Biological Safety Manual - Chapter 08: Agent Summary Statements (Section III: Parasitic Agents)

Additional details about occupationally-acquired cases of parasitic infections, as well as recommendations for post exposure management, are provided elsewhere.1-3 Effective antimicrobial treatment is available for most parasitic infections.4 Immunocompromised persons should receive individualized counseling (specific to host and parasite factors) from their personal healthcare provider and their employer about the potential risks associated with working with live organisms.

Title

Biological Safety Manual - Chapter 08: Agent Summary Statements (Section III: Parasitic Agents)

Table of Contents

1. General Issues
2. Agent: Blood And Tissue Protozoal Parasites
3. Agent: Intestinal Protozoal Parasites
4. Agent: Trematode Parasites
5. Agent: Cestode Parasites
6. Agent: Nematode Parasites
7. References

General Issues

Additional details about occupationally-acquired cases of parasitic infections, as well as recommendations for post exposure management, are provided elsewhere.^1-3 Effective antimicrobial treatment is available for most parasitic infections.⁴ Immunocompromised persons should receive individualized counseling (specific to host and parasite factors) from their personal healthcare provider and their employer about the potential risks associated with working with live organisms.

BSL-2 and ABSL-2 practices,⁵ containment equipment, and facilities are recommended for activities with infective stages of the parasites discussed in this chapter.

Microsporidia, historically considered parasites, are now recognized by most experts to be fungi; however, microsporidia are maintained in the parasitic agent chapter in this edition. These organisms are discussed here because a laboratory-acquired case of infection has been reported,⁶ and most persons currently still look for microsporidia associated with discussion of parasitic agents.

Importation of parasitic agents may require CDC and/or USDA importation permits. Domestic transport of this agent may require a permit from USDA/APHIS/VS.

Agent: Blood And Tissue Protozoal Parasites

Blood and tissue protozoal parasites that pose greatest occupational risk include Babesia, Leishmania, Plasmodium, Toxoplasma, and Trypanosoma. Other tissue protozoa of potential concern include free-living ameba (Acanthamoeba, Balamuthia mandrillaris, Naegleria fowleri) and some species of microsporidia including Encephalitozoon cuniculi that commonly cause extraintestinal infection.

Leishmania spp. cause human leishmaniasis; Plasmodium spp. cause human malaria, or some, such as P. cynomolgi cause nonhuman primate malaria;Toxoplasma gondii causes toxoplasmosis; Trypanosoma cruzi causes American trypanosomiasis or Chagas disease; and Trypanosoma brucei gambiense and T. b. rhodesiense cause African trypanosomiasis or (African) sleeping sickness. With the exception of Leishmania and Toxoplasma, these agents are classically thought of as bloodborne and have stages that circulate in the blood. Although not always recognized, both Leishmania andToxoplasma may have stages that circulate in the blood. Some, such asPlasmodium and Trypanosoma cruzi, also have tissue stages. Leishmaniaspp. are well recognized to have skin and deep tissue stages andToxoplasma gondii forms tissue cysts, including in the central nervous system.

Occupational Infections

Laboratory-acquired infections with Leishmania spp., Plasmodium spp., Toxoplasma gondii, and Trypanosoma spp. have been reported; the majority of these involved needlestick or other cutaneous exposure to infectious stages of the organisms through abraded skin, including microabrasions.^1,2

