This is the second lecture delivered in the winter course at IVRI,Izatnagar on 11th Dec 2013 and i am reproducing the same here . I will appreciate to receive any comments which may further the subject .It will be my pleasure if any research organisation is interested to collaborate in this endeavor.
M C AGRAWAL
FORMER NATIONATIONAL FELLOW AND EMERITUS SCIENTIST
COLLEGE OF
VETERINARY SCIENCE AND A H , JABALPUR 482001
It
is heartening to note that one part of this winter course is to teach molecular
techniques about control of parasitic diseases .In the past also, there had
been some advance courses and discussion about control of parasitic diseases .
But whether these discussions and advance courses can lead to control of parasitic diseases ? Obviously, the
answer is no. Now, with the changing time, it becomes imperative to know why we need to control parasitic diseases,
which diseases are given priorities , and how we can control these parasitic diseases. And this is what I am going to discuss ;
thus my lecture will not be a mere academic exercise of citing references from some research papers. There is now time
,we should discuss how we may try to control parasitic diseases and what should
be our research priorities that may help in achieving these goals.
If we analyze disease control
program of our country, it will be clear that the country has given top
priority ,logically ,for controlling those infectious diseases that are
affecting human population. Thus there are central government’s programs for
controlling tuberculosis, malaria, filariasis, guinea worm or naru ,polio (small pox already eradicated ) etc
Interestingly, almost no attention is paid on zoonotic aspects of these
diseases or medical faculty has not taken diseases where animals are playing
a crucial role in their maintenance. For example, we have not taken sincere steps for controlling rabies .This reflects
how wide apart are the two professions (medical and veterinary) which are
supplementary to each other to combat
zoonotic infections of the country.
When we come to animal diseases
,the control programs have been launched only to limited diseases like Rinder-pest,
FMD, anthrax with vaccination programs of these and other infectious animal
diseases. These are also the diseases ,where the veterinary hospitals
,districts and states generate the data and pass on to government of India.
Has government of India ever launched any control program related to
any parasitic disease of our domestic animal ? Here I mean control program
like that of Rinder-pest or FMD . To my knowledge, there was or is none. No doubt there have been some vaccination
programs for controlling parasitic diseases . The one was about lung-worm
vaccination for controlling lung-worm infection of sheep and goats
,particularly in Jammu & Kashmir , Himachal Pradesh ( now, vaccine
production has been stopped by IVRI though infection is still existing ). The other is Theileria vaccine produced by
NDDB and supplied for controlling theileriosis among cross bred cattle . Again
, this is not a infection which is affecting all our domestic animals. Thus we
have attempted to control a infection (lung-worm) which is restricted to
certain states or a infection which is affecting limited number of our domestic
animals. And we have shied away in
paying our attention to the parasitic diseases which are affecting almost all
domestic animals and existing in all the
states. Therefore, we have come to a crucial point where we need answer of
above questions - why we need to control
parasitic diseases, which diseases are given priorities , and how we can
control these parasitic diseases. And my this short lecture will try to discuss
some of these points with the hope that you , our young Parasitologists ,will
devote some time to find answers of these and related questions which are important for controlling
parasitic diseases in the country. Answer of these questions are important as
you will agree with me that all your research efforts will not fructify unless
and until you attempt to control the parasitic infections in our country,
thereby reduce mortality and animal production losses.
WHERE IS THE DATA :
If you go to any
funding agency or even any government, the obvious question will be why we wish
to control the particular parasitic disease. Naturally, you will put up the
data about mortality and pathology of that parasitic disease . By the way, from
where have you collected these data ? From some research paper or a review
article or from a book ? And how they
have calculated these data ?
I am sure that
your data have not been collected from
veterinary hospitals of the state or Animal Husbandry department of the country
. And when these data have not been collected from the villages whether they
are representing correct scenario of the infection is debatable.
VETERINARY RECORDS :
What I have said
above, is all because of my experiences . While working on my book
“Schistosomes and schistosomiasis in South Asia” (Agrawal,2012) ,I tried to collect the data of nasal and hepatic
schistosomiasis from veterinary hospitals and veterinary diagnostic
laboratories (division level),state and central governments ; as ,in my opinion, compilation of data from
these sources is important since research journals fail to provide a detailed
view of the infection ; these journals have not reported each and every
outbreak or prevalence of the infection in each animal species from each
geographical area .
