Parasites

Detail of an engraving of an allegory of Peru introducing Science to the Cinchona tree, the source from which quinine was derived.

Image from: "Peru Offers a Branch of Cinchona to Science (17th Century Engraving).jpg." Wikimedia Commons. Uploaded November 20, 2009. Accessed June 30, 2023. https://commons.wikimedia.org/wiki/File:Peru_offers_a_branch_of_cinchona_to_Science_(17th_century_engraving).jpg

1. Explain the difference between nematodes, cestodes, and trematodes.

Answer below.

All three are helminths, which is a non-taxonomic term used to classify parasitic worms.

Nematodes are roundworms, like Ascaris lumbricoides, Loa loa, Acyclostoma duodenale, and many more.

Cestodes and trematodes are also called "platyhelminths," as they are flat, parasitic worms. Cestodes are tapeworms, which are usually characterized by the presence of proglottids, which are independent but connected segments that often contain both male and female sexual organs and are responsible for producing eggs. Examples of cestodes include Taenia solium (the responsible agent of cysticercosis), Echinococcus granulosus (the responsible agent of hydatid disease), and Diphyllobothrium latum.

Trematodes are flatworms which include flukes and schistosomes. Examples include Schistosoma mansoni, Clonorchis sinensis, and Paragonimus westermani.

Maguire JH. "Introduction to Helminth Infections," in: Mandell, Dogulas, and Bennett's Principles and Practice of Infectious Diseases. Bennett JE, Dolin R, Blaser MJ, eds. 9th edition. Elsevier; 2020: 3433-3435.

2. Describe Löffler syndrome.

Answer below.

An acute, transient pneumonitis associated with substernal discomfort, shortness of breath, cough, fever, and eosinophilia. This occurs due to the larval migratory phase of nematodal infections, most commonly described due to ascariasis, but can occur with other nematode infections.

American Academy of Pediatrics. Ascaris lumbricoides Infections. In: Kimberlin DW, Barnett ED, Lynfield R, Sawyer MH, eds. Red Book: 2021 Report of the Committee on Infectious Diseases. Itasca, IL: American Academy of Pediatrics. 2021: 210-211

3. What are first-line agents for ascariasis?

Answer below.

Albendazole, mebendazole, and pyrentel pamoate.

4. Name the 2 hookworm species for which humans are the only reservoirs.

Answer below.

Ancylostoma duodenale and Necator americanus. Ancylostoma ceylanicum was previously considered a nonhuman parasite, but it has become an increasingly common infection in Asia, although it is primarily a zoonotic infection. Many other hookworms can be found throughout nature, and in humans may lead to cutaneous larva migrans, but they do not develop further or causes systemic infection.

American Academy of Pediatrics. Hookworm Infections. In: Kimberlin DW, Barnett ED, Lynfield R, Sawyer MH, eds. Red Book: 2021 Report of the Committee on Infectious Diseases. Itasca, IL: American Academy of Pediatrics. 2021: 421-2

Mejia R, Weatherhead J, Hotez PJ. "Intestinal Nematodes (Roundworms)," in: Mandell, Dogulas, and Bennett's Principles and Practice of Infectious Diseases. Bennett JE, Dolin R, Blaser MJ, eds. 9th edition. Elsevier; 2020: 3436-3442.

5. Name three treatments for hookworm infection.

Answer below.

Albendazole, mebendazole, and pyrentel pamoate.

6. Which tapeworm may cause human infection after accidental ingestion of a dog or cat flea?

Answer below.
-

Dipylidium caninum. According to the Centers for Disease Control and Prevention: "Most infections with Dipylidium caninum are asymptomatic. Pets may exhibit behavior to relieve anal pruritis (such as scraping anal region across grass or carpeting). Mild gastrointestinal disturbances may occur. The most striking feature in animals and children consists of the passage of proglottids. These can be found in the perianal region, in the feces, on diapers, and occasionally on floor covering and furniture. The proglottids are motile when freshly passed and may be mistaken for maggots or fly larvae."

Centers for Disease Control and Prevention. DPDx - Laboratory Identification of Parasites of Public Health Concern. Page last reviewed: July 10, 2019. Accessed June 6, 2023. https://www.cdc.gov/dpdx/dipylidium/index.html

7. What is the treatment of choice for balantidiasis?

Answer below.

