At Your Service….. Part II

By: Rosemary Stephen PMed, (cert) EOH, IPM, Elements: Environmental Health Intelligence

In Part I of our three part series, we looked at the contributions animals offer to Public health. Cats and dogs played an important a role in both World Wars, controlling mice and rats in the trenches, and today they are central in numerous beneficial therapies. We also discovered that many other animals, such as horses, zoo animals and dolphins, are used to improve mental and physical health. Animals also supply an inexpensive and accurate means of testing for cancer and for communicable diseases. In the second part of the series we look at how animals and insects contribute to Environmental Health.

The Sentinels of Environmental Health

The main role animals play in Environmental Health is as sentinels. When I think about a ’sentinel’, the first thing that comes to mind is a soldier standing guard on a route that could be used by invading enemies. Sentinel animals have a similar role — to protect humans from arboviral diseases [1F] or environmental contaminants. Sentinel animals are defined as “An animal deliberately placed in a particular environment to detect the presence of an infectious agent, such as a virus” [1]. These animals play an important role as an early warning system; they respond more quickly to environmental health hazards, and at a lower dosage, than human beings.

When monitoring diseases such as arbovirus [2F] transmission, sentinel animals are placed in specific locations. This allows for the detection of health parameters that will identify the mode of exposure and the type of hazardous infectious agent. These parameters are set from probability models [3F]; Epidemiologists use probability model mathematical formulae to estimate the number of animals required, the seroconversion rates, the blood sampling frequency, the vector infection rate and the health effects on human hosts [2]. Sentinel animals can be placed in any type of environment such as “homes, work place, farms and natural aquatic and terrestrial systems. They can be observed in their natural habitats or placed in work places or sites suspected of contamination”[3]. These animals help clarify uncertainty about “human risks from exposure to toxic chemicals” and serve in the establishment “of risk assessment which includes risk characterization, hazard identification, dose-response assessment and exposure assessment” [4]. Another advantage of using sentinel animals is the ability to detect physiological reactions which mimic human exposure to pollutants.

Sentinel Animals

Sentinel species have key requirements: “a) a wide-spread distribution; b) a high trophic [4F] status; c) the ability to bioaccumulate [5F] pollutants; d) the ability to be maintained and studied in captivity; e) be able to be captured in sufficient numbers; f) a restricted home range, g) well-known biology; h) be sensitive to pollutants” [5]. In general, herbivorous animals are used to detect contaminants in plants. Mussels, oysters and fish are frequently used to monitor water pollution because they accumulate environmental contaminates in their bodies at higher concentrations than other animals. Others species such as gulls, ospreys, seals as well as some reptiles and amphibians are used in the detection of water pollutants from soft or saline water sources. Cats and dogs have a tendency to lick their fur so they are used in the detection of lead contamination in homes thus protecting the health of children [6]. There are also many other specific animals that are used as environmental health sentinels….

Starlings (Sturnus vulgaris)

Introduced to North America from Europe in the late 1890’s, these birds have spread successfully across most of the continent. Starlings have been selected as sentinel species because they generally stay within 150 feet (46m) of their nests and they adapt easily to man made nest boxes. These characteristics allow researchers to set up nest boxes in target areas and to know the exact “numbers of nests built, eggs laid, chicks hatched, and chicks surviving until fledging time” [7]. Importantly too, in the spring breeding season, 50 % of a starling’s diet consists of protein-rich insects and other soil invertebrates [8]. This feeding habit allows researchers to biomonitor for soil contaminants; contaminant biomarkers can be identified by the analysis of tissue samples taken from chicks [9].

Backyard Poultry and Wild Fowl

People with small acreages raise chickens, turkeys, waterfowl, and game birds has a hobby. Frequently these birds are allowed to forage outdoors or, in external enclosures, so they can intermingle with wild birds [10]. The Alaskan Department of Environmental Conservation, Office of the State Veterinarian, uses domesticated ducks to detect the presence of Avian Influenza in wild water fowl populations. Backyard poultry flocks contribute to Environmental health by allowing the department to determine that the onset of Avian Influenza infection in sentinel ducks occurs in late July and early August at summer breeding sites. This time frame corresponds to when infected wild juvenile ducks leave their nest to intermingle with domesticated ducks and other wild fowl [11].

