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Animal transmitted disease

This is an umbrella project for Animal & Insect transmitted diseases.

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There are numerous diseases and infections that animals and insects including mosquitoes, fleas and ticks can transmit to humans. These are known as zoonotic diseases. Zoonoses can be caused by a range of disease pathogens including viruses, bacteria, fungi and parasites.

There are at least 39 important diseases people catch directly from animals. There are at least 48 important diseases people get from the bite of bugs that bit an infected animal. And there are at least 42 important diseases that people get by ingesting or handling food or water contaminated with animal feces. Some can result in epidemics and pandemics. Many are survivable, especially with treatment, however, some can be fatal.

Diseases that can be transmitted between animals and humans, such as bird flu and tuberculosis, can wreak havoc on the health of both organisms. Now researchers have found 13 so-called zoonoses are responsible for 2.2 million human deaths every year.

Classification of zoonoses:

  • Viral – HIV/AIDS, rabies, influenza, feline cowpox, monkeypox, chikungunya hantavirus, herpes B, Rift Valley fever, West Nile fever, orf, human or avian influenza virus, etc.
  • Bacterial – Bordetella bronchiseptica, Erysipelothrix rhusiopathiae, Clostridium difficile, Burkholderia mallei (glanders), Helicobacter, Pseudomonas (pseudoglanders), Pasteurella multocida (pasteurellosis), rat bite fever (Streptobacillus), Streptococcus, Yersinia enterocolitica, anthrax, brucellosis, etc.
  • Parasitic – angiostrongyliasis, anisakiasis, Chagas (Trypanosoma cruzi), dirofilariasis (roundworm), Baylisascariasis, cysticercosis (Taenia), cryptosporidiosis, dipylidiasis, echinococcosis, giardiasis, hookworm, leishmaniasis, toxocariasis, toxoplasmosis, trichinellosis
  • Fungal – cryptococcosis, dermatophytosis, sporotrichosis, histoplasmosis
  • Arthropods – scabies, other acariasis
  • Prions – transmissible spongiform encephalopathy (i.e. mad cow)

Modes of transmission:

  • Direct contact - contact with saliva, blood, urine, mucous, feces, or other body fluids of an infected animal, such as petting or touching animals, and bites or scratches or such as air (influenza) or through bites and saliva (rabies) or via an intermediate species (referred to as a vector), which carry the disease pathogen without getting infected.
  • Indirect contact - contact with areas where animals live and roam, or objects or surfaces that have been contaminated with germs (such as aquarium tank water, pet habitats, chicken coops, plants, and soil, as well as pet food and water dishes.)
  • Inhalation (airborne)
  • Ingestion (foodborne) - eating/drinking contaminated food (such as unpasteurized milk, undercooked meat or eggs, or raw fruits and vegetables that are contaminated with feces from an infected animal).
  • Dermal absorption
  • Animal bites & scratches
  • Arthropod vectors (vector-borne) - bitten by a tick, or an insect like a mosquitoes, fleas, flies, sandflies, triatomine bugs and some freshwater aquatic snails.

Statistical & Study info:

Anyone can become sick from a zoonotic disease, including healthy people. However, some people may be more at risk than others. These people are more likely than others to get really sick, and even die, from infection with certain diseases. These groups of people include:

  • Children younger than 5
  • Adults older than 65
  • People with weakened immune systems

About 60 percent of all human diseases and 75 percent of all emerging infectious diseases are zoonotic, according to the researchers. Most human infections with zoonoses come from livestock, including pigs, chickens, cattle, goats, sheep and camels. 

Out of 56 zoonoses studied, the researchers found 13 that were most important in terms of their impact on human deaths, the livestock sector and the severity of disease in people, along with their amenability to agriculture-based control.