Tetracyclines. Alternative drugs include metronidazole, iodoquinol, and nitazoxanide. The causative agent of balantidiasis is Balantidium coli, a ciliated protozoan. It is the largest pathogenic protozoan known to infect humans. Pigs are the primary reservoir, but it can be found in other domestic animals. While many human infections are asymptomatic, clinical manifestations include bloody or watery diarrhea, abdominal pain, anorexia, and weight loss. Overall, the presentation can be very similar to that of Entamoeba histolytica.

American Academy of Pediatrics. Balantidium coli Infections. In: Kimberlin DW, Barnett ED, Lynfield R, Sawyer MH, eds. Red Book: 2021 Report of the Committee on Infectious Diseases. Itasca, IL: American Academy of Pediatrics. 2021: 226

8. What are the two most common etiologic agents of human echinococcosis?

Answer below.

Echinococcus granulosus and Echinococcus multilocularis. The causative agents of hydatid cyst disease, high prevalence regions for these tapeworms include the Middle East, South America, East Africa, the Mediterranean, China, and Central Asia. Small foci of endemic transmission have been reported in the American West. Classically the infection is passed between dogs, coyotes, wolves, jackals, and other canine species and through sheep or other intermediate hosts. Other Echinococcus species reported to cause occasional human infections include vogeli and oligarthus.

American Academy of Pediatrics. Other Tapeworm Infections. In: Kimberlin DW, Barnett ED, Lynfield R, Sawyer MH, eds. Red Book: 2021 Report of the Committee on Infectious Diseases. Itasca, IL: American Academy of Pediatrics. 2021: 747-50

9. What is the treatment of choice for Strongyloides stercoralis infection?

Answer below.

Ivermectin. An alternative agent is albendazole, although this is reported to have lower cure rates.

American Academy of Pediatrics. Strongyloidiasis. In: Kimberlin DW, Barnett ED, Lynfield R, Sawyer MH, eds. Red Book: 2021 Report of the Committee on Infectious Diseases. Itasca, IL: American Academy of Pediatrics. 2021: 727-9

10. Name an infectious contraindication to the use of ivermectin in an individual with strongyloidiasis.

Answer below.

Coinfection with Loa loa. Ivermectin treatment in an individual with loiasis can provoke migration of microfliariae into the CNS and precipitate encephalopathy. This is an extremely rare phenomenon, however; out of 800,000 individuals who received mass ivermectin treatment for onchocerciasis in West, Central, and East Africa, only 65 cases or so of probably Loa loa-related encephalopathy were recorded.

Twum-Danso NA. Loa loa encephalopathy temporally related to ivermectin administration reported from onchocerciasis mass treatment programs from 1989 to 2001: implications for the future. Filaria J. 2003 Oct 24;2 Suppl 1(Suppl 1):S7.

11. What is preferred treatment for scabies in immunocompetent individuals >2 months of age?

Answer below.

Topical 5% permethrin cream. Two or more applications a week apart is usually recommended. Young children may require application on the entire head, neck, and body. All household members should be treated, regardless of symptoms. Bedding and clothing used within 3 days of treatment should also be laundered in hot water and dried using a hot cycle.

Oral ivermectin is also effective, but must be given as 2 doses 7-14 days apart, as it is not ovicidal. Note that ivermectin is not approved for children weighing less than 15 kg or pregnant women. An additional alternative regimen is 5-10% precipitated sulfuer compounded into petrolatum.

American Academy of Pediatrics. Scabies. In: Kimberlin DW, Barnett ED, Lynfield R, Sawyer MH, eds. Red Book: 2021 Report of the Committee on Infectious Diseases. Itasca, IL: American Academy of Pediatrics. 2021: 663-5

12. What is the treatment of choice against all three species known to cause lymphatic filariasis?

Answer below.

Diethylcarbamazine (DEC). This drug is both microfilaricidal and active against the adult worm. Note that it cannot be used in individuals with Loa loa or onchocerciasis as it can exacerbate skin or eye involvement or precipitate encephalopathy.

Combination therapy with doxycycline has also been used in the Global Program for Elimination of Lymphatic Filariasis.

