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Selected content from the Animal Health and Production Compendium (© CAB International 2013). Distributed under license by African Union – Interafrican Bureau for Animal Resources.

Whilst this information is provided by experts, we advise that users seek veterinary advice where appropriate and check OIE manuals for recent changes to regulations, diagnostic tests, vaccines and treatments.

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Identity    Pathogen/s    Overview    Distribution    Distribution Map for Africa    Distribution Table for Africa    Hosts/Species Affected    Host Animals    Pathology     Diagnosis    Disease Course    Disease Treatment Table    Vaccines    Prevention and Control    References    Links to Websites    OIE Reference Experts and Laboratories    Images

 

 Identity

Preferred Scientific Name
African horse sickness
English acronym
AHS

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 Pathogen/s

African horse sickness virus.

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Overview

African horse sickness is a highly infectious, non-contagious, insect-transmitted disease affecting all species of Equidae. It is characterized by respiratory and circulatory damage.

This disease is on the list of diseases notifiable to the World Organisation for Animal Health (OIE). Please see the AHPC library for further information on this disease from OIE, including the International Animal Health Code and the Manual of Standards for Diagnostic Tests and Vaccines. Also see the website: www.oie.int.

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Distribution

It is endemic in the central tropical regions of Africa and regularly spreads to Southern Africa and occasionally to Northern Africa. Outbreaks outside Africa in the Near and Middle East (1959-63), Spain (1966 (serotype 9), 1987-90 (serotype 4)), Portugal (1989, serotype 4) and Morocco (1989-91, serotype 4) have occurred.

The disease has a seasonal occurrence and its prevalence is influenced by climatic and other conditions that favour the breeding of its insect vectors. Recent northward expansion of the main African vector, Culicoides imicola, and bluetongue virus (a similar Orbivirus) into the Mediterranean Basin of Europe now threatens that region and beyond to African horse sickness (Mellor, 1992; Mellor and Hamblin, 2004; Dufour et al., 2008; Calvo et al., 2009). Due to the similarities between bluetongue and African horse sickness viruses and their vectors, there are fears that if African horse sickness should appear again in Europe, it could spread as widely as bluetongue virus.

During 2011, a total of 627 outbreaks of AHS were reported to AU-IBAR by 6 countries, compared to 305 outbreaks reported from 5 countries in 2010 and 15 outbreaks reported from 7 countries in 2009. Although the disease has been reported over the past years in five of the affected countries, the appearance of AHS in Somalia is regarded as a new epidemiological event. The highest numbers of AHS outbreaks were reported from South Africa with 447 outbreaks followed by Ethiopia with 167 reported outbreaks. Overall a total of 2754 horses were affected with AHS with 1013 reported mortalities representing a 36.8% case fatality rate. The highest numbers of outbreaks were reported in the month of March with 255 outbreaks (AU-IBAR, 2011).

Countries reporting African horse sickness
to the AU-IBAR
CountryOutbreaksCasesDeaths SlaughteredDestroyed
Ethiopia167267898203
Gambia15500
Namibia9371300
Somalia120700
South Africa447    
Swaziland214600
Total (6)6272754101303

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Distribution Map for Africa

Distribution Map for AfricaDistribution Map for Africa

present, no further details = Present, no further details    widespread = Widespread    localised = Localised
confined and subject to quarantine = Confined and subject to quarantine    occasional or few reports = Occasional or few reports
evidence of pathogen = Evidence of pathogen    last reported = Last reported...    presence unconfirmed = Presence unconfirmed

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 Distribution Table for Africa

The distribution in this summary table is based on all the information available. When several references are cited, they may give conflicting information on the status. Further information may be available for individual references may be available in the Animal Health and Production Compendium. A table for worldwide distribution can also be found in the Animal Health and Production Compendium.
 
