Review on Epizootic
Lymphangitis: Epidemiology and its Diagnosis
Ahmed Seid*, Mohammed Fedlu and Amana Mama
School of Veterinary Medicine, Wolaita Sodo University, Ethiopia
Submission: May 11, 2019; Published: May 29, 2019
*Corresponding author: Ahmed Seid, School of Veterinary Medicine, Wolaita Sodo University, Wolaita Sodo, Ethiopia
How to cite this article: Ahmed Seid, Mohammed Fedlu and Amana Mama. Review on Epizootic Lymphangitis: Epidemiology and its Diagnosis. Dairy and Vet Sci J. 2019; 12(1): 555830. DOI: 10.19080/JDVS.2019.12.555830
Epizootic lymphangitis is a contagious fungal disease principally of equines that results from infection by a dimorphic fungus, Histoplasma capsulatum var. farciminosum. The disease commonly develops into a chronic debilitating condition that can manifest itself in one of three clinical forms: cutaneous, ocular and respiratory forms. The disease is primarily an ulcerating, suppurative, pyogranulomatous dermatitis and in most cases lymphangitis. Epizootic lymphangitis is a relatively common infectious disease of horses and other equids in certain parts of the world. The infection rate of EPL varies with the geographic area and the age of the animal. The disease has the potential to significantly impact the health and welfare of equids in countries in which it is endemic. EPL is second only to African Horse Sickness as a most important disease of horses in Ethiopia. The wounds caused by harness are reported as major predisposing factors of EPL in carthorses in Ethiopia. Currently, due to limited available diagnostic technologies, veterinarians in Ethiopia diagnose the disease based on clinical appearance and microscopic examination for yeast cells within pus. This has the potential for misdiagnosis, as the clinical appearance can mimic that of other diseases. Diagnosis is possible by direct visualization of the yeast form of the fungus in pus from infected lymphatic nodules and by culture or histopathologic examination of tissues from clinically affected cases. It is also possible to visualize the organism in stained histological sections of matured or developing lesions. EPL is an economically important disease in some areas of the world, particularly where large numbers of horses, donkeys, or mules are assembled. Different treatment modalities are available some of which are successful in treating early cases of the disease. Effective prevention and control of epizootic lymphangitis is based on euthanizing infected equids and the application of strict biosecurity measures.
Keywords: Epizootic lymphangitis; H. capsulatum var. farsiminosum; Equines; Epidemiology; Diagnosis
Abbrevations: CDC: Center for Disease Control; CFSPH: Center for Food Security and Public Health; CO2: Carbon Dioxide; DACA: Drug Administration and Control Agency; EPL: Epizootic Lymphangitis; H&E: Haematoxylin and Eosin; HCD: Histoplasma Capsulatum Variety Duboisii; HCF: Histoplasma Capsulatum Variety Farciminosum; OIE: Office International Des Epizootics; SDA: Sabouraud‟s Dextrose Agar; SPANA: Society for the Protection of Animals Abroad
Equines have a prominent position in the countries agricultural and transport systems since the transportation activities are performed by equids . They are mainly used as draught and pack animals and they are also used for ploughing in some parts of the country. However, despite all these uses, equids have several diseases. One of such rampant diseases is epizootic lymphangitis . Epizootic lymphangitis is a debilitating fungal disease seen mainly in equids. The disease results from infection by a dimorphic fungus, Histoplasma capsulatum var. farciminosum. This organism has also been known as Histoplasma farciminosum, Cryptococcus farciminosum, Zymonema farciminosum and Saccharomyces farciminosum . HCF was formerly described as an independent species, but this assessment has been changed and it is now considered a variety of H. capsulatum due to the close morphological similarities of both the mycelial and yeast forms .The organism exists as yeast in animal tissues and a saprophytic mycelium in the environment .