American Academy of Pediatrics. Lymphatic Filariasis. In: Kimberlin DW, Barnett ED, Lynfield R, Sawyer MH, eds. Red Book: 2021 Report of the Committee on Infectious Diseases. Itasca, IL: American Academy of Pediatrics. 2021: 490-2

13. Why is doxycycline effective as a macrofilaricidal drug in lymphatic filariasis?

Answer below.

Doxycycline targets Wolbachia species, an intracellular rickettsial-like bacterial endosymbiont in adult worms.

14. Name all three etiologic agents of human lymphatic filariasis.

Answer below.

Wuchereria bancrofti, Brugia malayi, Brugia timori.

15. How is severe malaria defined?

Answer below.

Any of the following: cerebral malaria (characterized by altered mental status, seizures, increased intracranial pressure, coma); severe anemia; hypoglycemia; renal failure; respiratory failure; abnormal bleeding; jaundice; metabolic acidosis; vascular collapse and shock; and hyperparasitemia (>5% of erythrocytes are infected).

American Academy of Pediatrics. Malaria. In: Kimberlin DW, Barnett ED, Lynfield R, Sawyer MH, eds. Red Book: 2021 Report of the Committee on Infectious Diseases. Itasca, IL: American Academy of Pediatrics. 2021: 490-2

Centers for Disease Control and Prevention. Malaria - Disease. Page last reviewed: March 22, 2022. Accessed June 6, 2023. https://www.cdc.gov/malaria/about/disease.html

16. What is the treatment of choice in hookworm disease?

Answer below.

Albendazole and mebendazole are recommended. Pyrentel pamoate is considered an effective alternative.

17. What infections should be considered in a child adopted from abroad with peripheral eosinophilia but negative stool ova and parasite examinations?

Answer below.

Toxocara, Strongyloides, Schistosoma, and lymphatic filariasis, depending on the child's region of origin. These are not the only parasitic infections that may lead to peripheral eosinophilia in the absence of evident GI tract infection, although they are relatively more common depending on the region of origin.

American Academy of Pediatrics. Medical Evaluation for Infectious Diseases for Internationally Adopted, Refugee, and Immigrant Children. In: Kimberlin DW, Barnett ED, Lynfield R, Sawyer MH, eds. Red Book: 2021 Report of the Committee on Infectious Diseases. Itasca, IL: American Academy of Pediatrics. 2021: 163

18. What proportion of raccoons in the US harbor Baylisascaris parasites?

Answer below.

22 to 80%, depending on the region of the United States. Baylisascaris procyonis is a raccoon roundworm. Infection typically presents with nausea, fever, and fatigue. Neural larval migrans and CNS invasion may occur 2-4 weeks following initial infection, and outcomes are typically devastating. Additional complications include ocular larva migrans and subacute neuroretinitis and visceral larva migrans.

American Academy of Pediatrics. Baylisascaris Infections. In: Kimberlin DW, Barnett ED, Lynfield R, Sawyer MH, eds. Red Book: 2021 Report of the Committee on Infectious Diseases. Itasca, IL: American Academy of Pediatrics. 2021: 229

19. What is the treatment of choice for Baylisascaris infections?

Answer below.

Albendazole for up to 10-20 days is typically recommended for preventative therapy for children and adults who may have ingested material contaminated with raccoon feces. Adjunctive high-dose steroids are recommended in patients with clinical baylisascariasis.

Centers for Disease Control and Prevention. Parasites - Baylisascaris Infection: Resources for Health Professionals. Page last reviewed: August 28, 2019. Accessed June 7, 2023. https://www.cdc.gov/parasites/baylisascaris/health_professionals/index.html

20. Which roundworm is responsible for 90% of lymphatic filariasis cases globally? Where is it found?

Answer below.

Wuchereria bancrofti. It is found in Haiti, the Dominican Republic, Guyana, northeast Brazil, sub-Saharan and North Africa, and Asia from india through the Indonesia archipelago to the Western Pacific Islands.

American Academy of Pediatrics. Lymphatic filariasis. In: Kimberlin DW, Barnett ED, Lynfield R, Sawyer MH, eds. Red Book: 2021 Report of the Committee on Infectious Diseases. Itasca, IL: American Academy of Pediatrics. 2021: 490-1

21. What is "Laveran's bib"?

Answer below.

The remnant of a host erythrocyte cell membrane seen as a thin membrane surrounding a falciparum gametocyte.

