The Nature of Vaccines | Animal Husbandry & Veterinary Science Optional for UPSC PDF Download

Vaccines need to be highly immunogenic, capable of eliciting a robust immune response, while also being non-pathogenic.

Living and Killed Vaccines

• Live Vaccines: Offer stronger and longer-lasting immunity as living organisms persist in host tissues, triggering prolonged immune responses.
• Killed Vaccines: Typically provide less response over a shorter period as some vital antigenic components may be lost during preparation.
• Recent Developments: Efforts are made to develop living bacterial vaccines from attenuated or avirulent strains, ensuring safety and strong immune responses.
• Examples of Living Vaccines: Contagious bovine pleuropneumonia (CBPP), fowl typhoid vaccine from avirulent strains, and similar vaccines for various infections in animals.
• Examples of Living Bacterial Vaccines: Include vaccines against anthrax, brucella, swine erysipelas, and Johne's disease, using attenuated strains for safe immunization.
• Some killed bacterial vaccines have shown efficacy in controlling diseases like brucellosis, pasteurellosis, scours, and Erysipelas in animals. Examples:
  • Brucellosis Vaccine: Controls Br. abortus strain 45/20.
  • Pasteurellosis Vaccine: Targets Past. multocida.
  • Scours Prevention: Vaccines for E. coli in calves and young pigs.
  • Erysipelas Control: Vaccines for E. insidiosa in pigs.
  • Leptospiral Vaccines: Prevent leptospirosis in dogs using killed Leptospira icterohaemorrhagiae and I. canicola organisms.
  • Others: Various vaccines for clostridial infections and other experimental bacterial vaccines exist.

Mixed Vaccines

• Efforts to combat multiple infectious diseases through mixed vaccines have shown limitations.

  • Combining different organisms in a single vaccine can reduce the immune response to each component.
  • One component may dominate the immune response, affecting the overall effectiveness.

• Exceptions include successful responses from clostridial vaccines, notably in sheep diseases control.

  • Clostridial toxins are purified to create toxoids, maintaining antigenic properties while eliminating toxicity.
  • Various mixed clostridial vaccines are utilized, containing multiple components like Cl. welchii types B, C, D, Cl. septicum, Cl. chauvoei, Cl. oedematiens, and Cl. tetani.

Autogenous Vaccine

• Prepared from specific bacterial strains causing outbreaks, autogenous vaccines target particular infections.

  • Derived from organisms isolated from the condition, these vaccines stimulate stronger immunity against the disease-causing strains.
  • Offer effective treatment for chronic or subacute local suppurative conditions.

Adjuvants

• Killed vaccines, while safe, offer shorter immunity duration compared to live vaccines. However, the immune response to killed vaccines can be prolonged when the antigens in the vaccines are combined with certain substances known as adjuvants.

  • Combining antigens with adjuvants, like alum, extends the immune response duration.
  • Water-in-oil adjuvants, such as Freund's complete adjuvant, can enhance immune responses but may cause severe local reactions.

Subunit, Synthetic Peptide, and Virus Vector Vaccines

• Advances in genetic engineering have led to subunit, synthetic peptide, and vector virus vaccines.

  • Recombinant DNA technology allows for the expression of heterologous genes in viruses, enabling the production of isolated immunogens.
  • Subunit vaccines have shown efficacy against diseases like B. bovis.
  • Viruses can serve as vectors for immunogens, expressing proteins for diseases like Hepatitis B virus.

Preparation of Hyper-Immune Sera

• Horses are commonly used to produce antisera for disease prevention due to the large serum volume they provide.

Immune Sera Preparation and Passive Immunity

• Animal Selection for Immune Sera Production: Various species like cattle, sheep, goats, dogs, and rabbits are utilized to produce specialized antisera. These animals undergo a series of injections with specific bacterial antigens or toxoids. After the injection regimen, their blood sera are tested for antibody levels. Upon reaching satisfactory levels, the animals are bled, and the sera are collected, stored, or concentrated using ammonium sulfate precipitation to obtain globulin fractions.

• Duration of Passive Immunity: Passive immunity from hyperimmune serum lasts briefly in animals. The temporary immunity's duration may vary based on factors like homologous or heterologous antiserum administration. Homologous antiserum derived from the same species can provide immunity for 3-4 weeks, while heterologous antiserum may only be effective for about 1-3 weeks.

Extension of Passive Immunity

• Prolonging Immunity: To extend the protective effect of passive immunity, multiple injections of hyperimmune sera at intervals are considered. However, caution is necessary, especially with heterologous sera, as they can trigger hypersensitive reactions in recipients.

• Hypersensitive Reactions: Heterologous gamma-globulin can provoke hypersensitive reactions in recipients, leading to general anaphylactic or local Arthus reactions upon repeated doses. In contrast, homologous hyperimmune sera are less likely to induce hypersensitive reactions after multiple administrations.

