Lung Parasite Infections & Explanations - Part 2

CUTANEOUS LARVA MIGRANS - Excerpts from eMedicine

http://www.emedicine.com/ped/topic2407.htm

DIPHYLLOBOTHRIUM LATUM INFECTION (Fish Tapeworm)

Synonyms and related keywords: broad tapeworm, cestodes, diphyllobothriasis, Diphyllobothrium latum, D latum, Diphyllobothrium latum infection, fish tapeworm, megaloblastic anemia, sparganosis, vitamin B-12 deficiency.

 

Human intestinal infection with the fish tapeworm, or broad tapeworm, Diphyllobothrium latum is called diphyllobothriasis. It is endemic in areas where humans frequently consume raw or pickled fish. The associated symptomatology is nonspecific, but megaloblastic anemia is a well-described complication.

 

Cestodes, a subclass of the phylum Platyhelminthes, has 2 orders that infect humans: Cyclophyllidea and Pseudophyllidea. One of the main differentiating points between the genera of the 2 orders is that the genera of the first order typically have a scolex with 4 suckers whereas the genera of the second order have a scolex with 2 opposing sucking grooves. Another important point of differentiation is that Cyclophyllidae has 2 hosts in its life cycle whereas Pseudophyllidea requires 3.

 

A full-grown worm can vary in size from 1-15 m and is the longest human tapeworm. It consists of up to 3000-4000 proglottids. The scolex, as mentioned, has 2 sucking grooves, also called bothria. Proglottids are typically wider than they are long which is why D latum is called the broad tapeworm.

The plerocercoid larva infects humans who have incorrectly ingested heated or frozen freshwater fish. Because of the requirement for intermediate hosts, direct human-to-human transmission does not occur; therefore, no isolation measures are required.

Although actual results of infestation are not well studied, megaloblastic anemia can result. Some scientists believe the mechanism is related to the site of the worm, its marked affinity for vitamin B-12, and, perhaps, an underlying vitamin B-12 deficiency in patients at the outset.

 

Outbreaks associated with the increased popularity and availability of fresh salmon (as opposed to canned or frozen salmon) have been described. Also, infestation is related to the popularity of delicacies such as sushi. This is a worldwide disease that affects people near freshwater and appropriate intermediate hosts. Areas where consumption of raw/precooked fish is popular tend to have endemicity (eg, northern Europe, Scandinavia).

 

Occasionally, infestation can lead to severe megaloblastic anemia or intestinal obstruction.  Anemic patients can present with pallor, breathlessness, and neurological symptoms such as weakness, numbness, and disturbances in coordination. The symptoms depend on the severity.

 

 

DIROFILARIASIS (Dog Heartworm)

Synonyms and related keywords: Aedes, Anopheles, Culex, Dirofilaria immitis, D immitis, Dirofilaria lutrae, D lutrae, Dirofilaria (Nochtiella) repens, D repens, Dirofilaria spectans, D spectans, Dirofilaria striata, D striata, Dirofilaria subdermata, D subdermata, Dirofilaria tenuis, D tenuis, Dirofilaria ursi, D ursi, dirofilariasis, dog heartworm infection, human pulmonary dirofilariasis, HPD, diromicrofilaremia, Dirofilaria, canine dirofilariasis, canine dirofilariasis, antifilarials

 

The zoonotic filariae, Dirofilaria immitis and Dirofilaria (Nochtiella) repens, have become increasingly recognized worldwide as inadvertent human pathogens. The usual hosts of these infective nematodes are domestic and wild carnivores.

 

The dirofilarial life cycle, like that of all filarioids and helminthic nematodes, consists of 5 developmental or larval stages in a vertebrate host and an arthropod (mosquito) intermediate host and vector. Adult female worms produce thousands of first-stage larvae or microfilariae that a feeding insect vector ingests. Some microfilariae have a unique circadian periodicity in the peripheral circulation during a 24-hour period. The arthropod vectors, mosquitoes and flies, also have a circadian rhythm in which they obtain blood meals. The highest concentration of microfilariae usually occurs when the local vector is most actively feeding. Microfilariae then undergo 2 developmental changes in the insect. During the act of feeding, third-stage larvae are inoculated back into the vertebral host for the final 2 stages of development. Adult worms are 1-2 mm in diameter; females are 25-30 cm in length and males are typically shorter.