Laboratory-acquired infections may be asymptomatic. If clinically manifest, they may exhibit features similar to those seen in naturally acquired infections, although bypassing natural modes of infection could result in atypical signs and symptoms. Cutaneous leishmaniasis could manifest as various types of skin lesions (e.g., nodules, ulcers, plaques), while visceral leishmaniasis may result in fever, hepatosplenomegaly, and pancytopenia. However, only one of the laboratorians known to have become infected with L. (L.) donovani, an organism typically associated with visceral leishmaniasis, developed clinical manifestations of visceral involvement (e.g., fever, splenomegaly, leukopenia). ¹ The other laboratorians developed skin lesions. Laboratory-acquired malaria infections may result in fever and chills, fatigue, and hemolytic anemia. Laboratorians can become infected with T. gondii through accidental ingestion of sporulated oocysts, but also may become infected through skin or mucous membrane contact with either tachyzoites or bradyzoites in human or animal tissue or culture. Symptoms in laboratory-acquired T. gondii infections may be restricted to flu-like conditions with enlarged lymph nodes, although rash may be present. Trypanosoma cruzi infection could manifest initially as swelling and redness at the inoculation site, fever, rash, and adenopathy. Myocarditis and electrocardiographic changes may develop. Infection with T. b. rhodesiense and T. b. gambiense also may cause initial swelling and redness at the inoculation site, followed by fever, rash, adenopathy, headache, fatigue and neurologic signs.

Blood and tissue protozoal infections associated with exposure to laboratory animals are not common. Potential direct sources of infection for laboratory personnel include accidental needle-stick while inoculating or bleeding animals, contact with lesion material from cutaneous leishmaniasis, and contact with blood of experimentally or naturally infected animals. In the case of rodents experimentally inoculated with Toxoplasma gondii via the intraperitoneal route, contact with peritoneal fluid could result in exposure to infectious organisms. Mosquito- transmitted malaria infections can occur under laboratory conditions as nearly half of the occupationally acquired malaria infections were reported to be vector borne, and contact with body fluids (including feces) of reduviids (triatomines) experimentally or naturally infected with T. cruzi poses a risk to laboratory personnel.

Babesia microti and other Babesia spp. can cause human babesiosis or piroplasmosis. Under natural conditions, Babesia is transmitted by the bite of an infected tick, or by blood transfusion; in the United States, hard ticks (Ixodes) are the principle vectors. Although no laboratory infections withBabesia have been reported, they could easily result from accidental needle-stick or other cutaneous exposure of abraded skin to blood containing parasites. Persons who are asplenic, immunocompromised, or elderly have increased risk for severe illness if infected.

Natural Modes of Infection

Leishmaniasis is endemic in parts of the tropics, subtropics, and southern Europe, while malaria is widely distributed throughout the tropics. However, the prevalence of these diseases varies widely among endemic areas and they can be very focal in nature. The four species of malaria that infect humans have no animal reservoir hosts. Some Leishmania spp. may have a number of important mammalian reservoir hosts, including rodents and dogs. Only cats and other felines can serve as definitive hosts forToxoplasma gondii, which is distributed worldwide. Birds and mammals, including sheep, pigs, rodents, cattle, deer, and humans can be infected from ingestion of tissue cysts or fecal oocysts and subsequently develop tissue cysts throughout the body. Chagas disease occurs from Mexico southward throughout most of Central and South America, with the exception of the southern-most tip of South America. It has been characterized in some accounts as a zoonotic infection, yet the role of animals in maintaining human infection is unclear. A variety of domestic and wild animals are found naturally infected with T. cruzi, but human infection undoubtedly serves as the major source of infection for other humans. African trypanosomiasis is endemic in sub-Saharan Africa but is extremely focal in its distribution. Generally, T. b. gambiense occurs in West and Central Africa while T. b. rhodesiense occurs in East and Southeast Africa. T. b. rhodesiense is a zoonotic infection with cattle or, in a more limited role, game animals, serving as reservoir hosts whereas humans are the only epidemiologically important hosts for T. b. gambiense.

Leishmania, Plasmodium, and both American and African trypanosomes are all transmitted in nature by blood-sucking insects. Sandflies in the generaPhlebotomus and Lutzomyia transmit Leishmania; mosquitoes in the genusAnopheles transmit Plasmodium; reduviid (triatomine) bugs such asTriatoma, Rhodnius, and Panstrongylus transmit T. cruzi (in the feces rather than the saliva of the bug), and tsetse flies in the genus Glossina transmit African trypanosomes.

