Animal Zoonotic Related Diseases

What is Animal Zoonotic Related Diseases?

Animals have a significant place in our lives in many ways – they provide us with food, help in farming, are used for sports and travel, are common attractions at zoos and fairs, are invaluable for research, make wonderful pets, and even guide people in need. However, it’s crucial to note that animals can also pass on over 200 diseases to humans, known as zoonotic diseases. In such cases, humans are often unintentional hosts. The discovery of zoonotic diseases dates back to the 1800s when Rudolf Virchow and Osler first recognized its occurrence. The term “zoonosis” is made up of two parts; “Zoo” indicates an animal and “nosis” refers to sickness.

What Causes Animal Zoonotic Related Diseases?

Zoonoses are diseases that spread from animals to humans, a phenomenon that is becoming more common due to changes caused by human activities. Factors like population growth, interaction with animal habitats, deforestation, the formation of suburbs, and practices such as the bushmeat industry (worth $15 billion annually in the U.S.) play a big role. Other influences include global warming, widespread travel and open trade, keeping exotic pets, eating insects, genetic mutations, and the existence of animals that can carry diseases without showing signs of them. There’s also something called the spill-over effect; this is when a disease crosses from one species to another due to high infection rates in the first animal.

Certain groups are more vulnerable to these diseases, including kids under 5 years old, people over 65, people with weak immune systems, and pregnant women. Certain jobs, like being a veterinarian, butcher, or hunter, also put people at a higher risk. Even owning a new or young pet can increase the risk because they are likelier to transmit zoonoses than mature ones.

The main carriers of these diseases are usually rodents and bats, with over 2200 species of rodents and 1100 species of bats capable of acting as hosts. They carry dangerous diseases like Nipah, Hendra, Menangle, Corona, Ebola, and Marburg viruses. Carnivores, which are meat-eating animals, also carry a lot of zoonoses, especially bacteria and viruses.

Zoonotic diseases can be divided into various categories based on what causes them, how they are transmitted, their source, the part of the human body they affect or the ecosystem they exist in. The most common causes of zoonotic diseases include bacteria (42%), viruses (22%), fungi (5%), parasites (29%) and prion (a type of protein that can cause disease)(2%).

Here is a list of the most common diseases and their sources:

• Bacteria: Listeria, Clostridium botulinum, Bacillus anthracis, Rhodococcus equi, Mycobacterium bovis, Mycobacterium marinum, Mycobacterium leprae,
  Erysepilothrix, E.coli O157:H7, Salmonella, etc.
• Viruses: B-virus, Cowpox, Monkeypox, Orf, SARS/MERS/SARS-CoV-2, Influenza A, Nipah, Hendra, Rabies, Dengue, etc.
• Fungi: Dermatophytes, Sporothrix, Aspergillus, Cryptococcus,Histoplasma, Blastomyces, Coccidioides.
• Parasites: Fasciolae, Echinococcus granulosus, Dipylidium caninum, Toxocara canis / cati, Ancylostoma caninum/ braziliense, Trichinella spiralis, Capillariae, Dirofilaria immitis, Giardia lamblia, etc.
• Prion: vCJD.

Note: SARS: Severe Acute Respiratory Syndrome, MERS: Middle East respiratory syndrome, WNV: West Nile virus, EEE: Eastern Equine encephalitis, WEE: Western Equine encephalitis, VEE: Venezuela Equine encephalitis, LCMV: Lymphocytic Chorio-Meningitis virus, HIV: human immunodeficiency virus, vCJD: Variant Creutzfeldt-Jakob disease.

Risk Factors and Frequency for Animal Zoonotic Related Diseases

In the U.S., over two-thirds of households have pets. There are 45 million households with dogs and 77 million with cats. These pets can sometimes carry diseases that can be transmitted to people, known as zoonoses. These diseases make up 61% of all infectious diseases, 75% of new emerging diseases, and 80% of potential diseases used in bioterrorism.

According to the Centers for Disease Control and Prevention, the Department of the Interior, and the U.S. Department of Agriculture, the eight most significant zoonoses in the U.S. are:

• Influenza
• Salmonella
• West Nile virus
• Plague
• Coronaviruses
• Rabies
• Brucella
• Lyme disease

Let’s take a closer look at these diseases:

• Influenza has been responsible for several global outbreaks over the years, including the H1N1 swine flu in 2009 and the H5N1 avian flu since 2003.
• Salmonella is the main cause of zoonotic outbreaks in the U.S. over the past decade.
• West Nile virus is the most common mosquito-borne zoonosis in the U.S. It’s believed that for every reported case of the disease, there are 70 unreported cases.
• Plague is primarily found in western states such as California, Arizona, Colorado, and New Mexico, with 1-17 cases per year.
• Various coronaviruses, including the SARS virus that caused over 8000 infections in 2003 in Southeast Asia, the MERS virus that has infected over 2000 people since 2012, and the SARS-CoV-2 virus that has infected around 120 million people worldwide since 2019.
• Rabies results in around 40,000 exposures reported every year in the U.S., which costs the health system millions of dollars for post-exposure treatment. However, thanks to control measures, rabies in humans is rare in the U.S., with only nine cases from 2008 to 2019.
• Almost every case of Brucella in the U.S. is connected to immigrants, imported animals, or unpasteurized milk. There are around 100 reported cases of Brucella each year.
• Lyme disease is the most common insect-borne disease in the U.S. with 20,000 cases per year, 95% of which are in the Northeast and Mid-Atlantic states.

Other noteworthy zoonotic diseases include Leptospira, which is the most common worldwide and seen mostly in farmers, veterinarians, and surfers in Hawaii; RMSF, a common disease in North Carolina and Arkansas; Hanta, found mainly in the Western U.S states like Utah, Colorado, Arizona, New Mexico; and Babesiosis, seen mainly in the Northeastern states.

Furthermore, 30% of the U.S. population are symptomless carriers of the Toxoplasma parasite, and Giardia is one of the most common parasites affecting the digestive system.

Signs and Symptoms of Animal Zoonotic Related Diseases

When dealing with patients, it’s essential to get a comprehensive history, paying attention to their travel history, place of residence, job, vaccination status, hobbies, pets, interactions with other animals, and diet. People with weakened immune systems often experience more severe conditions than the general population.

The symptoms of zoonotic diseases, which are diseases transmitted from animals to humans, can vary depending on the part of the body they impact. Here are some examples:

Respiratory Infections:

• Influenza: Symptoms include fever, headache, muscle aches, cough, and sore throat.
• COVID-19: Symptoms range from no symptoms to fever, headache, fatigue, sore throat, cough, shortness of breath, loss of taste or smell, nausea, vomiting, and diarrhea.
• Psittacosis: Symptoms range from no symptoms to fever, headache, muscle aches, sore throat, cough, diarrhea, and confusion.

And so on for each category and specific disease.

Roughly, these categories of diseases can manifest the following ways:

Neurological Infections:

• Symptoms can include fever, headache, muscle aches, weakness, numbness, confusion, and in severe cases, a change in mental state.

Gastrointestinal Infections:

• Common symptoms are abdominal pain, diarrhea, nausea, vomiting, and bloody stool.

Musculoskeletal Infections:

• Symptoms can include fever, vomiting, muscle aches, and associated skin manifestations.

Dermatological Infections:

• These often present as different types of skin rashes and lesions, and in severe cases, confusion and shock.

Blood and Systemic Infections:

• These can result in symptoms like fever, headache, fatigue, various organ-related symptoms, and rash. They can span single or multiple body systems.

Note: WNV stands for West Nile Virus, vCJD stands for Variant Creutzfeldt-Jakob Disease, CLM stands for Cutaneous larva migrans, and RMSF stands for Rocky Mountain spotted fever.

Testing for Animal Zoonotic Related Diseases

Public health data at both national and local levels are crucial when considering a possible infection from animals or insects (known as a zoonotic infection).

Depending on the suspected infection, your doctor may order a variety of tests:

– A Complete Blood Count (CBC): This test is run to check the levels of different types of cells in your blood. For example, during a flu or brucellosis (an infection caused by bacteria found in animals), a high count of lymphocytes, a type of white blood cell, is common. However, lower lymphocyte counts typically indicate COVID-19. Other infections such as babesiosis, Coxiella, Rocky Mountain Spotted Fever (RMSF), and leptospirosis can result in low platelet counts. And with trichinellosis, a parasite infection, you may see a high count of eosinophils, another type of white blood cell.

– A peripheral blood smear: This test observes blood under a microscope. Babesiosis, a tick-borne disease, might show a ‘maltese cross’ appearance of certain cells in this test,

– Kidney and liver function tests: These tests can assess how well these vital organs are working,

– Imaging like a chest x-ray: This can highlight any abnormalities within the chest area,

– Sampling and testing Cerebrospinal fluid (CSF): This procedure checks for infections like West Nile Virus (WNV), variant Creutzfeldt-Jakob disease (vCJD, a rare and fatal brain disorder), or rabies,

– Electroencephalogram (EEG): It measures electrical activity of the brain looking for abnormal patterns, as seen with WNV and vCJD,

– Cultures of blood, sputum (mucus coughed up from the lower airways), or tissue: This can help detect infections like plague, anthrax, salmonella, and Capnocytophaga (a bacteria found in the mouths of dogs and cats),

– Serology: It’s a test done to detect presence of antibodies against certain diseases like Lyme disease, WNV, psittacosis (a bird-borne bacterial disease), and Bartonella (a group of bacteria that can infect humans and animals),

– Polymerase Chain Reaction (PCR) or Reverse Transcription PCR (RT-PCR): These tests look for genetic material of viruses or bacteria to detect infections like the flu, COVID-19, WNV, or psittacosis.

