Animal Diseases, Their Symptoms and Cell Structures

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Bacteria Structures and Function

The cell wall protects the structure and provides support for the bacteria, in a spirochete the cell wall is thin. The membrane is a semipermeable barrier and they don’t have a waterproof membrane.The flagellum is covered by the cell's plasma membrane, so that the interior of the flagellum is in contact with the cell's cytoplasm. The flagella function is to steer the cell. Ribosomes job is to create protein to repair damage. A pilus function is to attach the cell to a specific place and it is made out of protein.

Leptospirosis in Dogs

This is a bacterial infection that can occur in dogs. It is a spiral-shaped bacterium called a spirochete. The bacteria are thin, motile, slow growing anaerobes. There is two types of strains of leptospirosis one being leptospira canicola attacks the kidney (usually in dogs).

Leptospirosis is spread usually through infected urine however, it can be transmitted by any direct contact. Rodents can carry and spread the bacteria that causes this disease. It can also be transmitted through water. It is gram negative bacteria. Gram negative bacteria is adapted to thrive in high water content environments therefore usually found growing in water. It also makes the bacteria resistant to some antibiotics. the difference between gram positive and gram negative is the structure of the bacteria cell wall. Gram positive bacteria doesn’t have an outer cell membrane unlike Gram negative bacteria. The bacteria is easily destroyed by sunlight, temperature extremes and disinfectant.

They reproduce through binary fission, this is when bacteria divides into identical daughter cells which will have identical DNA to the parent cell.

Symptoms include; sore muscles and so reluctance to move, vomiting and diarrhoea, depression, shivering, kidney pain and swelling, dehydration, anorexia and pyrexia.

Strangles; Streptococcus Equi in Horses

This is a disease that occurs often in young horses. It is a highly contagious infection of the upper respiratory tract caused by the bacteria Streptococcus Equi. It is a gram-positive cocci in chains. Gram positive bacteria can survive and grow in more concentrated solution systems due to strong cell walls unlike in gram negative bacteria. This reproduces by binary fission a process of splitting bacteria.

When the bacteria is transmitted into the horse it travels to the epithelial lining of the upper respiratory tract and can invade its lymph nodes which causes abscesses.

Transmission occurs through both oral and nasal routes. It can be transmitted through shared environments such as water troughs. The discharge from any draining abscesses are also very infective. The disease can survive in environment for up to 3 weeks and it can spread systemically which causes abscesses in other lymph nodes and organs. However, shedding may be irregular and some horses become long-term carriers within the guttural pouch. It can survive for long periods in the environment, surviving in purulent discharges and in nasal discharges. Therefore, before any recovering horse can be proved clear of the disease a number of swab tests must be carried out.


  • Enlarged glands in the head and neck
  • Yellowish discharge from the nostrils
  • Pyrexia (39.5 to 41.5°C)
  • Difficulty swallowing
  • Loss of appetite
  • Coughing

Sarcoptes Scabiei in Dogs

This is an ectoparasite which lives on the outside of the subject. Adult Sarcoptes scabiei are oval shaped, light coloured and microscopic mites. They are ectoparasites and live 2-3 weeks in the host’s skin. After mating, the female burrows into the skin depositing 3-4 eggs in the tunnel behind her. The eggs hatch in 2-3 days producing larvae which, in turn, move about on the skin surface eventually molting into a nymphal stage and finally into an adult. The adults move on the surface of the skin where they mate and the cycle begins again with the female burrowing and laying eggs. At 10-15°C the mites can survive from 4 to 21 days in the environment without a host. At room temperature mites can survive for two to six days. This shows that mites survive longer in colder conditions.

Symptoms of Sarcoptes Scabiei Include:

  • Severe itching
  • Alopecia
  • Scabs and sores
  • Red skin/ inflammation
  • Bleeding

Dipylidium Caninum in Cats (tape worms)

The transmission route of a tapeworm is through ingesting the tapeworm. For example if a cat eats an infected flea then the cat becomes the host for the tapeworm.They grow in a cat's intestines after being ate or transmitted. They are flat and elongated in shape.

Tapeworms are hermaphroditic this means that they can reproduce sexually on their own by self fertilisation which can occur in each proglottid. They can also reproduce asexually by breaking up the proglottid into segments.

The proglottid contains muscle, nerves and male and female reproductive organs. The scolex, contain the rostellum, hooks and suckers function is to attach to specific structures, such as the intestinal wall. Tapeworms do not have a digestive tract and instead absorb food through their membrane.

Parasitic worms such as tapeworms are also called helminths. There is three different types of helminths, flatworms, roundworms and thorny worms. Tapeworms are cestodes and therefore flatworms. A helminths contain antigens (protein) that causes an immune reaction in the host’s body.