Laboratory Safety

Infective stages may be present in blood, CSF, bone marrow, or other biopsy tissue, lesion exudates, and infected arthropods. Depending on the parasite, the primary laboratory hazards are skin penetration through wounds or microabrasions, accidental parenteral inoculation, and transmission by arthropod vectors. Aerosol or droplet exposure of organisms to the mucous membranes of the eyes, nose, or mouth are potential hazards when working with cultures of Leishmania, Toxoplasma gondii, or T. cruzi, or with tissue homogenates or blood containing hemoflagellates. Immunocompromised persons should avoid working with live organisms.

Because of the potential for grave consequences of toxoplasmosis in the developing fetus, women who are or might become pregnant and who are at risk for infection with T. gondii should receive counseling from their personal physician and employer regarding appropriate means of mitigating the risk (including alternate work assignments, additional PPE, etc.). Working with infectious oocysts poses the greatest risk of acquiring infection; needle-sticks with material containing tachyzoites or bradyzoites also pose a significant risk. Infection with tachyzoites or bradyzoites through mucous membranes or skin abrasions is also possible. Kittens and cats that might be naturally infected with Toxoplasma pose some risk to personnel.⁵ Good hygiene and use of personal protection measures would reduce the risk.

One laboratory infection with microsporidia has been reported, associated with conjunctival exposure to spores leading to the development of keratoconjunctivitis. Infection could also result from ingestion of spores in feces, urine, sputum, CSF, or culture. No laboratory-acquired infections have been reported with Acanthamoeba spp., Balamuthia mandrillaris or Naegleria fowleri; however, the possibility of becoming infected by inhalation, by accidental needle-sticks, or through exposure to mucous membranes or microabrasions of the skin should be considered.

Containment Recommendations

BSL-2 and ABSL-2 practices, containment equipment, and facilities are recommended for activities with infective stages of the parasites listed.⁵ Infected arthropods should be maintained in facilities that reasonably preclude the exposure of personnel or the escape of insects (See Chapter 14). Personal protection (e.g., lab coat, gloves, face shield), in conjunction with containment in a BSC, is indicated when working with cultures, tissue homogenates, or blood containing organisms.

Special Issues

Treatment

Highly effective medical treatment for most protozoal infections exists.⁴ An importation or domestic transfer permit for this agent can be obtained from USDA/APHIS/VS.

Transfer of Agent

Importation of this agent may require CDC and/or USDA importation permits. Domestic transport of this agent may require a permit from USDA/APHIS/VS. A DoC permit may be required for the export of this agent to another country. See Chapter 12 for additional information.

Agent: Intestinal Protozoal Parasites

Intestinal protozoal parasites that pose greatest occupational risk includeCryptosporidium, Isospora, Entamoeba histolytica, and Giardia. Other intestinal pathogens of concern are some species of microsporidia, specifically Septata intestinalis and Enterocytozoon bieneusi.Cryptosporidium parvum, C. hominis, and Isospora belli cause intestinal coccidiosis, most often referred to as cryptosporidiosis and isosporiasis, respectively. Entamoeba histolytica can cause both intestinal and extraintestinal infection (e.g. liver abscess) called amebiasis, and Giardia intestinalis causes giardiasis.

Occupational Infections

Laboratory-acquired infections with Cryptosporidium spp., E. histolytica, G. intestinalis, and I. belli have been reported.^1-3 The mode of exposure in laboratory-acquired infections in this group of agents mimics the natural infection routes for the most part, and consequently, clinical symptoms are typically very similar to those seen in naturally acquired infections. For Cryptosporidium, E. histolytica, G. intestinalis, and I. belli, the common clinical manifestations are symptoms of gastroenteritis, e.g., diarrhea, abdominal pain and cramping, loss of appetite. Infection with E. histolytica may result in bloody stools.