Also, a technique called Matrix-Assisted Laser Desorption/Ionization (MALDI-TOF) can be used in the diagnosis of anthrax. For suspected rabies cases, an autopsy of the animal in question may be carried out.

Treatment Options for Animal Zoonotic Related Diseases

The treatment for diseases can vary greatly, and it often depends on the particular infectious organism causing the disease (often called the “pathogen”). Here are some examples:

People with the flu usually get better on their own over time. If necessary, medications like Oseltamivir or Baloxavir can help speed up recovery.

Salmonella, a type of harmful bacteria, is usually managed with supportive care, which means keeping the patient comfortable while their body fights off the infection. If necessary, medications like quinolones, azithromycin, trimethoprim-sulfamethoxazole, or ceftriaxone may be used.

The plague is traditionally managed with a class of antibiotics called aminoglycosides or tetracyclines. Quinolones can serve as a backup option.

Brucellosis, a bacterial infection, is typically treated with a mixture of doxycycline and an aminoglycoside or rifampicin (for adults who are not pregnant).

COVID-19 is managed according to the latest official guidelines, and often includes supportive measures and medications like remdesivir and dexamethasone.

Lyme disease is treated using doxycycline or a class of antibiotics called beta-lactams, depending on how far the disease has progressed and the patient’s symptoms.

Rocky Mountain Spotted Fever, a tick-borne illness, is usually treated with doxycycline.

Psittacosis, a disease transmitted via birds, is generally treated with tetracyclines, with azithromycin as an alternative option.

Coxiella, a bacteria causing Q fever, is managed with doxycycline, and sometimes hydroxychloroquine is added if there are complications involving the blood vessels.

Anthrax, a dangerous bacterial infection, is often treated with a combination of different medications like quinolones, carbapenems, linezolid, and immunoglobulin for systemic (whole-body) infections. Quinolones or doxycycline are used for skin-based infections.

Dermatophytes, a group of fungi causing skin, hair, and nail infections, are typically treated with either topical or systemic (whole-body) antifungal medications. Treating any infected animals is also important.

West Nile Virus, Rabies, and Rift Valley Fever are usually managed with supportive treatment, where the focus is on relieving symptoms and keeping the patient comfortable, as there are no specific treatments for these illnesses.

For the Ebola virus, new treatments are being suggested, such as atoltivimab, maftivimab, odesivimab (REGN-EB3), and ansuvimab.

Efforts to decrease diseases that spread from animals to humans, called zoonoses, include ensuring that foods made from animals are safe, reducing economic development in wild areas, paying more attention to preventing illnesses rather than just managing them, and making sure that travel medicine guidelines are easily available.

The ‘One Health 2006 Initiative’ emphasizes the importance of cooperation between human healthcare providers, animal healthcare providers, agricultural workers, environmental experts, and others. This approach was adopted after realizing that focusing on prevention in only one area wasn’t enough to handle the outbreak of West Nile Virus in New York City in 1999. One of the goals of the initiative is to figure out which diseases are the biggest threats and focus resources accordingly.

What else can Animal Zoonotic Related Diseases be?

Zoonotic diseases are illnesses that spread from animals to humans. However, they should not be mixed up with other similar disease groups:

• Zooanthroponosis (reverse-zoonosis) – illnesses that go from humans to animals, for example, tuberculosis
• Amphixenosis – diseases that move in both directions, from animals to humans and back, such as staph bacterial infections
• Euzoonosis – situations where humans are a required host in the disease’s life cycle, such as with Taenia solium and Taenia saginata

Zoonotic diseases also need to be separated from other common infections that may have similar symptoms. An individual’s exposure to a certain animal, for instance, could be misleading. Likewise, contact with animals, insects, and the outdoors can cause non-infectious health issues like allergic reactions. These also need to be taken into account when diagnosing the problem.

What to expect with Animal Zoonotic Related Diseases

The chance of surviving various diseases caused by pathogens (commonly known as germs) can differ a lot:

* Avian flu (a type of Influenza that comes from birds) has a fatality rate of up to 60%, whereas Swine flu (which comes from pigs) has a fatality rate of less than 1%.

* West Nile virus has a fatality rate of 6%.

* Plague, a severe and potentially deadly bacterial infection, has a fatality rate of 13% with treatment, and over 80% without treatment.

