Animals have a highly specialized mechanism consisting of organs, tissues and cells, whose objective is the detection and elimination of potentially pathogenic external agents. Such a defensive mechanism is what we call immunity.

The organism has two closely connected immune responses, innate or natural immunity and acquired or specific immunity

Innate or natural immunity is responsible for the primary recognition of antigens, acting as the first line of defense. In addition, it is essential for the activation of the acquired immune response. Antigens are recognized by epithelial cells and tissue resident cells, occurs the release of pro-inflammatory cytokines and the recruitment and activation of immune cells, macrophages, neutrophils, eonophiles, NK cells, dendritic cells… etc. This is a fast and short-lived response

Acquired or specific immunity consists of cellular immunity and humoral immunity. After a first exposure to a given antigen, the body is able to recognize that antigen as an exogenous and, in later exposures to such antigen, generate a more specific and long-lasting response. Cellular immunity is performed by T cells, which act as a defense mechanism against intracellular microorganisms, such as viruses or some bacteria. Humoral immunity acts as a defense mechanism against extracellular microorganisms and their toxins, through antibodies secreted by plasma cells and the complement system.

In the case of piglets, the immune system does not complete to fully develop until 4 weeks of age. In addition, the epitheliocorial placenta does not allow the passage of antibodies and immune cells from the mother to the piglet. Therefore, the immune capacity of piglets depends primarily on the antibodies and immune cells present in the colostrum. Therefore, it is essential to ensure an adequate immune status of mothers during lactation.

1. Immunodeficiency causes

There are several factors capable of affecting the immune system of pigs capable of generating immunodeficiency situations, which can lead to secondary conditions. These factors include chronic stress, certain infectious agents, as well as nutritional deficiencies.

1.1 Stress

Stress can be defined as a biological response produced by an organism when it perceives a threat to its homeostasis. The presence of a stressful agent leads to the activation of the hypothalamus-pituitary-adrenal axis and the consequent release of glucocorticoids and catecholamines. These molecules cause adaptive changes in cells and tissues aimed at protecting the body and ensuring its survival, such as an increase in heart and respiratory rate, as well as an increase in blood pressure.

If the stressful situation continues over time, the constant alert situation to which the animal is subjected ends up causing a wear on the immune effects of the animal. That is, the animal is not able to sustain this alert situation that leads to a state of immunodeficiency, which predisposes the animal to other pathologies.

In pigs the main stressors are related to environmental conditions such as high temperature and humidity or high breeding density; also, different manipulations of animals, vaccinations, blood draws; as well as changes in diet, transition from lactation to weaning.

1.2 Microorganisms

There are species of bacteria and viruses capable of depressing the immune system of pigs and generating immunodeficiency syndrome. Among them, it is worth highlighting the following:

1.2.1 Porcine respiratory and reproductive syndrome (PRRS)

Etiology

Pig respiratory and reproductive syndrome (PRRS) is caused by an RNA virus belonging to the Arteriviridae family of the genus Arterivirus, order Viral node. Two different genotypes of PRRSV, genotype 1, usually present in Europe, and the type II genotype, present in the Americas, have been identified. It is a virus with a high mutagenic rate.

Pathogenesis and symptomatology

The virus has a high affinity for alveolar macrophages found in the lung that play a key role in the pig’s immune system. The virus infects macrophages and causes their destruction, generating an immunodeficiency situation in the animal. At the same time the virus is able to cross the placenta in the pregnant sows and infect the fetuses in the last third of gestation, causing abortions.

Generally, the most characteristic symptoms are the presence of coughs and respiratory symptoms along with an increase in the number of piglets born alive. Also, characteristic is the appearance of cyanosis in the ears, which turn bluish.

Prevention and control

There is currently no effective treatment of PRRS. Disease control should be carried out by means of appropriate biosafety measures that prevent the virus from entering the farm, as well as the use of immunostimulant products that promote a proper health condition of the animals, so that they can deal with the infection.

1.2.2. Swine flu

Etiology

Swine flu is caused by the type A influenza virus that belongs to the family Orthomyxoviridae. It is a simple-chain RNA virus that has different serotypes. The most common serotypes in pigs are H1N1, H1N2 and H3N2.

Pathogenesis and symptomatology

The virus affects the airways and causes the alveolar macrophages to be depleted, affecting the immune state of pigs. The most common symptoms are the presence of cough and fever, which appear abruptly on the farm and spread rapidly, as well as secondary pneumonia associated with decreased immune capacity. Reproductive disturbances, such as absorptions or recurrences and decreased seminal fertility, may occur due to increased body temperature.

Prevention and control

Vaccines are available for disease control; however, it is necessary to confirm that the vaccine strain matches the strain present on the farm. It is also convenient to perform antibiotic therapy in order to control secondary pneumonia.