Centers for Disease Control and Prevention. DPDx - Laboratory Identification of Parasites of Public Health Concern. Page last reviewed: October 6, 2020. Accessed June 7, 2023. https://www.cdc.gov/dpdx/malaria/index.html

22. Which antiparasitic drug is most effective at treating adult tapeworms in taeniasis?

Answer below.

Praziquantel.

American Academy of Pediatrics. Tapeworm Diseases. In: Kimberlin DW, Barnett ED, Lynfield R, Sawyer MH, eds. Red Book: 2021 Report of the Committee on Infectious Diseases. Itasca, IL: American Academy of Pediatrics. 2021: 744-7

23. What kind of antiparasitic treatment is indicated for patients with calcified cysticercal cysts?

Answer below.

None. Patients with calcified cysts do not benefit from antiparasitic treatment.

24. How should ocular cysticercosis be treated?

Answer below.

Surgical excision of cysts only. Antihelminthics will exacerbate inflammation. In factm before starting antihelminthics in any patient with cysticercosis, ophthalmic examination is necessary to exclude ocular disease.

25. How should patients with viable or colloidal cysticerci be treated?

Answer below.

Albendazole or Praziquentel therapy, AND the addition of corticosteroids in patients with CNS basilar or subarachnoid, extensive parenchymal, or spinal cysticerci to decrease adverse effects from the host inflammatory response. This is also true for patients with arachnoiditis, vasculitis, or diffuse cerebral edema. Surgical management is indicated in patients with ocular disease. Intraventricular cysticerci with hydrocephalus also requires surgical management. Spinal cysticercosis may also benefit from surgical management.

26. Describe the appearance of gametocytes seen in Plasmodium falciparum infection.

A. Compact with abundant dark pigment
B. Crescent- or sausage-shaped

C. Round to oval with Schüffner’s dots

D. Amoeboid with pseudopodial processes

Answer below.
-

B. Crescent- or sausage-shaped. "Gametocytes of Plasmodium falciparum are crescent- or sausage-shaped, and are usually about 1.5 times the diameter of an RBC in length. The cytoplasm of the macrogametocytes (female) are usually a darker, deeper blue; the cytoplasm of the microgametocytes (male) is usually more pale. The red chromatin and pigment is more coarse and concentrated in the macrogametocytes than the microgametocytes. Sometimes in thin blood smears, the remnants of the host RBC can be seen; this is often referred to as Laveran’s bib."

Centers for Disease Control and Prevention. DPDx - Laboratory Identification of Parasites of Public Health Concern. Page last reviewed: October 6, 2020. Accessed June 7, 2023. https://www.cdc.gov/dpdx/malaria/index.html

27. What is the treatment for crusted scabies?

Answer below.

With both topical and systemic therapy. From the Centers for Disease Control and Prevention: "Topical permethrin should be administered every 2-3 days for 1-2 weeks to treat crusted scabies..." and "...ivermectin should be administered together with a topical agent. Oral ivermectin (200µg/kg/dose) should be taken with food. Depending on infection severity, ivermectin should be taken in three doses (approximately days 1, 2, and 8), five doses (approximately days 1, 2, 8, 9, and 15), or seven doses (approximately days 1, 2, 8, 9, 15, 22, and 29)."

Centers for Disease Control and Prevention. Parasites - Scabies: Medications. Page last reviewed: October 2, 2019. Accessed June 7, 2023. https://www.cdc.gov/parasites/scabies/health_professionals/meds.html

28. What is a reactive condition that can follow successful scabies treatment?

Answer below.

Itching may not subside for several weeks even with successful treatment, since itching is a reaction to the mite. In addition, some individuals can suffer postscabetic pustolosis, which is an episodic eruption of sterile, pruritic papules and pustules in an acral distribution.

29. Name 4 different treatment options for scabies.

Answer below.

Topical permethrin 5%; off-label ivermectin; 10% crotamiton cream or lotion; precipitated sulfur; lindane is not generally used due to safety concerns.

30. Describe Katayama syndrome and name the etiologic agent.

Answer below.

