1. A project of the National Center for Appropriate Technology 1-800-346-9140 • www.attra.ncat.org
Parasite Management for Natural and
Organic Poultry: Blackhead in Turkeys
By Terrell Spencer, Blackhead disease, also called Histomoniasis, is a serious disease capable of decimating turkey flocks
NCAT Agriculture and negatively affecting other poultry. Caused by the protozoan Histomonas meleagridis, Blackhead
Specialist can also have a significant economic impact on chicken production. Recent research has revealed new
© 2010 NCAT information about the bird-to-bird transmission of Blackhead through a previously unknown path-
way—cloacal drinking. This publication addresses the new research as well as focusing on the history,
Contents life cycle, diagnosis, prevention, and management of Blackhead disease, primarily in turkeys. The effect
Introduction ......................1 Histomoniasis has on other poultry species (chickens, gamebirds, and peafowl) is also discussed briefly.
The Life Cycle and
Infectious Pathway
of Blackhead......................2
Poultry Species as
Blackhead Reservoirs .....2
Blackhead Transmission
through Cecal Worm
Eggs and Soil.....................2
Horizontal Spreading
of Blackhead through
Turkey Flocks.....................3
Oral Ingestion
and Contraction
of Blackhead......................4
Diagnosis and
Symptoms of
Infected Turkeys ..............4
Prevention and
Management of
Blackhead Disease ..........5
Conclusion .........................8
References .........................8
Photo by Jeannette Beranger, American Livestock Breeds Conservancy.
demands of an expanding population, turkey
Introduction production dropped from 11 million birds in
1890, just years before the first Blackhead out-
History of Blackhead break, to an average of 3.7 million turkeys per
The National Sustainable
in the United States year during the 1910–1920 decade. The devel-
T
Agriculture Information Service, he first reported case of Blackhead dis- opment of antihistomonal drugs in the 1960s
ATTRA (www.attra.ncat.org),
was developed and is managed ease in the United States occurred in led to a dramatic decrease in Blackhead-related
by the National Center for
Appropriate Technology (NCAT). Rhode Island in 1893, possibly carried turkey deaths. Unfortunately for poultry pro-
The project is funded through to the U.S. by pheasants imported the decade ducers, the drugs developed to treat Histomo-
a cooperative agreement with
the United States Department before. Blackhead then spread throughout the niasis were eventually banned (McDougald,
of Agriculture’s Rural Business-
Cooperative Service. Visit the
U.S., ravaging turkey flocks in New England 2005). As more farmers enter into free-range
NCAT website (www.ncat.org/ and following production like a faithful shadow. and pastured-poultry systems, often combining
sarc_current.php) for
more information on Outbreaks of Blackhead rapidly spread down multiple poultry species on the same land,
our other sustainable
agriculture and
the Eastern Seaboard, into the Midwest and the Blackhead outbreaks may be of increasing
energy projects. far western United States. Despite the growing concern and economic impact.

2. The Life Cycle and Infectious Blackhead does not kill the infected bird, and the
disease requires a secondary bacterial infection to
Pathway of Blackhead be virulent and eventually fatal. Escherichia coli,
Blackhead occurs when the causal agent, the Bacillus subtilis, and Clostridium sp. are some of
protozoan Histomonas meleagridis, gains access the bacteria noted in the secondary infections
to the ceca, or blind pouches of the intestines. that caused death (McDougald, 2005).
Blackhead infects poultry using three separate
pathways that will be examined in detail in
this publication:
Poultry Species as
• Ingestion of soil or earthworms
Blackhead Reservoirs
containing eggs of the cecal worm Among poultry species, there are varying
Heterakis gallinarum, infected with degrees of susceptibility to Blackhead. Some
Related ATTRA birds, such as pheasants, ducks, and geese, are
publications H. meleagridis
nearly immune to the effects of Blackhead.
Parasite Management • Uptake of H. meleagridis directly into Chickens are somewhat resistant to the disease,
for Natural and Organic the lower digestive tract through the while turkeys and peafowl are extremely vulner-
Poultry: Coccidiosis process of “cloacal drinking” able and have high mortality rates when infected
• Oral ingestion of live H. meleagridis with H. meleagridis. Experiments have shown
protozoa when stomach is not acidic that infected pheasants and chickens are capable
enough to kill the pathogen of transmitting Blackhead to young turkeys
(Lund and Chute, 1972).