Microbial Infections and Pathogenicity

• Microbial Pathogens: Only a small fraction of bacteria, fungi, and viruses present in the environment can cause diseases by adapting to the body's conditions. These pathogens possess specific properties enabling them to resist the body's defense mechanisms and instigate disease development.

• Pathogenicity: Pathogenicity refers to an organism's ability to cause disease in a host. Different strains of microorganisms within the same species exhibit varying pathogenic potentials, influencing their disease-causing abilities.

• Virulence: Virulence characterizes a strain's capacity to induce disease under defined conditions. Variations in virulence levels among strains are associated with distinct properties of the organisms, such as toxin production or the presence of protective features like capsules.

Invasiveness in Pathogenic Organisms

• Invasiveness refers to how a pathogenic organism attacks a host.
• Example of Invasive Organism:
  • An example is Bacillus anthracis, which can spread throughout the body causing a sudden death in animals like cows.
• Example of Non-Invasive Organism:
  • Clostridium tetani, which causes disease but may not penetrate beyond the initial site of infection, exemplifies a non-invasive pathogen.

Development of Inflammatory Response

Primary Lesion Establishment:

• When bacteria are introduced, an inflammatory response occurs, often observed in the skin.
• Events in the inflammatory process:
  • Initial vasodilation and increased blood flow.
  • Role of histamine and kinins in the inflammatory response.
  • Mechanism of leukocyte migration and infiltration in the tissues.

Leukocyte Response to Microbial Infection

• Importance of Leukocyte Migration:
  • Migrating leukocytes play a crucial role in combating microbial infections due to their phagocytic properties.
• Factors Influencing Migration:
  • Chemotactic forces guide leukocytes to the site of infection.
  • Living bacteria like Streptococci, Salmonellae attract polymorphs, enhancing the immune response.

Cell Response in Inflammation

• Cell Type Transformation:
  • Polymorphs are initially present and later replaced by mononuclear cells like macrophages and lymphocytes.
  • Cell type variation in different infections.

Pathogenic Mechanisms of Bacterial Infections

• Diverse Symptoms of Infectious Diseases:
  • Illustration of symptoms caused by various pathogenic organisms.
  • Examples of specific infections and their associated symptoms.
  • Successful host-parasite relationship in carrier animals.
• Toxaemic Infection and Toxins:
  • Definition of toxins and their impact on tissue cells.
  • Characteristics of clostridia toxins and their neutralization by antitoxins.
  • Example of Clostridium tetani toxin actions and effects.

Toxins Produced by Clostridial Organisms

• Clostridium botulinum Toxins

  Clostridium botulinum produces potent neurotoxins that are absorbed through the intestine after ingestion. Unlike tetanus toxin, botulinum toxin acts on all cholinergic nerve fibers, affecting both peripheral and autonomic nerves.

• Clostridium oedematiens Toxins

  The alpha toxin from Clostridium oedematiens causes gelatinous edema and haemoconcentration by likely targeting blood vessel walls. Other toxins from this organism have various activities such as haemolytic and necrotizing effects.

• Clostridium sépticum Toxins

  The alpha toxin is associated with the lethal effects of Clostridium sépticum. Other toxins include beta toxin (deoxyribonuclease), gamma toxin (hyaluronidase), and delta toxin (haemolytic).

• Clostridium welchii Toxins

  Clostridium welchii strains produce various toxins, including the alpha toxin with lecithinase, haemolytic, necrotizing properties. These toxins can cause edema, hemorrhage, necrosis, and shock by affecting capillaries and cell structures.

Effects of Clostridial Toxins

• Tissue Cell Actions

  Clostridial toxins impact tissue cells in experimental settings. Antitoxins can neutralize these effects if administered early. Active immunization through vaccines can also help by producing antibodies before toxin exposure.

• Pyaemic Infections

  Pus Formation and Toxins

  Pyaemic infections involve pus formation at infection sites, spreading through the bloodstream causing a condition known as pyaemia. Staphylococci, streptococci, and corynebacteria produce toxins that lead to local pus formation and systemic toxemia.

Toxins Produced by Staphylococci

• Activities of Staphylococcal Toxins

  Staphylococci produce toxins with lethal, necrotic, and haemolytic effects, along with enterotoxins and enzymes like coagulase and hyaluronidase. These toxins facilitate bacterial spread in tissues.

Toxins Produced by Streptococci

• Range of Streptococcal Toxins

  Streptococci toxins include haemolysins, fibrinolysin, streptodornase, hyaluronidase, and an erythrogenic factor. These toxins collectively impair host defense mechanisms, aiding bacterial establishment in the body.

Bacterial Infections and Immune Responses

• Corynebacterium pyogenes Toxin Effects:

  A toxin produced by Corynebacterium pyogenes can destruct red blood cells, proving lethal to rabbits and mice while causing necrosis in guinea pigs. The exact mechanisms behind these toxic reactions and their impact on the host's cellular defenses remain unclear.

