**2.1. Inactivated**

Some vaccines contain killed, but previously virulent, micro-organisms that have been de‐ stroyed with chemicals, heat, radioactivity or antibiotics. Examples are the influenza vac‐ cine, cholera vaccine,bubonic plague vaccine, polio vaccine, hepatitis A vaccine, and rabies vaccine.

© 2013 He; licensee InTech. This is a paper distributed under the terms of the Creative Commons Attribution License (http://creativecommons.org/licenses/by/3.0), which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.

#### **2.2. Attenuated**

Some vaccines contain live, attenuated microorganisms. Many of these are live viruses that have been cultivated under conditions that disable their virulent properties, or which use closely related but less dangerous organisms to produce a broad immune response [1]. They typically provoke more durable immunological responses and are the preferred type for healthy adults. Examples include the viral diseases yellow fever, measles, rubella, and mumps. Attenuated vaccines have some advantages and disadvantages. They have the ca‐ pacity of transient growth so they give prolonged protection, and no booster dose is re‐ quired. But they may get reverted to the virulent form and cause the disease.

**2.4. DNA Vaccine**

erinary medicine [4].

West Nile virus

Infectious Haematopoietic necrosis virus

Growth hormone releasing hormone

Melanoma

**3. Antiviral agent**

ment [6].

Antiviral drugs are particularly useful in these cases.

**Vaccine Target Product Name Company involved**

West Nile Innovator

Canine Melanoma Vaccine

In the past decade and a half, the DNA vaccine concept has been tested and applied against various pathogens and tumor antigens [2]. The optimized gene sequence of interest is deliv‐ ered to the skin, subcutaneum or muscle by one of several delivery methods [3]. The expres‐ sion of plasmid-encoded genes will produce foreign antigens and elicits immunological response. Until now, four DNA vaccine products have been approved, all in the area of vet‐

Vaccines are very effective on stable viruses, but are of limited use in treating a patient who has already been infected. It is also difficult to successfully deploy them against rapidly mu‐ tating viruses, such as influenza (the vaccine for which is updated every year) and HIV [5].

Apex-IHN Novartis 2005 Canada Salmon

Antiviral drugs are a class of medication used specifically for treating viral infections. Like antibiotics for bacteria, specific antivirals are used for specific viruses. Unlike most antibiot‐ ics, antiviral drugs do not destroy their target pathogen; instead they inhibit their develop‐

Centers for Disease Control and Prevention and Fort Dodge Laboratories

LifeTide-SWS VGX Animal Health 2007 Austrilia

Merial, Memorial Sloan-Kettering Cancer Center and The Animal Medical Center of New York

**Table 1.** Current licensed DNA therapies (Adapted from Kutzler MA & Weiner et. al)

**Date licensed and country**

> 2007 USA, conditional license

**Target organism**

Swine and food Animals

Dogs

2005 USA Horses Protects against West

**Benefits**

Vaccines and Antiviral Agents http://dx.doi.org/10.5772/56866 241

Nile virus infection

Improves animal welfare, increase food quality and quantity

Increases the number of piglets weaned in breeding sows

Treats aggressive forms of cancer of the mouth, nail bed, foot pad or other areas as an alternative to radiation and surgery

**Figure 1.** H1N1 flu nasal spray as an example of attenuated vaccine

#### **2.3. Subunit**

Protein subunit- rather than introducing an inactivated or attenuated micro-organism to an immune system (which would constitute a "whole-agent" vaccine), a fragment of it can cre‐ ate an immune response. Examples include the subunit vaccine against Hepatitis B virus that is composed of only the surface proteins of the virus (previously extracted from the blood stream of chronically infected patients, but now produced by recombination of the vi‐ ral genes into yeast), the virus like particle (VLP) vaccine against human papillomavirus (HPV) that is composed of the viral major capsidprotein, and the hemagglutinin and neura‐ minidase subunits of the influenza virus. One method of production involves isolation of a specific protein from a virus and administering this by itself. A weakness of this technique is that isolated proteins can be denatured and will then bind to different antibodies than the proteins in the virus. A second method of subunit vaccine is the recombinant vaccine, which involves putting a protein gene from the targeted virus into another virus. The second virus will express the protein, but will not present a risk to the injector. This is the type of vaccine currently in use for hepatitis, and it is experimentally popular, being used to try to develop new vaccines for difficult to vaccinate viruses such as Ebola and HIV.
