Reducing the risk of zoonotic infection

Based on the article:

Walker, M.D. (2018) Cryptosporidiosis. Conservation Land Management, 16(2),19-22.

In May 2016 a small cluster of around 30 people living in the Rothwell area of Leeds began falling ill; all suffered similar symptoms of diarrhoea and sickness. They had contracted the illness Cryptosporidiosis, a disease caused by the protozoan parasite Cryptosporidium. The cases prompted Public Health England, the authority responsible for public health, to investigate. They discovered that the source of the outbreak was the nearby ‘Swithens Petting Farm,' which all the affected sufferers had recently visited.

Cryptosporidium is protozoan parasite which can cause illness in people. There are several types of 'Crypto'; some of which are zoonotic in nature; meaning they can be transmitted from animals to humans. Those working around either wild animals or domestic livestock are at risk of contracting the disease. This includes farm workers or people directly handling livestock. 'Crypto' can also be spread by vermin such as rats.

Protozoal Illness

The illness Cryptosporidiosis is caused by the protozoan parasite Cryptosporidium; this a parasite of the intestinal system. Infection causes gastroenteritis with symptoms including diarrhoea and stomach pain. Protozoa are small independently living organisms. They are a diverse group; not all are parasitic, some photosynthesise and are similar to algae. Cryptosporidium parasites belong in a grouping known as the Apicomplexa, a taxonomic group that contains other parasites such as the malarial causing Plasmodium. These parasites have special apical caps which secrete chemical substances helping them quickly invade host cells.

The name Cryptosporidium means 'hidden spore', and describes the encapsulated durable form in which the parasite occurs in the environment. There are around 20 species of Cryptosporidium, many specialising on specific hosts. The predominant kind affecting humans is C. hominis, which is transmitted from person to person. The most important zoonotic species is C. parvum which is seen in a variety of livestock and can be transferred to humans. Usually when outbreaks occur at wildlife or animal centres it is this species which is the cause. Large outbreaks can also occur when drinking supplies become infected; as is what happened in 2015 in Cumbria with the water for many thousands of people being contaminated .

Infection Routes

Ingestion of the infective oocysts results in infection (figure 1). These can be thought of as being 'inactive eggs'. Oocysts can be widespread in the environment, occurring in the water and soil where livestock have had access. The cysts have a tough outer protective layer meaning they are remarkably tough; able to resist cold and heat. Ingestion of only a small number of oocysts can cause infection; with as few as 30 being enough.

Figure 1: Simplified cycle of infection for Cryptosporidiosis.


walker conservation land management 2018 cryptosporidum

The oocysts become activated when ingested, the outer tough layer falls away. The oocyst splits into four active parts known as sporozoites. These embed in the epithelial cells of the small intestine where they can tap into the host’s resources. The epithelial cells of the gut has finger like projections known as villi which increase the surface area and help ingestion of food. It is these that the Cryptosporidia infiltrate. 

Now the life cycle becomes complex. Once embedded in the gut they reproduce, first asexually, multiplying and spreading rapidly (figure 2). They cause considerable damage to the lining of the gut. Later sexual forms are produced; with separate gametes being formed which join together to form a zygote. This goes on to develop into new oocysts which are excreted into the environment in the hosts faeces. Diarrhoea aids the widespread dispersal of oocysts and thus the infection of new hosts. The entire life cycle is contained within a single host.


Although unpleasant, Cryptosporidiosis is usually not serious. Most sufferers experience profuse watery diarrhoea and abdominal pain. Other less common symptoms include a slight fever, tiredness and headaches. Sometimes the diarrhoea can be severe, leading to dehydration. Sufferers also typically lose their appetite. Treatment options are limited. Antibiotics do not work against Cryptosporidium. If dehydration is experienced then fluids should be taken. Typically the illness resolves itself after 7 to 10 days. The condition can be more serious in those with weakened immune systems and those belonging to vulnerable groups. If belonging to such a potential risk group medical care should be sought promptly if Cryptosporidiosis is suspected. 

Figure 2: Cryptosporidium invading the mucosal layer of the small intestine. Courtesy of the Centers for Disease Control Public Image Library (PHIL). 1986. CDC/ Jonathan W.M. Gold. M.D.

walker cryptosporidum

It is easy for Ecology or countryside workers to not realise there are suffering from 'Crypto'. They may simply believe they have eaten something bad. They may not make the link between working in a livestock or wildlife infected area and there illness. However, the outside working habits of ecologists, and the particularly close nature of the association ecologists have with the ground makes them greatly at risk of obtaining infection.