Laboratory animal-associated infections with this group of organisms have been reported and provide a direct source of infection for laboratory personnel who are exposed to feces of experimentally ornaturally infected animals.³ HandlingCryptosporidium oocysts requires special care, as laboratory-acquired infections have occurred commonly in personnel working with this agent, especially if calves are used as the source of oocysts. Other experimentally infected animals pose potential risks as well. Circumstantial evidence suggests that airborne transmission of oocysts of this small organism (i.e., 4-6 µm diameter) may occur. Rigid adherence to protocol should reduce the occurrence of laboratory-acquired infection in laboratory and animal care personnel.

Natural Modes of Infection

All of these intestinal protozoa have a cosmopolitan distribution, and in some settings, including developed countries, the prevalence of infection can be high. The natural mode of infection for this group of organisms is typically ingestion of an environmentally hardy oocyst (for the coccidia) or cyst (for E. histolytica and G. intestinalis). The ID50, best established for Cryptosporidium, has been shown for some strains to be 5-10 oocysts.⁷ This suggests that even a single oocyst might pose a risk for infection in an exposed laboratorian. The infectious dose for other parasites in this group is not as well established, but is probably in the same range. Further, because these protozoa multiply in the host, ingestion of even small inocula can cause infection and illness. The role for animal reservoir hosts is diverse in this group of organisms. In the case of C. hominis, principally humans are infected, whereas for C. parvum, humans, cattle, and other mammals can be infected and serve as reservoir hosts for human infection. In the case of E. histolytica, humans serve as the only significant source of infection, and there is no convincing evidence that any animal serves as reservoir host for I. belli. The extent to which Giardia spp. parasitizing animals can infect humans is only now becoming better understood, but most human infection seems to be acquired from human-to-human transmission. The organisms in this group do not require more than one host to complete their life cycle because they infect, develop, and result in shedding of infectious stages all in a single host. Ingestion of contaminated drinking or recreational water has also been a common source of cryptosporidiosis and giardiasis.

Laboratory Safety

Infective stages may be present in the feces or other body fluids and tissues. Depending on the parasite, ingestion is the primary laboratory hazard. Immunocompromised persons should avoid working with live organisms. Laboratorians who work only with killed or inactivated parasite materials, or parasite fractions, are not at significant risk.

Similarly, no accidental laboratory infection with Sarcocystis has been reported, although care should be exercised when working with infected meat products to avoid accidental ingestion. It is not known if laboratorians could be accidentally infected through parenteral inoculation of Sarcocystis; nevertheless caution should be exercised when working with cultures, homogenates,etc.

Containment Recommendations

BSL-2 and ABSL-2 practices, containment equipment, and facilities are recommended for activities with infective stages of the parasites listed. ⁵ Primary containment (e.g., BSC) or personal protection (e.g., face shield) is especially important when working with Cryptosporidium. Oocysts are infectious when shed (i.e., are already sporulated and do not require further development time outside the host), often are present in stool in high numbers, and are environmentally hardy.

Commercially available iodine-containing disinfectants are effective against E. histolytica and G. intestinalis, when used as directed, as are high concentrations of chlorine (1 cup of full-strength commercial bleach [~5% chlorine] per gallon of water [1:16, vol/vol]).^1,2

If a laboratory spill contains Cryptosporidium oocysts, the following approach is recommended.² A conventional laboratory detergent/cleaner should be used to remove contaminating matter from surfaces (e.g., of bench tops and equipment). After organic material has been removed, 3% hydrogen peroxide (i.e., undiluted, commercial hydrogen peroxide, identified on the bottle as 3% or "10 vol" hydrogen peroxide) can be used to disinfect surfaces; dispensing bottles that contain undiluted hydrogen peroxide should be readily available in laboratories in which surfaces could become contaminated. Affected surfaces should be flooded (i.e., completely covered) with hydrogen peroxide. If surfaces are contaminated by a large volume of liquid, to avoid diluting the hydrogen peroxide, absorb the bulk of the spill with disposable paper towels. Dispense hydrogen peroxide repeatedly, as needed, to keep affected surfaces covered (i.e., wet/moist) for ~30 minutes. Absorb residual hydrogen peroxide with disposable paper towels and allow surfaces to dry thoroughly (10 to 30 minutes) before use. All paper towel litter and other disposable materials should be autoclaved or similarly disinfected before disposal. Reusable laboratory items can be disinfected and washed in a laboratory dishwasher, by using the "sanitize" cycle and a detergent containing chlorine. Alternatively, immerse contaminated items for ~1 hour in a water bath preheated to 50°C; thereafter, wash them in a detergent/disinfectantsolution.

