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Chapter 7 : Protozoa and Helminths
This chapter educates laboratorians, biosafety personnel, and health care workers about the potential hazards of working in settings in which exposures to viable parasites could occur. It provides information about parasites that have caused or could cause accidental infections in laboratorians and health care workers. Factors that influence whether infection and disease develop after accidental exposures are also provided in this chapter. The chapter focuses on the protozoa that cause leishmaniasis, malaria, toxoplasmosis, Chagas’ disease (American trypanosomiasis), and African trypanosomiasis. Summary data about 180 occupationally acquired cases of infection with the protozoa that cause these diseases are provided in this chapter. Blood and tissue protozoa of potential relevance to laboratorians and health care workers are also discussed in this chapter. Few laboratory-acquired helminthic infections have been reported. Even if laboratorians became infected by ingestion of infective eggs or through penetration of skin by infective larvae, they typically would have low worm burdens and few, if any, symptoms because most helminths do not multiply in humans. The fact that some of the persons who acquired parasitic infections did not recall discrete exposures suggests that subtle exposures (e.g., contamination of unrecognized microabrasions and exposure through aerosolization or droplet spread) can result in infection.
Incubation period (i.e., period from accidental exposure until first symptom or clinical manifestation attributed to infection) for the clinically evident occupationally acquired cases of infection with various blood and tissue protozoa. The ends of the lines designate the extremes of the ranges, and the short vertical lines designate the medians. For malaria, only non-vector-borne cases with available data were included (n = 20 caused by P. falciparum and n = 3 caused by P. vivax). For toxoplasmosis, only cases related to exposure to tissue stages of the parasite (rather than oocysts) were included. See text for discussion of general factors that affect incubation periods (e.g., virulence of parasite and accurate recall of timing of relevant exposure and first clinical manifestations) and specific issues about the data for the various parasites.
Natural pathogens of common laboratory animals a
Factors that affect whether accidental exposures to parasites cause infection and disease
Available data about rates of laboratory accidents and infections with specific parasites a
Criteria for including occupationally acquired (“laboratory-acquired”) cases of parasitic infection in this chapter and examples of types of cases that were and were not included a
Number of reported cases of occupationally acquired parasitic infections
Antibody and antigen detection tests available a in the United States for parasitic diseases b
Examples of practices and occurrences that have resulted in laboratory-acquired parasitic infections
Number of reported cases of laboratory-acquired infections caused by blood and tissue protozoa, by decade of occurrence (if known) or publication a
Number of reported cases of laboratory-acquired infections caused by blood and tissue protozoa, by country or region of the world where the case occurred a
Number of reported cases of laboratory-acquired infections caused by blood and tissue protozoa, by known or likely route of exposure a
Characteristics of the reported cases of laboratory-acquired infection with Leishmania spp. a
Characteristics of the reported cases of laboratory-acquired infection with Plasmodium spp. a
Characteristics of the reported cases of laboratory-acquired infection with T. gondii a
Characteristics of the reported cases of laboratory-acquired infection with T. cruzi a
Clinical and laboratory monitoring for T. cruzi infection after accidental exposures
Practical guide for detection of circulating T. cruzi trypomastigotes by light microsopy a
Characteristics of the reported cases of laboratory-acquired infection with T. brucei subspp. a