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PARASITOLOGY > TISSUE NEMATODES > Flashcards

TISSUE NEMATODES Flashcards

1
Q

Classify the major filarial worms based on the final habitat of adult worms in the human host.

A
  • Cutaneous filarial worms - Onchocerca volvulus, Loa loa , Mansonella streptocerca .
  • Lymphatic filarial worms - Wuchereria bancrofti, Brugia timori, Brugia malayi . Their vectors are mosquitoes.
  • Body cavity filarial worms - Mansonella perstans , Mansonella ozzardi.
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2
Q

State some of the causative agents of Lymphatic filariasis.

A

Caused by adult worms of :
* Wuchereria bancrofti
* Brugia malayi
* Brugia timori

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3
Q

Geographical distribution of Brugia malayi species ?

A

Mainly causes filariasis in Malaysia.

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4
Q

Briefly describe the concept of periodicity in regards to filariid worms.

A
  • Adult worms are found in the lymphatic vessels where the females release tiny larvae called microfilariae, into the lymph.
  • The microfilariae are swept into the peripheral blood , where they are found only during specific times of the day .
    *The periodicity depends on the blood feeding habits of their insect vector.
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5
Q

Difference in location of adults and microfilariae of filariid worms?

A
  • Adults are found in the lymphatic system.
  • Microfilariae are found in the blood - the microfilariae do not cause symptoms.
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6
Q

Striking feature of filariasis caused by Wuchereria bancrofti.

A

Elephantiasis - morbid enlargement of the limbs , breasts and genitalia.
* Occurs only in cases of chronic infection/ after years of infection by the parasite.

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7
Q

What is the primary cause of inflammation in infections caused by Wuchereria bancrofti ?

A
  • Adult worms infecting the lymph tissues are the primary cause of inflammatory and fibrotic reactions.
  • They cause inflammation that eventually obstructs the lymphatic vessels, causing edema.
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8
Q

What is the pathogenesis of Elephantiasis in infections caused by Wuchereria bancrofti?

A
  • It is an immunopathologic response to the presence of mature or dying adult worms in the lymph tissues.
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9
Q

State the major mosquito species that act as vectors for Wuchereria bancrofti worms.

A
  • Anopheles
  • Culex
  • Aedes
  • Mansonia
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10
Q

After penetrating the skin and entering the lymph nodes, how long does it take for the larvae of W. bancrofti to mature into adults that produce microfilariae?

A

About 1 year.

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11
Q

Only definitive host for Wuchereria bancrofti?

A

Humans .

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12
Q

What is the role of Wolbachia in the life cycle of Wuchereria bancrofti?

A
  • The Wolbachia species are Rickettsia like bacteria found intracellularly within filarial nematodes like Wuchereria & Onchocerca.
  • They release endotoxin like molecules which play a role in the pathogenesis of Wuchereria infections.
  • The bacteria have a symbiotic relationship with the adult parasites that cause Lymphatic filariasis, hence are a key component for their survival in the human host.
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13
Q

State the location of the Wolbachia species .

A

Found in the gut of the parasite.

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14
Q

What evidence proves the existence of a symbiotic relationship between Wolbachia bacteria and Wuchereria bancrofti?

A
  • In treatment of patients infected with Wuchereria bancrofti, a drug called Doxycycline can be used.
  • This drug targets and kills the Wolbachia bacteria, upon which the Wuchereria are dependent.
  • Death of Wolbachia results in death of the adult worms , resulting in a reduction in the number of microfilaria .
  • The inflammatory response to the nematode infection also reduces subsequently.
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15
Q

State some of the early clinical manifestations of filariasis caused by Wuchereria bancrofti.

A
  • AFL - Acute Filarial Lymphangitis - inflammation of the lymph vessels.
    – Painful lymph nodes, edema , and inflammation which spreads from the site of affected lymph nodes.
  • ADLA - Acute Dermatolymphangioadenitis.
  • Lymphadenitis .
  • Abscess of lymph nodes.
  • Headaches.
  • Fever.
  • Chills.
  • Orchitis - painful and swollen testicles.
  • Epididymitis - painful and swollen epididymis.
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16
Q

State some of the major clinical manifestations of ADLA.

A
  • Acute Dermatolymphangioadenitis is associated with:
  • Swelling of the affected limb.
  • Inflammation.
  • Fever .
  • General malaise.
  • Progression of lymphedema.
17
Q

State some of the macroscopic features that can be used to identify the microfilaria of Wuchereria bancrofti.

A
  • Sheathed microfilariae - the sheath stains with hematoxylin stain.
  • Nuclei are clearly separated.
  • The nuclei do not extend to the tip of the tail ( exhibits no terminal nuclei ).
  • The tail of the microfilaria tapers to a delicate point.
18
Q

What is the cause of Tropical Pulmonary Eosinophilia in infections by Wuchereria bancrofti?