Once access into the digestive tract has been
achieved, H. meleagridis multiplies in the ceca Traditional wisdom dictating that chickens and
and attacks the tissues of the cecal walls. As the turkeys not be raised together is most likely
disease progresses, a cheese-like, foul-smelling, based on experience with Histomoniasis. Chick-
yellow substance fi lls the ceca. Th is substance ens are excellent hosts for the cecal worm that
can vary in form from a hardened plug to more H. meleagridis uses as a vector. It is not unrea-
liquid in nature, and is composed of dead cecal sonable to assume that the majority of Black-
cells and blood. In highly susceptible birds such head outbreaks, especially among small, diver-
as turkeys, the Blackhead protozoa then enter sified farmers, can be traced back to chickens.
the bloodstream through the damaged ceca and
are deposited into the liver, where they do even Among chickens, laying hens and breeding
more damage, creating signature “bulls-eye” roosters have the potential to shed many more
zones of necrosis (dead tissue). Occasionally, cecal worm eggs than broilers due to age dif-
H. meleagridis also enters into other organs ferences in production—a broiler is usually
such as the kidneys, lungs, heart, and brain. slaughtered at six to 12 weeks (six to eight weeks
for Cornish cross; 12+ weeks for slower-grow-
ing breeds), while a hen may be kept for two or
Figure 1. Turkey Digestive Tract. By Terrell Spencer, NCAT.
more years. The cecal worm in question, H. gal-
linarum, takes approximately a month to mature
and begin shedding eggs. This time frame, cou-
pled with the two to four weeks chicks spend in
the brooder, allows little to no time for a broiler
to contaminate the soil with cecal worm eggs.
On the other hand, a hen in production for sev-
eral years can seed tremendous amounts of cecal
worm eggs into the soil during her lifetime.
Blackhead Transmission
through Cecal Worm Eggs
and Soil
The indirect ingestion of Blackhead protozoa
through consumption of earthworms and cecal
worm eggs is the most commonly known means
Page 2 ATTRA Parasite Management for Natural and Organic Poultry: Blackhead in Turkeys

3. Figure 2. Blackhead life cycle by By Terrell Spencer, NCAT.
of contracting Histomoniasis. When exposed Horizontal Spreading
to the elements, the Blackhead pathogen is
short-lived, being highly susceptible to envi- of Blackhead through
ronmental stresses—sunlight, wind, and tem- Turkey Flocks
perature extremes. H. meleagridis has over- The contraction of Blackhead disease by
come this limitation through infecting cecal turkeys has traditionally been attributed solely
worm eggs, as these eggs are extremely hardy. to the vectoring of the disease through cecal
The eggs can remain viable up to three years worm eggs and earthworms. However, recent
in the soil; in addition, cecal worms are very research has shown that turkeys can infect other
common in many poultry species, especially members of the flock directly through a process
chickens. Contaminated cecal worm eggs are known as cloacal drinking (Hu et al., 2004,
consumed when birds ingest soil either inten- McDougald and Fuller, 2005).
tionally or during foraging. Earthworms also
act as an intermediate vehicle for spreading
Cloacal drinking is the reflexive intake of fluids
the disease, as the earthworms consume soil through the cloaca in order to inoculate the
containing the infected cecal worm eggs. The young bird’s immune system with the micro-
earthworms, in turn, are readily consumed by bial flora of the surrounding environment.
all types of poultry.
www.attra.ncat.org ATTRA Page 3

4. Unfortunately for both the turkey and the ically, the proventriculus—due to the stomach
farmer, the turkey immune system has little to acids produced. Therefore, Blackhead is typi-
no defense against Blackhead, and the Black- cally not transmitted orally (Hu et al., 2004).
head protozoans that enter through the cloaca When a turkey feeds, acid is produced to aid
multiply unrestricted. Uptake of H. meleagridis in digestion, and this acidification destroys
through the cloaca occurs when a turkey’s clo- H. meleagridis. After six hours of not feeding,
aca comes into contact with contaminated fecal however, the lack of stomach acid allows the
matter, most likely while resting. The patho-
turkey’s gastrointestinal tract to go from being
genic protozoa are then drawn into the digestive
acidic to neutral in pH, and this change can
tract through the cloacal drinking process and
migrate to the ceca, where infection occurs. allow H. meleagridis to survive oral ingestion
(McDougald, 2010).
Historically, contraction of Blackhead through
cecal worm eggs has explained the begin-
ning of outbreaks in poultry f locks, but Diagnosis and Symptoms
failed to account for the rapidity with which of Infected Turkeys
Blackhead spreads throughout the flock. The
lack of an explanation for the continued trans- Physical Symptoms of Blackhead
mission of Histomoniasis through a f lock, • Mustardy, yellowish colored stool—
despite the exclusion of earthworms and soil varies from a watery, foamy diarrhea
containing cecal worm eggs, has been a source to a dry, solid black stool with waxy
of frustration and setback for farmers. Now, yellowish streaks
thanks to recent research findings, this gap in • Bulls-eye-shaped necrotic pitting
the basic understanding of the Blackhead life-
on liver
cycle has been closed.