To my dismay, I could not collect any data, related
to schistosomiasis, from any of above source ,details have been discussed in my book
.Here, it will be suffice to mention :
·
There is no
direction from the government to keep record of parasitic diseases and
details thereof. Neither any data are passed to state or central government .
·
The veterinary hospital registers are maintained in such a way that you cannot
extract any information from them. Even it is difficult to differentiate
between new and repeat cases, cattle and poultry (I have written about this topic which has
been published in the news letter of National Academy of Veterinary Sciences
when Dr S K Ranjan was the President).
·
The veterinary diagnostic laboratories are vague
in their reporting and counter checking is missing . While reporting
coprological results (generally by direct wet smear method ) ,generally
positive cases are reported as “positive
for helminth or fluke or roundworm eggs” . Thus they have not differentiated
the eggs where it was easy to differentiate .
It is clear
that we need changes in above system and a fresh outlook is needed to the problem so that we will be able to collect the data related to parasitic diseases.
WHICH PARASITIC DISEASES TO CONTROL ON
PRIORITY :
This is an
important question that if we decide to
control parasitic diseases what should be our priorities ?
Answer of this question , at first hand, appears simple i.e. the parasitic disease which is causing
greatest mortality and highest pathogenecity in domestic animals should be attended first. But how we will reach to this conclusion when we have not generated
data in this regards. And when we are attempting to generate the data, are
we using sensitive and specific methodologies ? This aspect is important else our results
will not be accurate. While deciding importance of the disease, we have to
examine its prevalence in each animal species, age and sex wise ; the seasons
when disease is occurring; animal husbandry practices and geographical areas where infection is existing.
With the above,
two more important aspects are also linked . One is the mortality occurring in
the infected animals. It may happen, looking to Indian conditions, that the
animal is not infected with single parasitic infection but multiple infections
and in such cases we have to device methods for ascribing death etiology . The
other aspect is related to pathology of the infection which is reflected to animal
production losses. No doubt we will need new methodologies to decide the above
facts and these may change as per advancement of our knowledge and environment.
If we will not follow new techniques , there are all chances of making mistakes
as has been done while reporting schistosomiasis in post-mortem cases ( Rathore,1998).
PRIORITY AMONG HELMINTHIC DISEASE :
As my present discussion
is related to schistosomiasis, I may raise a question to you – which is the
most important helminthic disease of our domestic animals ? Some of you will
answer - haemonchosis, or
gastro-intestinal nematodiasis, others may answer fasciolosis , or amphistomosis
; while some of you will say nasal schistosomiasis but a few or none will ascribe
hepatic schistosomiasis as the most important helminthic problem of our
domestic animals . May I ask the reasons
for your such conclusion ?
Those who are
ascribing fasciolosis as most important helminthic disease will put forward
their slaughter house experience where most of the livers yield adult Fasciola gigantica .Further, the faecal examination shows
presence of Fasciola eggs in many
cases ( its different that we are not differentiating eggs of Fasciola from those of amphistomes ). And
those who are new to Indian parasitology
will cite the reference of a foreign veterinary book where fasciolosis is
considered as most important helminthic disease of domestic animals.
Those who are
ascribing amphistomosis as most important will support their argument that
every rumen in slaughter house possess one or other species of amphistomes and
almost all faecal samples are positive for amphistome eggs.
Against these
arguments ,we do not have such visibility of hepatic schistosomiasis hence can
not be considered as most important helminthic disease in India. I have
discussed this topic elsewhere ( Agrawal,1999
2003) but will like to draw your attention to the need of employing correct
techniques for reaching a correct decision. As time does not permit me to go
into details of such discussion, I will mention only silent points emphasizing
how important it is to use a correct technique and unbiased attitude for
reaching to a correct conclusion. I am
mentioning some facts for your consideration and further investigations :
·
Fasciola
gigantica, the only existing Fasciola species in India , spreads through Lymnaea auricularia or Lymnaea acuminata which is a strict
fresh water aquatic snail (unlike to amphibian Lymnaea
truncatula –intermediate host for F.hepatica)
and survives only in perennial water sources hence animals will get infection
only from perennial water sources.