 

The usual definitive host of D immitis and D repens is the domestic dog, although cats, wolves, coyotes, foxes, muskrats, and sea lions may act as suitable hosts and reservoirs of the disease. Mosquitoes of the genera Aedes, Anopheles, and Culex are all suitable intermediate hosts and vectors. Some species of fleas, lice, and ticks may also act as vectors.

 

The prevalence of canine dirofilariasis has increased during the last 3 decades. Traditionally, human pulmonary dirofilariasis (HPD) has been localized predominantly to the Gulf of Mexico and southern Atlantic states, where the prevalence of canine D immitis infection has been documented to be as high as 40%. The range of canine D immitis infection now extends along the Mississippi River valley and into southern Canada. Canine dirofilariasis has been described in all of the lower 48 states, except Nevada. The geographic spread of human disease has paralleled that in the dog population.

 

The most commonly reported manifestation of human dirofilariasis worldwide is subcutaneous nodular disease caused by D repens, with more than 400 case reports in the medical literature. D repens is an Old World parasite and has not been described as endemic in the Americas, Japan, or Australia. Endemic foci for D repens exist in southern and Eastern Europe, Asia Minor, central Asia, and Sri Lanka.

 

Italy has the highest prevalence of human dirofilariasis (66%), followed by France (22%), Greece (8%), and Spain (4%). Cases of canine and human disease have been described in northern European countries, but they have been traced back to patient exposure during a southern European visit. HPD has been described in many other countries (including Brazil, France, Italy, Spain, Ukraine, Japan, India, Africa, and Australia) on all continents of the world, although it appears less common than D repens–induced subcutaneous disease. Exposure of humans to D immitis larvae has also been reported in isolated communities of Indians of the Colombian Amazon rain forest.

 

No fatality directly due to dirofilariasis has been recorded in the medical literature. HPD infection is symptomatic in 38-45% of patients. The primary significance of HPD infection in adults is the confusion and invariable radiologic misdiagnosis of a primary or metastatic lung tumor, which usually leads to thoracotomy with open lung biopsy or wedge resection of the lung to obtain the correct diagnosis.

 

D immitis infection: The reported male-to-female ratio of HPD is 2:1 in American patients. D repens infection: Women represent 55% of worldwide infections with D repens.

 

 

ECHINOCOCCOSIS (Small Tapeworm that causes hydatids, invades lungs, etc. )

Synonyms and related keywords: alveolar hydatid echinococcosis, cystic echinococcosis, echinococcosis, Echinococcus infection, Echinococcus granulosus, E granulosus, Echinococcus multilocularis, E multilocularis, Echinococcus vogeli, E vogeli, hydatid disease, hydatidosis, polycystic echinococcosis

 

Echinococcosis is the general term for 3 diseases caused by the larval stage of Echinococcus tapeworms, the smallest tapeworms in the Taeniidae family. Echinococcus granulosus causes cystic echinococcosis.

 

The tapeworm's life cycle involves a definitive host, usually a dog (although foxes and coyotes have also been implicated), and intermediate hosts such as sheep, goats, and swine. The 3- to 6-mm adult tapeworm is found in the definitive host's intestines. Eggs are excreted via the feces into the environment. Dogs typically become infected by eating the remains of infected sheep and other livestock.

 

Humans are accidental hosts and are not typically involved in the life cycle of the organism. Humans usually become infected through exposure to canine feces. Humans become infected by eating food contaminated with tapeworm eggs, which hatch in human small intestine under the influence of gastric and intestinal secretions. Larvae hatched from these eggs can penetrate the small intestine and become widely distributed in the human body. These larvae develop into a hydatid cyst. In alveolar echinococcosis, the liver is almost exclusively involved. In cystic echinococcosis, the liver is involved in two thirds of cases; in the remaining cases, other sites of involvement, in descending order of frequency, are the lung, spleen, skin, muscle, kidney, retroperitoneum, bone, heart, and brain.