• Ceca filled with yellow, cheesy substance
Oral Ingestion and Behavioral Signs of Blackhead
Contraction of Blackhead • Lethargy
When the turkey is given a constant supply of • Drooping wings
food, experiments have suggested that H. melea-
gridis ingested orally is not capable of surviving • Dry, ruffled feathers
the passage through the stomach—more specif- • Suppressed appetite, increased thirst
Regular (on left) and Blackhead-infected (right)
An ill turkey showing classic signs of sickness: lethargy (as seen by the closed eyes), turkey droppings. The tell-tale sulfur colored droppings
lack of inquisitiveness, retracted neck, and drooping wings. Photo by indicative of a Blackhead infection are clear.
Terrell Spencer, NCAT. Photo by Terrell Spencer, NCAT.
Page 4 ATTRA Parasite Management for Natural and Organic Poultry: Blackhead in Turkeys

5. On farm dissection showing characteristic liver necrosis due to Enlarged cecum filled with yellowish necrotic tissue in a Blackhead
Blackhead. Photo by Terrell Spencer, NCAT. infected turkey. Photo by Terrell Spencer, NCAT.
• Decreased/lack of f light distance in chickens often are undiagnosed, though
(distance the turkey keeps between in chickens the impact of Blackhead has
itself and humans) been described as being at least as severe as
• Decreased/lack of inquisitiveness coccidiosis, and in some broiler breeder flocks,
mortality may reach as high as 10% (McDou-
Blackhead infections vary in the time required
gald, 2005). Bobwhite quail farmers have also
to manifest signs, depending on the path-
occasionally experienced outbreaks of Black-
way and initial amount of infection. Signs
head disease, especially when these growers
of infection begin to appear seven to 14 days
utilize old chicken houses.
after exposure. In turkeys, the yellow-col-
ored fecal matter is the definitive symptom of
Blackhead disease. From personal experience, Prevention and Management
when behavioral symptoms become apparent, of Blackhead Disease
mortality usually occurs in one to three days.
Prevention is the key to successful Blackhead
Positive diagnosis of dead birds can be easily management. Due to the previously mentioned
obtained through a post-mortem dissection banning of the antihistomonal medicines used
(necropsy) by the farmer. The abdominal cavity to treat outbreaks, there are no established treat-
can be opened and the cecum examined. The ments for turkeys once they are infected and
chest/breast can then be split down the middle symptomatic. It is imperative that any truly
using heavy duty shears or tin snips to reveal sustainable turkey operation have a Blackhead
the liver. Once the ceca and liver are exposed, prevention plan.
the organs can be inspected for necrosis as
described above.
Preventative and
Despite the descriptive name of the disease,
Blackhead rarely, if ever, causes the head of
Post-Infection Measures
the infected bird to darken or turn black, so The most economical and sustainable method of
the common name is somewhat of a misnomer Blackhead management is complete avoidance
(Davidson and Doster, 2010). of the disease through preventive treatments.
Turkeys demonstrate the most severe symp- • Separation of poultry flocks by species
toms of any poultry from H. meleagridis infec- and age – separation of susceptible
tion and, consequently, the highest mortal- (turkeys and peafowl) and resistant
ity rates. Indeed, expectations of 80-100% (chickens, pheasants, quail, etc.) poultry
mortality are plausible in turkey Blackhead species has been the principal means of
outbreaks. Chickens are usually able to stop Histomoniasis prevention since the
the disease before destruction of the ceca and cecal worm role in disease transmission
degradation of the liver take place. Infections was identified in the 1930s. Separation
www.attra.ncat.org ATTRA Page 5

6. should also include ground that has been Whites, heritage turkeys can be selected
used for different poultry species. Land for resistance to Blackhead. If a Black-
that has been used to house/pasture head outbreak occurs in a heritage
chickens or gamebirds should not be flock, the surviving individuals may
used for turkeys or peafowl production. have some trait, either genetic or behav-
• Fallowing of contaminated ground or ioral, that increases their chance of sur-
houses – Cecal worm eggs are viable up viving or avoiding a Blackhead infec-
to three years in the soil and litter, and tion. These birds could be saved and
research has shown that H. meleagridis bred to obtain next season’s poults, and
harbored inside of the eggs remains at least some resistance to Blackhead
infectious even after 150 weeks. There- could be bred into a producer’s flock.
