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Dave J. Rupiper DVM
Kenneth T. Briggs Ph.D., DVM
Among long-time pigeon fanciers, you will hear a range of opinions about whether
"pigeon malaria" constitutes a major cause of compromised performance.
Confusion between Haemoproteus and similar blood parasites often clouds the
issue. Additionally, many fanciers will have tried various unsuccessful treatments
for poor performance, assuming this infection is the cause. Together, these factors
lead to misinformation and sometimes to unnecessary treatments. The question before
us is whether pigeon malaria is an important factor in pigeon flock health and performance. Before
we answer this important question let us first learn what Haemoproteus really
is and how we can use life cycle information to interrupt the disease.
Known as "pigeon malaria", Haemoproteus is a red-blood cell parasite
of pigeons and doves. Three species of Haemoproteus affect pigeons; H.
columbae, H. sacharrovi and H. maccallumi. These are similar to the true
malarial parasites (Plasmodium) of birds but do not cause the same disease
symptoms. Plasmodial malaria results in anemia, weakness, decreased oxygen carrying
capacity of the red blood cells and occasionally death.1 Fortunately these sign
are not seen with Haemoproteus in pigeons.2-4 As a matter of fact, Haemoproteus
does not cause disease and usually survives completely undetected in the pigeon loft.
In a rare case study of a pigeon which was "super infected" experimentally
with an unnaturally high number of infective organisms, the bird had a moderate intolerance
to cold stress.
Interestingly, the life cycle of "pigeon malaria" is very complex. The
cycle involves multiple hosts, including the pigeon fly as the primary vector, but
"No-see-um" flies such as Culicoides may also transmit Haemoproteus.1
It all starts when one of these flies, carrying infectious Haemoproteus particles
(sporozoites), takes a blood meal on a pigeon and injects these particles into the
bird. (Fig.1) From here, the sporozoites migrate to the lung, liver and spleen and
reproduce in two ways to eventually form large numbers of parasites which are released
into the blood. At this point, the male and female parasites (merozoites is what
they are now called) enter pigeon red blood cells where they are ingested by another
pigeon fly during a blood meal. After a number of reproductive steps, the parasites
(now known as sporozoites again) are found in the salivary glands of the pigeon fly,
where they can be injected into another pigeon to start the six week cycle once again.
Thus, the blood parasite requires a period of development in the fly (i.e. flies
are obligate vectors for Haemoproteus).
Fig. 1 Haemoproteus Life Cycle
The pigeon is infected with "sporozoites" during a fly blood meal (1),
Parasite reproduction occurs resulting in "schizonts" and "cytomeres"
within the pigeon's tissues (2), Parasite reproduction continues resulting in motile
"merozoites" in the pigeon's blood; the "merozoites" may re-infect
the pigeon and multiply repeatedly (3), The "gametocyte" is within the
pigeon's red blood cell, the parasite pushes the cell nucleus out of the way; note
the cell nucleus (4a), the parasite (4b) and the red blood cell (4c), Pigeon flies
ingest the infected red blood cell during a blood meal (5), Three stages of reproduction
occur in the fly, eventually leaving "oocysts" or eggs in the fly's intestine
(6), The "oocyst" or egg releases infectious "sporozoites" (7),
"Sporozoites" migrate to the fly's salivary glands (8) "Sporozoites"
may now be injected into another pigeon during a blood meal (9-1).
Why should this information be important to you? It turns out that the key to getting
rid of the parasite forever is to simply break the cycle. If we rid our lofts of
pigeon flies, we eliminate the means for transmitting the parasites. This is why
lofts where birds are dusted on a regular basis to control flies and lice seldom,
if ever, have "pigeon malaria." Even though birds that have become infected
probably remain as carrier birds for life, they pose little threat to their penmates.
Among racing pigeons that are shipped with birds from fly infested lofts, Haemoproteus
infections may be more prevalent and more serious. Fortunately, the parasite
has not been shown to cause any decrease in performance.
This was evaluated in a controlled experiment, where in previously healthy pigeons
were infected with Haemoproteus and then put under thermal stress. Subsequent
measurements revealed no difference in metabolism or oxygen consumption between "infected"
and "control" birds. It is important to note, however, that birds with
concurrent infections such as Paratyphoid, Circovirus and Paramyxovirus-1 may have
decreased immunity to Haemoproteus. Due to the stress of these other infections,
a diminished immunity may predispose them to abnormally heavy Haemoproteus
infections. Remember, that these other infections are commonly found in overpopulated
or poorly managed lofts where pigeon flies may also exist. As we have commented
before, good management is the key to unlocking most of our pigeon husbandry problems.
Antimalarials
Many fanciers swear by the use of antimalarial drugs, purportedly because they increase
the pigeons' performance. When these drugs are used, they should be administered
to the pigeons in an effort to prevent Haemoproteus infections, not
to treat existing infections. If infected pigeons are treated, the parasites will
re-infect the red blood cells when medication is discontinued. There is no cure
once the pigeons are infected. Additionally, when chloroquine, primaquine or quinacrine
are used as preventatives, even at low dosages, side effects may occur. The most
common side effects include liver toxicity and gastrointestinal, cardiac and neurologic
reactions. Therefore we advocate the use of insecticide powders before and after
races and shows as the best management practice to prevent infestation by pigeon
flies and thus infection by Haemoproteus.
So we come back to the question, "does Haemoproteus slow your pigeons
down?" In general, the answer is no.4 However, if pigeons are concurrently
infected with other diseases, or are housed under sub-optimal conditions and subjected
to inappropriate husbandry practices, it may seem that "pigeon malaria"
is the cause for poor performance.
Acknowledgments
The authors would like to extend their gratitude to Dr. Wallace Harmon for his advice,
information and support. They would also like to note the support which the Los
Angeles Pigeon Club members provided for Dr. Harmon's work.
References
1) Tudor DC. Parasitic diseases. In: Pigeon Health and Disease. Ames, IA:
Iowa State University Press, 1991.
2) Harmon WM. Personal communication. Dept Biology, CA St Univ-Fresno, Fresno,
CA, 1994.
3) Rupiper DJ and Ehrenberg M. Diagnostic Procedures For Pigeon Loft Management.
Proc Annu Conf Assoc Avian Vet, 1994; 225-229.
4) Greiner EC and Ritchie BW. Parasites. In: Avian medicine: Principles
and Application. Ritchie BW et al (eds). Lake Worth, FL: Wingers Pub., Inc., 1994.
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