Helminths

Helminths -> parasitic worms -> multicellular

Classes:

Nematoda: roundworms

-> Nematodes

Platyhelminths: flatworms with subclasses:

-> Trematodes: flukes (suckers)

-> Cestodes: tapeworms

STHs = Soil Transmitted Helminths

• highly adapted to vertebrate hosts

• among most prevalent negleted tropical diseases (NTD)

• lifecycle: egg -> intermediate -> adult

-> associated woth pverty, sanitary infrastructure

• water filtration devices -> reduce infection

• treat water source -> vector control

• containment of human and animal cases -> prevent transmission

• cash reward for case report -> raise awareness

• Trichuris spp. (whipworm)

• Acaris spp. (roundworm)

1. Oral ingestination of embryonated eggs

2. Eggs hatch in large-intestine (bacteria-driven)

3. L1 larvae -> gut epithelial cells

4. L1/L2 larvae = intra-epithelial

5. L3 and L4 -> inner gut lumen

6. Adult worms -> large intestine

7. unembryonated eggs -> fecies

8. eggs develop -> (10-15 days) embryonated eggs (infective) -> external environment

1. Oral ingestion of embryonated eggs

2. Eggs hatch -> L3/L2 -> small intestine

3. L3 -> liver

4. L3 -> lung

5. Cough -> swallow -> small intestine

6. Adult worms in small intestine

7. Shedding of unembryonated eggs

8. Develop in external environment -> infective embryonated eggs

Benzimidazole:

• Mebendazole

• Albendazole

Mass drug administration (MDA) programs:

• treatment in schools

• health education

• clean water sources

• Ancylostoma duodenale

• Necator americanus

zoonotic: accidental host -> larvae die after couple of days

human-specific: blood suckers in the small intestine -> Anemia

-> human feces

• Cutaneous route: Penetration of the skin by infective filariform larva (L3)

• Oral route: Ingestion of L3 larva present in the soil, occurs less frequency. Larva develops directly into adult worms

• Transmammary transmission: Breast feeding by mothers to infants

1. L3 penetrate skin (or ingestion)

2. L3 -> blood stream

3. -> Lung -> cough -> swallow -> intestine

4. Adult -> small intestine

5. eggs -> feces

6. Soil -> develop to Rhabiditform L1

7. L1 -> L3 -> 5-10 days -> infectious

• typical antihelminitic drugs from MDA -> low success rate & resistance over time

• development of vaccine on the way

Microfilariae (MF): smaller forms of Filariae

Filariae:

• Nematodes of the superfamily Filarioidea

• live in cavities -> never intestine

• dont lay eggs -> release MF

• day: larger vessels, deep tissue blood

• night: surface vessels -> feeding time of (mosquito) vectors

-> Tropical pulmonary eosinophilia (TPE)

• asthma-like symptoms

• Inflammation -> modifies lymphatic drainage

• time-sensitive collection -> when they are in blood stream

• thick and thin blood films

• Giemsa, Wright-Giemsa, and Delafield’s hematoxylin

• lymphatic vessels (LV) -> remove fluids, proteins form extracelular space

• Adult worms nest in LV -> response regulates severity of disease

Filariae can carry a symbiotic partner -> Wolbachia

• Loa Loa -> eye worm

• Wucheria bancrofti -> elephantantiasis -> giant testicles

• Onchocerca volvulus -> river blindness

1. L3 in vector (mosquito) -> Transmission to human

2. Adult filariae -> release of microfilariae (MF)

3. Vector -> uptake of MF

4. MF -> L2 in vector

5. L2 -> L3

• mosquitoes (W. bancrofti and Brugia spp.)

• black flies (O. volvulus)

• deer flies (L. loa).

They kill the endosymbiont Wolbachia which also causes the parasite to die

by Rudolph Virchow

1. checked larval stages on human cadaver with white flecks

2. fed an old dog infected human meat

3. found adult enternal stages of larvae in autopsie of dead dog

   
   

viviparous = gives birth to live offspring instead of laying eggs (=ovoparous)

dead-end host = human

= unique consequence of host cells association with infections of L1 larvae of T.spiralis

morphologically distinct from any other cell type

functions: nourish and protect from host immune response

—> can survive in human host up to 30 years

in intestine or tissues

polyzoic organisms: scolex, head, no mouth, no intestine

use hooks or suckers

—> infection mostly over food

Disease: Cystic Echinococcus

grow unlimited, producing protoscolices and daughter cysts

—> spontaneous cystic rupture —> abaphylactic shock

• Imaging testing like CT-scan

• ultrasonography

• MRI (only CE)

• serological test (only AE)

Granulosus —> causes CE, less serious

Multilocularis —> cause AE, mortality 50-70%

CE (Cystic echinococcal disease) —> multiple liver cysts

albendazole as neoadjuvant agent (used before other treatments) —> inactivate cysts and reduce cystic wall tension

AE (Alveolar echinococcal disease)

albendazole —> suppress progess of infection (no cure!!)