fore, three years should be the mini- • Preventative feed additives:
mum time considered for fallowing. – Histostat™ (active ingredient is Nitar-
• Selecting for resistance – while this strategy sone) is an effective preventative feed
is not plausible for Broadbreasted additive and can be premixed into
feed. It is a non-organic additive that
contains arsenic and is the only drug
Breeding Resistance approved for the prevention of Black-
into the Flock head. At the time of this writing, Blue
Nature’s Harmony Farm Seal Feeds™, located in the Northeastern
Located in Elberton, Georgia, and Mid-Atlantic regions of the United
Nature’s Harmony Farm is a 126- States, sells a pre-mixed medicated
acre diversified meat and dairy turkey feed containing Histostat.
farm built by Tim and Liz Young.
Raising pasture-based pork, poul-
Other than within the Blue Seal prod-
try, cattle, sheep, and rabbit, as uct, the use of Histostat is difficult at
well as running a grass-fed dairy, best for a small producer. The drug is
the Youngs have taken a holistic only sold in 55-pound bags – enough
approach towards the manage- Histostat to mix more than 65 tons of
ment of their farm. Tim and Liz again.’ We said no, we’re going to feed. Additionally, the drug can only
examine all of their endeavors build resistance to Blackhead, and be purchased by registered feed mills,
with an eye towards long-term all the other diseases. We raise tur- and Histostat must be mixed into the
biological sustainability. One criti- keys with our chickens, we don’t ration as the feed is milled. Finally, at
cal objective of Nature’s Harmony worry about any of these things, approximately $15/pound, Histostat
Farm’s holistic planning is breeding and we just let nature sort it out.”
is a costly drug to buy in bulk. Histo-
disease resistance into their live-
stock, including Blackhead resis- Liz adds, “We find the strongest stat cannot be fed to actively produc-
tance in turkeys. birds, those are the ones we breed ing layers and has a short withdrawal
and their offspring have proven to period (5 days) to allow the arsenic
“Now that we’re breeding our own be so much hardier than all the ingested by the bird to be flushed
animals on the farm”, says Tim, other animals on the farm. It will from the system. In addition, Histostat
“we worry a lot less about disease take a number of years to get where is toxic to dogs, ruminants, and water-
mortality problems. We had such we want to be, but the results so far
huge issues with pastured poul- fowl. The toxicity to other species is an
give us a lot of hope.”
try two years ago with Blackhead, additional burden to mills that must
sinusitis, mycoplasm, etc., which “This was a huge, calculated risk thoroughly clean their feed machinery
we either don’t see any more or we took as new farmers a couple of before mixing non-poultry feeds.
see drastically less of. Our birds years ago,” Tim acknowledges, “but
look so healthy now, but just a we were so convicted in our values – Natustat™ is a plant-based additive
few years ago, we had depressing that we felt it was the right thing to manufactured by Alltech, Inc. that,
mortality rates among birds that do, even though it was counter to just like Histostat, is mixed into the
were shipped in from commer- all the advice. We’re really happy ration when the feed is milled. Natu-
cial hatcheries. We’d have experts with the decisions we made back stat promotes poultry well-being
come out, and they’d say ‘Just burn then, and with the health of the and discourages Blackhead by act-
your entire flock and start all over birds we have today.” ing as an immune system booster
that stimulates good health. The
Page 6 ATTRA Parasite Management for Natural and Organic Poultry: Blackhead in Turkeys

7. company’s research trials have shown • Good biosecurity techniques – infected
that it is comparable to Histostat in cecal worm eggs can be transported
the prevention of Blackhead when on the bottom of boots/equipment
birds are exposed to infected litter, into brooders, clean pastures, land,
but it is not effective in preventing and poultry houses. On small farms,
Blackhead when poultry are exposed where multiple poultry species are often
to the parasite directly (as through kept, pay particular care when incor-
cloacal drinking). porating new stock from off the farm
into the existing operation. When pos-
Natustat is available to small growers
sible, chores and farm activity should
directly in 55-pound bags. During the
be planned around dealing with sus-
summer of 2010, the price per bag was
$175, enough to treat 25 tons of feed. ceptible poultry first and dealing with
Natustat doesn’t have the legal purchas- resistant species later when Blackhead is
ing restrictions that make Histostat so suspected or a concern. The American
difficult for small producers to access. Livestock Breed Conservancy (ALBC)
There is no withdrawal time, and there has excellent resources for addressing a
is no secondary toxicity threat to other farm’s biosecurity needs. The resources
animal species. can be viewed on their website at
www.albc-usa.org/EducationalResources/
Feed additives are effective only if biosecurity.html.
