Serosurvey of infectious laryngotracheitis in laying hens, and economic impact of vaccination in Algeria

The purpose of this study was to demonstrate the presence of virus disease of infectious Laryngotracheitis (ILT) in Algeria in laying hen farms; through the demonstration of seroconversion signing a recent viral passage and also a comparative study cost / benefit of vaccination against this disease.

Up ‘til 2011, no study was conducted to highlight the presence of the virus suspected of being responsible for the Egg drop syndromeand the recentseroconversion of infected farms. There are several methodsfor the diagnosis of these diseases such as virus isolation, inoculation of chicken, immunofluorescence, histopathology and finally the gel diffusion (Tripathy and Hanson, 1980). Enzyme-linked immune-sorbent assay (ELISA) is also an effective method of diagnosis as well as being a sensitive test. This method has the advantage of being commonly used to measure antibodies of many different pathogens in the serums including VILT (Barhoom, 2009 and Gomes, 2008; Piroird and Lombard, 1980).

 

From March 2010 to April 2011, 15 laying hen farms spread across the country, namely 11 farms in central Algeria, 02 farms in the East, and 02 farms in the West. These farms have a capacity of 4800 up to 130,000 laying hens, observed by sentinel veterinarian after an egg drop; a data sheet for the laying hens was established containing the following information: The capacitystrains, vaccination programs applied, accidentslaying observed (percentage drop, external appearance of eggs), the associated clinical symptoms, autopsy examinations and mortality rates recorded during an episode of the egg drop

Blood samples at the wing vein according to the method of Campbell (1995) were performed on 15 hens per farm right at the moment of the egg drop (S1) and another sample made three weeks later (S2), a total of 450 serums were made .Technically, a volume of 3 ml of blood /chicken wastaken at the wing vein and collected in drytubes and directlycentrifuged (3000 rpm / min, 6 min). After centrifugation, a volume of 300ul plasma was collected using a capillary pipette and divided into two Eppendorf tubeslabeled for each sample and keptcold in a freezer (-20 ° C) until the serological analysis performed at the analytical laboratory (LAB-VET in partnershipwith the laboratory of BIO CHENE-VERT-France). The kits are supplied by Bio Check(Check Bio BV Holland), theycontain 05 plates and all reagentsrequired (readyto use). Each sample was diluted to 1/500 1ul adding 0.5 ml dilution buffer. Measuring results of the ELISA test is performed with a microplate reader: with a spectrophotometer at 405 nm filter.

 

 

The purpose isto assessthe different types ofcosts and benefits, through description and quantification. The generalstructure of this analysis is organized in two columns, costs and benefits, including each of the elements and more elements within

In this study, we will evaluate the different costs and benefits ofvaccination of the ILT on a farmfor a sample of 10,000 laying hens.

Technique estimation, Currency Conversion, Comparison Benefits / Costs.

 

 

Regarding the ILT on the international market, there are two attenuated vaccines packaged in vials of 1,000 doses. The price of the bottle is about 25 €. The vaccine is made by eye drop and without a booster at 12 weeks of age. The cost of applying the product depends on the number of procedures performed. In this case, the beginning of vaccination of pullet against the ILT is only done once, to do this, one person is sufficient to vaccinate up to 1000 subjects. Beyond this level, it will be necessary to hire a second person who can achieve as 1000 subjects, and so on. So the number of people is 10, under the direction of a veterinarian or a livestock technician. Throughout our study we have concluded minimal or no side effects of vaccination.

Any action to fight the contamination with a disease is designed to achieve an improvement in the health situation and consequently a reduction in losses. The principle of estimating the benefits is to of asses and evaluates the losses in the absence ofvaccination. The gain calculation eggsis based on the difference between the actual laying hens and the theoretical curve multiplied by the unit price of egg consumption which is 0.06 €, representing the selling price of the market during the study period. The shortfall in producing eggs for human consumption, which represents the amount of eggs that have been laid by individuals with during the clinical episode of ILT multiplied by the price of the egg is 0.06 €. In our study we used a rate of egg drop of 5%. Another benefit of vaccination is to reduce the number of subjects who would have died by the ILT during the clinical phase of the disease multiplied bythe unit price hen, which isvalued at € 3.75. The mortalityrate attributed to ILT is 1.3% to 16%, We chose a rate of 1%. Applying proper vaccination significantly reduces the potential treatments. Treatment costs consist of the administered MEDICINES as curative, according to their prices in the market drugs.

All validity tests were positive. Calculations of securities by breeding with the average, maximum, minimum and coefficients of variation Series Collection.

 

Serological results of the first round of sampling revealed 20% of the positive ILT farms namely E1 and E7. These livestocks have presented positive seroconversion. Adair et al in 1985, showed that neutralizing antibody virus ILT becomes detectable in 5-7 days pi (Post infection), and makes a peak around 21th days, then drops to their lowest level over the following months.