Another agency called “Global Avian Influenza Network for Surveillance” (GAINS) is presently involved in the global surveillance of Avian Influenza H5N1 as well as examining the results found by other research agencies. GAINS surveillance looks at the pattern of distribution of H5N1, genetic changes in the virus and differences in migration patterns of wild birds.

In 2006, GAINS reported on information presented by the Johns Hopkins Bloomberg School of Public Health. Johns Hopkins published the results of a large scale survey done in Thailand of backyard poultry (chicken, ducks and geese). The study, done in 2004 by the Department for Livestock Development (DLD) in Thailand, showed that highly pathogenic avian influenza (HPAI) is more prevalent in commercially raised birds than backyard poultry. With this data in mind, the Johns Hopkins Bloomberg School of Public Health felt that policy makers and public health officials in developing countries should concentrate on controlling the spread of highly pathogenic avian influenza (HPAI) in commercial operations instead of adversely effecting the livelihood of small-holder poultry producers [12, 13].

Western Honeybee (Apis mellifera) and Outdoor Air Quality

There are three main advantages of using honey bees as sentinels of Environmental Health: Western honey bees are the most widely use bees in the world today for the production of honey [14], bees are inexpensive — one hive can contain from 30,000 to 70,000 bees [15] and they forage widely for pollen and nectar hence becoming dusted with air contaminants during the process. These contaminants cling to their bodies or collect in their pollen sacs so they can be collected and sampled. It is easy to perform measurements on the bee’s body to detect inorganic elements, such as arsenic, cadmium, lead, zinc, copper, and fluoride. Measurements are done either by using small collectors which scrape off pollen sacs from bees’ legs or, by sampling the air inside the beehive. When bees return from foraging, air contaminants are release into the hive when they land at the entrance and fan the air furiously with their wings to regulate the temperature inside the hive [16].

Beehives are placed in contaminated zones to identify how contaminants move with outdoor air currants. Interesting characteristics emerge once hives are placed side by side in a contaminated zone. Sampling results differ from hive to hive because bees do not forage the same areas. The variation from hive to hive actually demonstrates how contaminants have dispersed over a site. Results are plotted on maps which are then compared to existing maps of contaminated soil. The forage samples are highly accurate and is a confirmation that bees are excellent indicators of how outdoor air contaminants move. This allows Environmental Health Agencies to predict how humans may be exposed to pollution [17].

Mink (Mustela vison)

Mink are aquatic animals of the weasel family found over most of North America. They are good sentinel animals because they bioaccumulate pollutants ingested from a diet that consists of small mammals, muskrats, fish, crayfish, frogs and insects [18]. Mink are the ideal to detect mercury (Hg) and PCBs in the environment since approximately 50% of their diet is fish [19]. The United States Department of Agriculture (USDA) uses mink to detect the type, amounts, availability and effects of these environmental contaminants.

Horses (Equus ferus)

Horses are used as sentinel animals to identify the appearance of specific viruses and to confirm their circulation. Humans and horses do not play a significant role in the spread of diseases such as West Nile (WNV) because they are considered ‘dead end hosts’, in other words, these viruses do not transmit from horse to horse or from horses to humans. The presence of horses in specific areas has helped to identify risk factors associated with WNV. In Guadeloupe for instance, 359 horses living within 1mile (approximately 1.5 km) of humid coastal swamps and marshes were compared to horses living close to shrimp basins and to sugar cane fields. This comparison helped to identify a higher risk for horses, and hence by extension for humans, to contract WNV in humid coastal areas as versus the shrimp basins and sugar can fields [20]. Italy saw the re-emergence of WNV during their 2009 active surveillance. They found that both horse and the human populations had WNV lineage 1, a strain that is less virulent than in North America. Italian health officials are continuing passive surveillance of horses. Monthly veterinarian reports are compared against bird and mosquito WNV findings to determine how WNV moves into the horse population [21].