Special Issues

Treatment

Highly effective medical treatment exists for most protozoal infections; treatment with nitazoxanide for Cryptosporidium is now available, but efficacy has not been proven.⁴

Transfer of Agent

Importation of these agents may require CDC and/or USDA importation permits. Domestic transport of these agents may require a permit from USDA/APHIS/VS. A DoC permit may be required for the export of this agent to another country. See Chapter 12 for additional information.

Agent: Trematode Parasites

Trematode parasites that pose greatest occupational risk are theSchistosoma spp., although others including Fasciola are of concern.Schistosoma mansoni causes intestinal schistosomiasis or bilharziasis, also known as Manson’s blood fluke, in which the adult flukes reside in the venules of the bowel and rectum. Fasciola hepatica, the sheep liver fluke, causes fascioliasis, where the adult flukes live in the common and hepatic bile ducts of the human or animal host.

Occupational Infections

Laboratory-acquired infections with S. mansoni and F. hepatica have been reported, but accidental infections with other Schistosoma spp. could also occur.^1,2 By nature of the infection, none have been directly associated with laboratory animals, with the exception of infected mollusk intermediate hosts.

Laboratory-acquired infections with F. hepatica may be asymptomatic, but could have clinical manifestations such as right upper quadrant pain, biliary colic, obstructive jaundice, elevated transaminase levels, and other pathology associated with hepatic damage resulting from migration of the fluke through the liver en route to the bile duct. Most laboratory exposures to schistosomes would result in predictably low worm burdens with minimal disease potential. However, clinical manifestations of infection with S. mansoni could include dermatitis, fever, cough, hepatosplenomegaly, and adenopathy.

Natural Modes of Infection

Fasciola hepatica has a cosmopolitan distribution and is most common in sheep-raising areas, although other natural hosts include goats, cattle, hogs, deer, and rodents. Snails in the family Lymnaeidae, primarily species ofLymnaea, are intermediate hosts for F. hepatica, and release cercaria that encyst on vegetation. Persons become infected with F. hepatica by eating raw or poorly cooked vegetation, especially green leafy plants such as watercress, on which metacercariaehave encysted.

Schistosoma mansoni is widely distributed in Africa, South America, and the Caribbean; the prevalence of infection has been rapidly changing in some areas. Infection occurs when persons are exposed to free-swimming cercariae in contaminated bodies of water; cercariae can penetrate intact skin. The natural snail hosts capable of supporting development of S. mansoniare various species of Biomphalaria.

Laboratory Safety

Infective stages of F. hepatica (metacercariae) and S. mansoni (cercariae) may be found, respectively, encysted on aquatic plants or in the water in laboratory aquaria used to maintain snail intermediate hosts. Ingestion of fluke metacercariae and skin penetration by schistosome cercariae are the primary laboratory hazards. Dissection or crushing of schistosome-infected snails may also result in exposure of skin or mucous membrane to cercariae-containing droplets. Additionally, metacercariae may be inadvertently transferred from hand to mouth by fingers or gloves, following contact with contaminated aquatic vegetation or aquaria.

All reported cases of laboratory-acquired schistosomiasis have been caused by S. mansoni, which probably reflects the fact that many more laboratories work with S. mansoni than with other Schistosoma spp. However, accidental infection with S. haematobium, S. japonicum, and S. mekongi could easily occur in the same manner as described for S. mansoni.

Exposure to cercariae of non-human species of schistosomes (e.g., avian species) may cause mild to severe dermatitis (swimmer’s itch).