CountryDistributionLast ReportedOriginFirst ReportedInvasiveReferencesNotes
AFRICA
AlgeriaLast reported1966   OIE, 2012 
AngolaNo information available    OIE, 2009 
BeninDisease not reported    OIE, 2009 
BotswanaDisease not reported    OIE, 2009 
Burkina FasoNo information available    OIE, 2009 
BurundiDisease not reported    OIE, 2012 
CameroonDisease not reported    OIE, 2012 
Cape VerdeLast reported2001   OIE Handistatus, 2005 
Central AfricaWidespread    Mellor & Boorman, 1995 
Central African RepublicDisease not reported    OIE, 2012 
ChadNo information available    OIE, 2012 
CongoNo information available    OIE, 2009 
Congo Democratic RepublicDisease not reported    OIE Handistatus, 2005 
Côte d'IvoireDisease not reported    OIE Handistatus, 2005 
DjiboutiDisease never reported    OIE, 2012 
EgyptDisease not reported    OIE, 2009 
EritreaPresent    OIE, 2012 
EthiopiaPresent    OIE, 2012 
GabonNo information available    OIE, 2009 
GambiaPresent    OIE, 2012 
GhanaLast reported2010   OIE, 2012 
GuineaNo information available    OIE, 2009 
Guinea-BissauNo information available    OIE, 2009 
KenyaDisease not reported    OIE, 2012 
LesothoLast reported2011   OIE, 2012 
LibyaLast reported1964   OIE, 2012 
MadagascarDisease never reported    OIE, 2012 
MalawiDisease not reported    OIE, 2009 
MaliNo information available    OIE, 2009 
MauritiusDisease never reported    OIE, 2012 
MoroccoLast reported1991   OIE, 2012; Mellor & Boorman, 1995 
MozambiqueLast reported2006   OIE, 2012 
NamibiaLast reported2011   OIE, 2012 
NigeriaDisease not reported    OIE, 2009 
North AfricaPresent    Mellor & Boorman, 1995 
RéunionDisease never reported    OIE Handistatus, 2005 
RwandaNo information available    OIE, 2009 
Sao Tome and PrincipeDisease not reported    OIE Handistatus, 2005 
SenegalLast reported2009   OIE, 2012 
SeychellesDisease not reported    OIE, 2012 
SomaliaLast reported2011   OIE, 2012 
South AfricaPresent    OIE, 2012; Mellor & Boorman, 1995 
SudanDisease not reported    OIE, 2009 
SwazilandPresent    OIE, 2012; OIE, 2004a 
TanzaniaLast reported2006   OIE, 2012 
TogoNo information available    OIE, 2009 
TunisiaLast reported1966   OIE, 2012 
UgandaDisease never reported    OIE, 2012 
ZambiaNo information availableNULL   OIE, 2012; OIE, 2004b 
ZimbabweLast reported2004   OIE, 2012 

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 Hosts/Species Affected

A proven vector of the disease is Culicoides imicola (Mellor and Boorman, 1995). Other Culicoides spp., notably C. bolitinos may also play a role in transmission (Venter et al., 2000; Meiswinkel and Paweska, 2003).

Usual hosts of the disease include horses, mules, donkeys and zebra. Other occasional hosts include elephants, camels, and dogs (after eating infected blood or horsemeat).

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Host Animals

Animal name Context 
Camelus bactrianus (Bactrian camel) Domesticated host 
Camelus dromedarius (dromedary camel) Domesticated host 
Canis familiaris (dogs) Domesticated host, Wild host 
Elephantidae Wild host 
Equus asinus (donkeys) Domesticated host, Wild host 
Equus caballus (horses) Domesticated host, Wild host 
Mules Domesticated host 

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Pathology

The pulmonary form of the disease gives oedematous lungs, with abundant serous fluid present in the pleural cavity and occasionally in the pericardium. Affected animals also get enlarged thoracic and abdominal lymph nodes. There are petechial haemorrhages in the mucosa and serosa of the small and large intestines and pericardium. The renal cortex becomes congested and hyperaemic glandular fundus of the stomach occurs.

In the cardiac form of the disease, haemorrhages in the epicardium, myocardium and endocardium can be seen along the coronary vessels and beneath the bicuspid and tricuspid valves.