·
F.hepatica is more damaging to domestic animals than
F.gigantica .
·
Against one species of Fasciola, there are at-least five schistosome species (Schistosoma indicum,S.spindale,S.incognitum,
Orientobilharzia dattai and S.nasale)
which are affecting our domestic animal species.
·
Schistosome infections spread through Indoplanorbis exustus and Lymnaea luteola – both species are
capable to survive not only in perennial water sources but also in temporary
water bodies thereby giving higher geographical spread.
·
A large number of amphistome species (40-42) are
existing in the country (Dutt,1980)
some of which have been synonymized. However, only four genera have been
incriminated in pathogenesis to domestic animals .
·
In amphistomosis , it is only young animals
which suffer and that too only from immature amphistomosis.
·
Many fresh water snails are acting as
intermediate hosts for amphistomes hence their geographical spread is as large
as that of schistosomes.
Now you have to determine ,using new methodologies, which
helminthic disease is more important in our domestic animals. Here, you might
have noted one more fact ; this
importance will vary as per our husbandry practices. All these fluke infections
are important only in grazing animals with limited effect in stall fed. Thus
our priorities will vary as per animal species, husbandry practices and
geographical areas. Therefore, you will identify those parasitic diseases to be given national
importance and those with regional importance etc.
HOW TO CONTROL SCHISTOSOMIASIS :
We have come to
the last part of our lecture .And that is if we decide to control any parasitic
disease in our domestic animal , how we can control it . I will take references from
schistosomiasis which have been discussed in more details in my book
(Agrawal,2012). Indeed, this is the only helminthic disease that has been given
so much importance and where so many countries agreed to launch control program
in collaboration with WHO (1985) . Ironically , India has not participated in
such program. Interestingly, WHO have
not touched zoonotic aspects of the infection while attempting control program
of human schistosomiasis . The review of this program may high light our short comings which are important to get rid of for
achieving any success in controlling any parasitic disease and also animal schistosomiasis in India or South Asia.
MULTIPLE APPROACH :
No disease can
be controlled by following a single step approach , how so ever, effective it may be . The infection has to be
tackled from all aspects so that prevalence of it may be reduced to the levels
where further transmission becomes difficult .Following multiple approaches
were followed in schistosomiasis :
·
Chemotherapy
·
Health education
·
Snail control through use of molluscicides
·
Environmental modifications
You will realize that such
program is not possible without a large team and funds which a department of Parasitology of an
institute cannot afford . No doubt , this
control program of schistosomiasis was able to reduce prevalence rate as well
as pathogenesis ,as the latter is directly proportion to the intensity of the
infection; and the success was both due
to political will and scientific team
work . Here, it will be prudent to discuss scientific reasons for their success
and how it will fit in our program of controlling animal schistosomiasis in
India. One important difference has to be remembered that while following any
control program ,we have to monitor not one
but more than one animal species.
CHEMOTHERAPY :
The most important reason of the
success ,perhaps, was mass treatment of the population with a most effective
schistosomicide (Praziquantel) whose single oral dose @ 40-60 mg/kg body weight
was 80-95% effective in urinary and hepatic schistosomiasis . Since the weight
of children varied between 20-50 kg, the dose of Praziquantel was cost
effective, beside easy in administration .
When we compare this scenario
with that of India, our schistosome
species are different from those dealt
by WHO hence there are all differences in schistosome bionomics . And
praziquantel against any of these Indian schistosome species (S.indicum,S.incognitum, S.spindale ) has
not proved as effective as reported against S.haematobium
or S.mansoni . In fact, our
experimental work on pig- S.incognitum
model has failed to reduce schistosomes to a significant level with presence of left over schistosome
population as high as 40% ( Shames et al
2000) A same scenario was observed when
the drug was tried in other experimental models ,with schistosome reduction
ranging from 50-65% (left over fluke population between 50-35% ) , but using other Indian schistosome species.
