The immune system is the part of the body responsible for the defence and protection against diseases and infections. Under normal conditions, it is able to detect and attack external agents (such as bacteria, viruses, toxic substances, etc.) and to distinguish them from the healthy tissues of the organism. However, in certain cases, and for unknown reasons, the immune system does not recognize its own tissues and begins to attack healthy cells. This set of pathologies are called autoimmune diseases. Autoimmune diseases are characterized by a variety of symptoms depending on the organ affected but it is known that both environmental and genetic factors play a preponderant role in the origin of these diseases.
Allergies are another type of diseases that involve the immune system. These are characterized by an excessive and disproportionate response of the immune system to substances or particles normally harmless to the body, called allergens. Allergies have been increasing in prevalence in the last decades, particularly in industrialized countries, emphasizing the importance of scientific research to better help us understanding these diseases.
Similarly to the humans, both allergies and autoimmune diseases can also affect animals. In dogs and cats, allergies are extremely frequent and are usually caused by agents similar to those that cause allergies in humans, such as pollen, dust, plants, certain foods, insect bites or chemicals such as medicines, perfumes or cleaning products, etc. The symptoms can vary according to the allergen, often leading to itching; inflammation of the skin, ears or legs; watery eyes; sneezing; vomiting and diarrhoea; coughing and difficulty breathing. The best remedy for the allergies is to reduce exposure to the allergen, but there are also some medicines available in the market, such as antihistamines, to help reduce the symptoms. Even though any animal can suffer from allergies, some breeds of dogs are more susceptible, such as Terriers, Setters, Retrievers, Pugs and Bulldogs.
Autoimmune diseases are usually less frequent but more serious than allergies. The symptoms are diverse according to the part of the body that is attacked by the immune system. For instance, hypothyroidism is a condition in which immune cells attack the thyroid, the organ responsible for regulating the organism’s metabolism. Animals suffering from this condition appear lethargic, lazy and gain weight, and in certain cases, if it affects the muscles of the head and muzzle, it makes them shrink, giving the appearance of sadness. Autoimmune hemolytic anemia is another example of a devastating autoimmune disease, primarily affecting healthy animals. In this condition, the immune system destroy the blood cells and the animal have pale gums, lethargy and intense tiredness. In extreme cases, it is necessary to carry on blood transfusions or administer medicines to suppress the immune system. Female dogs from breeds such as Cocker Spaniels and Water-dogs are particularly susceptible to this pathology. Thrombocytopenia is an autoimmune disease that attacks platelets, the blood components that promote coagulation and stop bleeding. Initially, the symptoms are subtle such as presence of bruises in areas such as the gums, ears and belly, but if remained untreated with suppressors of the immune system, the disease can lead to severe haemorrhage in the lungs. Female from Water-dog breed are particularly vulnerable.
Other autoimmune diseases can affect the skin causing hair loss, whilst others can affect the muscles leading generalized and abnormal weakness and fatigue. Masticatory myopathy is a specific autoimmune disease that affect particularly the chewing muscles.
Like humans, dogs, cats and horses can also suffer from Lupus, a generalized autoimmune disease that affects several organs simultaneously. The symptoms are very diverse according to the organ affected but can include arthritis, alopecia, high temperature, anemia, loss of appetite and loss of weight. Shepherd Germans and Water-Dogs as well as cats from Siamese, Persian and Himalayan are among the most affected breeds.
Besides dogs and cats, also horses, pigs and cattle can suffer from allergies and autoimmune diseases, and even chickens can experience autoimmune hypothyroidism.
Awareness of the pet owners for this set of diseases is essential to enable early detection and appropriate treatment.
Dr. Ricardo Ribas, PhD
Veterinary doctor, doctorate in veterinary sciences and researcher in the area of oncology.