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The Veterinary Journal 172 (2006) 402–404

TheVeterinary Journal

Guest editorial

Epizootic lymphangitis:The impact on subsistence economies and animal welfare

Epizootic lymphangitis (EL) (also known as equine his-toplasmosis) is a contagious, chronic disease of horses andother Equidae characterised clinically by a spreading, sup-purative, ulcerating pyogranulomatous dermatitis andlymphangitis. It can also present as an ulcerating conjunc-tivitis, or multifocal pneumonia. Transmission is by con-tact of infected material with traumatised skin, bitingflies, or inhalation. The causative agent, Histoplasma cap-

sulatum var. farciminosum (HCF), is a dimorphic fungalsoil saprophyte. Differential diagnoses include glanders(farcy), ulcerative lymphangitis due to Corynebacterium

pseudotuberculosis, sporotrichosis, and the skin lesions ofhistoplasmosis caused by Histoplasma capsulatum var.capsulatum.

Previously an Office International des Epizooties (OIE)List B disease, EL is no longer listed as notifiable (OIE,2004), although the disease is still present in many partsof the world and is endemic in North Africa, the MiddleEast and parts of Asia. The Veterinary Journal has recentlypublished a small series of papers on EL from Ethiopia, thelatest of which, on the reproducibility of EL through exper-imental infection of two horses, is published in this issue(Ameni, 2006b).

In an earlier paper on the epidemiology of the disease,Ameni (2006a) recorded the prevalence of EL in carthorsesin 28 towns in different climactic zones of Ethiopia. Theoverall prevalence was 18.8% (range 0–39%) in line witha previous paper that reported a prevalence of 26.2%(Ameni and Siyoum, 2002) and a study in mules that founda prevalence of 21% (Ameni and Terefe, 2004). A higherprevalence was observed in towns in mid-altitude regionsbetween 1500 and 2300 m above sea level – an associationthat was found to be statistically significant. An increasinghorse population in a town was also associated with an in-creased prevalence of EL. A statistically significant associ-ation was also found between prevalence and averageannual temperature, but not with mean annual rainfall.Ameni (2006a) concluded that EL was prevalent in hotand humid towns between 1500 and 2300 m above sea leveland that in Ethiopia the disease requires a control strategy.

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The Society for the Protection of Animals Abroad(SPANA) works in Ethiopia and other countries in NorthAfrica and the Middle East. In Ethiopia, we encounter ELon a daily basis in taxi horses in five major towns. In 2005,of 9000 horses examined for treatment or preventive care,432 cases of EL were identified, with most being seen inthe months November to January following the long rains,possibly coinciding with the peak fly breeding season. Inour experience, the disease occurs in horses and mules, withdonkeys seemingly more resistant. The importance of taxihorses to the people that work with them is critical, andthe impact of EL on poor families, as well as in terms ofanimal welfare is devastating.

Diagnosis of EL in Ethiopia is based on clinical recogni-tion of lesions and microscopic examination of the yeastforms of HCF in pus. Elsewhere, serological and skinhypersensitivity tests have also been tried (Soliman et al.,1985). Dr Ameni and his colleagues, Woldu Terefe and As-rat Hailu, have looked at the development and field valida-tion of the histofarcin test in Ethiopia (Ameni et al., 2006)where histofarcin is produced locally from the mycelialform of HCF and the antigen prepared and quantified.Following a pilot trial to determine the optimum concen-tration of histofarcin required, field validation was carriedout in endemic and non-endemic areas. Eighty-one muleswere used, some affected clinically by EL and others clini-cally healthy. The sensitivity of the test was found to be90.3%, but specificity in endemic areas was only 69%. Itwas felt that the large number of false positives found inendemic areas may be due to preclinical stages of the infec-tion causing skin sensitisation to histofarcin. The authorsacknowledged that there is a need for further study, usingslaughter and isolation of tested animals in order to have a‘‘gold standard’’ for comparison and to obtain more accu-rate sensitivity and specificity values.

Control of EL, once diagnosed, is problematic. Treat-ment is often said to be unsuccessful (Morrow, 1990) butintravenous sodium iodide, oral potassium iodide (KI),excision of lesions, topical treatments and administrationof modern antifungal compounds have all been attempted,

Guest editorial / The Veterinary Journal 172 (2006) 402–404 403

either alone or in combination, in various countries. Somecases may heal spontaneously without treatment a fewweeks after the appearance of clinical signs (Al-Ani,1999) and these animals are reputedly immune for life – abelief which has led in endemic areas to a premium beingplaced on horses with characteristic EL scars. This beliefhas not, however, been confirmed and recurrence mayoccur up to a year later.

SPANA has tried several treatment protocols in the fieldin Ethiopia (Getachew, 2004) and the following regime isnow applied to early stage EL cases presented:

� On the initial day of presentation the animal is sedated,all nodules incised and treated with topical 4% tinctureof iodine. KI in solution is given by stomach tube(30 g for a horse of 200–250 kg).� Ideally cases are seen daily, nodules treated topically

and any new lesions incised.� Oral KI is given at the same dose daily for 5 days and

then every other day for a further 3–4 weeks, or for aslong as there is owner compliance.

Signs of iodism are rarely encountered. Most animalsunder treatment continue to work as taxi horses, despitethe clinical team’s efforts at persuading owners to rest themor allow hospitalisation. Understandably, completion of atreatment regime is often difficult, and we now commonlygive KI in weighed sachets for the owners to administerthemselves, mixed with feed. It appears to be palatable,particularly in horses that are rarely provided with hardfeed.