Containment Recommendations

BSL-2 and ABSL-2 practices, containment equipment and facilities are recommended for laboratory work with infective stages of the parasites listed.⁵ Gloves should be worn when there may be direct contact with water containing cercariae or vegetation with encysted metacercariae from naturally or experimentally infected snail intermediate hosts. Long-sleeved laboratory coats or other protective garb should be worn when working in the immediate area of aquaria or other water sources that may contain schistosome cercariae. Water from laboratory aquaria containing snails and cercariae should be decontaminated (e.g., ethanol, hypochlorite, iodine, or heat) before discharged to sanitary sewers.

Special Issues

Treatment

Highly effective medical treatment for most trematode infections exists.⁴

Transfer of Agent

Importation of these agents may require CDC and/or USDA importation permits. Domestic transport of these agents may require a permit from USDA/APHIS/VS. A DoC permit may be required for the export of this agent to another country. See Chapter 12 for additional information.

Agent: Cestode Parasites

Cestode parasites of potential risk for laboratorians include Echinococcusspp., Hymenolepis nana, and Taenia solium. Echinococcosis is an infection caused by cestodes in the genus Echinococcus; E. granulosus causes cystic echinococcosis, E. multilocularis causes alveolar echinococcosis, and E. vogeli and E. oligarthrus cause polycystic echinococcosis. Humans serve as intermediate hosts and harbor the metacestode or larval stage, which produces a hydatid cyst. Hymenolepis nana, the dwarf tapeworm, is cosmopolitan in distribution and produces hymenolepiasis, or intestinal infection with the adult tapeworm. Taenia solium, the pork tapeworm, causes both taeniasis (infection of the intestinal tract with the adult worm), and cysticercosis (infection of subcutaneous, intermuscular, and central nervous system with the metacestode stage or cysticercus).

Occupational Infections

No laboratory-acquired infections have been reported with any cestode parasite.

Natural Modes of Infection

The infectious stage of Echinococcus, Hymenolepis, and Taenia is the oncosphere contained within the egg. Hymenolepis nana is a one-host parasite and does not require an intermediate host; it is directly transmissible by ingestion of feces of infected humans or rodents. The life cycles of Echinococcus and Taenia require two hosts. Canids, including dogs, wolves, foxes, coyotes, and jackals, are the definitive hosts for E. granulosus, and various herbivores such as sheep, cattle, deer, and horses are the intermediate hosts. Foxes and coyotes are the principle definitive hosts for E. multilocularis, although dogs and cats also can become infected and rodents serve as the intermediate hosts. Bush dogs and pacas serve as the definitive and intermediate hosts, respectively, for E. vogeli. Dogs also may be infected. Echinococcus oligarthrus uses wild felines, including cougar, jaguarondi, jaguar, ocelot, and pampas cat, as definitive hosts and various rodents such as agoutis, pacas, spiny rats, and rabbits serve as intermediate hosts. People become infected when eggs shed by the definitive host are accidentally ingested. For T. solium, people can serve both as definitive host (harbor the adult tapeworm), and as accidental intermediate host (harbor the larval stages cysticerci). Pigs are the usual intermediate host, becoming infected as they scavenge human feces containing eggs.

Laboratory Safety

Infective eggs of Echinococcus spp. may be present in the feces of carnivore definitive hosts.³ Echinococcus granulosus poses the greatest risk because it is the most common and widely distributed species, and because dogs are the primary definitive hosts. For T. solium, infective eggs in the feces of humans serve as the source of infection. Accidental ingestion of infective eggs from these sources is the primary laboratory hazard. Ingestion of cysticerci of T. solium (Cysticercus cellulosae) leads to human infection with the adult tapeworm. For those cestodes listed, the ingestion of a single infective egg from the feces of the definitive host could potentially result in serious disease. Ingestion of the eggs of H. nana in the feces of definitive hosts (humans or rodents) could result in intestinal infection.