Dog (Canis lupus familiaris)

Dogs have a very keen sense of smell. Thanks to a nasal membrane that covers an area of 900 sq inches (5806 sq cm) compared to humans with only 65 sq inches (409 sq cm), their nose is one million times more sensitive than a human’s [22]. This is why dogs have been used extensively to detect specific scents. Dogs are trained to detect ammunition, drugs and even cancer. Recently, a dog was trained to detect raw sewage and detergents. Sable, a German Shepperd cross, is said to be 87% accurate in finding illegal connections in sewage systems. He can also quickly find the origin of raw sewage, decreasing time and money spent doing dye tests and sending samples to labs. Communities in Maine and New Hampshire who are struggling to protect shellfish beds and beaches from sewage leaks, eye Sable as a tool to achieve this goal. Sable’s owner is now training other dogs to detect of raw sewage and /or detergents [23, 24, 25].

Pigs (Sus scrofa scrofa)

The domestic pigs of Egypt are descended from indigenous wild boar. Archaeological evidence indicates there was a long tradition of pig husbandry in ancient Egypt and papyrus texts record that Egyptian healers even used pig body parts to make medicinals to cure human ailments [26]. Recently, however, with the onset of H1N1 in Mexico, Egypt’s health ministry was concerned with the possible spread of this virus within the human population. In May 2009, because of the initial association of this new disease with pigs, the government decided to cull every specimen in their country [27]. Despite World Health Organization criticism, the government culled approximately 300,000 pigs.

Garbage collection was partially done by the Zabaleen community (an Arabic word that means ‘garbage collectors’). Zabaleens are rural migrants who came to Cairo in the 1950’s [28]. They were poor and had no jobs, so they started collecting the city’s garbage. As time went on, they became expert garbage collectors, reusing and recycling 80% of what they collected [29]. Glass, plastic paper and aluminum were collected and sold for recycling. The organic portion of the waste was fed to their large herds of pigs. The indigenous Egyptian pigs proved to be highly efficient at transforming organic wastes into meat; for each 5-6 lbs (3 kg) of feed, these pigs would gain 2.2 pounds (1kg) of weight [30]. For pig farmers, this is an excellent trait because it takes less than 6 months for pigs to reach marketable weight [31].

The cull had disastrous consequences in Egypt. Since the cull, the Zabaleen community has greatly decreased their trash collecting activities. They no longer collect organic waste as they no longer have large herds of pigs to feed and they no longer collect waste from door to door. In Cairo, waste dumps have appeared in empty lots. Snake and rat populations have increased as they now forage freely in the trash, as do feral dogs and cats. The outdoor air quality has worsened due to garbage fires lit by people who want space for more garbage [32]. Now, everyday, the 14,000 tons of waste produced by Cairo’s 12 million inhabitants needs to be hauled away [33]. Not all waste was removed by the Zabaleens. Ten years ago multinational haulage companies were hired to collect garbage as well, but since the cull these companies have not been able to keep up with the quantity of waste. The haulage companies have installed garbage bins throughout Cairo where residents can dump all their garbage, but residents, used to having their garbage picked up at their doors, pile their waste up outside, often against the empty bins. Garbage is also no longer being picked up in small alleyways because the modern garbage tucks are too wide for the old, narrow streets [34]. The cull also did not have any affect on cases of H1N1 in Egypt. Prior to the cull, there were no recorded cases of the virus in Egypt, since the cull in May of 2009, there have been 891 cases of H1N1, including two deaths [35].

The Egyptian government is now realizing that it overreacted. They are considering “increasing landfill and composting capacity, paying Zabaleen to deliver organic waste to compost plants, or establishing goat farms outside the city to fill the role once occupied by hogs” [36]. Goats, however, are are not as efficient as pigs in converting food into weight gain [37]. A recent approach has been to teach Cairo citizens to separate organic waste from other waste. This was met with a success rate between 35% to 90 % depending on the community. Lowest income people complied in higher numbers than their richer counterparts [38].