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Diagnosis

Differential diagnosis should include Anthrax, equine infectious anaemia, equine viral arteritis, trypanosomosis, equine encephalosis, piroplasmosis and purpura haemorrhagica.

Laboratory diagnosis

Virus isolation can be achieved by suckling mice or cell cultures. Virus identification is carried out using ELISA, virus neutralisation (Serotyping) and PCR. Serological diagnosis is carried out using ELISA, complement fixation tests and immunoblotting.

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Disease Course

Mortality rates are 50-95% (horses), 50% (mules) and 10% (donkeys). There are four classical forms of AHS, pulmonary (acute), cardiac (subacute), mixed, and horse sickness fever (House, 1992).

The acute (pulmonary) form is characterized by a fever (40-41°C) after an incubation period of 3-5d. This is accompanied by dyspnoea when the respiratory rate may increase to 60-75 breaths/minute. Animals also experience spasmodic coughing, have dilated nostrils with frothy fluid oozing out and redness of the conjunctivae. Animals often die from anoxia within 1 week (more than 95% cases).

The subacute (cardiac) form is characterized by a fever (39-41°C) following an incubation period of 7-14 d. Infected animals also experience swelling of the supraorbital fossa, eyelids, facial tissues, neck, thorax, brisket and shoulders. The animal finally becomes restless and may show signs of colic before death from cardiac failure, usually within 1 week (50% of cases). In recovering cases, swelling gradually subsides within a period of 3-8 days.

The mixed form (cardiac and pulmonary) of the disease occurs frequently and has an incubation period of 5-7 d. It is characterized by mild pulmonary signs that do not progress, oedematous swellings and effusions. Again, in more than 80% of cases, death from cardiac failure occurs, usually within 1 week. In the subclinical form ('Horse sickness fever') a fever (40-40.5°C) occurs following an incubation period of 5-14 days and a general malaise for 1-2 days is observed. Conjunctivae may be slightly congested, the pulse rate increased, and a certain degree of anorexia and depression may be present. A fifth, nervous form of the disease may occur, but this is rare.

Lesions

In the pulmonary form of the disease, oedema of the lungs, hydropericardium, pleural effusion, oedema of thoracic lymph nodes and petechial haemorrhages in the pericardium occur. With the cardiac form, subcutaneous and intramuscular gelatinous oedema, epicardial and endocardial ecchymoses, myocarditis, haemorrhagic gastritis are observed.

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Disease Treatment Table

DrugDosage, administration and withdrawal timesLife stagesAdverse affectsDrug resistanceType
African horse sickness virus vaccine A polyvalent and monovalent live vaccine are most used. Minimum immunization of 1000 PFU/dose. Two vaccinations, at 21 day intervals are recommended. Annual revaccination is advised. All Stages None have been reported. No Vaccine 

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Vaccines

VaccineDosage, Administration and Withdrawal TimesLife StagesAdverse Affects
African horse sickness virus vaccine A polyvalent and monovalent live vaccine are most used. Minimum immunization of 1000 PFU/dose. Two vaccinations, at 21 day intervals are recommended. Annual revaccination is advised. -Other: All Stages None have been reported. 

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Prevention and Control

Vaccines

Vaccines are used against African horse sickness in sub-Saharan Africa, where the disease is endemic. There are vaccines for all 9 serotypes of African horse sickness virus. These are either cell culture adapted or mouse brain attenuated and provide long-lasting protection. Inactivated vaccines are not readily available. As there are concerns over the use of live vaccines, the development of efficacious vaccines, suitable for use in both endemic and non-endemic regions is an important focus of research (MacLachlan et al., 2007).

