Introduction

A zoonotic disease is a disease that can be passed between animals and humans which is caused by viruses, bacteria, parasites, and fungi. These zoonotic diseases are very common due to the high contact between humans and animals on a daily basis either at home or in the workplace. The scientific world has estimations that 6 out of every 10 infectious diseases in humans are spread from animals.
Echinococcosis can also be called a hydatid disease, hydatidosis, or echinococcal disease and is a disease which involves Echninococcus tapeworm parasites with two main types which are cystic echinococcosis (CE) and alveolar-echinococcosis (AE) (CDC, 2012). According to the World Health Organization (2014) up to 1 million people globally are affected at any one time. As shown in Figure 1 below, it is easy to transmit the disease between species. However, although humans can be infected which according to the WHO (2015) means they are accidental intermediate hosts but they cannot transmit the disease.

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Figure 1: The cycle of echinococcosis (Source: www.cieh.org )

The importance of the disease

The importance of the disease is that it has been present and well known for many years but has been rather neglected by the health organizations. However according to the WHO (2014; Higuita et al 2015) echinococcosis was recently introduced in the list of neglected tropical diseases and is one of the six priority neglected zoonotic diseases which are rabies, echinococcosis, leishmaniasis, cysticercosis, human African trypanosomiasis, and food-borne trematodiases. More control strategies are being implemented and so according to the WHO (2014) by 2020, validated control strategies should be available and control interventions increased.

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Diagram 1: Global location of AE echinococcosis (Source: Torgerson et al, 2010)
The disease in general occurs globally, although Antarctica is unaffected, currently with approximately one million individuals infected and in areas such South America, Africa, and Asia up to 10% of the certain populations are affected. However it is considered to be controllable if interventions are used more quickly and effectively and so recorded deaths from echinococcosis in 1990 were 2000 but by 2010 that number was down to 1200 (Lozano, 2012).
The economic cost of the disease has been estimated to cost US$3 billion each year (WHO< 2015).

The basic lifecycle or transmission cycle details,

As shown in figure 1 the disease can be transmitted between the species including humans.
There are two strains to the disease mentioned above but it often goes unnoticed and certainly undiagnosed for many years.

With the cystic echinococcosis (CE) type, large cysts can appear on the liver, lungs and other organs but my go unnoticed for years. It is caused by infection with the larval stage of Echinococcus granulosus, which is a 2-7 millimetre long tapeworm found in dogs (definitive host) and sheep, cattle, goats, and pigs (intermediate hosts) (CDC, 2012). Cystic echinococcosis is usually found in a dog–sheep–dog cycle, although other domestic animals may be involved, including goats, swine, horses, cattle, camels and yaks.

The alveolar type (AE) of the disease begins in the liver and can spread to other parts of the body including the lungs and the brain although less frequently in the bones, kidneys, spleen, muscles, central nervous system and eyes and the sufferer has stomach pains as well as weight loss with the individual eventually turning yellow with jaundice. There can also be chest pains, breath shortness and coughing (CDC, 2012). It is caused by infection with the larval stage ofEchinococcus multilocularis, which is a 1-4 millimetre long tapeworm found in foxes, coyotes, and dogs (definitive hosts). AE is common in endemic areas with human cases much more rare but it causes more health threats in humans and if untreated it can be fatal. However the difficulty is that it may take between 5 to 15 years before the symptoms appear. AE is found in a wildlife cycle between foxes, other carnivores and small mammals, mostly rodents, although domesticated dogs and cats can also be infected. Torgerson et al (2010) state that China is believed to account for the majority of global AE cases

The disease is diagnosed through an ultrasound or CT which is computer tomography or MRI which is magnetic resonance imaging can also be used for diagnosis as well as using blood tests and biopsies taken from the infected animal or human.

The current status of the disease

According to the WHO (2014) echinococcocis is found in every continent except Antarctica, with over 1 million people at one time globally affected by the disease and with the fact that humans live alongside many domesticated and even wild animals it should be no surprise that there could be cross contamination. AE is found in northern hemisphere, in particular to regions of China, the Russian Federation and countries in continental Europe and North America.

The disease is spread when food or water that contains the eggs of the parasite is eaten or by close contact with an infected animal. The eggs are released in the stool of meat-eating animals that are infected by the parasite (CDC, 2012). Commonly infected animals include dogs, foxes and wolves and they become infected by eating parts of an animal which contains the cysts such as sheep or rates and mice (CDC, 2012).

