Trichinosis is a common food-borne illness that affects a large group of individuals due to a lack of food hygiene and awareness. Read and find out all about this condition, including its symptoms, causes, diagnosis treatment and complications.
This is a dreadful infection caused by a species of roundworm called Trichinella spiralis that occurs in rats, pigs, bears and humans as a nematode parasite. It is often mistaken as “Trichomoniasis”, which is actually a sexually transmitted disease (STD) caused by a protozoan parasite called Trichomonas vaginalis.
The condition is also known by other names like:
A first-year medical student named James Paget in 1835, observed for the first time the larval form of Trichinella spiralis while conducting an autopsy at St. Bartholomew’s Hospital in London. He noticed that some muscles had white streaks and described it as a “sandy diaphragm”. However, the credit for the discovery of the larval form of Trichinella spiralis was actually given to his professor Richard Owen.
Picture 1 – Trichinosis
A group of German researchers comprising of Rudolf Virchow, Rudolf Leuckart and Friedrich Albert von Zenker conducted several experiments between 1850 and 1870. In these experiments, a dog was made to consume meat infected with the roundworm. The following necroscopy, which is an autopsy performed exclusively on animals, revealed the exact life cycle of Trichinella spiralis. The development and spread of infection was determined by Rudolf Virchow.
Trichinosis Life Cycle
A parasite generally resides within or over another organism and benefits by deriving nutrients at the expense of the host. The life cycle of the roundworm essentially determines the development of the condition. It typically involves pigs, humans, and rodents. Encapsulated cysts present in the infected pigs are consumed by humans in the form of raw or undercooked diseased pork. In humans, larvae are released in large numbers by the stomach acids like pepsin and hydrochloric acid. The development of the disorder can be divided into the following phases:
Enteral phase/Intestinal phase
The larvae migrate to the small intestine and gradually develop into adult male and female worms. These worms undergo mating within 30-34 hours after ingestion of the cysts. After 5 days, young larvae are produced that immediately get expelled from the small intestine by the immune system of the body.
Parenteral phase/Muscle phase
In this phase, the larvae penetrate the gastrointestinal tract and enter the bloodstream as well as lymph drainage system. They now start invading vital organs like retina, lymph nodes and myocardium. Larvae that get distributed in the skeletal muscle cells may survive and undergo encystation- the process by which parasites become enclosed within a cyst. Some skeletal muscle cells functions as nurse cells by supporting and protecting the larvae from getting destroyed by the immune system. These parasites are also capable of stimulating the development of blood vessels around the host cells in order to receive the required nutrients for their growth.
In most cases, the symptoms of the condition are mild and do not produce any major repercussions in the initial stage. The two phases of the condition display different symptoms that are highly dependent on factors like:
- Phase of the condition
- Number of larvae ingested
- Type of Trichinella species
- Immunity of the affected patient
Young larvae do not produce any symptoms. Mature worms inhabiting the intestine give rise to a host of features that are visible, 2 to 7 days post-infection. Some of these include:
The migration of larvae from the intestine to other parts of the body produces inflammatory reactions that give rise to the following problems:
- Muscle pain
- Puffy eyes or swelling around the eyes
- Splinter hemorrhage
In rare cases, the condition may give rise to a few neurological symptoms such as:
- Respiratory paralysis
As aforementioned, raw or undercooked pork as well as other pork products normally contain Trichinella cysts. Infected carnivores and omnivores can easily transmit the disorder to other meat-eating mammals such as humans. The diet of some individuals mainly comprises of wild game- meat of hunted animals such as turkey, pig, or duck. These animals pose huge risk of infection as they are generally contaminated and improperly cooked. There are totally 8 Trichinella species that infect humans world-wide. However, only three of them are known to cause the parasitic condition. The different species of Trichinella include:
It is found in most number of carnivorous and omnivorous animals all over the world, and is highly pathogenic to humans.
It is the most widely distributed species in Europe, Africa and Asia that infects humans.
The worm particularly inhabits Arctic and subarctic animals like polar bears, walruses and arctic foxes, owing to its high resistance to freezing.
The mammals as well as reptiles of Papua New Guinea and Thailand are usually infected by it.
It is a non-encapsulated species that is found in mammals and birds.
Infected wild carnivores in North America can adversely affect humans if consumed after a wild game.
It infects both mammals and humans residing in Africa.
African mammals, including lions and hyenas are often infected by this type of Trichinella species.
Trichinosis in dogs
Contaminated pork can also infect dogs. Vomiting, diarrhea, muscle pain and stiffness are some of the common symptoms observed. Puppies generally have a higher chance of getting infected than adult dogs.
Clinical assessment of the condition is based solely on the presence of various symptoms. It even determines the phase and severity of the disorder. The diagnosis of the condition encompasses a wide spectrum of techniques like:
Elevated levels of creatine kinase and lactate dehydrogenase indicate muscle cell damage due to the parasitic infection. Complete blood count (CBC) helps in evaluating the cellular elements of blood. The eosinophil count that specifically determines the amount of white blood cells in the blood is generally found high in infected individuals. However, the increase in WBC count occurs only during the muscle phase.
These chemical tests detect or quantify a specific component in blood or body fluid, using an immunological reaction. Qualitative immunoassays are typically used to detect antigens on infectious agents and the antibodies produced by the body against them. Indirect immunofluoresence and enzyme-linked immunosorbent assay (ELISA) are the most frequently-used techniques to determine the condition.
In this procedure, a small piece of muscle tissue is removed by using a biopsy needle and is examined microscopically for any abnormality. Identification of encysted larvae in biopsy confirms the disorder.
The condition can remain infectious for months or years as long as it does not undergo encystation in the skeletal muscle tissues. In the initial stage of infection, Antihelmenthics like albendazole and mebendazole are administered to inhibit the formation of encysted larvae. These drugs are however, not recommendable for pregnant women and children below the age of 2.
Steroids such as Pyrantel and Prednisone are used if the condition has reached the last stage. These are generally administered to ease muscle pain.
Affected individuals have an increased risk of developing the following conditions:
In developed countries like UK, USA and Germany various precautionary measures have been taken for complete eradication of the disorder. Some of these include:
Picture 2 – Trichinosis Image
The European Commission, which is the executive body of the European Union, has constituted certain laws and rules that must be followed by food producers to ensure food safety. The United States Department of Agriculture also consists of a few guidelines that strictly aim at establishing proper sanitation and inspection of the meat products.
Public education and awareness
The public must be given appropriate education regarding the harmful effects of consuming raw or undercooked meat. In many states, individuals have to complete a course in order to acquire a hunting license as hunters are at a higher risk of developing the condition.
Elimination of the number of larvae in infected meat can be accomplished by following certain techniques while cooking. Encysted larvae can be easily destroyed by cooking the meat to a temperature of 70 degrees Celsius or 158 degrees Fahrenheit, or higher. They can also be killed by freezing the meat for one week to a temperature of -30 degrees Celsius or -22 degrees Fahrenheit. The other methods that could kill the encysted larvae include:
Proper pig farming
The pigs must be given properly-cooked meat to eat and must be kept in hygienic pens. The Centers for Disease Control and Prevention, Plant Health Inspection Service, and the Foreign Origin Meat and Meat Products have given the following recommendations:
Trichinosis is not a lethal or contagious condition and is usually self-limited in majority of the patients with resolution of the clinical symptoms within a short duration of time. Individuals, who develop serious complications due to the migration of larvae to major organs, recuperate well after treatment. One must abstain from eating undercooked meat unless proper cooking techniques are followed.