The incidence of the disease increases with assembling of equids . The disease is primarily an ulcerating, suppurative, pyogranulomatous dermatitis and in most cases lymphangitis . It was seen commonly in the extremities along front and hind legs, chest wall, belly and the neck. Moreover, it can also be detected as an ulcerating conjunctivitis of the palpebral conjunctiva with excessive ocular serious discharge, or rarely as a multifocal pneumonia . The organism might also invade open fresh or non-fresh lesions including ruptured strangle‟s abscesses and male castrated wounds . The disease is more common in the tropical and subtropical regions, than in temperate areas . It is mostly diffused in areas characterized by humid and hot climates . Biting flies and ticks can also transmit the disease . The incubation period of epizootic lymphangitis is variable and it
has three forms: the cutaneous, the ocular and the pulmonary
depending on the route of entry . In a recent study, the
incubation period was much longer in a horse inoculated with
mycelial organisms than in a horse inoculated with the yeast form
. Diagnosis of EPL is based on clinical signs, laboratory tests
and isolation of the causative agent.
Many treatments have been tried largely without success.
The disease is rarely responding to treatment . Parenteral
Amphotericin B and iodides have been reported as effective .
Successful treatment with intravenous administration of sodium
iodide, oral administration of potassium iodide and surgical
excision of lesions are limited, since recurrences of clinical signs
months later is possible, Furthermore, in vitro sensitivity of the
organism to amphotericin B, nystatin and clotrimazole has been
reported However, in most areas, Epizootic Lymphangitis is a
notifiable disease, and treatment is not allowed thereby, diseased
animals must be forsaking . Epizootic lymphangitis can be
controlled or eradicated by quarantines and the euthanasia of
infected animals . Formularized aluminum hydroxide adsorbed,
and heat attenuated vaccines have been widely used apparently
with success . The importance of epizootic lymphangitis is
very considerable in countries in which it is prevalent not only
with respect to the chronic debilitating effects of the disease on
the health and welfare of affected animals but also on its socioeconomic
impact on their owners who are entirely dependent on
these animals for their livelihood and the support of their families
. Epizootic lymphangitis is reported to have a significant
impact upon livelihoods within resource poor settings .
Therefore, the objective of this seminar paper is:
a. To review epizootic lymphangitis: epidemiology and its
b. To highlight on the economic impacts of epizootic
Epizootic lymphangitis is a contagious fungal disease
principally of horses and other equids, which is responsible for
significant morbidity and debilitating illness in affected populations
of horses, mules and to a lesser extent, donkeys . The disease
was also being called pseudofarcy or pseudoglanders. Moreover,
another synonym is Equine histoplasmosis, Histoplasmosis,
Farciminosis, African farcy, Equine Blastomycosis and Equine
Cryptococcosis. It is clinically characterized by a spreading
suppurative inflammation of cutaneous lymphatic vessels, lymph
nodes and adjacent skin . This disease is a chronic infectious
granulomatous disease of the skin, lymph vessels and lymph nodes
of the neck and legs of horses and other equines . Epizootic
lymphangitis is among the top diseases of equids that have severe
economic and veterinary consequences in Ethiopia .
Epizootic lymphangitis results from infection by a dimorphic
fungus, Histoplasma capsulatum var. farciminosum . The
organism exists as yeast in animal tissues and saprophytic
mycelium in the environment . Not surprisingly, it can survive
in the environment for extended periods of time, for about a
month in dust or dirt and up to 10 weeks in non-sterile water.
Warm, moist conditions are believed to favor its survival .
Identification of the agent is made by its appearance in smears of
exudates or in histological sections of lesion material . The most
likely source of environmental contamination is pus discharging
from cutaneous lesions primarily on the limbs of affected animals
. It is also believed that ticks may play a good role in the
transmission of this agent .
Epizootic lymphangitis is endemic in some countries of west,
north and northeast Africa and Asia including India, Pakistan and
Japan, where it is mostly diffused in areas characterized by humid
and hot climates . It is most commonly reported from North
Africa and has been well documented in India . In the endemic
areas in certain regions of the world, the occurrence of seasonal
dusty winds exposes horses to the inhalation of dust and spores,
leading to pneumonia . The infection rate of EPL varies with
the geographic area and the age of the animal . Historically,
the disease was far more widely distributed than it is today, having
been introduced into many European countries in which it was
subsequently eradicated through implementation of a compulsory
slaughter policy .
Transmission: The mode of transmission of EPL includes
transmission by direct or indirect contact with traumatized
skin, by biting flies, by ticks or by inhalation of HCF . HCF is
introduced via open wounds . Spread of infection can also
occur by indirect contact through contaminated objects such as
grooming tools, feeding and watering utensils, and harnesses
and through wound dressings . Little evidence is available to
describe risk factors for EPL, such as factors favoring persistence of
the organism within the environment, the routes of transmission
and potential vectors .