The Egyptian government has not discussed reintroducing pigs as a tool in waste management, which, to me, is unfortunate. Well integrated pig raising managed by the Zabaleens would be a sound approach to improving environmental health for the citizens of Cairo as well as the rest of the country.

Conclusion:

Sentinel species are important in Environmental Health. They serve as an early warning system with a quicker response to diseases (and at lower doses) than humans. Sentinel animals help clarify human risks from exposure to toxic chemicals and serve in the establishment of risk assessment which includes risk characterization, hazard identification, dose-response assessment and exposure assessment. Starlings help researchers to biomonitor for soils contaminants. Bees are excellent indicators of outdoor air pollution allowing mapping of contaminants and their movement through the atmosphere. Mink, because of their diet, are the ideal sentinel animals to detect mercury (Hg) and PCBs in the environment. Humans and horses do not play a significant role in the spread of diseases such as West Nile (WNV), but because horses can be placed in specific areas, they have helped in the identification of risk factors. Training dogs in the detection of raw sewage in the environment is an excellent tool in the protection of fisheries, beaches and human health, complementing the existing tools (dye test and lab analysis) used to detect these types of contaminants.

Egypt’s decision to cull all its pigs had a tremendous negative impact on the environmental health of its people. Cases of H1N1 emerged in the country despite the cull and the capital city Cairo saw the degradation of its outdoor air quality and the inability to manage its waste. With the Zabaleens refusal to collect the organic waste (which was once fed to their pigs), the government is now faced with setting aside sites for landfill and composting facilities.

Rosemary Stephen PMed, (cert) EOH, IPM (2010). At Your Service…. Part II Elements: Environmental Health Intelligence

References:

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[2] Xiaohong, L. and Rossignol, P. A. Probability Model on the use of Sentinel Animal Monitoring for Arbovirius (2009) Trusted archives for scholarship, JSTOR, University of Illinois. (On-line) Available: http://www.jstor.org/pss/3702718. Cited 2009 Nov 17.

[3] Animal as Sentinels of Environmental Health Hazard (1991) Commission on Life Sciences (CLS), The National Academies Press. (On-line) Available: http://www.nap.edu/openbook.php?record_id=1351&page=4. Cited 2009 Nov 09.

[4] Ibid. Cited 2009 Nov 09.

[5] Bursian, S. The Fate and Biological Effects of Xenobiotics in Animals (2008) Animal Science, Michigan State University.(On-line) Available: http://www.reeis.usda.gov/web/crisprojectpages/163167.html. Cited 2009 Nov 16.

[6] Animal as Sentinels of Environmental Health Hazard (1991) Commission on Life Sciences (CLS), The National Academies Press. (On-line) Available: http://www.nap.edu/openbook.php?record_id=1351&page=4. Cited 2009 Nov 09.

[7] Starlings and Their Control (2001) Agriculture and Rural Development, Government of Alberta. (On-line) Available: http://www1.agric.gov.ab.ca/$department/deptdocs.nsf/all/agdex729. Cited 2009 Nov 24.

[8] Davis, M. Sentinel Species (2000) Perspectives, Southern Illinois University Carbondale. (On-line) Available: http://perspect.siuc.edu/00_fall/wildlife_toxicology.html. Cited 2009 Nov 16.

[9] Overview, Sentinel Animal Methods (2006) Attachment 6. (On-line) Available: http://www.usda.gov/documents/wildbirdstrategicplanpdf_seg6.pdf. Cited 2009 Nov 09.

[10] Ibid. Cited 2009 Nov 09.

[11] Ibid. Cited 2009 Nov 09.

[12] About GAINS (2009) Global Avian Influenza Network for Surveillance. (On-line) Available: http://www.gains.org/. Cited 2009 Nov 25.

[13]Otte, J. and al. Pro-Poor Livestock Policy Initiative, A Living from Livestock Reaserch report (2006) Evidence-based Policy for Controlling HPAI in Poultry : Biosecurity Revisited. PPLPI, Johns Hopkins Bloomberg School of Public Health. (On-line) Available: http://www.gains.org/DataTools/GAINSDocs/tabid/114/language/en-US/Default.aspx. Cited 2009 Dec 17.