Katayama syndrome is a consequence of Schistosoma infection, most often seen in nonimmune hosts, like travelers. This condition develops 4-8 weeks following initial exposure, when worms develop into adults and begin egg deposition. Katayama syndrome consists of an acute serum-sickness-like illness with fever, malaise, cough, rash, abdominal pain, hepatosplenomegaly, diarrhea, nausea, lymphadenopathy, and eosinophilia.

American Academy of Pediatrics. Schistosomiasis. In: Kimberlin DW, Barnett ED, Lynfield R, Sawyer MH, eds. Red Book: 2021 Report of the Committee on Infectious Diseases. Itasca, IL: American Academy of Pediatrics. 2021: 666-8

31. Six trematodes are responsible for human schistosomiasis. Which five are responsible for intestinal schistosomiasis? Which one is responsible for urogenital schistosomiasis?

Answer below.

S mansoni, S japonicum, S mekongi, S guineensis, and S intercalatum cause intestinal schistosomiasis. S haemotobium is responsible for urogenital schistosomiasis.

32. What is the drug of choice for elimination of the hepatic stage of malaria parasites?

Answer below.

Primaquine.

American Academy of Pediatrics. Drugs for Parasitic Infections. In: Kimberlin DW, Barnett ED, Lynfield R, Sawyer MH, eds. Red Book: 2021 Report of the Committee on Infectious Diseases. Itasca, IL: American Academy of Pediatrics. 2021: 972-6

33. Which malaria species necessitates the use of primaquine for elimination of hyponozoite stage plasmodia?

Answer below.

P vivax or P ovale.

34. How can schizonts be differentiated between P vivax and P ovale?

Answer below.
-

P vivax has more merozoites (typically described as 12-24), versus P ovale has fewer (4-16).

Centers for Disease Control and Prevention. DPDx - Laboratory Identification of Parasites of Public Health Concern. Page last reviewed: October 6, 2020. Accessed June 7, 2023. https://www.cdc.gov/dpdx/malaria/index.html

35. Describe the treatment for onchocerciasis.

Answer below.

Ivermectin decreases dermatitis and reduces risk of ocular disease, but it does not kill adult worms. Because it is not curative, ivermectin is given every 6-12 months until the patient becomes asymptomatic. Moxidectin is a newly approved medication that shows superiority to ivermectin Neither medication can be given in pregnancy.

A 6-week course of doxycycline can be given instead of years' worth of ivermectin.

American Academy of Pediatrics. Ochocerciasis. In: Kimberlin DW, Barnett ED, Lynfield R, Sawyer MH, eds. Red Book: 2021 Report of the Committee on Infectious Diseases. Itasca, IL: American Academy of Pediatrics. 2021: 550-2

36. Why is doxycycline an alternative treatment aside from ivermectin for ochocerciasis?

Answer below.

Doxycycline depletes the endosymbiotic rickettsia-like bacteria Wolbachia. These bacteria appear to be necessary for the survival of O volvulus. A 6-week course is usually recommended to obviate the need for years of ivermectin treatment.

37. Which forms of cysticercosis require coadministration of corticosteroids with antihelminthic therapy?

Answer below.

CNS basilar or subarachnoid, extensive parenchymal, or spinal cysticerci require coadministration of steroids with antihelminthic therapy to decrease adverse effects from the host inflammatory response. This is also true for patients with arachnoiditis, vasculitis, or diffuse cerebral edema.

38. What kind of secondary infections are seen in individuals with Strongyloides hyperinfection?

Answer below.

Gram-negative sepsis and meningitis. Strongyloides hyperinfection syndrome typically occurs in immunocrompromised individuals, such as those receiving systemic corticosteroids, or in recipients of solid organ or hematopoietic stem cell transplants.

39. Which tapeworm (also known as the dwarf tapeworm) is acquired by ingestion of infected fleas or beetles, as we well as the fecal-oral route?

Answer below.

Hymenolepis nana. Dipylidium caninum can also be acquired through accidental ingestion of dog or cat fleas.

40. Which tapeworm is the most common tapeworm of dogs and cats?

Answer below.

Dipylidium caninum.

41. Describe the management of cystic Echinococcus granulosus infection (liver hydatid cyst).

Answer below.