administered before a Blackhead infec-
• Encouragement of roosting behavior –
tion occurs. Once signs of infection are
getting poultry off of the ground and
present (yellow fecal matter, behavioral
onto roosts reduces the chance of cloa-
signs), preventative drugs are no longer
cal contact with infected fecal matter.
effective. There are no legal drugs or
Turkeys and other poultry will huddle
substances to treat Histomoniasis once
together and sleep on the ground in
the infection has occurred.
absence of a suitable roost. The direct
– Dimetridazole was a low-cost, highly contact from huddling greatly increases
effective drug that was once used to the chance of Blackhead transmission
cure infected turkey flocks and regen- as the birds defecate through the night.
erate liver damage. The drug was Heritage breeds of turkeys will roost
banned in 1988 in the US and the instinctively. Broadbreasted Whites
late 1990s in Europe and Bronzes have difficulty flying onto
– Capsicum from hot peppers (i.e., Cay- roosts due to their size, but can be
enne) has anecdotal success as a natural coaxed into roosting by providing a lad-
treatment for Blackhead disease. How- der or some type of plane.
ever, the effectiveness of treating Black-
head with Capsicum has not been veri- Management During Infections
fied through documented research. • Frequent movement to fresh ground –
once a flock has been infected with
• Promotion of good health and robust
Blackhead, frequently moving the flock
immune systems – generally, a stressed
to fresh pasture minimizes the amount
animal is more susceptible to any dis-
of manure and exposure time that the
ease, so reducing the stresses (by pro-
birds are subject to the pathogens shed
viding adequate shelter, balanced feed,
proper stocking densities, clean water in the infective manure.
access) in turkeys and other poultry can • Isolation of sick birds – isolation of
help develop robust immune systems less sick birds removes the source of direct
susceptible to Blackhead. As mentioned transmission from the flock. Identifica-
before, running out of feed can allow tion of sick birds before behavioral signs
establishment of H. meleagridis through develop can occur by spotting the birds
oral ingestion, so care must be taken to that expel the yellow manure characteristic
assure that feeders are never empty. to the disease.
www.attra.ncat.org ATTRA Page 7

8. • Reduction in stocking rate – reducing the • Preventative feed additives – once Black-
amount of birds in a given unit of area head has appeared in the flock, it is of
(acre, paddock, etc.) has an effect similar critical importance to prevent the rest
to moving the turkeys to fresh ground. of the flock from becoming infected.
Feed preventatives can be a powerful
• Encourage natural sterilization – ultra- tool against contraction or the spread of
violet light from sunshine, the drying Blackhead in poultry flocks.
action of wind, the heat of summer,
and the chill of winter are all detri-
mental to the survival of H. meleagri- Conclusion
dis. Any natural weathering process Blackhead is a serious disease in poultry that
that breaks down poultry manure— has affected poultry farmers in the United States
and therefore the hospitable niche of for well over a century. Turkeys and peafowl are
the Blackhead pathogen—should be highly susceptible to death from the disease.
encouraged. H. meleagridis requires Chickens are excellent carriers of Blackhead, and
moisture to survive and spread, and care must be taken to keep chickens and turkeys
moving the flock to dry ground makes separate. There is no treatment for Blackhead,
the spread of Blackhead more difficult. and so the best strategy is prevention.
Heterakis gallinarum, Histomonas meleagridis, and
References Parahistomonas wenrichi. Journal of Parasitology.
Davidson, W.R. and G.L. Doster. 2010 (viewed). Blackhead Volume 58, p. 940-945.
Does Not Cause Blackhead. National Wild Turkey Federation.
McDougald, L.R. 2005. Blackhead Disease (Histomoniasis)
Bulletin 25.
in Poultry: A Critical Review. Avian Diseases. Vol. 49, p.
Hu, J., L. Fuller and L.R. McDougald. 2004. Infection of 462–476.
Turkeys with Histomonas meleagridis by the Cloacal Drop
McDougald, L.R. and L. Fuller. 2005. Blackhead Disease
Method. Avian Diseases. Vol. 48, p. 746-750.
in Turkeys: Direct Transmission of Histomonas meleagridis
Lund, E.E. and A.M. Chute. 1972. Reciprocal Responses from Bird to Bird in a Laboratory Model. Avian Diseases.
of Eight Species of Galliform Birds and Three Parasites: Vol. 49, p. 328–331.
Parasite Management for Natural and Organic Poultry:
Blackhead in Turkeys
By Terrell Spencer
NCAT Agriculture Specialist
© 2010 NCAT
Tracy Mumma, Editor
Amy Smith, Production
This publication is available on the Web at:
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or
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