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References

African Union-Interafrican Bureau for Animal Resources, 2011. Panafrican Animal Health Yearbook 2011. Pan African Animal Health Yearbook, 2011:xiii + 90 pp. http://www.au-ibar.org/pan-african-animal-health-yearbook

Calvo JH, Calvete C, Martinez-Royo A, Estrada R, Miranda MA, Borras D, Sarto i Monteys V, Pages N, Delgado JA, Collantes F, Lucientes J, 2009. Variations in the mitochondrial cytochrome c oxidase subunit I gene indicate northward expanding populations of Culicoides imicola in Spain. Bulletin of Entomological Research, 99(6):583-591. http://journals.cambridge.org/action/displayAbstract?fromPage=online&aid=6545284&next=true&jid=BER&volumeId=99&issueId=06

Coetzer JAW, Guthrie AJ, 2004. African horsesickness. In: Infectious Diseases of Livestock, Second Edition [ed. by Coetzer, J. A. W. \Tustin, R. C.]. Cape Town, South Africa: Oxford University Press, 1231-1246.

Dardiri AH, Brown CC, 1989. African horse sickness update. In: 11th International Symposium of the World Association of Veterinary Microbiologists, Immunologists and Specialists in Infectious Diseases, Perugia, Mantova, Italy, October 2-6, 1989. 40131 Bologna, Italy: Società Editrice Esculapio, 287-289.

Dufour B, Moutou F, Hattenberger AM, Rodhain F, 2008. Global change: impact, management, risk approach and health measures - the case of Europe. Revue Scientifique et Technique - Office International des Épizooties, 27(2):541-550.

El-Husseini MM, Salama SA, Abdallah SK, Bakr HEA, Hassanein MM, 1986. Role of Culex pipiens L. in recovering latent African horse sickness virus from dogs. Journal of the Egyptian Society of Parasitology, 16(1):249-258.

Hamblin C, Salt JS, Mellor PS, Graham SD, Smith PR, Wohlsein P, 1998. Donkeys as reservoirs of African horse sickness virus. In: African horse sickness [ed. by Mellor, P. S.\Baylis, M.\Hamblin, C.\Calisher, C. H.\Mertens, P. P. C.]. Vienna, Austria: Springer-Verlag, 37-47.

House C, 1992. African Horse Sickness. In: Castro AE, Heuschele WP, eds., Veterinary Diagnostic Virology. Mosby Year Book, 165-159.

MacLachlan NJ, Balasuriya UB, Davis NL, Collier M, Johnston RE, Ferraro GL, Guthrie AJ, 2007. Experiences with new generation vaccines against equine viral arteritis, West Nile disease and African horse sickness. Vaccine [4th International Veterinary Vaccines and Diagnostic Conference, Oslo, Norway, 25-29 June 2006.], 25(30):5577-5582. http://www.sciencedirect.com/science/journal/0264410X

Meiswinkel R, Paweska JT, 2003. Evidence for a new field Culicoides vector of African horse sickness in South Africa. Preventive Veterinary Medicine, 60(3):243-253.

Mellor PS, 1992. Culicoides as potential orbivirus vectors in Europe. In: Bluetongue, African horse sickness, and related orbiviruses: Proceedings of the Second International Symposium [ed. by Walton, T. E.\Osburn, B. I.]. Boca Raton, Florida, USA: CRC Press, Inc., 278-283.

Mellor PS, 1993. African horse sickness: transmission and epidemiology. Veterinary Research, 24(2):199-212.

Mellor PS, Boorman J, 1995. The transmission and geographical spread of African horse sickness and bluetongue viruses. Annals of Tropical Medicine and Parasitology, 89(1):1-15; 6 pp. of ref.

Mellor PS, Hamblin C, 2004. African horse sickness. Veterinary Research, 35(4):445-466.

Meyden CHvan der, Erasmus BJ, Swanepoel R, Porzesky OW, 1992. Encephalitis and chorioretinitis associated with neurotropic African horsesickness virus infection in laboratory workers. Part I. Clinical and neurological observations. South African Medical Journal, 81(9):451-454.

OIE Handistatus, 2002. World Animal Health Publication and Handistatus II (dataset for 2001). Paris, France: Office International des Epizooties.

OIE Handistatus, 2003. World Animal Health Publication and Handistatus II (dataset for 2002). Paris, France: Office International des Epizooties.