  • eggs, larvae, or segments from the tapeworm in stools
  • abdominal pain
  • Vomiting and dizziness
  • Inflammation of the intestine
  • diarrhoea
  • weight loss
  • sleeping difficulties this may be as a result of other symptoms.
  • convulsions in severe cases
  • Malnutrition
  • Simple virus structure

A genome is the set of genetic material present in a cell or organism such as a virus. A capsid is a protein structure made of capsomeres which protects the viral genome. The nucleocapsid is the capsid and the nucleic acid combined to create a protein coat. The viral envelope is a protein covering the capsid it is usually created from the hosts cell membrane in an attempt to avoid the host’s immune system. Prions are proteins that cause degenerative disease in the nervous system. A virion is the complete virus. Virions reproduce using hosts DNA. Some have an outer envelope. Bacteriophage is a virus that reproduces inside bacteria.

Canine Distemper Virus in Dogs

Its is a virus which affects a dog’s respiratory, gastrointestinal, and central nervous systems. This is an enveloped, single-stranded RNA virus (DNA virus is usually double stranded). It is transmitted by aerosol exposure and by direct contact with infected animals and fomites (infected objects). Dogs which already have canine distemper can pass the infection on through its blood, saliva and urine. The incubation period (how long until symptoms show) is around 3-10 days. The virus is duplicated and spread throughout the dog by viral replication.This is where the virus invades the cell and goes into the cells nucleus and injects DNA into the nucleus and then its replicates and breaks out of the host cell. The virus can survive at cold temperatures easily.

Main symptoms include; Sneezing, coughing, mucus discharge from the eyes and nose, high fever, lethargy, vomiting, diarrhoea and a decrease in appetite.

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Myxomatosis in Rabbits

This is a very contagious viral disease in rabbits which is normally fatal.


  • Swelling/ inflammation
  • Blindness
  • Nasal and eye discharge
  • Lethargy
  • Respiratory problems
  • Loss of appetite

This virus is transmitted by blood-sucking insects, such as fleas, ticks and mites.It can remain in the blood of a flea for months. The myxomatosis virus does not replicate in these insect hosts but can be physically carried by an insect. Fleas are a vector for the disease and throughout winter they keep the infectivity. The virus replicate inside the rabbit it does this by injecting the rabbits cells with nuclei acid to control the cell and reproduce with a special protein coat which protects it from the rabbits immune response. The virus matures by breaching the surface membrane of the host cell. The virus blocks the caspase activity in the host cells. The genome in this virus has double stranded DNA in it. It doesn’t always have an envelop it develops one when it breaks out of a dead cell.


  • Fungal cell walls are rigid and contain chitin.
  • Fungi is unicellular or multicellular depending on environmental conditions.
  • Fungi thrive in a moist and slightly acidic environment. They can grow with or without light or oxygen.
  • There is two different morphological stages vegetative and reproductive stages.

Fungus can be split into two different types multicellular (mould) and unicellular (yeast) fungi such as microsporum canis is multicellular and therefore a mould. Fungi reproduce both sexually and asexually. Imperfect fungi reproduce by mitosis (asexually)

Microsporum Canis (ringworm) in Dogs

This is a dermatophyte which means it is a fungus that grows on keratin structures such as skin and hair. It affects animals and humans but microsporum canis commonly effects dogs. This has multi celled spores called macroconidia which has thick walls and are spindle shaped. Ringworm is a eukaryotic cell with a cell wall made of chitin. The cell doesn’t have chlorophyll so it does not use photosynthesis to create food. Ringworms are heterotrophs this means they get food from their environment. The fungi grows aerobically.

Ringworm reproduces sexually and asexually by budding and producing spores. When budding occurs a lump forms on the side of the cell, the bud then detaches after the nucleus divides by mitosis. When it is reproduced asexually the spores are genetically identical to the parent. This is a common fungal disease that is transmitted by direct contact. It can also be transmitted by indirect contact through fomites.

Symptoms Include:

  • Hair Loss
  • Scaling on the scalp
  • Itching
  • Blisters

Blastomycosis Dermatitidis Cats

This is a non-contagious fungal infection that can be potentially deadly for cats. Blastomycosis thrives in damp and warm conditions. It is a unicellular fungi meaning it is a yeast. It is usually found in the cats body for example its lungs, eyes or nose. Its is caused by inhalation to spores of the fungus Blastomyces dermatitidis.When in the body the conidia fungus transforms into the yeast and attacks the lungs. You can only get it from fungus that is in soil or spores in the air.

It is a dimorphic fungi so has two forms. At room temperature it is at the vegetative stage then at 37°C, the mycelium changes to a large yeast which has thick cell walls and broad-based buds

Symptoms of Blastomyces include decreased appetite, coughing and breathing difficulties. They can also get a fever, lose weight and get skin abscesses in addition to blindness and other eye problems.

Blastomyces reproduces asexually through budding and also sexually. The nucleus is replicated by mitosis then the bud has the replicated nuclei and becomes a separate daughter cell, the budding carries on to create a chain of cells.

