MadSci Network: Zoology
Query:

Re: What exactly are heartworms and what do they do to animals?

Date: Thu Jun 22 21:02:21 2000
Posted By: Gloria Palma, M.D., National Program of Science & Technology in Health, COLCIENCIAS
Area of science: Zoology
ID: 959295941.Zo
Message:

“Heartworm” is the common name given to  the nematode  _Dirofilaria  
immitis_ of the Class Filarioidea. All  filarids are thin, long worms 
(“philum” in Latin means “thread”) and are transmitted by  insect vectors.

Dirofilaria  infects mostly  dogs, but other animals like cats, foxes or 
wolves can also  become infected. Man is an  occasional  (accidental) 
host. The insect vectors are  mosquitoes  of the genus  _Aedes_ or  
_Anopheles_, which  transmit  infective larvae when they  obtain a blood 
meal. The larvae go  into  the conective tissues where they  mature  into  
young adults. These  worms go  into the  bloodstream and via the venous  
circulation reach  the  pulmonary  arteries. There they  mature to  
sexually  active  males and  females and copulate. Filarids, unlike other  
roundworms (nematodes)  do not lay  eggs. Instead, the female  releases  
from the uterus  embryos   known as microfilariae. These microfilariae 
reach the bloodstream and when another mosquito  obtains a boodmeal, they  
are sucked into  the insect’s gut.  Inside the  mosquito, microfilariae 
undergo changes  until they molt into  infective larvae after  several  
weeks. 

The presence  of  adult worms in the pulmonary  arteries can cause 
inflammatory  changes in the  walls of these blood vessels, which  can 
lead to  partial  occlusion of them. This  in turn can produce  pulmonary  
hypertension, which   in turn can cause  hypertrophy  of the right 
ventricle of the heart and subsequent heart failure. The  inflammatory  
changes can also  disrupt  the blood flow and thrombi  can  be produced. 
These  can  embolize to  the lungs and other organs. Additionaly, very  
heavy  infections produce large accumulations of  adult worms in the  
pulmonary  arteries and the right  ventricle, leading to   mechanical 
obstruction and failure.of these organs.  

In conclusion, heartworms will  cause   death because  of the severe  
cardiovascular changes that  they  will  induce in the host. 

 http://math.smith.edu/~sawlab/fgn/pnb/diro.html
 http://cal.vet.upenn.edu/parasit/heartworm/hw_1.html
 http://www.biosci.ohio-state.edu/~parasite/dirofilaria.html



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