  • These were, in descending order:
    • zoonotic gastrointestinal disease;
    • leptospirosis;
    • cysticercosis;
    • zoonotic tuberculosis (TB); symptoms include chest pain, cough, fever, and fatigue.
    • rabies; starts with flu-like symptoms. Without treatment, it leads to agitation, delirium, hallucinations, and partial paralysis. Worldwide, the disease causes 55,000 deaths a year.
    • leishmaniasis (caused by a bite from certain sandflies);
    • brucellosis (a bacterial disease that mainly infects livestock); The resulting illness causes pain and flu-like symptoms and is treated with antibiotics.
    • echinococcosis;
    • toxoplasmosis;
    • Q fever;
    • zoonotic trypanosomiasis (sleeping sickness),
    • hepatitis E;
    • anthrax.
      • Though a rare disease, human anthrax, when it does occur, is most common in Africa and central and southern Asia. It also occurs more regularly in Southern Europe than elsewhere on the continent, and is uncommon in Northern Europe and North America. Globally, at least 2,000 cases occur a year with about two cases a year in the United States. Skin infections represent more than 95% of cases. Without treatment, the risk of death from skin anthrax is 24%. For intestinal infection, the risk of death is 25 to 75%, while respiratory anthrax has a mortality of 50 to 80%, even with treatment. Until the 20th century, anthrax infections killed hundreds of thousands of people and animals each year. Anthrax has been developed as a weapon by a number of countries.

They found many livestock were infected with these zoonoses in poor countries, where:  

  • 27 percent of livestock showed signs of current or past infection with bacterial food-borne disease that causes food contamination (a type of zoonotic gastrointestinal disease)
  • 12 percent of animals have recent or current infections with brucellosis
  • 10 percent of livestock in Africa are infected with trypanosomiasis
  • 7 percent of livestock are currently infected with TB
  • 17 percent of smallholder pigs show signs of current infection with cysticercosis
  • 26 percent of livestock show signs of current or past infection with leptospirosis
  • 25 percent of livestock show signs of current or past infection with Q fever
  • An estimated 50 million people caught diseases from animals such as dogs, cattle, chickens and mosquitoes between 2000 and 2005, according to a new study. Some 78,000 of them died.
  • Zoonotic killers between 2000 and 2005 included:
    • Rabies (range of host animals such as dogs, cats and horses): killed an estimated 30,000 people
    • Dengue Virus (spread by mosquitoes): affected 50 million people and killed around 25,000
    • Japanese Encephalitis Virus (spread by mosquitoes): up to 15,000 estimated deaths
    • Lassa Fever (spread by a rodent known as the "multimammate rat”): affected up to 300,000 people and killed about 5,000
    • SARS Corona virus (host unknown): killed 774 of the 8,102 people infected

Most recently, the bird flu, or H5N1, has garnered public attention for its potential not only to spread from chickens and other birds to humans, but also for the virus to mutate in a way that allows it to spread between humans. During the study period, bird flu killed just over half of the 145 people infected with the virus.

An estimated 700,000 to 2.7 million people — 75 percent of them African children— die of malaria each year. However, malaria doesn’t count as a zoonotic disease, because the virus depends on a human host for part of its life cycle.

Cat-scratch fever, for example, infects as many as 20,000 Americans a year. Most people with CSD develop a mild infection, though some get swollen lymph nodes, fever, and fatigue. The illness can be particularly severe for people with reduced immunity.

Vector-borne diseases:

  • Vector-borne diseases are human illnesses caused by parasites, viruses and bacteria that are transmitted by mosquitoes, sandflies, triatomine bugs, blackflies, ticks, tsetse flies, mites, snails and lice.
  • Vector-borne diseases account for more than 17% of all infectious diseases, causing more than 700 000 deaths annually from diseases such as malaria, dengue, human African trypanosomiasis, yellow fever, Japanese encephalitis and onchocerciasis, globally.
  • More than 3.9 billion people in over 128 countries are at risk of contracting dengue, with 96 million cases estimated per year.
  • Malaria causes more than 400 000 deaths every year globally, most of them children under 5 years of age.
  • Other diseases such as Chagas disease, leishmaniasis and schistosomiasis affect hundreds of millions of people worldwide.
  • Many of these diseases are preventable through informed protective measures.

Zoonotic Diseases

Chart listing Zoonotic Diseases which includes: Disease, Pathogen(s), Animals involved & Mode of transmission found in: Wikipedia - Zoonosis

Resources & Additional Reading:

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