20 for 20: Day 3 : Identity crisis with feline Trichuris

 At the WAAVP conference held in Kuala Lumpur this year, one of the last talks on the last day was delivered by Dr. David Elsemore from IDEXX. IDEXX has developed a battery of fecal antigen ELISAs to detect nematode infections in small animals. This particular talk was about the detection of cat whipworms by the antigen ELISA originally designed to detect the canine whipworm. One of the advantages of the whipworm antigen ELISA is that it detects excretory-secretory antigens produced by the live worm, but not egg antigen. So, any spurious parasites are not detected, eliminating false positives. The ES whipworm antigen used is apparently involved with maintenance of the infection in the host.

The talk got me thinking about Trichuris of felines, a rather uncommon parasite in the United States. A quick search on PubMed to look for recent articles brought up a SpringerPlus article by Dr. Jennifer Ketzis, titled "Trichuris spp. infecting domestic cats on St. Kitts: identification based on size or vulvar structure?". Dr. Ketzis covers the history of the taxonomy of the two species of feline Trichuris – T. serrata and T. campanula first. It turns out that there is a debate about the existence of two species, since early descriptions were based on size of the parasite and size of the eggs with some discrepancies occurring due to the examination of only a handful of worms in some cases.  After examining 96 male and 113 females, the researchers concluded that the Trichuris found on St. Kitts is T. serrata.

So, how does one distinguish between T. serrata and T. campanula?
a. Egg size is not definitive. Both speces have typically trichuroid eggs that are light brown, with bipolar plugs and a morula, but egg sizes overlap. Also, eggs recovered from feces and from adult worms vary in size.

b. Adult worm size is not definitive either, although that had been the defining feature in the original descriptions. Worm size according to Dr. Ketzis and others seems to depend on number of worms sharing the same host, host immunity affecting worm size in repeat infections, exposure to lots of infective eggs all at once resulting in smaller adults, and natural biological variation.

c. The only distinction between the two species is the presence of a finger like vulvar projection in the females of Trichuris serrata, but not Trichuris campanula, and the presence of a bacillary band in the former.

Although there are claims that the presence of many Trichuris in cats cause gross and histopathological lesions, Dr. Bowman in Georgi’s Parasitology for Veterinarians says that they are of “little practical importance” except to complicate the differential diagnosis of feline capillariasis.

Therefore, it is incumbent upon veterinary parasitologists to interpret with caution the presence of trichuroid eggs in feline feces, given that (a) they could be other capillarids, (b) there is no molecular data available to distinguish between T. serrata and T. campanula and (c) the antigen ELISA cannot distinguish between them either.

References:

Ketzis, Jennifer K. "Trichuris spp. infecting domestic cats on St. Kitts: identification based on size or vulvar structure?." SpringerPlus 4.1 (2015): 115.

Bowman, Dwight D. Georgis' Parasitology for Veterinarians. Elsevier Health Sciences, 2014.

This post is part of a goal to write for 20 mins for 20 days.