[14] Honeybee (2009) (On-line) Available: http://www.gpnc.org/honeybee.htm. Cited 2009 Nov 16.

[15] Western Honey Bee (2009) Orkin (On-line) Available: http://www.orkin.com/other/bees/western-honey-bee. Cited 2009 Nov 24.

[16] Chemical buzz: honeybees and their hives act as sensors for pollution. (1997) The Free Library. (On-line) Available: http://www.thefreelibrary.com/Chemical+buzz:+honeybees+and+their+hives+act+as+sensors+for+pollution-a019481623. Cited 2009 Nov 16.

[17] Ibid. Cited 2009 Nov 16.

[18] Mammals, American Mink (2009) Nature.ca. (On-line) Available: http://nature.ca/NOTEBOOKS/english/ammink.htm. Cited 2009 Nov 24.

[19] Basu, N. Mink (2007) The Encyclopedia of Earth.(On-line) Available: http://www.eoearth.org/article/Mink. Cited 2009 Nov 16.

[20] Pradel, J. and al. Risk factors for West Nile virus seropositivity of equids in Guadeloupe (2009) ScienceDirect (Online) Available: http://www.sciencedirect.com/science?_ob=ArticleURL&_udi=B6TBK-4WXXV41-1&_user=10&_rdoc=1&_fmt=&_orig=search&_sort=d&_docanchor=&view=c&_searchStrId=1097432311&_rerunOrigin=google&_acct=C000050221&_version=1&_urlVersion=0&_userid=10&md5=47d9f415f0596f723b522aeb4c5a9c62. Cited 2009 Nov 17.

[21] Drs Robert, H. Calistri, P. and Sabirovic, M. Disease Report, West Nile Virus in horses in Italy (2009) Veterinary Science Team, Global Animal Health – International Disease Monitoring, Preliminary Outbreak Assessment. (On-line) Available: http://www.defra.gov.uk/foodfarm/farmanimal/diseases/monitoring/documents/wnv-italy091023.pdf. Cited 2009 Nov 17.

[22] How Dogs Communicate with Scent (2009) Kryptiks Lair German Shepherds. (On-line) Available: http://kryptiks-lair.tripod.com/id12.html. Cited 2009 Nov 27.

[23] Luntz, T. Dog Provides Low-Cost, Low-Tech Fix for Cities’ Sewer Problems (2009) Energy and Environment, The New York Times. (On-line) Available: http://www.nytimes.com/gwire/2009/08/18/18greenwire-dog-provides-low-cost-low-tech-fix-for-cities-27746.html. Cited 2009 Nov 27.

[24] Luntz, T. Dog Provides Low-Cost, Low-Tech Fix for Cities’ Sewer Problems (2009) The New York Times. (On-line) Available: http://bluewatertaskforce.blogspot.com/2009/08/sable-sewer-sniffing-dog.html. Cited 2009 Nov 13.

[25] Payne, A.L. Get a whiff of this: Sewage-sniffing dog hunts for E. coli sources along Kawkawlin River (2008) Bay City News Archives. (On-line) Available: http://blog.mlive.com/bctimes/2008/09/get_a_whiff_of_this_sewagesnif.html. Cited 2009 Nov 13.

[26] Parsons, M. Pigs in Ancient Egypt (2005) Tour Egypt. (On-line) Available: http://www.touregypt.net/featurestories/pigs.htm. Cited 2009 Nov 26.

[27] Ahmed, A. Egyptian farmers protest mandatory swine slaughter (2009) CNN.com/world. (On-line) Available: http://www.cnn.com/2009/WORLD/meast/05/03/egypt.pig.farmers.protest/. Cited 2009 Nov 26.

[28] Zabbaleen (2009) Wikipedia, The Free Encyclopedia. (On-line) Available: http://en.wikipedia.org/wiki/Zabbaleen. Cited 2009 Nov 26.

[29] Swine-Flu Slaughter Leaves Cairo Without Pigs to Devour Trash (2009) New on Urban Health Issue, Urban Health Updates. (On-line) Available: http://urbanhealthupdates.wordpress.com/2009/09/29/swine-flu-slaughter-leaves-cairo-without-pigs-to-devour-trash/. Cited 2009 Nov 17.