Ironically, no available flukicide (including anthiomaline ) was found to lead
to a significant reduction in schistosome population in any experimental model,
tried in our laboratory or by other workers ( Agrawal ,2012).
Therefore, it is not advisable to
use Praziquantel or any other flukicide in any mass treatment program which has
failed to reduce schistosome population to a significant level in our animals.
This is because such use will lead to the high probability of development of
resistance of left over schistosome population against praziquantel .
One more hindrance in using
praziquantel for mass treatment in animal schistosomiasis is with regards to
its cost for treating bovines against schistosomiasis. In one field trial
against nasal schistosomiasis in Balaghat district of Madhya Pradesh , 60
tablets of Prazi Plus@ , which works out approximately to 20 mg/kg
body wt was effective in eliminating completely clinical symptoms of snoring
disease from 14 out of 18 cattle. However, cost of one treatment comes to Rs
1500/ per animal as market cost of two tablets is Rs 50/ (Agrawal, 2012) .
DIAGNOSTIC METHOD :
While implementing any control
program, it is important to monitor the rate of infection and its intensity in the given population prior and
after the treatment. This monitoring is possible by using a simple, rapid, economic but
sensitive parasitological diagnostic
technique that may detect, light ,moderate and heavy infections. In WHO case ,
Kato-Katz technique was applied that fulfilled all the above criteria and was
able even to detect light infections ( 24-96 epg) with presence of 1-4
eggs/slide, made of 41.7 mg of faeces (WHO,1985). In contrast , a very low epg ,ranging between
2-4 in ruminants and 10-50 in pigs has been reported by almost all the Indian
workers (Agrawal,2012) ; for this reason almost all egg detection methods have
poor efficacy ,cannot be employed in control program, hence warranting further work on this issue . We may
also undertake further research on hatching process, as this has proved
superior over egg detection methods.
SNAIL
CONTROL :
The snail control ,in WHO program , was undertaken by using Niclosamide
which has proved highly effective in killing the intermediate hosts i.e. Bulinus and Biomphalaria . Ironically , Niclosamide is not available in Indian
markets and has to arrange its import from other country. We were able to
procure Niclosamide and undertook both
experimental and field trials on fresh water snails , observing its high
efficacy in killing Lymnaea luteola,
Indoplanorbis exustus and Gyraulus
but without affecting other water fauna and flora (Agrawal et al ,2005, Agrawal 2012).
However,
ecological conditions of fresh water snails in India ,differ from those of
other endemic countries. In India, these are the ponds, tanks and other water
sources, both perennial and temporary , which are inhabited by these fresh water snails, where as in
endemic countries these were the rivers where snails are surviving. Thus , we have more wide spread
population of the snails , making our efforts more difficult while attempting
snail control.
BIOLOGICAL CONTROL :
As
use of chemical molluscicides may cause
environmental pollution , efforts are being made to find other alternatives for
snail control . Work is being carried out to find Plant molluscicides which are
more eco-friendly . Likewise, search is being made to find natural enemies of
the snails that may be used as biological control agents for reducing snail
population. However, it must be remembered that the biological enemy or
competitor should not be introduced from outside the country/area as they may
prove harmful afterwards as experienced by WHO (1985).
One
natural enemy of young fresh water snails has been identified by us
(Agrawal,2012) in the form of nymphets of dragonfly which co-habitat with the
snails under same ecological conditions ; these nymphets are carnivorous in
nature ,devouring young snails with their life span ranging from 1-3 years (
hence once introduced in the ponds, there is no need of re-introduction every
year ). There is the need to develop the techniques for mass production of
these nymphets which also feed on mosquito’s larvae (Agrawal 2012). Here is the
importance and need of your molecular techniques which may pave the way of
producing eggs and nymphets in large number , for their use in controlling
snails or mosquito larvae.
HYPER-PARASITISM :
As
stated above, Praziquantel and anthiomaline
are not able to kill a significant number of Indian schistosomes, which
is not the case with S.haematobium or
S.mansoni. There are also chances of
development of resistance of the schistosome population ,left over after wide use of these less
effective drugs. Therefore, there is the
need to think alternatives against chemotherapy for parasitic diseases.
