Covering sickness

{{Short description|Disease of horses and other Equidae}} thumb|Mohler, John R., ''Dourine of horses – its cause and suppression'' (1911) '''Covering sickness''', or '''dourine''' (French, from the Arabic ''darina'', meaning mangy (said of a female camel), feminine of ''darin'', meaning dirty),<ref>{{cite web | title = Dourine | website = American Heritage Dictionary of the English Language: Fifth Edition | year = 2017| url = https://ahdictionary.com/word/search.html?q=dourine | accessdate = 2017-05-19 }}</ref> is a disease of horses and other members of the family Equidae. The disease is caused by ''Trypanosoma equiperdum'', which belongs to an important genus of parasitic protozoa.<ref name="Gillingwater">{{cite journal|last1=Gillingwater|first1=K.|last2=Büscher|first2=P.|last3=Brun|first3=R.|title=Establishment of a panel of reference ''Trypanosoma evansi'' and ''Trypanosoma equiperdum'' strains for drug screening|journal=Veterinary Parasitology|date=September 2007|volume=148|issue=2|pages=114–121|doi=10.1016/j.vetpar.2007.05.020|pmid=17624671}}</ref> The occurrence of dourine is notifiable in the European Union under legislation from the OIE.<ref name="2020 Codes of Practice">{{cite book|title=Codes of Practice 2020|url=https://codes.hblb.org.uk/downloads/2020/Codes%20of%20Practice%202020%20Complete.pdf|publisher=Horserace Betting Levyboard|accessdate=24 May 2022|pages=59–65|archive-date=4 April 2022|archive-url=https://web.archive.org/web/20220404175031/https://codes.hblb.org.uk/downloads/2020/Codes%20of%20Practice%202020%20Complete.pdf|url-status=live}}</ref> There currently is no vaccine and although clinical signs can be treated,<ref name="Gillingwater" /> there is no cure.<ref name=Hagos/>

== Parasite == thumb|''Trypanosoma equiperdum'' Out of the ''Trypanosoma'' genus, ''Trypanosoma equiperdum'' has been discovered to be most closely linked to ''Trypanosoma evansi'', so much so that even observation under microscope is not sufficient to differentiate between the two as their structure is very similar.<ref name=Brun1998>{{cite journal|last1=Brun|first1=Reto|last2=Hecker|first2=Hermann|last3=Lun|first3=Zhao-Rong|title=''Trypanosoma evansi'' and ''T. equiperdum'': distribution, biology, treatment and phylogenetic relationship (a review)|journal=Veterinary Parasitology|date=October 1998|volume=79|issue=2|pages=95–107|doi=10.1016/S0304-4017(98)00146-0|pmid=9806490}}</ref>