[30] Taking control of feed conversion ratio (2009) PigProgress.net (On-line) Available: http://www.pigprogress.net/article-database/taking-control-of-feed-conversion-ratio-id927.html. Cited 2009 Nov 26.

[31] Samaan, M. Pig Farming Halted (2009) American Chamber of Commerce in Egypt. (On-line) Available: http://www.amcham.org.eg/Publications/BusinessMonthly/July%2009/indepth(PIG_FARMING_HALTED).asp. Cited 2009 Nov 26.

[32] Swine-Flu Slaughter Leaves Cairo Without Pigs to Devour Trash (2009) New on Urban Health Issue, Urban Health Updates. (On-line) Available: http://urbanhealthupdates.wordpress.com/2009/09/29/swine-flu-slaughter-leaves-cairo-without-pigs-to-devour-trash/. Cited 2009 Nov 17.

[33] Egypt deals with the aftermath of killing the country’s 300,000 pigs (2009) Pippa’s Place – Environmentally Speaking. (On-line) Available: http://philippa-pippasplace.blogspot.com/2009/09/egypt-deals-with-aftermath-of-killing.html. Cited 2009 Nov 26.

[34] Ibid. Cited 2009 Nov 26.

[35] Swine-Flu Slaughter Leaves Cairo Without Pigs to Devour Trash (2009) New on Urban Health Issue, Urban Health Updates. (On-line) Available: http://urbanhealthupdates.wordpress.com/2009/09/29/swine-flu-slaughter-leaves-cairo-without-pigs-to-devour-trash/. Cited 2009 Nov 17.

[36] McGrath, C. Environment: Cairo Sinking in Garbage (2009) IPS. (On-line) Available: http://ipsnews.net/news.asp?idnews=48491. Cited 2009 Nov 17.

[37] Ibid. Cited 2009 Nov 17.

[38] Ibid. Cited 2009 Nov 17.

Endnotes:

[1F] Arboviral Disease in Washington State, Arboviral Disease (2008) Notifiable Conditions, Washington State Department of Health. (On-line) Available: http://www.doh.wa.gov/Notify/nc/arbo.htm. Cited 2009 Nov 09.

Arboviral are diseases that are exclusively transmitted by mosquitoes, sandflies and ticks. They includes West Nile virus, Eastern and Western Equine encephalitis, dengue, St. Louis encephalitis, La Crosse encephalitis, Japanese encephalitis, Powassan, yellow fever, and other less common infections.

[2F] Steel E. The Definition of Arbovirus (2009) How to do just about everything, eHow. (On-line) Available: http://www.ehow.com/about_5070528_definition-arbovirus.html. Cited 2009 Nov 27.

Arboviruses (arthropod-borne viruses) are a large group of viruses that are spread mainly by blood-sucking insects. This name refer to mostly blood-sucking insects such as mosquitoes. Called zoonotic, they can cause disease when spread from animals to humans.

[3F] Hodges, J.H. And Lehmann, E.L. Basic concept of probability and statistics (2005) Philadelphia PA, Society for Industrial and Applied Mathematics. (On-line) Available: http://www.inderscience.com/search/index.php?action=record&rec_id=11282&prevQuery=&ps=10&m=or. Cited 2009 Nov 20.

[4F] Wetzel Formal definition of trophic status (2009) Freshwater- Master Homepage. (On-line) Available: http://www.chebucto.ns.ca/ccn/info/Science/SWCS/index.html. Cited 2009 Nov 20.

Refers to the rate at which organic matter is supplied by or to the lake per unit time.

[5F] Glossary of Terms (2009) Biosolids Lifecycle. (On-line) Available: http://www.biosolids.state.va.us/research.htm. Cited 2009 Nov 24.

The tendency for substances to increase in concentration in living organisms as they take in contaminated air, water, or food because the substances are very slowly metabolized or excreted.

Tagged as: Animals in service, Environmental Health, Sentinel Animals