The wounds caused by harness are reported as major
predisposing factors of EPL in carthorses in Ethiopia .
Experimentally, the disease can be transmitted by biting flies, e.g.
Musca and Stomoxys spp that feed on open, discharging lesions.
Flies may also transmit the skin form mechanically when they feed
on lesions and exudates .Fungal spores can be trans-mitted to
healthy animals by direct contact with infected animals or with
inanimate objects or fomites, such as grooming equipment,
bedding, saddler, etc., and enter the skin through cutaneous
Both the yeast form found in animals and the mycelial form
in the environment can produce epizootic lymphangitis after experimental inoculation. The source of the organisms can be the
skin lesions and nasal and ocular exudates of infected animals, or
the soil . Ticks (Amblyoma and Boophilus) may also be involved
in transmission. In a recent study, tick bites appeared to be a
predisposing factor for epizootic lymphangitis in mules .
Species Affected: Epizootic lymphangitis mainly affects
horses, donkeys and mules. H. capsulatum var. farsiminosum has
also been reported in camels, cattle and dogs, and experimental
infections have been established in mice, guinea pigs and rabbits
. Horses under six years of age are most susceptible . In
Africa, a third variety, which is known as Histoplasma capsulatum
var. Duboisii (HCD), is the cause of human Histoplasmosis .
Morbidity and Mortality: The incidence of this disease is
much higher when large numbers of animals are gathered together
than when populations are less dense . It causes considerable
debility but low mortality that doesn’t usually exceeds 10% to
15% . The main loss results from the inability of animals to
work for several weeks because of extremely painful lesions .
Death is uncommon if an animal is in good condition and receives
good care, but animals with extensive lesions may die .
Clinical signs of Epizootic lymphangitis are described based
on the pathological lesions; otherwise the body temperature
and general character of the animals are not changed. On the
other hand, most of the animals will lose their body condition
. There are three forms of the disease. The three forms are
cutaneous (skin), ocular and respiratory forms. The form that the
disease takes seems to depend primarily on the route of entry .
The most common form of epizootic lymphangitis affects the Skin
and lymphatic. It often occurs on the extremities, chest wall, face
and neck, but can be seen wherever the organism is inoculated
into a wound . The cutaneous form of the disease, after which
the disease was named, is the most common. The initial lesion is
an open granulomatous wound along the course of a lymphatic
vessel, which tends to ulcerate, or to undergo alternating periods
of discharge and closure for some weeks before healing with
residual scar formation . The disease is insidious in onset,
with a variable incubation lasting week to months. Clinically,
the disease is characterized by a chronic suppurative, ulcerating
pyogranulomatous dermatitis and lymphangitis. Severely affected
animals become anorexic, deteriorate in condition and where
there is joint involvement and lame  (Figure 1).
The ocular form of the disease results from inoculation of the
organism into the eye, likely by biting flies . It is less frequently
observed and very rarely becomes generalized . Initially,
infection is characterized by a watery ocular discharge that may
be unilateral or bilateral and variable swelling of the eyelids. This
leads to the appearance of papules and button-like growths on the
conjunctivae and nictitating membranes. The infection may extend
to the periorbital tissues with formation of a granulomatous
reaction. The secondary complications of the ocular form of the
disease include corneal ulceration, panopthalmitis and myiasis
 (Figure 2). Respiratory cases are thought to occur through
inhalation of the organism either as spores from the environment
or through extension of infection from the external mucous
membranes of the nares or from the naso-lachrymal duct. Nodules
can be present around the mucocutaneous junction of the nose
and at postmortem are commonly seen to extend from the nasal
passages, through the trachea and into the lung parenchyma .
At the hematological findings, leukocytosis, neutrophilia and an
increase in the erythrocyte sedimentation rates can be observed
. The lesions are usually found near the external nares. These
lesions may also occur in the lung. Affected animals develop a
viscous mucopurulent nasal discharge and may exhibit dyspnea.
Advanced cases exhibit progressive weakness, coughing and loss
of bodily condition  (Figure 3).
The diagnosis of EPL is based on the clinical examination of
the lesions, microscopic examination of the yeast form of HCF
in pus, serological tests and skin hypersensitivity testing .