Dourine has no known vectors or fomites existing in the natural world, being known only as a sexually transmitted disease of members of the equine family, including donkeys, mules, and horses.<ref name="Gillingwater" /> In a laboratory setting, ''Trypanosoma equiperdum'' has been manipulated to adapt to and proliferate in other species, such as dogs, rabbits, mice and rats, but this has never been observed to occur naturally.<ref name="Hagos"/> Although this limits spread of the disease because it is restricted to the equine population alone, the organism has developed complex mechanisms over time to better equip itself for prolonged survival in the equine species. As normal for its genus, the parasite efficiently evades the host animal's immune system through the use of variable surface glycoproteins or VSGs.<ref name="Raibaud">{{cite journal|last1=Raibaud|first1=A|last2=Gaillard|first2=C|last3=Longacre|first3=S|last4=Hibner|first4=U|last5=Buck|first5=G|last6=Bernardi|first6=G|last7=Eisen|first7=H|title=Genomic environment of variant surface antigen genes of ''Trypanosoma equiperdum''|journal=Proceedings of the National Academy of Sciences of the United States of America|date=July 1983|volume=80|issue=14|pages=4306–10|pmid=6308614|pmc=384026|doi=10.1073/pnas.80.14.4306|bibcode=1983PNAS...80.4306R|doi-access=free}}</ref> These VSGs allow the organism to constantly manipulate and change the surface structure of its proteins, which means it is constantly being presented to the immune system as a new foreign organism and this prevents the body from mounting a large enough immune response to eradicate the disease.<ref name="Raibaud" /> ==Transmission and symptoms== Dourine is spread venereally,<ref name=Gizaw>{{Cite journal|title=Dourine: a neglected disease of equids|first1=Yonas|last1=Gizaw|first2=Mulisa|last2=Megersa|first3=Teka|last3=Fayera|journal=Tropical Animal Health and Production |year=2017 |volume=49 |issue=5 |pages=887–897 |doi=10.1007/s11250-017-1280-1 |pmid=28439783 |pmc=5432633 }}</ref> and causes disc-shaped<ref name=Tibary /> lesions of the reproductive organs, nervous system and skin,<ref name=Gizaw /> acute inflammation and edema of the genitals, followed by hindlimb paralysis, paraplegia and death in more than fifty percent of cases.<ref name=Tibary>{{Cite book|title=Equine Infectious Diseases|chapter=Chapter 8 - Reproductive Tract Infections|first1=Ahmed|last1=Tibary|first2=Lisa K.|last2=Pearson|first3=Cheryl L.|last3=Fite|edition=Second }}</ref><ref name="2020 Codes of Practice"/>

==Treatment== Because this disease is highly durable in its equine host, it has proved very difficult to develop a vaccine for it. There are four main drugs on the market that are used to treat the clinical signs of dourine: Suramin, Diminazen, Cymerlarsan, and Quinapyramin.<ref name="Gillingwater" /><ref>{{cite web|last=Merck Veterinary Manual|title=Trypanosomiasis|url=http://www.merckvetmanual.com/circulatory-system/blood-parasites/trypanosomiasis|accessdate=19 May 2017}}</ref> However, none of the listed drugs is a cure and even the individual animals that are treated will experience relapses.<ref name=Hagos>{{cite journal|last1=Hagos|first1=A|last2=Goddeeris|first2=BM|last3=Yilkal|first3=K|last4=Alemu|first4=T|last5=Fikru|first5=R|last6=Yacob|first6=HT|last7=Feseha|first7=G|last8=Claes|first8=F|title=Efficacy of Cymelarsan and Diminasan against ''Trypanosoma equiperdum'' infections in mice and horses|journal=Veterinary Parasitology|date=4 August 2010|volume=171|issue=3–4|pages=200–6|doi=10.1016/j.vetpar.2010.03.041|pmid=20417035}}</ref> Although this disease is not fatal in all cases and spontaneous recovery can occur, the death rate is relatively high and listed at a mortality rate of over fifty percent.<ref name="2020 Codes of Practice"/>

This lack of a cure or vaccine is a definite problem in the equine industry, especially in developing countries where equines are highly valuable for both agriculture and transportation.<ref name="Brun1998" /> Dourine is considered an endemic problem in developing countries, where over sixty percent of equines in the world are located.<ref name="Hagos" /> The protocol for this disease, as stated by OIE, currently stands at slaughter of seropositive animals.<ref>{{Cite web|url=https://www.oie.int/app/uploads/2021/03/dourine-1.pdf|title=OIE Technical Disease Card: Dourine}}</ref> This is not an economically feasible option for many people who depend on horses for their livelihood. Therefore, it is crucial to continue research in this field and develop a viable vaccine.

==References== {{Reflist}}

==External links== * {{MeshName|Dourine}} *[http://www.oie.int/wahis_2/public/wahid.php/Diseaseinformation/Diseasehome Current status of Covering sickness worldwide] at OIE. WAHID Interface - OIE World Animal Health Information Database *[http://www.oie.int/en/animal-health-in-the-world/technical-disease-cards/ Disease card]

Category:Horse diseases Category:Horse breeding and studs Category:Theriogenology Category:Veterinary protozoology