Plant viruses and Animal Viruses

Course: Virology

Lecturer: Dr. Weam Saad
Lecture: Plants and Veterinary viruses

Plant viruses

Plant virus are called viroids, they infect plants and cause loss of the yield and bad quality of agricultural products, viroids spread from plant to plant by other organisms, known as vectors mostly insects and other vectors like fungi, nematode worms, and single-cell organisms. Plants infections with viruses cannot be controlled because of economic cost.
Plant viruses cannot infect humans and other animals because they are specific for plant and their receptors are only on plant cells, they can reproduce only in living plant cells.
Plants have defense mechanisms against viruses. One of the most effective mechanisms is the presence of resistance (R) genes. Each R gene gives resistance to a particular virus by triggering localized areas of cell death around the infected cell, which can be seen with naked eye as a spot. The mode of infection transmission is from large spots to stops. RNA interference is also an effective defense in plants. Also, after infection; plants produce natural disinfectants that kill viruses, such as salicylic acid, nitric oxide, and reactive oxygen molecules.
Plant virus particles (sometimes called virus-like particles, VLPs) have applications in both biotechnology and nanotechnology. The capsids of most plant viruses are simple and can be produced in large quantities. Plant virus particles can be modified genetically and chemically to be encapsulated with foreign material and used in biotechnology.
The examples of plant viruses are; helical Potato and Tomatoes spindle tuber viroid, helical Tobacco mosaic virus and Icosahedral Cauliflower mosaic virus (CaMV).

Pepper mottle virus Cauliflower mosaic virus

Tobacco mosaic virus

Control Plant viral diseases:
Plant viruses cannot be directly controlled by chemicals application. The major ways of control depending on the disease type include:
Chemical or biological control of the vector (the organism that transmitting the disease between plants, e.g. an insect): this can be very effective where the vectors need to feed for some time on a crop before the virus is transmitted then transmission occurs very rapidly and the virus spread before the vector affected by the pesticide.

Growing resistant crops: in some crops and for some viruses, there are highly resistant plants have been growing for many years. Transgenic resistance technology showed considerable promise for many plant-virus. For example, the use of this approach in Hawaii to control Papaya ringspot virus saved the local papaya industry.

Use of virus-free planting material: in vegetative propagated crops (e.g. potatoes) and many fruit crops and where viruses are transmitted through seeds, major efforts are made through breeding to ensure that the planting material is virus-free.

Exclusion: the prevention of disease establishment in areas where it does not yet occur. This is a major objective of plant quarantine procedures over the world.

Animal Viruses (Veterinary viruses):

Viruses are important pathogens of livestock and pets animals such as chicken, cats, dogs, and horses. Veterinary diseases such as foot-and-mouth disease and bluetongue are caused by viruses. Animals that are in contact with human need vaccines because they are susceptible to serious viral infections. Also, invertebrates e.g. the honey bee are susceptible to many viral infections.
Viral infections of wild animals have great impact on ecosystem e.g. infection with ranaviruses in amphibians, viral haemorrhagic septicemia in fish and myxomatosis in rabbits.
The concept of one health in the recent years represented the goal of scientific community, fight against diseases in animals is important to both human and its environment.

Avian influenza (birds flu)

The influenza caused by viruses with highly pathogenic avian influenza (HPAI). Bird flu is similar to swine flu, dog flu, horse flu and human flu as an illness caused by strains of influenza virus. The three types of influenza viruses (A, B, and C), influenza A virus is a zoonotic infection, the natural reservoirs are birds. Avian influenza refers to the influenza A virus. Several domestic species also infected with this viral infection, including cats, dogs, pigs, and birds.

H5N1

The highly pathogenic influenza A virus subtype H5N1 is the avian influenza virus that is causing global pandemic threat "bird flu" or "avian influenza". H5N1 has killed millions of poultry in many countries throughout Asia, Europe, and Africa. Health experts are concerned that the existence of human flu viruses and avian flu viruses (especially H5N1) will provide an opportunity for genetic material to be exchanged between the two species of viruses and cause creating a new virulent influenza strain that is easily transmissible and lethal to humans. The mortality rate for humans with H5N1 is 60%.
H7N9
Influenza A virus subtype H7N9 is a new avian influenza virus first reported to have infected humans in 2013 in China. Most of the reported cases of human infection are severe respiratory illness. During one month following the report of the first case, more than 100 people were infected, a fifth of patients (1/5) died. The World Health Organization (WHO) called H7N9 as (an unusually dangerous virus for humans)

Newcastle disease

The causative virus is Avian avulavirus 1 (NDV-1), a negative-sense, single-stranded RNA virus, (Family: HYPERLINK "https://en.wikipedia.org/wiki/Paramyxoviridae" Paramyxoviridae), it is a highly contagious (highly virulent) epizootic viral bird disease affecting many domestic and wild avian species; it is able to be transmitted to humans. The most affected animals are the domestic poultry due to their high susceptibility. It is endemic to many countries.







Transmission occurs by exposure of healthy birds to fecal and other excretions of infected birds, and through contact with contaminated food, water, equipment, and clothing of farmers. Infections produce severe nervous and respiratory signs, spread rapidly, and cause up to 90% mortality. Some viral strains can be mild with no mortality.
The incubation period for this disease ranges from 4 to 6 days. An infected birds show many clinical signs, including respiratory signs (gasping, coughing), nervous signs (depression, drooping wings, twisting of head and neck, circling, complete paralysis), swelling of the tissues around the eyes and neck, greenish, watery diarrhea, rough- or thin-shelled eggs and reduced egg production. Sudden death in acute cases, there is a good vaccine against this virus (live and inactivated Newcastle virus vaccines) usually used for protection of healthy birds.
Foot and mouth disease
Foot-and-mouth disease or hoof-and-mouth disease (FMD), causative virus is picornavirus, it is an infectious and fatal viral disease that affects cloven-hoofed animals, including domestic and wild bovid. The virus causes a high fever for 2-6 days, the incubation period between 1-12 days, clinical signs are high fever followed by blisters inside the mouth and on the feet, and blister in mouth may rupture and lead to excessive secretion of foamy saliva.
It is highly infectious disease and can be spread by infected animals easily through contact with contaminated farming equipment, vehicles, clothing, and by domestic and wild predators. Susceptible animals include cattle, water buffalo, sheep, goats, pigs, antelope, deer, and bison, also infect elephants. Human infection with this virus is extremely rare.
There is a vaccine for this viral disease, but it is not very effective because the virus is genetically highly variable. Infection lead to decline of milk production significantly, weight loss in adults and death, especially in newborn animals. Contact animal-to-animal can spread the virus, aerosols contain viruses humans can spread the disease by carrying the virus on their clothes and bodies. Control measures include quarantine of infected livestock.