* SARS, MERS, and SARS-CoV-2 (the virus causing COVID-19) have fatality rates of 9.6%, 35%, and between 3% to 6% respectively. So far, SARS-CoV-2 has caused over 2.5 million deaths.

* Rabies, a viral disease that causes inflammation of the brain in humans and other mammals, causes more deaths globally than any other zoonotic disease (diseases that can spread from animals to people), causing between 30,000 to 70,000 deaths per year.

* Brucella, a group of bacteria that can cause a range of symptoms from fever, headache, weakness and more, has a fatality rate of between 2% to 5% if left untreated.

* Anthrax, a serious disease caused by a bacterium called Bacillus anthracis, has an over 80% fatality rate when contracted through inhalation.

* Coxiella, the bacteria that cause Q fever, has a 2% fatality rate in its acute (short-term) form and a 20% rate in its chronic (long-term) form.

* Ebola, a severe and often deadly disease caused by a virus, has a fatality rate around 50%.

* Rocky Mountain spotted fever, a bacterial disease spread through the bite of an infected tick, has a 22% fatality rate without treatment and 6% with treatment.

Less deadly diseases (with fatality rates of less than 1%) include salmonellosis (a type of food poisoning caused by bacteria), Lyme disease (an infectious disease spread by ticks), rift valley fever (a viral disease most commonly observed in domesticated animals), and psittacosis (a type of lung infection contracted from certain birds).

Possible Complications When Diagnosed with Animal Zoonotic Related Diseases

Zoonotic diseases, or diseases that can be passed from animals to humans, come with a range of complications:

• Influenza: Can lead to conditions like pneumonia, muscle inflammation, heart inflammation, brain inflammation, and Guillain-Barre syndrome (a rare neurological disorder)
• Salmonella: Can cause bacteremia (bacteria in the blood), bone infection, heart infection, and mycotic aneurysms (a type of blood vessel aneurysm)
• West Nile Virus (WNV): May result in meningitis, encephalitis (brain inflammation), eye inflammation, fatal bleeding fever, liver inflammation, and heart inflammation
• Plague: Can lead to meningitis, shock, Disseminated Intravascular Coagulation (a condition that causes blood clots and bleeding), and multiple organ failure
• COVID-19: Could lead to respiratory failure, heart rhythm problems, acute coronary syndrome (sudden reduced blood flow to the heart), shock, blood clot issues, acute kidney injury, and widespread inflammation in the body
• Rabies: May result in seizures, coma, breathing failure, heartbeat irregularities, and heart inflammation
• Brucella: Can cause arthritis, meningitis, pneumonia, orchitis (inflammation of the testicles), miscarriages, eye inflammation, and heart infection
• Lyme disease: Can lead to Bannwarth’s syndrome (a rare neurological condition), facial paralysis, meningitis, restricted heart rhythm, a skin condition called acrodermatitis chronica atrophica, and post-Lyme disease syndrome (persistent symptoms after treatment)

The diseases also bring major economic implications since they greatly affect areas like international travel, tourism, and the trade of animals and animal products. For instance, the avian flu outbreak of 2015 led to a loss of $3.3 billion for the U.S. economy.

In addition, zoonotic diseases can cause severe complex illnesses in individuals with weakened immune systems, such as transplant patients. In a more distressing aspect, these diseases could potentially be used as biological weapons in acts of terrorism.

Preventing Animal Zoonotic Related Diseases

Regular visits to the vet are important for your pet’s health and to address any illnesses they might have. Clipping your cat’s claws can prevent scratches. Pet owners should avoid feeding pets raw meat or eggs. It’s strongly recommended that homes with children less than 5 years old or kitchens, steer clear from having reptile pets.

It’s very important to follow the guidelines for tetanus shots, with or without additional antibodies, especially after animal bites. Keeping your pets vaccinated against diseases like rabies, leptospirosis, and brucellosis is a must. Horses must be vaccinated against the West Nile Virus (WNV). New vaccines are also being developed for many animal-transmitted diseases, such as new types of bird flu and the plague.

You can control ticks and fleas in several ways. People should wear light-colored clothes, long-sleeve shirts, and pants tucked into their socks. Using a bug repellent spray with DEET, checking your body for ticks after spending time outside, and checking your pets for ticks after they’ve been in wooded areas can help. Removing leaf piles and having fire ants (which eat tick eggs) introduced to the area can be arranged with environmental authorities to help control tick and flea populations. It’s also crucial to take precautions to avoid mosquito bites.

Raising awareness about washing hands through public programs is another important step. Healthcare workers should be educated about emerging infectious diseases and the resources available to treat them. Ongoing efforts include continuous monitoring, reporting and mapping of diseases transmitted from animals to humans.