How Long Can Parasite Eggs Survive in the US Mail?

The Effects of Temperature
on Fecal Samples

Horse parasite and worm tests (a.k.a. fecal egg count tests) reveal the type and number of parasite eggs present in your horse’s feces. Conducting a parasite or worm test requires you to collect a fecal sample from your horse and send it to a laboratory for analysis.

Most mail-in parasite and worm test kits have you send your horse's sample to a lab using the US Postal Service.

So, how long can a parasite egg survive in the US Mail?

In an environment of moderate moisture and mild temperatures, horse parasite eggs (i.e., strongyles) will hatch and become infective larvae over a two or three week period. However, in the right circumstances, parasite egg hatching and fecal sample degradation of your horse's sample can be delayed up to few weeks.

Generally speaking, colder temperatures slow or stop the rate of development, and excessive heat kills parasite eggs and larvae. At the same time, other environmental factors like moisture, oxygen, and time also play a role.

What Parasites Need to Survive During Shipping (and any other time)

Graphic 1 depicts the three factors (well its actually 4) that promote parasite egg hatching into larvae.

  • Moisture content level of a sample
  • Time it takes a sample to arrive at the lab
  • Oxygen levels a sample exposed to during shipping
  • Temperature a sample is exposed to during shipping

Graphic 1 - Three Factors that affect the accuracy of fecal egg count testing

One of these factors deals with the selection and collection of your horse's sample, and the other three deal with how your horse's sample is prepared for shipping. Controlling each of these factors helps preserve the eggs and slow the hatching and degradation of the sample's parasite eggs in transit to the lab. I'll go into more detail about the effect of each of these factors on your horse's fecal sample.

Pile of horse manure

Graphic 2 - Select an ample sample that is fresh as possible

Moisture - not too wet, not too dry

Horse parasite and worm testing start with collecting an ample fecal sample from your horse, and when it comes to horse manure, the fresher, the better.  

There is no need to grab a large hunk of poo (see Graphic 2.) Select a fresh golfball size manure sample that is to quote Goldilocks, "not too dry, not too wet, not too big, and not too small but just right." BTW - Never eliminate or add water to/from your horse's sample. A typical sample will contain plenty of moisture and will not dry out during transport when properly sealed.

 

SCIENTIFIC SIDEBAR

Anaerobic – an·aer·o·bic, without oxygen. Relating to, involving, living, occurring, active, or existing without oxygen. Requiring an absences of free oxygen – which means reducing the air surrounding the object. Like when food is vacuum sealed to preserve freshness. The opposite of aerobic.

Graphic 3 - Collapse collection bags allow you to remove air from the bag to help preservate the sample during transport

Moisture - not too wet, not too dry

Horse parasite and worm testing requires an ample sample from your horse, and when it comes to horse manure, the fresher, the better.  

There is no need to grab a large hunk of poo (see Graphic 2.) Select a fresh golfball size manure sample that is "not too dry, not too wet, not too big, and not too small but just right," to quote Goldilocks. BTW - Never eliminate or add water to/from your horse's sample. A typical sample will contain plenty of moisture and will not dry out during transport when properly sealed.

Table 1 below, shows the effects of temperature on parasite eggs and larvae.

Development Temperature range Survival

No development above this level

>104o

Free‐living parasite stages die rapidly. Intact fecal balls may retain enough humidity to enable mature larvae to survive for a shorter time period

Very rapid development of the infective stage larvae (often less than 1 day)

104oF to 91.4oF

Mature larvae will die quickly, but are able to survive for a few weeks inside intact fecal balls

Optimal temperature range for development (hatching) of eggs and larvae. Larvae reach infective stage in less than 4 days

91.4oF - 77oF

Larvae survive on the shorter term (i.e., a few weeks), but conditions are too warm for long term survival

Eggs develop into infective larvae in 2–3 weeks

77oF - 50oF

Mature larvae capable of surviving for several weeks to a few months

Lower limit for egg hatching is about 43°F. Development to infective larvae will take several weeks to a few months

50oF - 42.8oF

Mature larvae survive for many weeks and months

No hatching and no development

42.8oF- 32oF

Eggs and mature larvae can survive for several months at temperatures just above the freezing point

No development during frost

<32oF

Developing larvae are killed, but unembryonated eggs and mature larvae can survive and persist for months, especially if protected by intact fecal balls and/or snow

Alternation between freezing and thawing will usually not lead to development unless temperatures exceed 43°F

<32>oF

Repeated freeze–thaw cycles are detrimental to egg and larval survival

 Table 1-Effects of temperature on persistence - Handbook of Equine Parasite Control (eBook) by Reinemeyer, C.R. & Nielsen, M.K. Second Edition Publication Date: 2018

Summary

Due to the lack of research, assumptions and opinions dominate the information landscape when it comes to the effects of temperature on equine parasites eggs and larvae. However, some recent research has determined that eggs and larvae survived for longer intervals at 23 °F and 37 °F than at 79 °F and 88 °F. At the same time, another study reported that freezing for 30 minutes over 72 hours had no effect on parasite larvae, whereas constant freezing for five or eight months did reduce their survival rate. This preliminary research seems to indicate that if eggs or maturing larvae can find appropriate cover in certain environments, parasite eggs and larvae can last for much longer than originally thought possible.

About Zero Egg Count

Zero Egg Count is an animal healthcare company offering diagnostic fecal egg count test kits and laboratory services. Zero Egg Count Parasite Test Kits are used by veterinarians, e-commerce sites, catalogs, retailers, trainers, barns, and horse owners across the United States.

Our inexpensive mail-in test kits can be used on all horses regardless of age or breed. Each kit contains all the materials you need to test your horse for internal parasites and worms. Our kits allow horse owners the freedom to pick the time they want to test—no waiting on the vet or driving to the vet's office. Just scoop, seal and send--- it's that easy.


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