1.2.3 Porcine epidemic diarrhea

Etiology

Porcine epidemic diarrhea (PED) is caused by a virus involved in the genus Alphacoronavirus of the family Coronaviridae. Like PRRSV, it is a single-catenary RNA virus with a high mutagenic capacity. It is a virus with high environmental resistance capable of surviving long periods of time outside the host.

Pathogenesis and symptomatology  

The virus is introduced by oral way and affects cells in the intestinal epithelium, where it multiplies. The destruction of intestinal villus results in a diarrheal picture and immunodeficiency.

Disease is transient and of moderate severity in the sows and in the boars, where it produces a diarrheal picture that lasts between 7 and 14 days.  After this time, the animals develop short-lived immunity (4-6 months). Lactation sows exposed to the virus are able to transmit antibodies (IgA) to piglets, protecting them during lactation and transition.

The disease becomes severe when it affects piglets from unimmunized sows, where mortality can reach 100%. Therefore, it is important to ensure the correct immune status of mothers, as well as to enhance the transmission of antibodies.

Prevention and control

PED is not clinically different from other enteric conditions affecting pigs, and therefore, laboratory testing is necessary to establish a definitive diagnosis.

Vaccines have been developed that allow to immunize breeding sows, ensuring the passage of protective antibodies to piglets. The use of disinfectants, together with appropriate biosecurity measures, is essential to prevent the pathogen from entering the farm.

In addition, it has been observed that the combination of natural immunostimulants with the administration of vaccines to pregnant sows improves the immunological quality of the colostrum and allows greater protection of piglets against this infection.

1.2.4 Delta-coronavirus

Etiology

Like the PED virus, it is a coronavirus, simple chain RNA virus, in this case it is a Deltacoronavirus. Deltacoronavirus (PDCoV) was first isolated in the United States (2014) from pigs with neonatal diarrhea.

Pathogenesis and symptomatology

PDCoV multiplies in the enterocytes of the digestive tract and affects both the small intestine and the large intestine, causing acute necrosis of these and the atrophy of intestinal villus. The clinical picture is of diarrheal type, with a higher intensity in lactating piglets. Mortality varies depending on the infective strain (40-80%).

Prevention and control

In this case there are no vaccines available so preventing the pathogen from entering the farm is essential. Appropriate biosecurity measures are essential. At the same time, it is possible to enhance the immunity of animals through various natural solutions.

It is a disease to be taken into account in the near future, as its transmissibility to humans has recently been demonstrated, and may pose a health risk in the future.

1.2.5 Rotaviruses

Etiology

Rotaviruses are dual-chain RNA viruses, with 7 serogroups (A-G) currently described. The serogroups that affect the pig are serogroup A, B, C and E, the latter being exclusive to this species. Rotaviruses have a thick lipid wrap that makes them resistant to environmental conditions. It is a widely distributed disease and of high prevalence on farms.

Pathogenesis and symptomatology

It is a low pathogenic disease that occurs mainly in piglets between the 3^rd and 5^th week of life, when maternal antibodies decrease. Rotaviruses are replicated exclusively in mature enterocytes, causing villus atrophy. However, the reduction in the height of villus is not as severe as in another neonatal diarrhea.

The main clinical symptom is white-yellow liquid diarrhea in piglets that subsides within 2-3 days. Severe clinical tables are due to secondary infections by other microbial agents.

Prevention and control

Rotaviruses are present in virtually all farms due to their high environmental resistance, so disease control should be based on ensuring the animal’s health conditions and their immune status to enhance transmission of maternal antibodies to piglets during lactation.

1.3 Nutritional deficiencies

Although feed is formulated to meet all the nutritional needs of pigs, there are active molecules present in various plant species that escape the formulation.

Animals in the wild have access to these plants and therefore to the active molecules they contain. These molecules, defined as pronutrients, are essential for optimal physiological functioning of different organic systems.

Pronutrients act to increase the synthesis of RNAm and thus the synthesis of active proteins. These molecules allow to optimize organic performance without causing a pharmacological effect.

It has been found that certain pronutrients are able to stimulate the immune system of animals and even enhance the transmission of immunoglobulins from mothers to piglets during lactation.

2. Conclusion

3. Animals have a complex immune system, however, there are various agents that can affect their defensive ability and generate immunodeficiency states.In the case of pigs, these agents are stress, capable of causing immunodeficiency by exhaustion when prolonged over time, different microorganisms that directly and indirectly are able to generate immunodeficiency syndromes, as well as deficiencies in certain nutrients and pronutrients, which impede the proper functioning of organic systems.

   It is advisable to add these active molecules to the feeding of pigs as they allow to enhance their immune system and, at the same time, improve the transmission of protective antibodies from mothers to piglets via lactogenic.

   Therefore, the use of these pronutrients helps us to protect our animals from the different factors capable of generating immunodeficiencies.

   Immunostimulant pronutrients are marketed under the name Alquernat Inmuplus by Biovet, S.A.