 

Table 1: Farms seroconversion

 

Vaccination against ILT is nonexistent in Algeria;so positive serologyreveals necessarilythe presence of thisvirus. We observed (Table 1) an increase in antibodies at farm level E1 and E7 signing a clearseroconversion, 1890 and 1253 AC log 10 for the first samples (S1) respectively, to reach 3257 and 1706 AC log 10 three weeks later E1 and E7 respectively.

However, livestock E2 has given us quite atypical results, indeed the first round of sampling has revealed an average rate of 5617 AC log 10, and three weeks later an average rate of 3448 AC log 10, showing sharply at the beginning of the series of sampling an AC level large enough for three weeks later this AC level drops slightly.

These results are probably due to a very late intervention on the animals for the first round of sampling therefore follows the image of a curve in the descending phase of the production of antibodies.

For comparison work Barhoom 2009 show seropositivity 3 laying flocks. Ebrahimi in 2003, in a study focused on five farms hens(Iran) reported a prevalence of 100% breeding. Johnson et al. In 2004, observed that 57.1% of broiler farms and breeding flesh were positive for ITL. Similarlyin Brazil, Gomes(2008) reported a relatively high prevalence in the region of Bastos(59.4%) in flocks of laying hensin a studyfrom 2002 to 2006). Study wasconducted on reporting of the occurrence of atypical respiratory symptoms in laying hen Region Bastos.

 

Table 2: Séroprévalence of the ILT depending of the duration of the Egg drop

 

Our study allowed us to highlighting ILT in different regions of Algeria. Depending on the duration of egg drop, our results are consistent with the study by Callison et al (2007), the manifestation of ILT in a breeding laying hens causes egg drop for more than 3 weeks.

 

Table 3: Seroprévalance of the ILT depending on the rate of the Egg drop

 

We notice from Table 3 that the relationship between seroprevalence and the percentage of egg drop is very variable. indeed in farms with egg drops from 5 to 15% only 37% were positive, however on farms with higher nesting drops to 15% almost 57% were seropositive Our results compliant with those of Barhoom (2009) and Gomes (2008) who reported that the LTI can cause a drop in egg production up to 30%.

It is very crystal clear that the ITL strongly affects the production of consumed egg leads to serious economic losses due not only to the drop in production but also because of fragile and discolored eggs.

 

Table 4: Seroprevalance of the ITL depending on clinical signs at the farms

 

The clinical signs in studied animal farms when present consisted of moderate respiratory illness with conjunctivitis, nasal discharge, infra orbital edema, tracheitis ... to renal impairment.

It appeared in this study (Table 4) that the onset of the ILT animals from breeding submitting a status to the LTI is very variable. Indeed, among the 10 farms assigns presented clinical signs of ILT only 3 of them were positive meaning 30% in total. Among the five Farms presenting no clinical signs of ILT, 4 were positive 80%.

These results are consistent with other studies that indicate that in recent years the infectious laryngotracheitis (ILT) HAS returned in a very mild form ,causing problems in laying hen farms (Barhoom, 2009. Shan-chia, 2010) ,Gomes et al 2008; confirmed by requiring only a few birds in an infected flock may show the classic respiratory signs and mortality can be low with a drop in egg production up to 30%.

 

Table 5: Economic conversion (costs and benefits) of the vaccination against ILT.

 

Following the small economic study carried out in Table 5, this somehow shows literally that vaccination against ILT has some significant economic benefits.

 

The results obtained from this study highlight serological biomarkers of infection ILT farms studied in laying hens which is in itself a first in Algeria.

Based on these results, we could easily make identifythe link between the detection of anti ILT antibodies and seroconversion in these farms that can cause a drop in egg. In the economic part of the study, we discussed a project to fight against the ILT in a livestock of 10,000 laying hens, through establishing reports of the costs and benefits of this control program.

This micro-economic financial approach in Algeria allowsthe conclusion that it is desirable to develop a systematicvaccination ofchickensstarted against the ILT. Such application could avoid and prevent lossesvalued at 1,488 € / 10,000 subjects (Table 5) due to a possible clinical manifestation of ILT.

 

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Gomes, B., “Planification, mise en œuvre et gestion des mesures de protection de la santé animale contre la Laryngotrachéite infectieuse aviaire dans la région de Bastos“, Jaboticabal, Sao Paulo, Brésil, (2008).

Callison S.A, S.M. Riblet, I. Oldoni, S. Sun, G. Zavala, S. Williams, R.S. Resurreccion, E. Spackmand, M. Garcia, “Development and validation of a real-time Taqman® PCR assay for the detection and quantitation of infectious laryngotracheitis virus in poultry“ Journal of Virological Methods 139, (2007), 31–38.

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Johnson, Y.J.; Colby, M.M.; Tablante, N.L, “Application of commercial and backyard poultry geographic information system databases for the identification of risk factors for clinical Infectious laryngotracheitis in a cluster of cases on the Delmarva Peninsula”. (2004).International Journal of Poultry Science,v. 3, n 3.