July 6th marked World Zoonoses Day, a day to highlight transmissible diseases between animals and humans and to increase awareness of current and potential zoonotic diseases.
Zoonoses encompass many different types of disease: viral, bacterial, parasitic and fungal, but all are transmissible between animals and humans.
Zoonotic diseases can be transferred between animals and humans through a number of ways:
- Direct contact: Coming into contact body fluids of an infected animal.
- Indirect contact: Coming into contact with areas contaminated with pathogens
- Vector-borne: Being bitten by a tick, or an insect like a mosquito or a flea.
- Foodborne: Eating or drinking something unsafe, like unpasteurized (raw) milk or undercooked meat or eggs.
- Waterborne: Drinking or coming in contact with water that has been contaminated with faeces from an infected animal.
Pandemics and zoonoses
Coronavirus disease 2019 is the most notable recent zoonotic pandemic, but other recent noteworthy outbreaks of zoonoses include pandemic influenza H1N1 2009, Ebola virus, Middle Eastern respiratory syndrome (MERS CoV), Rift Valley Fever and Zika virus.
The majority of emerging infectious diseases that have pandemic potential are zoonotic in origin, there are concerns with population growth, habitat destruction and the increasing demand for animal products as food – zoonotic diseases will only increase.
The UN has released a report on how learning from previous zoonotic outbreaks will help us fight future ones. The report included ten recommendations including: raising awareness of zoonotic diseases; expanding scientific enquiry into zoonotic diseases and sustainable management of landscapes and seascapes that enhance sustainable co-existence of agriculture and wildlife.
Origins of COVID-19
Scientists and researchers have been working non-stop since the initial outbreak of COVID-19 to establish where it came from, identifying the animals the virus originated in (viral reservoir), and which animals carried the virus (intermediary hosts) that ultimately made the leap to infecting humans. This identification is a very important step to help safeguard against future zoonotic pandemic.
Researches have established that the likely source of the virus is bat populations in rural mid-eastern China (WHO et al 2021, Chakraborty et al 2020). Another notable infectious disease (but not a zoonosis), Swine Acute Diarrhoea Syndrome (SADS)-CoV has caused the death of over 25,000 pigs in farms within Guangdong province- it also has been confirmed to have originated from bats in the area.
The outbreak of SARS in the early 2000’s, a virus genetically very similar to SARS-CoV-2 - the viral agent of COVID-19, was found to have originated in bats and then onto civet cats and other mammals before infecting humans.
Other species identified that maybe implicated in the spread of coronavirus disease 2019 from bats to humans are snakes (Bungarus multicinctus and Naja atra), Malayan pangolin (Manis javanica), Himalayan palm civets (Paguma larvata), Asian palm civet (Paradoxurus hermaphroditus). (Li et al. 2020).
Coronavirus disease 2019 has also been confirmed in other animals including zoo animals (big cats, otters and gorillas), companion animals (dog, cats and ferrets), animals bred for fur (mink) and livestock (pigs) (CDC 2021). These animals have become infected through exposure to a human carrying the virus – a zoonosis can work both ways.
The coronavirus disease 2019 pandemic is estimated to have claimed over 4.03million lives and infected more than 187 million individuals across the globe. Lessons learnt about the origins of the virus and surveillance of potential virus reservoirs may help prevent future zoonotic pandemics and save lives.
Centers for Disease Control and Prevention (2021) One health https://www.cdc.gov/onehealth/index.html
Chakraborty C, Sharma AR, Bhattacharya M, Sharma G, Lee SS. The 2019 novel coronavirus disease (COVID-19) pandemic: A zoonotic prospective. Asian Pac J Trop Med [serial online] 2020 [cited 2021 Jul 12];13:242-6. Available from: https://www.apjtm.org/text.asp?2020/13/6/242/281613
Li C, Yang Y, Ren L (2020) Genetic evolution analysis of 2019 novel coronavirus and coronavirus from other species. Infect Genet Evol:104285. https://doi.org/10.1016/j.meegid.2020.104285
UN (2020) Preventing the next pandemic - Zoonotic diseases and how to break the chain of transmission. https://www.unep.org/resources/report/preventing-future-zoonotic-disease-outbreaks-protecting-environment-animals-and?_ga=2.59688174.2144436919.1626083792-1745692469.1626083792[accessed 12/07/2021]
World Health Organization (2021) WHO-convened global study of origins of SARS-CoV-2: China Part - Joint WHO-China Study Team report 14 January-10 February 2021 https://www.who.int/publications/i/item/who-convened-global-study-of-origins-of-sars-cov-2-china-part [accessed 12/07/2021]