Download Safety Precautions for Working with African trypanosomes

Safety Precautions for Working with African trypanosomes
The African trypanosome, Trypanosoma brucei, causes African sleeping sickness in man. This
disease is a potentially life-threatening infection caused by a flagellated blood-dwelling
protozoan. It is invariably fatal without therapeutic intervention. Fortunately, chemotherapeutic
options exist.
In the laboratory setting, one of three species of parasites is typically studied. T. b. gambiense is
responsible for what is considered classical human sleeping sickness, with a typically slow
progression of the disease (weeks to months from time of infection to development of
neurological symptoms that are a prelude to death) that includes the disruption of sleep cycles
due to parasite activity in the brain. T. b. rhodesiense causes a more acute disease and is
generally triggers a more rapid onset of disease symptoms and outcomes. T. b. brucei, perhaps
the most commonly studied species as a consequence of safety concerns, is not pathogenic to
man due to a serum-based resistance factor (known as trypanosome lytic factor or TLF) in our
blood. It is a parasite of rodents and other mammals.
Generally, two lifecycle stages of African trypanosomes are cultured in the laboratory. The
insect-dwelling stage (insect stage, or procyclic form) parasites are not competent to infect
mammals. The blood stages (long slender, bloodstream form) are potentially infectious so
accidental exposure to these by needle stick, eye splash or other means warrants medical
intervention.
Accidental exposure to any of these parasites requires immediate attention, as it is formally
possible that human infectious species of parasites have been inadvertently confused with nonpathogenic T. b. brucei during handling. Distinguishing these from each other morphologically
is challenging, so in parallel assessment of sensitivity of the source of accidental exposure to
human serum (which causes rapid lysis of T. b. brucei in vitro and can confirm the identity of
that parasite) should be prioritized (please consult with Dr. Steve Hajduk, UGA, 706-542-1676
or Dr. Jayne Raper, Hunter College, (212) 396-6644) for experimental guidance as needed for
TLF lysis analysis.)
Individuals unable to mount an effective immune response may be at potentially greater risk,
although otherwise healthy individuals can develop infection to the human parasites.
We therefore take the following precautions for working with African trypanosomes:
Ø Live trypanosomes should always be treated with respect; exercise extreme care
whenever using sharps (needles, forceps, Pasteur pipettes, etc.). Also note that
hemocytometer coverslips may have sharp edges! Sharp needles should only rarely by
required (e.g. for animal inoculation).
Ø All infected material must be decontaminated (in bleach or by autoclaving) immediately
after use. Please pay particular attention to sharps and hemocytometer cover glasses.
Any possible infection, no matter how small or unlikely, must be reported immediately and
should be treated as outlined below.
In Case of Possible Laboratory Infection with Trypanosoma brucei
What to do:
Ø First of all, do not panic.
Ø Try to clarify the nature of your exposure:
o Needle-stick, broken pipette, glass cut, eye-splash, other?
o Known/likely/unlikely to be contaminated with T. brucei?
o What species/strain: if T. b. brucei, has sensitivity to human serum been
confirmed?
o Any transgenic plasmids, markers, reporters?
o Drug-resistance status?
Ø Contact James Morris immediately at: (864-650-2777, cell) any time day/night.
Ø Print out a copy of this protocol to bring with you to Clemson Student Health,
Occupational Health, the Emergency Room, or elsewhere, as appropriate.
Ø Students and staff should contact Will Mayo (office: 864-656-5529) at Clemson Medical
Surveillance Program.
Ø Your physician should contact should contact the Division of Parasitic Diseases and
Malaria (telephone, 404-718-4745; email, [email protected])
Treatment: For diagnostic and treatment approaches and for access to suramin, melarsoprol, or
eflornithine, physicians should contact the Division of Parasitic Diseases and Malaria (telephone,
404-718-4745; email, [email protected])
Ø General Post-accident management approaches
o Diagnosis: usually confirmed by detection of trypanosomes in peripheral blood,
CSF, or from chancre (at site of infection), lymph nodes, or bone marrow.
o Detection in the CNS indicates significant disease progression
o Concentration of blood samples (for examination of buffy coat, for example) can
be useful.
Ø Therapeutics
o Pentamidine is usually used to treat T. b. gambiense infections
o Suramin is usually used to treat T. b. rhodesiense infection. Severe side-effects
are possible with this compound.
o If either parasite is detected in the CNS, alternative treatments will be required.
Difluoromethylornithine (DFMO) is effective against blood and CNS stages of T.
b. gambiense but not T. b. rhodesinse. Both parasites are sensitive to melarsoprol,
but the considerable toxicity of this compound warrants careful consideration.