Animal Immunity

An animal's immune system helps to defend the body from infection. It is made up of antibodies and white blood cells (leukocytes) that identify the foreign pathogens and destroy them. The thymus and tonsil develop antibodies (a protein that stops pathogens). The lymphatic system contain lymph nodes and vessels sive the fluid that flows through their system and trap any foreign objects such as bacteria which is then destroyed by lymphocytes (white blood cells). Bone marrow produces white and red blood cells (erythrocytes). The spleen filters the blood and collects and removes damaged and old red blood cells and helps the immune system by destroying bacteria and antigens (toxins).

Secondary organs create immune responses.

Types of Immunity

  • Innate immunity; This is a type of immunity where it is present at birth and has a natural resistance to certain organisms already. This immunity can be passed down through genetics or be given physically.
  • Adaptive immunity; by adapting to certain bacteria and viruses the bodies immune system can become immune to the specific organism in the future.
  • Active immunity; there is two types natural and artificial. Natural active immunity is where the animal catches for example a virus then develops the disease however overcomes the disease and becomes immune to it due to the immune response (creates antibodies to destroy antigens). Artificial active immunity is where the antigen is purposefully given to the animal via vaccine which induces the primary response against the antigen (without developing any of the diseases symptoms).
  • Passive immunity; there is two types natural and artificial. The natural passive immunity happens when an animal is pregnant and involves the mother passing certain antibodies into the fetal bloodstream. Artificial passive immunity is when an animal is immune for a short term due to injection of antibodies that are not produced by the animal (transfer of humoral immunity).

Humoral Immunity

This is where antibodies are produced by B-lymphocytes. The B-cells are activated due to an invading antigen. The cells divide, some mature and create plasma cells which produce more antibodies. Others change back into memory cells which are small lymphocytes this increases the bodies antibody productions, so it is prepared if the infection returns. This type of immunity can be gained from either the mother or colostrum.

Cell Mediated Immunity; T-cells are lymphocytes created by the thymus gland and they respond to infection by causing inflammation this alerts the phagocytes so they can go through the process of phagocytosis (engulfing harmful particles like bacteria). There is three main types of t-cells; helper t-cells, cytotoxic t-cells and suppressor t-cells. Helper t-cells help macrophages and b-cells in the immune response. Cytotoxic t-cells get rid of cells infected with viruses. Suppressor t-cells suppress the body's immune reaction to stop the body damaging its own cells. Natural Killer Cells; these cells go throughout the body and destroy any cell which does not have the protein class 1 MHC molecule on the surface. This is because if the cell does not have that protein then it is a virus or cancer cell. To destroy the cell the NKCs release toxins into the foreign cell.

Physical barriers; this is an initial barrier such as skin and surfaces of the urogenital, gastrointestinal and respiratory tracts. In addition to this sneezing, mucus secretions, coughing, vomiting and urine flow also help to block and clear pathogens.

Blood clotting is also another physical barrier, the blood vessel clots so any foreign pathogens cannot enter the bloodstream also phagocytes can go into the the clot and engulf any pathogens. A cause of disease is damaged cells due to an infection when the disease is developed symptoms of the disease will show. The symptoms of a disease are the indicating factors that collectively show weather an animal has a certain disease or not.

In active immunity the effects on symptoms change for example if the immunity is naturally acquired then the symptoms of the disease would show as the animal would have had to develop the full disease in order to gain immunity. However, with artificially acquired active immunity the animal would show no symptoms. With cell mediated immunity the t-cells create inflammation which can cause symptoms. The less severe symptoms you have when ill the stronger your immune system is. Artificial passive immunity is only gives immunity for short term so doesn’t last forever unlike active immunity.

Systemic Autoimmune Disease in Cats

This is a disease that cats can get and it is where the immune system starts to attack its own cells. The overall severity of the disease fluctuates as it depends which cell the system is targetting. For example if the immune system is targeting red blood cells then the cat would become weaker due to anemia. Due to the variation of the disease the symptoms can be vague and change for each case. The disease is caused by the immune systems antibodies attacking its own antigens instead of foreign antigens. This disease is an example of where the immune system fails to protect.

Cells reproduce by mitosis this is where the DNA in the nucleus is replicated and then the cell divides into two. The cells repeated this process several times to continually grow and reproduce. A problem with this is that if the process of mitosis goes wrong and a if the chromosomes don't align correctly in the metaphase plate one cell will have an extra chromosome and another have one less chromosome. This can lead to serious consequences such as cell death or cancer.

Pathogenesis happens as a result of interactions between an infecting pathogen and the immune system. For example the pathogenesis for a dog with leptospirosis is; the leptospira being present in water and skin and mucous membranes protecting the dog as a physical barrier. If the dog has a graze the leptospira will enter through the graze and the bacteria will enter the bloodstream and the dog will produce a fever. The bacterial infection could then spread to the liver (leading to jaundice) or kidney (which can then lead to renal failure).

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