Preventative Measures

Breaking the cycle of infection is key to stopping an outbreak. Better is to ensure infection does not occur in the first place. Good hygiene measures are key. However, Cryptosporidium is tough; the outer shell means they are durable and long lasting, resistant to cold, heat, and even resistant to disinfectant. This includes chlorine based disinfectants. Many outbreaks centred on swimming pools are known, despite such locations typically being well chlorinated. Public Health England suggests the following preventative measures:

Education: Those working in outdoors areas where wild mammals and farm animals have access should be aware of the condition. All those working in areas of possible contamination should ensure good hygiene. Those managing livestock and animals to which the general public have access, such as petting farms, should be aware of Cryptosporidiosis. There should be adequate signage prompting visitors to wash their hands after coming into contact with animals.

Hygiene: Hand washing with warm soapy water is the main method to prevent infection. Wash hands after contact with livestock and before eating (figure 3). Those with responsibility for others should ensure they have a good level of personal hygiene; hand washing should be encouraged or supervised. This includes children, those with learning disabilities, and possibly the elderly.

Contaminated areas: High risk areas include livestock housing or where animal faeces are stored Care should be taken when working in such locations and hygiene measures should be enhanced. Thoroughly hygiene after working in such areas is essential.

Rodent Control: Rodents act as a reservoir of infection. Faeces may contaminate areas which they visit. Areas affected include around livestock foodstuffs, picnic sites, litter bins, camping grounds, and BBQ sites. Ensure prompt removal of waste, waste food, litter and debris amongst which rodents could hide and nest. 

Figure 3:  Clear signage promoting hand washing.

walker cryptosporidiosis

Those with responsibility for sites to which the public have a daily plan of regular hygiene measures to prevent the spread of infectious disease; this should include the regular cleaning of public facilities, litter clearance, and rubbish removal. An action plan should be in place in the eventuality that an isolated outbreak of illness occurs. Park managers should take active measures to prevent further spread of disease; enhance hygiene, fumigation and possible closure of areas where transmission may occur. 

Dr Mike Gent, PHE's consultant in communicable disease control commented on the Leeds case saying 'It's important to remember that contact with farm animals carries a risk of infection because of the bacteria they naturally carry.' He added that basic hygiene was the best step in preventing infection, 'It's really important to wash your hands thoroughly using soap and water after you have been in contact with animals and especially before eating or drinking anything.'

Table 1: Notable outbreaks of Cryptosporidiosis at animal centred countryside attractions.




March 2005


128 laboratory confirmed cases centred on a wildlife centre. (McGuigan et al. 2010)

April 2011

Erddig Hall, Wrexham, Wales

Cases in a dozen people following a lamb feeding event.

April 2013

Fife, Scotland

23 people suffered, mostly under 10's after visiting a children's farm.

April 2013

Home Open Farm, Cumbria

12 primary school children fell ill after a farm visit.

May 2013

Cheltenham, Gloc.

Adam Henson's Farm Park. 5 fell ill with Cryptosporidiosis.

A version of this article appeared in Conservation Land Management in 2018. Thank you to Guy Freeman and the team at Conservation Land Management.

Please cite as:

Walker, M.D. (2018) Cryptosporidiosis. Conservation Land Management, 16(2),19-22.

Further Information

NHS Website. 2017. Gastroenteritis.

Public Health England (PHE). Cryptosporidiosis: guidance, data and analysis.

Scientific References

Cryptosporidium biology:

Chalmers, R.M., Davies, A.P. (2010) Clinical Cryptosporidiosis. Experimental parasitology, 124(1), 138-46.

Davies, A.P., Chalmers, R.M (2009) Cryptosporidiosis. British Medical Journal (Clinical Research Edition), 339, b4168.

Dillingham, R.A., Lima, A.A., Guerrant, R.L. (2002) Cryptosporidiosis: epidemiology and impact. Microbes Infect. 4(10), 1059–1066.

Papers concerning Cryptosporidiosis outbreaks at farms/wildlife attractions:

Gormley, F.J., et al. (2011) Zoonotic cryptosporidiosis from petting farms, England and Wales, 1992–2009. Emerging Infectious Diseases, 17, 151–152.

McGuigan, C.C., Steven M.K,, Pollock,K.G.J. (2010) Cryptosporidiosis associated with wildlife center, Scotland. Emerging Infectious Diseases 16, 895–896.

Utsi, L., Smith, S.J., Chalmers, R.M., Padfield, S. (2016) Cryptosporidiosis outbreak in visitors of a UK industry-compliant petting farm caused by a rare Cryptosporidium parvum subtype: a case-control study. Epidemiol Infect. 144(5), 1000-9.

About the Author

Mark Walker is a parasite biologist from Sheffield. He has worked on research projects studying conditions such as Lyme disease and Leptospirosis.