One promising area of research
might be searching hyper-parasites of schistosomes or of any other parasite which is causing disease in
man and his animals. As you are aware these hyper-parasites are those organisms
which parasitize on the parasite itself e.g. schistosomes . This hyper-parasite
may be a bacteria or a virus or even a
fungus. We have to search those hyper parasites which are lethal to these
parasites and should be host specific thereby eliminating our animals or human
beings in causing any harm .
NEED OF A NATIONAL INSTITUTE OF PARASITOLOGY :
With this lecture, I tried to
discuss how ill equipped we are for launching a state or national level control
program against any parasitic disease of our domestic animals. There is the
need to re-think on our research programs and to develop methodologies which
may help directly or indirectly in controlling parasitic diseases of the nation
. But it will be a bad idea not to take any control measure and waiting for
developing proper techniques or drugs prior launching any control program .
Notwithstanding these facts , management of animal excreta may greatly help in
controlling parasitic diseases. If we start collecting all cattle dung to fill
our gobar gas plants or to convert it into vermin-compose , this will not only
control parasitic diseases but will also improve rural economy.
At last, I once again emphasize
the need of a National Institute of Parasitology in country for paying proper
attention on the parasitic diseases ,which are causing not only mortality but
also production losses thereby affecting adversely national economy. I am
avoiding repetition what I have already
said during my lecture of Dr SC Parija oration gold medal award in 2012 at Indore and which has been published in Para Sight 2 Volume 2 ,issue 1 of IAAVP
and is also posted on my blog www.indianschistosomiasis.blogspot.com
SUMMARY :
Launching of control program for
any animal disease which is causing
mortality and production losses is important for any country . Ironically , the
government of India has launched control
programs for viral and bacterial diseases but there is no control program ,ever
launched by any government against any parasitic disease of our domestic
animals. Neither , there is any system of collecting data ,related to animal
parasitic diseases, from our veterinary hospitals and veterinary diagnostic
laboratories . Therefore, it becomes difficult to answer- why we need to control parasitic diseases, which diseases are
given priorities , and how we can control
these parasitic diseases ?
When we come to the question of
how we can control animal schistosomiasis in India , we observed that our
diagnostic technique is not sensitive due to low egg production of Indian
schistosomes and requires further research. Likewise, the most effective
Praziquantel drug is not able to kill significant number of Indian schistosomes
with 35-50% left over blood-flukes . To circumvent this situation, it will be
prudent to find out hyper-parasites of schistosomes and other parasites which
will selectively kill these without harming their hosts. However, it will be
futile to wait for developing proper techniques. Instead , animal excreta may
be collected at mass scale and may be used in gobar gas plants or for preparing
vermin-compose which will not only reduce prevalence of parasitic diseases but will also improve rural
economy. The author has again emphasized
opening a national institute of parasitology so that a holistic view may be
developed towards parasitic diseases ,existing in the country .
REFERENCES :
Agrawal, M.C. 1999. Schistosomosis : an underestimated
problem in animals in South Asia. World Animal Review 92 : 55-57.
Agrawal,M.C. 2003. Epidemiology of fluke infections . In
(ed Sood ML) Helminthology in India .Inrtenational
Book Distributors, Deharadun . Page 511—542
Agrawal MC. 2012. Schistosomes and schistosomiasis in South Asia. Springer India Pvt Ltd , New Delhi.
Agrawal MC ,Singh KP, George J and Gupta S 2005.
Niclosamide trials on Indoplanorbis existus and Lymnaea luteola under different
conditions. J Parasit Dis 29: 53-58
Dutt SC 1980. Paramphistomes and
paramphistomiasis of domestic animals of India. Punjab Agriculture University,
Ludhiana . Page 162.
Rathore BS 1998 . An epidemiological study on buffalo
morbidity and mortality based on four year observations on 18630 buffaloes
maintained at 28 livestock farms in India. Indian J Comp Microbiol. 19 :43-49
Shames N,Agrawal MC and Rao KNP
2000. Chemotherapeutic efficacy of praziquantel and closantel in experimental
porcine schistosomiasis. Indian J Anim Sci 70 : 797-800
WHO 1985. The control of schistosomiasis.
Technical report series 728. World Health Organization ,Geneva Page 113