The use of antifungal preparations in Ethiopia iscurrently limited by financial constraints, as well as thepractical problems of sourcing and administration.Amphotericin B has been used successfully in other areas(Al-Ani, 1999), but more modern antifungal agents mayturn out to be more effective.

Controlling EL depends upon elimination of the infec-tion by culling infected horses, and preventing spread bygood hygiene practices (Al-Ani, 1999). The disease waseradicated from the UK by 1906 and, in non-endemicareas, slaughter of affected animals is recommended. How-ever, in an endemic country like Ethiopia where socio-eco-nomic conditions are poor, a slaughter and eradicationpolicy would neither be acceptable nor enforceable. So,SPANA in Ethiopia concentrates on educating owners topresent cases early for treatment and advises on basic hy-giene of harnessing and equipment and fly control. Weadvocate euthanasia in advanced cases. The lack of locallyavailable disinfectants or antiseptics with known effectiveanti fungal properties has prompted us to try productsbrought from the UK, although we also use what is avail-able in the country such as kerosene washes for flyprevention.

Attempts at production and use of a vaccine forequine histoplasmosis have been tried in the past. A livevaccine tested in China was reported to protect 75.5% of

animals inoculated, with immunity persisting for morethan two years (Zhang et al., 1986). Other evidence ofvaccine use is scarce, but more work is urgently neededas an important part of disease control. As reported inthis issue, Ameni (2006b) carried out a preliminary trialon the reproducibility of EL through the experimentalinfection of two horses. One was infected with the yeastform of (HCF) and the other with the mycelial form;both horses subsequently showed clinical and microscopicevidence of the disease. This experiment was undertakenas a necessary step in future evaluation of the potencyof a vaccine against EL using a vaccination and challengeexperiment.

The series of papers presented by Dr Ameni and hiscolleagues takes our knowledge of this debilitating,chronic and economic disease forward. There is plentymore to be done to fill in the information gaps – in partic-ular there is a need for further epidemiological studies.The taxi horses in Ethiopia are highly mobile, usuallyborn in the highlands (EL free areas), and work as ridingor farm work horses before being sold to dealers whotransport them (usually on the hoof) to lower altitudeswhere they end up as taxi horses. They may then bebought and sold many times. Getting an accurate historyof these animals when presented is unreliable, but it isimportant to try to obtain a clearer picture of their move-ments and the effect on disease spread. Natural immunity,recovered immunity and vaccination potential are alsocritical areas for investigation. Further refinement of sim-ple, field-based, affordable, diagnostic tests is certainly re-quired and treatment with modern antifungal drugs needsto be tested.

Gobena Ameni and his colleagues are to be congratu-lated for boosting the knowledge base on EL and so help-ing to find solutions to a disease that can have adevastating effect on the livelihood of economically chal-lenged horse owners in Ethiopia and elsewhere.

Karen JonesSociety for the Protection of Animals Abroad (SPANA),

14, John Street, London, WC1N 2EB,

UK

E-mail address: Karen@spana.org

References

Al-Ani, F.K., 1999. Epizootic lymphangitis: literature review. RevueScientifique et Technique 18, 691–699.

Ameni, G., 2006a. Epidemiology of equine histoplasmosis (epizooticlymphangitis) in carthorses in Ethiopia. The Veterinary Journal 172,160–165.

Ameni, G., 2006b. Preliminary trial in the reproducibility of epizooticlymphangitis through experimental infection of two horses. TheVeterinary Journal 172, 553–555.

Ameni, G., Siyoum, F., 2002. Study on histoplasmosis (epizooticlymphangitis) in three towns of central Ethiopia. Journal of VeterinaryScience 3, 135–139.

404 Guest editorial / The Veterinary Journal 172 (2006) 402–404

Ameni, G., Tefere, W., 2004. A cross-sectional study of epizooticlymphangitis in cart-mules in western Ethiopia. Preventive VeterinaryMedicine 66, 93–99.

Ameni, G., Terefe, W., Hailu, A., 2006. Histofarcin test for the diagnosis ofepizootic lymphangitis in Ethiopia: development, optimisation, andvalidation in the field. The Veterinary Journal 171, 358–362.

Getachew,A.,2004.Clinicaltrialofiodidescombinedwithancillarytreatmenton epizootic lymphangitis in carthorses at Debre Zeit and Akaki towns.DVM Thesis, Faculty of Veterinary Medicine, Addis Ababa University.

Morrow, A.N., 1990. Epizootic lymphangitis. In: Sewell, M.M.H.,Brocklesby, D.W. (Eds.), Animal Disease in the Tropics. BailliereTindall, London, pp. 364–367.

Office Internationale des Epizooties, 2004. ‘Epizootic Lymphangitis’Manual of Diagnostic Tests and Vaccines for Terrestrial Animals,2.5.13. Available at: <http://www.oie.int/eng/normes/mmanual/A_00091.htm/> (accessed 21.05.06).

Soliman, R., Saad, M.A., Refai, M., 1985. Studies of histoplasmosisfarciminosii (epizootic lymphangitis) in Egypt III. Application for askin test (Histofarcin) in the diagnosis of epizootic lymphangitis inhorses. Mykosen 28, 457–461.

Zhang, W.T., Wang, Z.R., Liu, Y.P., Zhang, D.L., Liang, P.Q., Fang,Y.J., Huang, Y.J., Gao, S.D., 1986. Attenuated vaccine againstepizootic lymphangitis of horses. Chinese Journal of VeterinaryScience and Technology 7, 7.