• Bacteraemic Infections:

  In certain bacterial infections, organisms can enter the bloodstream, spreading rapidly to various body organs. For instance, in pyaemic infections, infected clots can dislodge and migrate to different body sites. Severe trauma or contaminated wounds may also introduce bacteria into blood vessels, leading to widespread distribution.

• Bacillus anthracis Infection:

  Acute infection with Bacillus anthracis showcases rapid bacterial multiplication overwhelming the body's defense mechanisms. The disease's pathogenesis involves three bacterial products, including a toxin causing edema and lethality.

• Bacteraemia by Salmonella and Escherichia:

  Salmonella and Escherichia bacteria can induce significant bacteraemia during initial infection stages, especially in young animals. These organisms can enter the bloodstream, leading to severe bacteraemia, potentially fatal during acute generalized infections.

• Granulomatous Infections:

  After primary infection establishment, the body's response and lesion development depend on the infecting microorganism and tissue characteristics. Granulomatous reactions, seen in chronic infections like tuberculosis, involve defensive and reparative responses within tissues.

Viral Infections and Immunological Reactions

• Specific hypersensitivity in animals against chronic microbial infections leads to antibodies distributed in tissues.
• Contact between cell-fixed antibodies and bacterial antigens can cause cellular damage and inflammation.
• Lesions can grow due to immunological reactions, characterized by lymphocytes, plasma cells, and eosinophils.

Development of Viral Infections

• Animal viruses can lead to viraemia, spreading via the blood and affecting various organs.
• Viral multiplication occurs in specific tissues before spreading in the body.
• Viruses need living cells for their life cycles and evade antiviral agents by residing within susceptible cells.

Viral Multiplication and Spread

• Viral particles attach to tissue cells, multiply intracellularly, and may be found in various organs.
• Secondary viraemia marks an important stage where viral spread can occur to different hosts via arthropod vectors.

Pathogenicity and Symptom Development

• Pathogenicity of viruses varies, leading to diverse responses in host animals.
• Cellular damage from viral multiplication can release toxic products, causing symptoms and organ damage.
• The severity of infection and symptoms depends on factors like viral strain virulence.

Viral infections and immunological reactions are complex processes that involve interactions between pathogens and host immune responses. Understanding these mechanisms is crucial for developing effective treatment and prevention strategies.

Development of Fungal Infections in Animals

• Overview of Fungal Infections

  Fungal infections in animals, specifically the pathogenesis of these infections, have historically received limited attention. Recent studies indicate that these infections are rare and typically occur under specific favorable conditions despite the prevalence of potentially pathogenic fungi on or within animal bodies.

• Dermatophytes

  Ringworm fungi, known as dermatophytes, can exist in the soil and easily come into contact with animal skin. These fungi target keratinized tissue and produce enzymes that digest keratin, leading to skin and hair infections. The initial stage involves hyphae penetrating hair follicles, causing mild tissue reactions like congestion and exudate formation.

• Other Mycotic Infections

  Similar to dermatophytes, little research has been done on the pathogenesis of systemic mycotic infections in animals. Conditions that trigger pathogenic effects often involve changes in microbial morphology. Aspergillus species, for example, can transition into mycelia in active lesions, affecting various animal species.

• Allergic Skin Reactions

  Aspergillus infections can lead to allergic skin reactions, especially in rabbits, after exposure to spores. Likewise, Coccidioides immitis infections can cause skin eruptions. Moniliasis, caused by Candida albicans, involves toxin production and tissue penetration by mycelia.

• Herd Immunity

  Herd immunity refers to a group of animals' ability to resist infection collectively. Factors like frequency of contact and the number of susceptible individuals influence herd immunity, similar to individual immunity. Lack of herd immunity can result in increased disease occurrence in animal groups.

• Disease-Free Zone & Zero-Disease Concept

  The zero-disease concept aims to eliminate specific diseases through vaccination and surveillance within a defined period. Achieving 100% vaccination in high-risk areas is crucial. This concept, successfully implemented in smaller countries, faces challenges in larger countries like India, where efforts are being made, such as for rinderpest eradication.

Chemoprophylaxis

• It is a vaccination program that typically involves a drug combined with a killed vaccine, providing lasting protection while allowing gradual infection.
• Commonly used in controlling Babesiosis in cattle.

Chemoimmunization

• This method involves vaccinating with virulent organisms and administering a suitable chemical simultaneously or subsequently.

Application in Humans

• Chemoprophylaxis is utilized against malaria and amoebiasis in humans by administering drugs preventatively in endemic regions to avoid infection.
• The prophylactic use of antibiotics is debated due to the risk of widespread resistance among bacteria when used in healthy animals.
• Antibiotic prophylaxis is still prevalent, especially in animals under stress, but excessive use is discouraged due to the emergence of resistance.
• Metaphylaxis, a more limited form of prophylaxis, is justified when a disease is already present in a group of animals, such as diarrhea in a litter of pigs.