Trichinella

Parasite nematode

There Trichinella is a nematode parasite that is the protagonist of infections known as trichinosis or trichinellosis: we are talking about an omnipresent cylindrical worm in nature, transmitted to man through the ingestion of infected, raw or undercooked meats. Trichinella infections require immediate drug therapy: therapeutic delay can be fatal for the victim. Trichinellae can in fact induce the death of the host from heart attack, kidney complications or severe respiratory system compromise.

Microbiological description

Also called Trichina, the multicellular parasites Trichinella belong to the phylum of the Nematodes and to the order of Trichurida.

The Trichinelle have a cylindrical and fusiform body; they have a tubular alimentary tract that extends from the anterior end (mouth) to the opposite one (anus).
The anterior portion of the Trichinellae is typically tapered, while the posterior one, swollen and rounded, contains the genital glands.
The male Trichinella is smaller than the female, and is provided with a testicle and two conical spicules. It is estimated that the female Trichinella is capable of producing up to 1,500-2,000 larvae in its lifetime.

From the pathological point of view, the most interesting species belonging to the genus "Trichinella" are:

• Trichinella spiralis: probably the most important species of the genus Trichinella. It is found in many carnivorous and omnivorous animals from all over the world
• Trichinella britovi: found in carnivores of Europe and western Asia
• Trichinella nelsoni: Trichinella species found in predators of Africa (eg hyenas and lions)
• Trichinella pseudospiralis: the parasite has been isolated from mammals and birds everywhere
• Trichinella murrelli: parasite found in wild animals of the USA
• Native Trichinella: parasite typical of arctic animals such as bears and foxes

Two other Trichinella species have been identified (T. papuae And T. zimbabwensis, respectively in New Guinea and in Tanzania) which do not appear to carry trichinellosis in humans.

Biological cycle

The biological cycle of Trichinella is rather unusual: the small parasites of the genus Trichinella mature in the intestinal tract of an intermediate host (eg pigs, foxes, cats, bears). The adult females of Trichinella produce small groups of live larvae: crossing the intestinal wall of the host, the Trichinella larvae, greedy for blood, first enter the bloodstream, then the lymphatic one. Within a short time, the Trichinelles reach the striated muscle tissue. , where they encyst and enclose themselves in a capsule.
Humans can contract the infection by eating raw or battered meat infected with Trichinella. In humans, the Trichinella cysts are digested in the stomach; subsequently, the larvae migrate into the intestinal tract of the victim, where they begin a new life cycle. Over six weeks, the females of Trichinella release the larvae which subsequently encyst. , causing pain, fever and, in severe cases, death.

Trichinellosis is caused by the ingestion of raw or undercooked meat containing encysted larvae (except for T. pseudospiralisAnd T. papuae which do not encyst) of the various species of Trichinella.

. After exposure to gastric acid and pepsin, the larvae are released from the cysts

and invade the mucosa of the small intestine where they develop into adult worms

. Females measure 2.2 mm in length; males 1.2 mm. These worms live about four weeks in the small intestine. After a week the females release their eggs

which migrate into the striated muscles where they encyst

.

Symptoms

For further information: Trichinosis Symptoms

The characteristic symptoms of Trichinella infections essentially depend on the infectious load, the Trichinella strain involved and the reactivity of the host.
Trichinella is a sneaky parasite: after 2-4 days from the intake of raw / undercooked meat infected with Trichinella, man complains of purely gastrointestinal symptoms. After 1-3 weeks, the clinical picture of the victim precipitates into intense muscle pain, edema, fever and skin rashes. Let's see in detail the most recurrent symptoms that distinguish the different developmental stages of the disease.

1. Gastrointestinal phase (after 24-48 hours from "infection): the patient complains of diarrhea, abdominal pain, vomiting and fever.
2. Muscle phase (7 days after the infection): once arrived in the muscular tissues of the host (man), the Trichinella larvae cause joint pain, periorbital and facial edema, headache, petechiae and itching. Larval encystment in the muscles causes weakness and myalgia. Conjunctivitis is also a fairly common symptom in this phase of trichinellosis.
3. Critical phase: the vital functions of the patient can be severely compromised when the Trichinella infection spreads in the various parts of the organism. Possible complications include: central nervous system involvement (ataxia, confusion, convulsions, delirium, depression, respiratory paralysis, dizziness), adrenal insufficiency, myocarditis, obstruction of blood vessels and lung damage (pulmonary haemorrhage, shortness of breath, pneumonia, cough ). In the most serious cases - albeit rare - death occurs within 2-8 weeks: in the absence of treatment, the patient dies as a result of pneumonia, pulmonary embolism, encephalitis, arrhythmia or heart failure.

Let us briefly recall that milder Trichinellosis infections can be completely asymptomatic, therefore the patient does not realize the infection. It is estimated that 90-95% of patients with Trichinellosis complain of mild symptoms: in this case, the " infection tends to resolve without complications.

Diagnosis and therapies

For the recognition of Trichinella in meat, laboratory investigations are necessary: ​​the molecular biopsy ascertains the presence of these parasites (first-line diagnostic test). Numerous immunological tests are also currently available. Other diagnostic tests may be required in case of suspected CNS involvement: ECG (electrocardiogram), rachycentesis (lumbar puncture), electromyography.
The treatment of choice for the treatment of mild trichinellosis is purely symptomatic, therefore aimed at removing the symptoms: in this sense, the most suitable drugs are analgesics and corticosteroids (eg prednisone). For the more severe forms, thiabendazole may be effective in eliminating adult Trichinella parasites from the human gastrointestinal tract. Albendazole is also quite suitable for this purpose, while mebendazole (associated with steroid drugs) is useful for invasive forms.

Prevention

The prevention of Trichinella infections is rather simple and obvious: cooking (> 62 ° C) or freezing meat - especially pigs and other wild animals - reduces the risk of infection. Despite what has been stated, freezing does not constitute a very effective method of killing Trichinella larvae.