to manifest symptoms of Pork-cat syndrome in <1 hr. after ingesting pork meat.

A study by Hilger et al. (2010) presented a case of sequential allergy to pork and then chicken in a worker from the pork-processing industry. The worker presented respiratory symptoms at work while handling pork gut and also developed allergic airway symptoms while eating pork. Later she developed an allergic reaction after eating chicken. On testing, the hemoglobin of pork and chicken was found to be a cross-reactive allergen. She was also allergic to cats. It was anticipated that pork and chicken serum albumin cross-reactivity may be linked with a previous sensitization to serum albumin of cats.