Culture of the organism is necessary to confirm the presence
of Histoplasma species but this is not without difficulty as the
organism is slow growing and care must be taken to reduce
overgrowth by contaminants. It is preferable to aspirate a sample
from un-ruptured nodule after clipping and disinfecting the skin to
reduce contamination. It is also possible to visualize the organism
in stained histological sections of matured or developing lesions
. Inoculation of samples into immune suppressed mice can
also be used for diagnosis . Histofarcin, a skin test antigen for
the diagnosis of epizootic lymphangitis is locally produced from
the mycelial form of HCF in disease-endemic districts. Microscopic
and mycological examinations of clinical lesions should be used as
the „„gold standard‟‟ for the validation of this test .
Laboratory Diagnosis: Laboratory tests used in the diagnosis
of epizootic lymphangitis include: identification of the yeast
form of HCF in smears of exudates or in histological sections of
material from lesions, serological tests (i.e., fluorescent antibody
test, enzyme-linked immunosorbent assay and passive hem
agglutination tests), skin hyper sensitivity test and isolation of the
causative agent by culture . The organism in the tissues is in its
yeast form. It may be stained with Giemsa, Diff-Quick, or Gomori
methenamine silver .
Pus samples collected from un-ruptured nodules were used
for direct microscopic and mycological examinations. The nodules
were washed with soap and water, shaved, and disinfected with
alcohol. The contents of the nodules were aspirated with sterile
needles and syringes and used for the preparation of smears for
microscopic examination and isolation. The smears were fixed
with methanol, stained with Gram‟s stain. Samples of lesions that
include both viable and non-viable tissue should be collected in
10% neutral buffered formalin for histopathology. They should be
kept refrigerated and sent to the laboratory on wet ice as soon as
possible. Air–dried smears from exudates should be prepared on
glass slides and fixed immediately for direct examination . For
the identification of the yeast form of HCF examination was made
using oil immersion at 100 magnifications. In addition, material
was inoculated aseptically onto slants of Sabouraud‟s Dextrose
Agar (SDA, Oxoid) containing chloramphenicol (0.5 g/l) and
enriched with 2.5% glycerol. For the isolation of the mycelial form,
incubation was made at 26.8 °C and 5% CO2 and isolation of the
yeast form was made at 37.8 °C and 5% CO2 . The media were checked periodically and Gram-stained preparations were made
from suspicious growth. Sub-culturing was made in antibiotic-free
SDA slants of universal bottles.
Air–dried smears from exudates should be prepared on glass
slides and fixed immediately for direct examination . Before
collection of samples the nodules were washed with soap and
water, shaved, and disinfected with alcohol. The contents of the
nodules were aspirated with sterile needles and syringes and
used for the preparation of smears for microscopic examination.
The smears were fixed with methanol, stained with Giemsa stain
for the identification of the yeast form of HCF . Microscopic
examination of Giemsa or Gram-stained smears of pus/swabs
aspirated from a nodule reveal Gram- positive yeast forms with a
halo (unstained capsule-like) structure .
The lung tissue sample was taken from a nodular lesion on
the lung, it was grinded with pistol and mortar and inoculated
aseptically onto slants of Sabouraud‟s Dextrose Agar (SDA, Oxoid)
containing chloramphenicol (0.5g/ liter) and enriched with 2.5%
glycerol. Incubation was made at 26 0C and 5% CO2 for 8 weeks.
The media were checked periodically for the presence of growth of
mycelial form of HCF . Primary isolation of the mycelial forms
was obtained within 6–8 weeks as white to grayish white, folded,
raised cerebriform colonies on SDA. The colonies were adherent to
the medium and became brownish on aging. In Haematoxylin and
Eosin (H&E) stained histological sections, the appearance of the
lesions is quite characteristic that it consists of pyogranulomatous
inflammation with fibroplasia. Langerhans giant cells are common
. The presence of numerous HCF, some of which show budding,
both intra and extracellularly in tissue sections stained with H&E
stain is of diagnostic value .
Postmortem Lesions: At necropsy, areas of the skin and
subcutaneous tissue are thickened, and the skin may be fused to
the underlying tissues. The regional lymph nodes may be enlarged
and inflamed. Nodules in the skin have a thick, fibrous capsule and
the affected lymphatic vessels are usually thickened or distended.