The current approaches to control/treatment.

The disease is so globally widespread that it is difficult and expensive to control s it has been neglected in importance for so long. However, prevention of cystic disease (CE) is by treating dogs that may carry the disease and vaccination of sheep. The cysts may have to be drained through the skin using a ‘percutaneous treatment of the hydatid cysts with the PAIR (Puncture, Aspiration, Injection, Re-aspiration) technique’. There can be surgery and an anti-infective medication or even a ‘wait and watch’ treatment (WHO, 2015). However with CE the WHO (2015) states that there is an average 2.2% death rate after surgery for patients and about 6.5% of cases of relapsing after intervention as the recovery period is long term that requires. It is estimated that CE results in the loss of at least 1 million DALYs annually and possibly up to 3 million. A DALY is a ‘disability-adjusted life year’ which is counted as a loss of one healthy year of life. These DAYLYs are considered as the gap between current health status and an ideal situation of a population’s health where there is ‘an age free of disease and disability’ (WHO, 2015).

Treatment for AE may have to be surgical treatment which is also followed by ‘anti-infective prophylaxis with albendazo’ medication which may have to be taken for many years as AE can be fatal. The AE type is often diagnosed too late and only palliative care is possible to make individuals comfortable before they die (WHO, 2015).

The WHO (2015) does suggest that there should be more research the vaccine ‘for E. granulosus recombinant oncosphere antigen (EG95)’ which is currently being trialled in sheep to impede E. granulosus infection of lambs. It is thought that this could add to the control measures such as treating dogs and cats and killing off the older sheep.

The CDC (2012) suggests simply ways to stop transmission to humans as shown in Appendix A

References:

CDC (2012) Control and Prevention of Echinococcosis online at http://www.cdc.gov/parasites/echinococcosis/prevent.html accessed 20/1/16

CDC (2012) Parasites - Echinococcosis online at http://www.cdc.gov/parasites/echinococcosis/ accessed 20/1/16

Higuita, N.I., Brunetti, E. and McCloskey, C. (2015) Cystic Echinococcosis Journal of Clinical Microbiology 2015

Lozano, R. (2012) Global and regional mortality from 235 causes of death for 20 age groups in 1990 and 2010: a systematic analysis for the Global Burden of Disease Study 2010. (Dec 15, 2012). Lancet 380 (9859): 2095–128.

Torgerson, P.R.; Keller, K.; Magnotta, M. and Ragland, N. (2010) The Global Burden of Alveolar Echinococcosis PLOS June 22 2010 online at http://journals.plos.org/plosntds/article?id=10.1371/journal.pntd.0000722 accessed 20/1/16

World Health Organization (WHO) (2013) Report of the WHO Informal Working Group on Echinococcosis on the occasion of the XXV World Congress of Echinococcosis held in Khartoum, Sudan, 25 November 2013 Number of pages: 4 p.January 2014 WHO reference number:WHO/HTM/NTD/NZD/2014.1online at http://www.who.int/echinococcosis/WHO_HTM_NTD_NZD_2014.1/en/ accessed 20/1/16

WHO Factsheet (2015) Echinococcosis online at http://www.who.int/mediacentre/factsheets/fs377/en/ accessed 19/1/16

Appendix:

Appendix A: Prevention & Control (Source: CDC (2012) http://www.cdc.gov/parasites/echinococcosis/prevent.html accessed 20/1/16

Cystic echinococcosis is controlled by preventing transmission of the parasite. Prevention measures include limiting the areas where dogs are allowed and preventing animals from consuming meat infected with cysts. • Prevent dogs from feeding on the carcasses of infected sheep. • Control stray dog populations. • Restrict home slaughter of sheep and other livestock. • Do not consume any food or water that may have been contaminated by fecal matter from dogs. • Wash your hands with soap and warm water after handling dogs, and before handling food. • Teach children the importance of washing hands to prevent infection.

Alveolar echinococcosis can be prevented by avoiding contact with wild animals such as foxes, coyotes, and dogs and their fecal matter and by limiting the interactions between dogs and rodent populations. • Do not allow dogs to feed on rodents and other wild animals. • Avoid contact with wild animals such as foxes, coyotes and stray dogs. • Do not encourage wild animals to come close to your home or keep them as pets. • Wash your hands with soap and warm water after handling dogs or cats, and before handling food. • Teach children the importance of washing hands to prevent infection.