OIE Handistatus, 2004. World Animal Health Publication and Handistatus II (data set for 2003). Paris, France: Office International des Epizooties.

OIE, 2004. African horse sickness in Swaziland. Disease Information, 17(21).

OIE, 2004. African horse sickness in Zambia. Disease Information, 17(19).

OIE, 2005. World Animal Health Publication and Handistatus II (data set for 2004). Paris, France: Office International des Epizooties.

OIE, 2009. World Animal Health Information Database - Version: 1.4. World Animal Health Information Database. Paris, France: World Organisation for Animal Health. http://www.oie.int

OIE, 2012. World Animal Health Information Database. Version 2. World Animal Health Information Database. Paris, France: World Organisation for Animal Health. http://www.oie.int/wahis_2/public/wahid.php

Sailleau C, Hamblin C, Paweska JT, Zientara S, 2000. Identification and differentiation of the nine African horse sickness virus serotypes by RT-PCR amplification of the serotype-specific genome segment 2. Journal of General Virology, 81(3):831-837.

Sánchez-Vizcaíno JM, 2004. Control and eradication of African horse sickness with vaccine. In: Control of infectious animal diseases by vaccination [ed. by Schudel, A.\Lombard, M.]. Basel, Switzerland: S Karger AG, 255-258.

Theiler A, 1906. Transmission of horse sickness into dogs. Report of the Government Veterinary Bacteriologist. 160-162.

Venter GJ, Graham SD, Hamblin C, 2000. African horse sickness epidemiology: vector competence of South African Culicoides species for virus serotypes 3, 5 and 8. Medical and Veterinary Entomology, 14(3):245-250.

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Links to Websites

 

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OIE Reference Experts and Laboratories

(http://www.oie.int, accessed 5 June 2013)

Dr Baratang Alison Lubisi
Onderstepoort Veterinary Institute
Agricultural Research Council
Private Bag X05
Onderstepoort 0110
SOUTH AFRICA
Tel: +27-12 529 91 17 Fax: +27-12 529 94 18
Email: This email address is being protected from spambots. You need JavaScript enabled to view it.

Dra. Concepción Gómez-Tejedor (1)
Ministerio de Agricultura, Alimentación y Medico Ambiente
S.G. Sanidad e Higiene Animal y Trazabilidad
LCV-Algete, Ctra. Algete Km 8
28110 Algete (Madrid)
ESPAÑA
Tel: +34-913 47 83 24 Fax: +34-913 47 82 99
Email: This email address is being protected from spambots. You need JavaScript enabled to view it.

Dr José Manuel Sánchez-Vizcaíno (2)
Centro de Vigilancia Sanitaria Veterinaria (VISAVET)
Facultad de Veterinaria
HCV Planta sótano
Universidad Complutense de Madrid (UCM)
Avda Puerta de Hierro s/n
28040 Madrid
ESPAÑA
Tel: +34-91 394.40.82 Fax: +34-91 394.39.08
Email: This email address is being protected from spambots. You need JavaScript enabled to view it.

Dr Javier Castillo-Olivares
Institute for Animal Health
Ash Road, Pirbright
Woking, Surrey, GU24 0NF
UNITED KINGDOM
Tel: +44-1483 23 24 41 Fax: +44-1483 23 24 48
Email: This email address is being protected from spambots. You need JavaScript enabled to view it.

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Images

A horse infected with African horse sickness virus (subacute, cardica form): oedema of the supraorbital fossa. © Philip Mellor/Institute for Animal Health, Pirbright, UKA horse infected with African horse sickness virus (subacute, cardica form): oedema of the supraorbital fossa. © Philip Mellor/Institute for Animal Health, Pirbright, UK A horse infected with African horse sickness virus (acute, pulmonary form): excessive nasal discharge, which will be followed by death from anoxia. © Philip Mellor/Institute for Animal Health, Pirbright, UKA horse infected with African horse sickness virus (acute, pulmonary form): excessive nasal discharge, which will be followed by death from anoxia. © Philip Mellor/Institute for Animal Health, Pirbright, UK 
    