Although no laboratory acquired infections with either Echinococcus spp. or T. solium have been reported, the consequences of such infections could be serious. Laboratory acquired infections with cestodes could result in various clinical manifestations, depending upon the type of cestode. Human infection with Echinococcus spp. could range from asymptomatic to severe. The severity and nature of the signs and symptoms depends upon the location of the cysts, their size, and condition (alive versus dead). Clinical manifestations of a liver cyst could include hepatosplenomegaly, right epigastric pain, and nausea, while a lung cyst may cause chest pain, dyspnea, and hemoptysis. For T. solium, ingestion of eggs from human feces can result in cysticercosis, with cysts located in subcutaneous and intermuscular tissues, where they may be asymptomatic. Cysts in the central nervous system may cause seizures and other neurologic symptoms. Ingestion of tissue cysts of T. solium can lead to development of adult worms in the intestine of humans. Immunocompromised persons working with these cestodes must take special care as the asexual multiplication of the larval stages of these parasites makes them especially dangerous to such persons.

Containment Recommendations

BSL-2 and ABSL-2 practices, containment equipment, and facilities are recommended for work with infective stages of these parasites.⁵ Special attention should be given to personal hygiene (e.g., hand washing) and laboratory practices that would reduce the risk of accidental ingestion of infective eggs. Gloves are recommended when there may be direct contact with feces or with surfaces contaminated with fresh feces of carnivores infected with Echinococcus spp., humans infected with T. solium, or humans or rodents infected with H. nana.

Special Issues

Treatment

Highly effective medical treatment for most cestode infections exists.⁴

Transfer of Agent

Importation of these agents may require CDC and/or USDA importation permits. Domestic transport of these agents may require a permit from USDA/APHIS/VS. A DoC permit may be required for the export of this agent to another country. See Chapter 12 for additional information.

Agent: Nematode Parasites

Nematode parasites that pose greatest occupational risk include the ascarids, especially Ascaris and Baylisascaris; hookworms, both human and animal; Strongyloides, both human and animal; Enterobius; and the human filariae, primarily Wuchereria and Brugia. Ancylostoma braziliense and A. caninumcause hookworm infection in cats and dogs, respectively. Ascaris lumbricoides causes ascariasis and is known as the large intestinal roundworm of humans. Enterobius vermicularis, known as the human pinworm or seatworm, causes enterobiasis or oxyuriasis. Strongyloides, the threadworm, causes strongyloidiasis. Ancylostoma, Ascaris, andStrongyloides reside as adults in the small intestine of their natural hosts, whereas E. vermicularis colonizes the cecum and appendix.

Occupational Infections

Laboratory associated infections with Ancylostoma spp., A. lumbricoides, E. vermicularis, and Strongyloides spp. have been reported.^1-3 Laboratory infections with hookworms and Strongyloides presumptively acquired from infected animals have been reported. Allergic reactions to various antigenic components of human and animal ascarids (e.g., aerosolized antigens) may pose risk to sensitized persons. Laboratory-acquired infections with these nematodes can be asymptomatic, or can present with a range of clinical manifestations dependent upon the species and their location in host. Infection with hookworm of animal origin can result in cutaneous larva migrans or creeping eruption of the skin. Infection with A. lumbricoides may produce cough, fever, and pneumonitis as larvae migrate through the lung, followed by abdominal cramps and diarrhea or constipation from adult worms in the intestine. Infection with E. vermicularis usually causes perianal pruritis, with intense itching. Infection with animal Strongyloides spp. may induce cutaneous larva migrans.

Natural Modes of Infection

Ancylostoma infection in dogs and cats is endemic worldwide. Human infection occurs through penetration of the skin. Cutaneous larva migrans or creeping eruption occurs when infective larvae of animal hookworms, typically dog and cat hookworms, penetrate the skin and begin wandering.Ancylostoma larvae can also cause infection if ingested. These larvae do not typically reach the intestinal tract, although A. caninum has on rare occasions developed into non-gravid adult worms in the human gut. Ascaris lumbricoides infection is endemic in tropical and subtropical regions of the world. Infection occurs following accidental ingestion of infective eggs. Un-embryonated eggs passed in the stool require two to three weeks to become infectious, and Ascaris eggs are very hardy in the environment.