Both nodules and lymphatic contain purulent exudates. In some
cases, the lesions may extend to the underlying joints, resulting
in arthritis, Periarthritis or periostitis. Multiple, small, gray–white
nodules or ulcers with raised borders and granulating bases may
be apparent on the nasal mucosa, and lesions may be found on the
conjunctiva and cornea. The lungs, spleen, liver, testes and other
internal organs may also contain nodules and abscesses .
5.8.2. Differential Diagnosis: Several infectious diseases can be
confused on clinical grounds with epizootic lymphangitis, the most
important of which is glanders, especially “farcy” or the skin form
of the disease . Differential diagnoses include glanders (farcy),
caused by Burkholderia mallei, ulcerative lymphangitis due to
Corynebacterium pseudo tuberculosis, sporotrichosis caused
by Sporothrix schenckii and the skin lesions of Histoplasmosis
caused by H. capsulatum var. capsulatum .
Epizootic lymphangitis is one of the infectious diseases
causing huge economic losses and low productivity in horses .
It is an economically important disease in some areas of the world,
particularly where large numbers of horses, donkeys, or mules are
assembled. This disease was a serious concern during the early
twentieth century when large numbers of horses were stabled
together (www.qldhorsecouncil.com). This disease continues to be
a significant concern in some countries such as Ethiopia, where the
prevalence in carthorses is nearly 19%and economic losses from
this disease are high . The impact of EPL was multi-dimensional
and encompassed effects upon the horse, the individual owner
and the wider society. Working equids provide a vital utility and
source of income to many people in resource-poor settings. Often,
infection with EPL resulted in a reduction in working ability which
had a direct impact upon the livelihoods of owners and their
dependent family members. EPL also impacted upon the welfare of
the horse as sick animals continued to be worked and, in advanced
cases, horses were abandoned due to ineffective or unavailable
treatment . Treatment costs in terms of money and time lost
by owners without effective treatment outcomes contribute to the
suffering and death of animals. In Ethiopia equines are important
animals to the resource-poor communities in rural and urban
areas of Ethiopia, providing traction power and transport services
at low cost. The use of equines in door-to-door transport service
also provides urban dwellers with the opportunity of income
generation . In general, the study has shown that EPL greatly
affects the economic and social wellbeing of equine owners. Direct
effects include reduced income due to lower work capacity or
inability to work at all, cost of treatment, loss of customers and
the need to purchase new equines. In addition, the owner faces
social stigma due to foul smelling .
Although Epizootic lymphangitis has been eradicated from
Europe, it is currently prevalent in Ethiopia, where between 0%
and 39% of equids may be infected, with the rate being dependent
upon the region . In two separate participatory studies in
different areas of Ethiopia, horse owners consistently volunteered
EPL as a high-priority disease . EPL contributes to extensive
morbidity and subsequent mortality due to abandonment of
chronically infected animals and can have a devastating impact
on the incomes of poor families . Within regions where the
disease is endemic, access to treatment is a significant challenge.
The Society for the Protection of Animals Abroad (SPANA)
currently provides free veterinary care within its clinics; however,
topical treatment with tincture of iodine and oral dosing with
potassium iodides are labor intensive, expensive, and of limited
efficacy in moderate to severe cases of EPL. It is imperative
that animals be diagnosed early during the disease to improve treatment outcomes, conserve resources, and reduce the burden of
infection within the population. Currently, due to limited available
diagnostic technologies, veterinarians in Ethiopia diagnose the
disease based on clinical appearance and microscopic examination
for yeast cells within pus.
This has the potential for misdiagnosis, as the clinical
appearance can mimic that of other diseases (e.g., ulcerative
lymphangitis, sporotrichosis and the cutaneous form of glanders
. Culture of H. capsulatum var. farciminosum from clinical
lesions would be definitive but is challenging and rarely attempted.
Therefore, reliable and robust approaches to diagnosis are required
to support clinical decision making and enable epidemiological
studies to provide the rationale for the development of disease
prevention strategies. EZL has recently been highlighted to be
a priority neglected disease of working equids . Epizootic
lymphangitis is a common infectious disease of horses in Ethiopia.