It's a little complicated for practice question, and treatment ultimately depends on sonographic staging and the circumstances of the case, but the systemic antiparasitic of choice is albendazole (given for several weeks before and after any surgical or percutaneous intervention, followed by several weeks to months thereafter), along with surgical excision of cysts. PAIR therapy is also used in when large, uncomplicated liver cysts are present. This consists of Puncture, Aspiration, Injection of protoscolicidal agents, and Reaspiration. Contraindications to PAIR therapy include communication of liver cysts with the biliary tract, superficial cysts, and heavily septated cysts.

Centers for Disease Control and Prevention. Parasites - Echinococcosis: Resources for Health Professionals. Page last reviewed: May 21, 2020. Accessed June 8, 2023. https://www.cdc.gov/parasites/echinococcosis/health_professionals/index.html

42. What are the two stages of Trypanosoma cruzi in the human body?

Answer below.

Bloodstream trypomastigotes infect cells in various tissues, where they transform into intracellular amastigotes and undergo binary fission, eventually releasing more bloodstream trypomastigotes.

Centers for Disease Control and Prevention. DPDx - Laboratory Identification of Parasites of Public Health Concern. Page last reviewed: June 16, 2021. Accessed June 8, 2023. https://www.cdc.gov/dpdx/trypanosomiasisamerican/

43. How many different malarial species are there? Which ones are the main causes of human infection? Which additional zoonotic malarias have been reported to cause occasional human infection?

Answer below.

There are over 150 Plasmodium species reported to cause infections in vertebrate species. Of these, 4 are of main concern to human health: falciparum, ovale, vivax, and malariae. Another 4 zoonotic species have been reported to cause human malaria: knowlesi, cynomolgi, brasilianum, and simium.

Centers for Disease Control and Prevention. DPDx - Laboratory Identification of Parasites of Public Health Concern. Page last reviewed: October 6, 2020. Accessed June 8, 2023. https://www.cdc.gov/dpdx/malaria/index.html

Ramasamy R. Zoonotic malaria - global overview and research and policy needs. Front Public Health. 2014 Aug 18;2:123.

44. Describe the life cycle and stages of malaria in the mosquito vector.

Answer below.

The Plasmodium's replication within the mosquito is called the sporogonic cycle. The vector mosquito ingests a blood meal from a host, and in the process ingests microgametocytes (male) and macrogametocytes (female). The microgametocytes penetrate the macrogametocytes while in the mosquito's stomach, generating a zygote, which becomes motile and elongated, the ookinete stage. The ookinete invades the midgut wall of the mosquito and becomes an oocyst. The oocyst grows, ruptures, and releases sporozoites. These migrate to the mosquito's salivary glands, and are inoculated into the next host for the mosquito's blood meal.

45. What does a blood smear from a patient with falciparum infection with only mature gametocytes potentially represent (isolated gametocytaemia)?

Answer below.

Successful treatment. Antimalarials are often not gametocidal, especially not against mature gametocytes. Interestingly, antimalarials may even precipitate gametocytogenesis, and some believe this is a precursor to population antimalarial resistance.

Drakeley C, Sutherland C, Bousema JT, Sauerwein RW, Targett GA. The epidemiology of Plasmodium falciparum gametocytes: weapons of mass dispersion. Trends Parasitol. 2006 Sep;22(9):424-30.

Peatey CL, Skinner-Adams TS, Dixon MW, McCarthy JS, Gardiner DL, Trenholme KR. Effect of antimalarial drugs on Plasmodium falciparum gametocytes. J Infect Dis. 2009 Nov 15;200(10):1518-21.

46. Describe the life cycle and stages of malaria in the human host.

Answer below.

Sporozoites are inoculated into the human host as the mosquito vector takes its blood meal. These sporozoites infect the host liver cells and mature into schizonts. The schizonts subsequently rupture and release merozoites into the host bloodstream. (Of note, vivax and ovale are capable of a dormant stage--hypnozoites--that can persist in the liver for years). The merozoites infect host erythrocytes, producing trophozoites. Trophozoites will produce further schizonts and merozoites, continuing the erythrocytic cycle, or produce gametocytes, which will be ingested by another mosquito during a blood meal.

47. How is paragonimiasis contracted?

Answer below.