Enterobius vermicularis occurs worldwide, although infection tends to be more common in school-age children than adults, and in temperate than in tropical regions. Pinworm infection is acquired by ingestion of infective eggs, most often on contaminated fingers following scratching of the perianal skin. Eggs passed by female worms are not immediately infective, but only require several hours’ incubation to become fully infectious. Infection with this worm is relatively short (60 days on average), and reinfection is required to maintain an infection.

Strongyloides infection in animals is endemic worldwide. People become infected with animal Strongyloides when infective, filariform larvae penetrate the skin, and can develop cutaneous creeping eruption (larva currens).

Laboratory Safety

Eggs and larvae of most nematodes are not infective in freshly passed feces; development to the infective stages may require from one day to several weeks. Ingestion of the infective eggs or skin penetration by infective larvae are the primary hazards to laboratory staff and animal care personnel. Development of hypersensitivity is common in laboratory personnel with frequent exposure to aerosolized antigens of ascarids. Ascarid eggs are sticky, and special care should be taken to ensure thorough cleaning of contaminated surfaces and equipment. Caution should be used even when working with formalin-fixed stool samples because ascarid eggs can remain viable and continue to develop to the infective stage in formalin.⁸

Working with infective eggs of other ascarids, such as Toxocara andBaylisascaris, poses significant risk because of the potential for visceral migration of larvae, including invasion of the eyes and central nervous system. Strongyloides stercoralis is of particular concern to immunosuppressed persons because potentially life-threatening systemic hyperinfection can occur. Lugol’s iodine kills infective larvae and should be sprayed onto skin or laboratory surfaces that were contaminated accidentally. The larvae of Trichinella in fresh or digested tissue could cause infection if accidentally ingested. Arthropods infected with filarial parasites pose a potential hazard to laboratory personnel.

Containment Recommendations

BSL-2 and ABSL-2 practices, containment equipment, and facilities are recommended for activities with infective stages of the nematodes listed here.⁵ Exposure to aerosolized sensitizing antigens of ascarids should be avoided. Primary containment (e.g., BSC) is recommended for work that may result in aerosolization of sensitization from occurring.

Special Issues

Treatment

Highly effective medical treatment for most nematode infections exists.⁴

Transfer of Agent

Importation of these agents may require CDC and/or USDA importation permits. Domestic transport of these agents may require a permit from USDA/APHIS/VS. A DoC permit may be required for the export of this agent to another country. See Chapter 12 for additional information.

References

1. Herwaldt BL. Laboratory-acquired parasitic infections from accidental exposures. Clin Microbiol Rev. 2001:14:659-88.
2. Herwaldt BL. Protozoa and helminths. In Fleming DO and Hunt DL (eds). 4^th ed. Biological Safety: Principles and Practices. Washington, DC, ASM Press, 2006.
3. Pike RM. Laboratory-associated infections: summary and analysis of 3921 cases. Health Lab Sci 1976;13:105-14.
4. The Medical Letter [www.medicalletter.org]. New York: The Medical Letter; [cited 2007]. Drugs for Parasitic Infections; [about 24 screens].
5. Hankenson FC, Johnston NA, Weigler BJ, et al. Zoonoses of occupational health importance in contemporary laboratory animal research. Comp Med. 2003;53:579-601.
6. van Gool T, Biderre C, Delbac F, Wentink-Bonnema E, Peek R, Vivares CP. Serodiagnostic studies in an immunocompetent individual infected with Encephalitozoon cuniculi. J Infect Dis 2004;189:2243-9.
7. Messner MJ, Chappel CL, Okhuysen PC. Risk assessment for Cryptosporidium: a hierarchical Bayesian analysis of human dose response data. Water Res 2001;35:3934- 40.
8. Ash LR, Orihel TC. Parasites, a guide to laboratory procedures and identification. Chicago: ASCP Press; 1991.