 Foam from the nares is due to pulmonary oedema. © USDA, 2002. Foreign Animal Diseases Training Set. USDA - Animal & Plant Health Inspection ServiceFoam from the nares is due to pulmonary oedema. © USDA, 2002. Foreign Animal Diseases Training Set. USDA - Animal & Plant Health Inspection Service Depressed horse; note the bilateral supraorbital oedema. © USDA, 2002. Foreign Animal Diseases Training Set. USDA - Animal & Plant Health Inspection ServiceDepressed horse; note the bilateral supraorbital oedema. © USDA, 2002. Foreign Animal Diseases Training Set. USDA - Animal & Plant Health Inspection Service
    
Congestion and oedema of the conjunctiva. Congestion is a consistent clinical finding in AHS. © USDA, 2002. Foreign Animal Diseases Training Set. USDA - Animal & Plant Health Inspection ServiceCongestion and oedema of the conjunctiva. Congestion is a consistent clinical finding in AHS. © USDA, 2002. Foreign Animal Diseases Training Set. USDA - Animal & Plant Health Inspection Service 	Excessive fluid in the thoracic cavity and pulmonary oedema; note the distended interlobular septa. © USDA, 2002. Foreign Animal Diseases Training Set. USDA - Animal & Plant Health Inspection Service Excessive fluid in the thoracic cavity and pulmonary oedema; note the distended interlobular septa. © USDA, 2002. Foreign Animal Diseases Training Set. USDA - Animal & Plant Health Inspection Service
  
Cut surface of an oedematous lung; note the distended interlobular septa. © USDA, 2002. Foreign Animal Diseases Training Set. USDA - Animal & Plant Health Inspection ServiceCut surface of an oedematous lung; note the distended interlobular septa. © USDA, 2002. Foreign Animal Diseases Training Set. USDA - Animal & Plant Health Inspection ServicePetechial haemorrhages on the serosa are indicative of a viremic or septicemic condition. © USDA, 2002. Foreign Animal Diseases Training Set. USDA - Animal & Plant Health Inspection ServicePetechial haemorrhages on the serosa are indicative of a viremic or septicemic condition. © USDA, 2002. Foreign Animal Diseases Training Set. USDA - Animal & Plant Health Inspection Service
  
Petechial haemorrhages on the diaphragm are indicative of a viremic or septicemic condition. © USDA, 2002. Foreign Animal Diseases Training Set. USDA - Animal & Plant Health Inspection ServicePetechial haemorrhages on the diaphragm are indicative of a viremic or septicemic condition. © USDA, 2002. Foreign Animal Diseases Training Set. USDA - Animal & Plant Health Inspection ServicePathology. Pericardium. © USDA, 2002. Foreign Animal Diseases Training Set. USDA - Animal & Plant Health Inspection ServicePathology. Pericardium. © USDA, 2002. Foreign Animal Diseases Training Set. USDA - Animal & Plant Health Inspection Service
  
Supraorbital oedema. © USDA, 2002. Foreign Animal Diseases Training Set. USDA - Animal & Plant Health Inspection ServiceSupraorbital oedema. © USDA, 2002. Foreign Animal Diseases Training Set. USDA - Animal & Plant Health Inspection Service 	Oedema in the intermuscular fascia of the neck may be the only lesion in AHS. © USDA, 2002. Foreign Animal Diseases Training Set. USDA - Animal & Plant Health Inspection Service Oedema in the intermuscular fascia of the neck may be the only lesion in AHS. © USDA, 2002. Foreign Animal Diseases Training Set. USDA - Animal & Plant Health Inspection Service
  

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Date of report: 22/05/2013

© CAB International 2013. Distributed under license by African Union – Interafrican Bureau for Animal Resources.

Creative Commons Attribution-NonCommercial-NoDerivs 3.0 Unported License

This work is licensed under a Creative Commons Attribution-NonCommercial-NoDerivs 3.0 Unported License.