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Trichinella, hyena and humans

fserrano at unex.es fserrano at unex.es
Fri Mar 31 05:00:59 EST 2000


On 23 Mar 2000, James Mahaffy wrote:

> Folks,
> 
> In preparing for a lecture in Zoology, I mentioned that there was an
> Torrid or tropical Trichinella that is found in the hyena and some other
> carnivores in Africa. I got this information from the latest edition of
> Schmidt and Roberts who on their illustration cite ingestion by humans
> as a possible means of infection.  
> 
> However, I grew up in Africa (Eritrea) and never heard of hyena's being
> eaten.  Can anyone tell me more about this life cycle and how it can be
> transmitted to human.  About the only place I found some mention of this
> (T8) strain was in a couple of medline articles. From one of those it
> appeared that humans are not often infected and another indicated (all I
> read was abstracts) that native livestock did not carry it (as I
> recall).  
> 
Trichinella species have a wide range of hosts, some are more susceptible
than others, but the cycle is basically the same. The hyena is important
because maintain the parasite. This is a source of infection for another
animals, wich can be eaten by humans.

There are two species in Africa, probably the "tropical Trichinella" is T7
(not T8). The latest revision that I kown about Trichinella species was
made by C.M.O. Kapel and E. Pozio in the last WAAP Congress. Also Dr.
Murrell and many others can help a lot. Please visit
http://euliste.krenet.it/ict/welcome.htm for more information.   

A brief information, mainly extracted from these authors, about african
species:

Trichinella nelsoni (T7) is the etiological agent of sylvatic
trichinellosis in Africa south of the Sahara. The main reservoir is the
spotted hyena, but other carnivores can also play a role
as reservoir. The infection in wild pigs is rare; T. nelsoni have a
moderate infectivity but a good persistence in both domestic pig and wild
boar. Trichinella nelsoni have a better survival in decaying meat and at
slightly elevated temperature than the other species; an adaptation to
survival in the tropics. Human infections have been reported, but the
species has a low pathogenicity in man. 

Trichinella T8 (T8) is a genotype strictly related to T. britovi 
(T3).T8 has been detected only 3 times in carnivores from South Africa and
Namibia. There is no explanation of its genetic relationship with T.
britovi, but it could have been introduced from Europe in the l7th
century.  Trichinella britovi produce a sylvatic trichinellosis in Europe
and Asia. Muscle larvae of T3 can survive in frozen muscle tissue of
carnivores.The main reservoirs are carnivores: red fox, raccoon dog, and
others (wolf, bear, mustelids, etc.). T. britovi have a moderate
infectivity but a good persistence in wild boars, and in a lesser extent
in pigs. It has been detected also in horses. Prevalence in wild boar is
very low. 

However, in some areas, as in Extremadura (SW Spain), prevalence of
Trichinella spp. in wild boars is relatively high (about 0,25%) and is the
most important source of human infections, since humans almost never eat
carnivores and, unlike another areas of Europe, horse meat is hardly
consumed. This illustrate that even an accidental host may become 
important for humans under certain circunstances.    

-----------------------------------------
Francisco J. Serrano
Laboratorio de Parasitología
Departamento de Medicina y Sanidad Animal
Facultad de Veterinaria
Universidad de Extremadura
Avda de la Universidad s/n
10071-Cáceres (Spain)
tfno: 00 34 927 25 71 32
fax:  00 34 927 25 71 10
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