Paragonimiasis is attributed to the lung fluke, the trematode Paragonimus, of which multiple species are capable of causing human disease (westermani, heterotremus, africanus, uterobilateralis, kellicotti, skrjabini). Classical paragonimiasis is caused by the adult flukes and eggs of P westermani and P heterotremus. Transmission occurs when raw or undercooked freshwater crabs or crayfish containing larvae are ingested. Pickled and soy sauce-marinated products may contain live larvae and can be a risk factor for transmission. P kellicotti infection has occurred among people consuming undercooked crayfish in the Midwestern United States.

American Academy of Pediatrics. Paragonimiasis. In: Kimberlin DW, Barnett ED, Lynfield R, Sawyer MH, eds. Red Book: 2021 Report of the Committee on Infectious Diseases. Itasca, IL: American Academy of Pediatrics. 2021: 554-5

48. What are the clinical manifestations of paragonimiasis?

Answer below.

Patients may be asymptomatic or only have mild symptoms, but pulmonary infections are associated with chronic cough, dyspnea. Onset may be insidious. Heavy infestations can lead to severe hemoptysis, eosinophilic pleural effusion, pneumothorax, bronchiectasis, and pulmonary fibrosis. Extrapulmonary manifestations can occur to aberrant migration of immature flukes, involving the liver, spleen, abdominal cavity, intestinal wall, and CNS. Cerebral paragonimiasis is the most common extrapulmonary manifestation, especially in children.

49. What is the treatment of choice of paragonimiasis?

Answer below.

Praziquantel for 2-3 days. Triclabendazole is an alternative that is approved for tratment of human fascioliasis with activity against Paragonimus. Adjunctive corticosteroids may be needed for patients with CNS paragonimiasis to reduce the inflammatory response against dying flukes.

50. What are some treatment options for pediculosis capitis?

Answer below.

Permethrin 1% lotion, pyrethrin products, malathion 0.5%, spinosad 0.9% suspension, abametapir lotion, ivermectin lotion, oral ivermectin. Lindane is not recommended due to toxicity.

American Academy of Pediatrics. Pediculosis capitis. In: Kimberlin DW, Barnett ED, Lynfield R, Sawyer MH, eds. Red Book: 2021 Report of the Committee on Infectious Diseases. Itasca, IL: American Academy of Pediatrics. 2021: 567-71

51. What do most patients experience who are infected with Entamoeba histolytica?

Answer below.

Nothing. Most cases of E histolytica infection are noninvasive and asymptomatic.

American Academy of Pediatrics. Amebiasis. In: Kimberlin DW, Barnett ED, Lynfield R, Sawyer MH, eds. Red Book: 2021 Report of the Committee on Infectious Diseases. Itasca, IL: American Academy of Pediatrics. 2021: 190-3

52. How might an amebic granuloma (ameboma) present? How would it be treated?

Answer below.

An annular lesion of the colon possibly palpable on exam. These usually do not require surgery and resolve with antiamebic therapy.

53. What is the treatment for amebiasis?

Answer below.

Asymptomatic cyst excreters: treat with an intraluminal amebicide alone (paromomycin, diiohydroxyquinolone/iodoquinol, or diloxanide furoate).

Invasive colitis (mild to moderate to severe intestinal symptoms): treat with metronidazole or tinidazole, followed by an intraluminal amebicide (paromomycin if there is no intestinal obstruction, diiohydroxyquinolone/iodoquinol, or diloxanide furoate).

Nitazoxanide is used off-label for mild to moderate amebic colitis.

54. What is the drug of choice for Naegleria fowleri amebic meningoencephalitis?

Answer below.

Amphotericin B is usually used as the backbone in combination with other drugs, including azithromycin, fluconazole, miltefosine, and rifampin. There have been 4 US survivors of primary amebic meningoencephalitis. These patients also received dexamethasone to control cerebral edema.

American Academy of Pediatrics. Amebic Meningoencephalitis and Keratitis. In: Kimberlin DW, Barnett ED, Lynfield R, Sawyer MH, eds. Red Book: 2021 Report of the Committee on Infectious Diseases. Itasca, IL: American Academy of Pediatrics. 2021: 193-6

55. What is thought to be the route of entry for Balamuthia mandrillaris?

Answer below.

Balamuthia have been isolated in soil, although their exact environmental niche is not clear. It is believed they enter via the respiratory tract or primary cutaneous lesions and then disseminate to the brain. Fatal encephalitis transmitted from a donated organ has also been reported.

One Thousand Days of Plague

Parasites

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