A
  • TPE is a condition caused by presence of microfilariae in the lungs. These microfilariae elicit the TPE which is an immediate hypersensitivity reaction characterized by coughing and wheezing especially at night.
  • Majorly occurs in Asia.
19
Q

State some of the major clinical manifestations of Tropical Pulmonary Eosinophilia.

A
  • Coughing and wheezing especially at night.
  • Chest pains.
  • Shortness of breath.
  • Blood stained sputum .
  • Splenomegaly - enlargement of the spleen .
  • Massive enlargement of lymph nodes in children.
  • Pulmonary infiltrates in adults.
20
Q

What are the features likely to be found in a blood sample from a patient with Tropical Pulmonary Eosinophilia?

A
  • Absence of microfilariae from the circulating blood.
  • Intense eosinophilia - accompanied by high levels of IgE .
  • Presence of antifilarial antibodies.
21
Q

State some of the clinical manifestations that occur in later stages of infection by Wuchereria bancrofti.

A
  • Lymphedema of the legs, arms and breasts . This is caused by blockage of lymphatic flow in lymphatic channels .
  • Elephantiasis - massive enlargement of the legs, arms , breasts and scrotum. The skin also becomes rough.
  • Secondary bacterial infections - bacteria may penetrate through the interdigital spaces.
  • Hydrocele - fluid accumulation in the scrotum , leading to swelling.
  • Chyluria - production of whitish urine due to rupturing of lymphatics into the urinary system.
22
Q

What are the means of diagnosing a patient with filariasis caused by Wuchereria bancrofti?

A
  • History of living in an endemic zone for many years.
  • Physical examination findings e.g elephantiasis, hydrocele & lymphedema.
  • Examination of blood samples obtained from the patients.
  • DEC Provocation test.
  • Ultrasound of the scrotum to observe the Filarial Dance Sign .
23
Q

What is the appropriate time to obtain blood samples from patients for examination of microfilariae of Wuchereria bancrofti?

A
  • The samples should preferably be obtained at night - from 10pm to 2pm .
  • This is because the microfilariae of Wuchereria bancrofti exhibit nocturnal periodicity, they mainly appear at night.
  • Blood samples should therefore be collected at night to coincide with appearance of the microfilariae.
24
Q

What are some of the findings from Serological tests that may be useful in diagnosis of infections by Wuchereria bancrofti?

A
  • Presence of IgG antibodies.
  • Presence of CFAs - Circulating Filarial Antigens. These are more specific because they are part of the invading parasite.
  • Patients with active filarial infections have elevated levels of antifilarial IgG4 in the blood - these can be detected with routine assays.
25
Q

How does the DEC Provocation test help in diagnosis of Wuchereria?

A
  • If the patient has the parasite , a 50mg dose of Diethyl carbamazine will agitate the microfilariae to come into the peripheral blood in less than 30 minutes.
  • The microfilariae can then be examined to determine whether they are of the Wuchereria species.
26
Q

State some of the blood tests useful in diagnosis of Wuchereria.

A
  • Thick blood smears - A thick blood smear sample obtained from the patient at night may reveal the microfilariae when viewed microscopically. The smear should be stained with Giemsa or Haematoxylin and Eosin stain.
  • Capillary Tube Exam.
  • Blood filter test ( nucleopore ) .
  • Concentration techniques are recommended for increased sensitivity.
27
Q

State the drugs that are effective in treatment of filariasis caused by Wuchereria bancrofti.

A
  • Diethyl carbamazine - Drug of Choice.
  • Ivermectin.
  • Albendazole.
  • Doxycycline can also be used to kill the Wolbachia which in turn kills the parasite.
    – DEC and Ivermectin are the most effective and can be used either individually or in combination with Albendazole.
  • Albendazole cannot treat the Lymphatic filariasis on its own.
28
Q

Effectiveness of Ivermectin?

A
  • Kills only the microfilariae but not the adult worms which are responsible for the pathologies such as lymphedema and hydrocele.
29
Q

What precautions should be taken when prescribing Diethyl carbamazine to patients diagnosed with Wuchereria bancrofti?

A
  • DEC should not be prescribed in places where there is Onchocerciasis occurring together with LFs .
  • DEC may be contraindicated in such cases.
  • It may worsen Onchocercal eye disease.
  • It may also cause adverse reactions in patients with loiasis e.g encephalopathy and death.
30
Q

State some of the measures useful in the prevention of spread of Wuchereria bancrofti.

A
  • Vector control - through use of insecticides and larvicides .
  • Personal protective measures - treated mosquito nets , insect repellents, protective clothing and sleeping in air conditioned rooms.
  • Annual treatment with DEC or Ivermectin to kill the microscopic worms . Use of DEC treated salt. Annual mass treatment reduces the levels of microfilariae in the blood, thus diminishing the transmission of infections.
  • Health education on the prevalence of the parasites, spread , clinical manifestations and control measures against it .

PARASITOLOGY (11 decks)

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