It is a significant concern in the country, where the prevalence in
carthorses is nearly 19%, and economic losses from this disease
are high . It is particularly prevalent in carthorses in most
parts of Ethiopia studied. For instance, it occurs in 24.9% horses
in Woliso . Similarly, studies conducted in Ethiopia in horses
showed that EPL is endemic to Ethiopia and its distribution covers
humid and hot areas. Epizootic lymphangitis is second only to
African Horse Sickness as a most important disease of horses in
Ethiopia . The disease primarily occurs in areas with altitudes
ranging from 1600 to 2400mm above sea level, which allows the
environmental form of HCF to persist for several months. It is
common in Ethiopia, especially in cart horses, affecting an average
of 18.8% of horses in warm and humid areas .
The prevalence of disease accounts for 26.2% in cart horses and
21% in cart mules. Although a few studies have been conducted in
western and central Ethiopia there is a lack of information on the
epidemiology of EPL in large parts of the country . Recently, an
overall prevalence of 18.8% was recorded for EPL in carthorses in
28 Ethiopian towns  (Figure 4).
Although successful treatment with intravenous administration
of sodium iodide, oral administration of potassium iodide and
surgical excision of lesions has been reported, there is no completely
satisfactory treatment against the disease . Inorganic
iodides can be used on early cases and amphotericin B is also recommended
as a drug of choice. Both treatment options, however,
are not available in the local veterinary service partly because of
cost. Even if the drugs are available, early identification of cases
is critical for successful therapy. Localized nodules can also be
lanced, the pus drained and the nodules packed with a 7% tincture
of iodine. In most areas, epizootic lymphangitis is a reportable disease
and treatment is not allowed (CFSPH, 2009).
The control of epizootic lymphangitis according to the
World Organization for Animal Health (OIE) is usually through
elimination of infection. This can only be achieved by culling
infected equids and applying strict biosecurity measures to prevent
spread of the infectious agent . Strict hygienic precautions are
essential to prevent spread of epizootic lymphangitis, moreover
great care should be taken to prevent spread by grooming or
harness equipment, as contaminated bedding should be burned,
since the organism may persist in the environment for long time.
The disease is eradicated by the humane slaughter of infected
horses, disinfection of infected premises and restricting the
movement of equids from infected premises . In endemic
areas where eradication is not possible, inorganic iodides can be
used for therapy in early cases . The methods used to control
epizootic lymphangitis in large endemic regions will depend
on disease prevalence, methods of husbandry, attitude and the
economic capacity of the horse-owning community to bear the
costs involved. Cleaning and disinfection will help in preventing
the disease from spreading .
Epizootic lymphangitis is a debilitating fungal disease seen
mainly in equids. The disease results from infection by a dimorphic
fungus, Histoplasma capsulatum var. farsiminosum. EPL is endemic
in some countries of west, north, and northeast Africa, and Asia
where it is mostly diffused in areas characterized by humid
and hot climates. The disease is common and has recently been
highlighted to be a priority neglected disease of working equids in
Ethiopia. The disease can be transmitted by biting flies, e.g. Musca
and Stomoxys spp that feed on open, discharging lesions. There are
three forms of the disease: cutaneous (skin), ocular, and respiratory
forms. The diagnosis of EPL is based on the clinical examination of
the lesions, microscopic examination of the yeast form of HCF in
pus, serological tests and skin hypersensitivity testing. The impact
of EPL was multi-dimensional and encompassed effects upon the
horse, the individual owner and the wider society. Intravenous
administration of sodium iodide, oral administration of potassium
iodide and surgical excision of lesions can be used as a treatment
for EPL. Strict hygienic precautions are essential to prevent
spread of epizootic lymphangitis moreover great care should be
taken to prevent spread by grooming or harness equipment. The
disease is eradicated by the humane slaughter of infected horses,
disinfection of infected premises and restricting the movement of
equids from infected premises .
Based on the above conclusion, the following recommendations
a. Owners should be educated on proper use of harness
and avoiding any contact of healthy equine with the infected
b. In advanced cases equines should be killed in humane
way rather than leaving them outdoors since they are source
c. Low-priced and effective antifungal drugs should be
sought to treat the disease which will be readily available to
equine owners and drivers both in government and private
animal health sectors.
d. The control and prevention of this disease should be the
focus of the government.
e. Awareness enhancement education should be provided
to equine owners and to the public on importance of early
treatment of EPL and preventive measures.