 

Hydatid cysts may contain many protoscolices, each with the ability to develop into an adult tapeworm in a definitive host. The definitive host usually becomes infected by ingesting the protoscolices in hydatid cysts from the intermediate host; adult tapeworms only develop in the intestines of the definitive host.

Human disease is usually caused by the mass effect of slow-growing hydatid cysts, although bacterial superinfection or allergic symptoms from cyst rupture has also been reported. Because of the hydatid cyst's unhurried growth, infected humans may remain asymptomatic for 20 years.

 

Echinococcosis is rare. Indigenous cases have been reported in Minnesota and among Native Americans in western Alaska. Imported cases are uncommon. Echinococcosis has been reported in Manitoba, Canada. Outside North America, incidence rates vary considerably, from less than 1 case per 100,000 people in many parts of the world, to 13 cases per 100,000 people in Greece, 143 cases per 100,000 people in Argentina, 197 cases per 100,000 people in the Xinjiang province of China, and 220 cases per 100,000 people in Kenya's Turkana district.

 

Most human infection is probably asymptomatic. Death may occur from hydatid rupture, which may lead to anaphylactic shock, or from the extreme progression of cysts in vital organs.

 

HYMENOLEPIASIS (Dwarf Tapeworm)

Synonyms and related keywords: diarrhea, dwarf tapeworm, gastrointestinal infection, hymenolepiasis, Hymenolepididae, Hymenolepis diminuta, H diminuta, Hymenolepis nana, H nana, parasite, parasitic infection, rodent tapeworm

Hymenolepis nana is the cestode that most commonly infects humans, especially school-aged children. In contrast, only a few hundred human infections with the rodent tapeworm, Hymenolepis diminuta, a tapeworm for which the human is an incidental host, have been reported.

Hymenolepiasis most frequently occurs in warm, dry regions of the developing world, where exposure to human feces results in hand-to-mouth infection. Direct person-to-person spread of H nana may occur.

 

Humans become infected with H nana when they ingest infective eggs, most commonly by direct fecal-oral exposure. The eggs pass into the ileum and hatch into oncospheres (the larval form), which penetrate the lamina propria of the villus. Within 3-4 days, the larvae mature into the preadult cysticercoid, which then enters the gut lumen to attach to the mucosae of the villus. Mature adults, measuring 35-45 mm in length and comprising 150-200 proglottids, result within about 3 weeks. Self-mating between adjacent proglottids generates hundreds of eggs, some of which penetrate intestinal villa and some of which pass into the feces. Occasionally, rodents may ingest the eggs in feces and serve as incidental hosts and reservoirs for spread of infection. Although infection usually does not produce infection, autoinfection (which is common) or intense exposure may result in a symptomatic infection caused by a heavy parasite burden.

 

Human infection with H diminuta results from accidental ingestion of insects (immature fleas, flour beetles, meal worms, cockroaches) that carry the parasite in their body cavities. Infective eggs are ingested by insects and hatch in their guts. After hatching, they invade into the body cavity and become cysticercoid larvae, which are infectious for humans. After the insects are consumed and digested, the larvae are released in the small intestine and mature within 25 days into 50-cm adults. When the adult tapeworm begins to pass eggs, insect hosts can become infected again. Most infections produce no symptoms.

 

Infection is most common in the Southeast and among institutionalized children. Among more than 200,000 stool specimens submitted to the state laboratories in 1987 for ova and parasite analysis, 0.4% were positive for H nana. Because most infections do not produce symptoms, the true incidence is likely considerably higher. H nana infection affects millions of people, primarily children, worldwide. Estimated rates of infection in various regions range from 0.1-58%. Regions with high reported infection rates include Sicily (46%), Argentina (34% of school children), and southern areas of the former Soviet Union (26%). In contrast, only 0.1% of stools examined at a children's hospital in Calgary were positive for H nana. Most cases with associated neurologic symptoms have been reported from the former Soviet Union.

 

Morbidity is uncommon, only occurring when parasite burden is very high. Death has not been reported in association with this infection.