Parasitic worm egg preservation

A mature  Trichuris  worm

A mature Trichuris worm

A    Trichuris    egg

A Trichuris egg

Trichuriasis

Trichuriasis is a tropical disease caused by a soil-based helminth worm called Trichuris trichiura, or whipworm, and is the third most common roundworm-based disease in the world. Persistent infection leads to colonic prolapse, and early age infection can lead to severe anemia, growth retardation, and impaired cognitive development. Trichuriasis is also one of the Bill and Melinda Gates Foundations's seven most high-opportunity tropical diseases in terms of eradication. Using a grant from the Gates Foundation, we study the potential for egg preservation and transport of the related species found in pigs Trichuris suis

 

Life Cycle and transmission

The life cycle of   Trichuris trichiura  involves stages both   inside and outside of the body. 

The life cycle of  Trichuris trichiura involves stages both inside and outside of the body. 

A key part of the Trichuris life cycle requires the eggs to develop outside of the host's body, which happens in soil. The disease is contracted via fecal-oral transmission, commonly occurring when human waste is used as fertilizer for food crops. Lack of proper sanitation leads to contaminated feces ending up in crop soils, thus perpetuating the infection cycle.

Lab diagnosis under most conditions is rudimentary, and involves a fecal smear suspended in a water and identification of eggs  using basic microscopy. Eggs have characteristic hyperpolar plugs, making them straighforward to identify when purified, but in a real life scenario, seeing the eggs among the mess of other fecal material is exceedingly difficult and not reliable. Most critically, repeated freeze/thaw cycles or complete lack of cooling caused by inconsistent availability of refrigeration in the transport chain leads to egg degradation. Bacteria in the samples also cause significant issues by releasing nucleases that degrade the egg genomes, making molecular detection difficult as well. Diagnosis would be significantly improved if degradation from heat and desiccation could be prevented between field sampling and testing. 

 

egg preservation

An SEM image of a silicified  T. suis  egg at 9000x magnification

An SEM image of a silicified T. suis egg at 9000x magnification

In 2013, Dr. Stedman and Ph.D. student Jim Laidler showed that viruses could be reversibly inactivated and protected from damage by encasing them in a silica coating. Based on these findings, it was predicted that the same method could work for other microscopic entities, such as Trichuris eggs.

Some of the  T. suis  eggs that we work with under a light microscope.

Some of the T. suis eggs that we work with under a light microscope.

Our main goal for this research is to test both morphological and DNA stability after silica treatment. Is the integrity of the genomic material still sufficient enough for PCR detection after being in silica? Can we still detect the eggs microscopically? Current work is underway to answer these questions and more. 

 

Key Publications

Laidler et al., 2013