Human Vs. Animal Diseases

Differences in Cancers

Cancer in Humans

  • Although there are over 1000 different forms of cancer, they all begin with the same thing - abnormal cell growth. Cancer cells grow continuously, instead of dying and being replaced by new cells as they should be. Cancer is the most harmful because it can invade other tissues. Cancer cells are formed because of damage to the cell’s DNA. The mutated cells replicate and pass the damaged DNA onto new cells, which causes the spread of cancer cells.
  • People can inherit damaged DNA, but it is most often caused by environmental factors, or mutations during DNA replication. There is no way to be sure about the causes of a certain person’s kind of cancer.

  • In most forms of cancer, the cells form a tumor, or a growth of cells, that would replace, crowd, or push normal tissues aside. These kinds of tumors are called malignant tumors. Other tumors that aren’t cancer are called benign.

  • Cancer cells spread throughout the body through a process called metastasis. They break away from the normal cells and move through the bloodstream to other places of the body where more tumors can start to grow.

  • Different types of cancers have different forms, so they grow differently, present differently, and/or have to be treated differently.

Cancer in Animals

  • Cancer in animals is most common in cats and dogs or other animals that live to be older than 10 years.

  • The symptoms are very similar to those in humans (unexplained weight loss, fatigue, etc.)

  • The signs and symptoms of cancer can change based on where the cancer has spread, or what stage it is in. Some cancers don’t show any signs or symptoms until it is too late to do much of anything about it. Other cancers show signs very early.

  • Most of the knowledge we have about cancer in animals comes from previous knowledge from humans.

  • In order for animal cells to become cancerous, they must have their DNA altered in an unchangeable way at least two times. One time will initiate the DNA to change, but it will not affect the cell’s growth patterns. The second time will start the abnormal growth and cell cycle of whichever kind of cell was altered.


  • In most forms of cancer, the cells form a tumor, or a growth of cells, that would replace, crowd, or push normal tissues aside. These kinds of tumors are called malignant tumors. Other tumors that aren’t cancer are called benign.
  • Some examples of symptoms are weight loss, jaundice, fever, fatigue, weakness, or dizziness because the cancer cells take away much of the energy that should go to other cells.
  • Knowledge about both animals and people is more or less the same because the information known about cancer in animals came from cancer research in humans.
  • There are many different kinds of cancers that require different treatments. The different stages of cancer determine the severity and treatment plan of that specific kind of cancer. Stage 0 cancer is where there are only abnormal cells in the layer of cells in which they developed. Stages I, II, and III indicate large tumor size and spread of cancer cells to other nearby organs. Stage IV cancer is when the cancer cells metastasize to distant organs.

Bacterial Infections


  • Only certain kinds of bacteria cause harm or diseases to the body. These types of bacteria are called pathogens. There are always bacteria living in the body of animals (in the airways, stomach, intestines, urinary tract, etc.). Some of these kinds of bacteria can cause diseases in the body. Bacteria cause disease by invading the tissue of an organism, producing toxins that are secreted into the organism, or both.
  • Some kinds of bacteria almost always causes disease or infection when they enter someone’s body. Others can be inside someone without doing any harm, until the immune system is harmed or weakened.
  • Bacteria cause illnesses in many different ways. They can destroy tissue, become too numerous for the body to function, or produce cell-killing toxins. Bacteria can be spread through water, food, air, contact with animals, contact with other people, or spreading to different parts of the body.
  • Bacterial infections in people are treated with antibiotics and are prevented with vaccines at a young age.


  • Bacterial infections in animals are treated in the same was as humans - with antibiotics. Vaccines are also administered to animals at a young age, and continued through their adulthood, to prevent different kinds of diseases (ex. bordetella, leptospirosis, DAHPP, etc.)
  • Most treatment plans of bacterial infections in animals do not include antibiotics. They are put in a warm, stress-free environment and allowed plenty of fluids and rest. If the condition continues or worsens then antibiotics are used.
  • Ex. of symptoms - fever, weakness, jaundice, nasal discharge, depression, lack of appetite, vomiting, diarrhea, swollen lymph nodes


  • Certain kinds of bacterial infections can be passed from animals to humans or vice versa such as leptospirosis, tuberculosis (human TB, avian TB, bovine TB), salmonella, etc. When treating antibiotic resistant infections, doctors may use a different antibiotic drug, or use fluid replacement.
  • Most bacterial infections are spread by direct contact with an infected organism, or ingesting contaminated food or water.

Viral Infections


  • Symptoms of a viral infection include fever, headache, fatigue, sore throat, coughing, diarrhea, etc.
  • Viral infections usually aren't very serious, but there are no effective ways to treat viral infections using medications. Antibiotics are also useless because they focus on bacteria. The best way to get rid of a viral infection is to rest and drink fluids. There are only a few different kinds of antiviral medications, and even those can only treat specific types of viruses.
  • Viruses with the genus Influenza B are more specific to humans.


  • Viruses with the genus Influenza A are mostly prominent in animals and can have many different kinds of animal hosts.
  • Animal viruses are virtually the same as those in humans and are treated in similar ways. They both become infected in the same ways, and they both have similar symptoms from certain kinds of viruses or viral infections that are specific to one part of the body.


  • Viruses are protected by a coating, so they are more difficult to get rid of than bacteria. They are also harder to treat because they are immune to antibiotics. The use of antibiotics to treat viral infections leads to antibiotic resistance to that specific type of antibiotic which could be needed in the future.Vaccines are used to prevent viral infections before they start.
  • Viruses must have a “host” or some living organism with host cells for the virus to survive.
  • Viruses infect the cells of their host by injecting their RNA into the cell, which is then used for protein synthesis. The DNA of the host is not shown in protein synthesis and proteins are translated from the viral RNA, therefore expressing the virus in the host.