Nematodes are such a group of parasites that rank high in the spread of zoonotic disease as compared to other groups of parasites.
By Asma Hamid1, Muhammad Kasib Khan1, Muhammad Adnan Sabir Mughal1, Arsalan Zafar1
Parasitic MeningoencephalitisAmong 2600 species of nematodes mostly are soil metazoan cause infection to both vertebrate and non vertebrate. Equines are most susceptible animal to host nematodes parasites due to grazing habits and many times have great load of worm eggs. Halicephalobus gingivalis is an opportunistic parasite, found in soil and decay matter, belongs to order Rhabditida, family paragrolaimidae. H. gingivalis is differentiating from its eight species morphologically by difference in size and body length. H. gingivalis cause fatal infection in horses. Micronema deletrix is synonyms for this parasite in 20th century. Generic name is mostly used for all species of H. gingivalis because all other have same morphology.
Transmission of parasites to host is unclear but hematogenous route spread parasite to other parts of body through blood and lymph, by getting entry through skin lesion and wound and contaminates the oral mucosa. Optic tract is another route of infection. H. gingivalis has been previously isolated from urine and fecal sample and fly can be carrier of larvae may be source of infection. Environmentally horse manure and compost also contain larvae.
Life cycle of H.gingivalis is very interesting as there is no sexual reproduction, only female is responsible for the production of eggs and immature larvae in large numbers by the asexual reproduction through parthenogenesis. Asexual reproduction usually takes less time as compared to sexual reproduction with male. Female finds food and shelter throughout her life and well adapted to this environment. Larvae and eggs associated with female are identified on tissue sample. Larvae of H.gingivalis are similar to adult worm but lack reproductive system.
H.gingivalis mostly cause infection in horse but other animals like donkey, zebra and recently ruminants are also susceptible for the infection of brain, spinal cord, heart ,lymph nodes, kidney, stomach and bone. Geographically it is distributed throughout the world but rare cases reported from Africa. 3 cases in human and 30 fatal infection have been reported. H. gingivalis has recently been linked to bovine meningoencephalomyelitis in ruminants, with parasites being recognized visually and the diagnosis validated by molecular analysis of the parasite’s large subunit and small subunit rRNA genes.
Clinical findings of H. gingivalis in equines and human
Equines are more susceptible to H. gingivalis infection having normal temperature, pulse, breathing and heart rate with anorexia and circling movement of animal. With the passage of time condition get worsen with seizure at short intervals of time. Horse muscles got contracted, ataxia, unable to stand due to gluteal muscle pain and swelling. Ocular pain and blepharospasm leads towards visual impairment and horse can only differentiate between black and white colors.
Postmortem finding shows kidney failure with granulomatus foci of white and grey color on both kidneys and worm larvae. Cerebellum and spinal cords of horse has granulomatous meningoencephalitis with vasculitis. Grey and white matter loaded with anti inflammatory cells along with nematodes eggs and larvae. Gross lesions present on every organs especially heart, lungs, bones, kidney, bones, lymph nodes. Death host organs have great proliferation of nematodes eggs and larvae. Human mainly have meningoencephalitis and peripheral eosinophilia with perivascular inflammation and macrophages infiltration. Cortical hypoxic ischemic injury and multiple foci of necrosis also observed in brain. Nematodes larvae and eggs infiltrated into brain and CSF.
Diagnosis and Treatment
Diagnosis is mainly done with autopsy by recognization of parasites eggs of H.gingivalis. Different development stages of egg and larvae present during examination. Previously diagnosis was done with MRI, hematology and other serum biochemical parameters.CSF fluid is obtained with lumber puncture and DNA is extracted with kit from nematodes present at the site of lesion, and with the help of PCR sequencing is done. Treatment is done with anthelmintic; usually combination of 2 drugs is used. Ivermectin has little ability to travel in to CNS, mostly Thibandazole and ivermectin in combination is used. Thiabendazole shows inhibiotory effects on hatching of eggs but not on the larvae. There is no effective treatment for H.gingivalis because poor ability of drugs to achieve therapeutic level in CNS. Treatment is successful only in that horse which have no involvement of CNS.
Management of horse with H.gingivlis should be considering. Depend upon the location of infection surgery and medical treatment must be given. Due to limited data available no specific control measures have be developed. Good pasture management and prevention from marshy environment can prevent horse from infection. In human proper hand washing is recommended after exposure of horse manure.
Authors : Asma Hamid1, Muhammad Kasib Khan1, Muhammad Adnan Sabir Mughal1, Arsalan Zafar1 Department of Parasitology, University of Agriculture, Faisalabad-38040, Pakistan