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Zoonotic Disease Prevention and Control Strategies

Introduction Zoonotic diseases are of major concern to both animal and human health and welfare. Zoonoses are diseases caused by pathogens capable of spreading from animals to humans and vice versa. Of the 1,415 known human pathogens, more than 60% are zoonotic and kill over 14 million people annually (Taylor et al. 2001). Zoonotic pathogens damage biodiversity in sensitive wildlife (Daszak et al. 2000), cause tremendous loss of income in agriculture (Phiri et al. 2003), and cost millions in health care (Torgerson 2003). Since zoonoses affect humans and animals in many ways, it is important to study them. Understanding the zoonotic pathogen and animal interactions aids human health in reducing exposure, developing vaccines, and developing diagnostic and epidemiological tests.
Reducing Exposure Zoonotic disease prevention is of critical important to humans; if zoonoses cannot infect new hosts, then the large devastation wrought by the pathogens is greatly reduced. One aspect of disease prevention is reducing exposure to the pathogen. Studying animal and zoonotic pathogen interactions can reduce exposure.
Studies on zoonotic pathogens and animal interactions can identify routes of transmission. When routes of transmission are known, then exposure to the pathogen can be avoided. A classical example, toxoplasmosis, caused by the parasite Toxoplasma gondii, is a major health concern in humans. Infections of T. gondii in humans cause abortions in pregnant women, encephalitis, retinochoroiditis and hydrocephalus in children infected while a foetus, and death of patients suffering from acquired immunodeficiency syndrome (AIDS) (Innes 2008). In studying the animal/pathogen interactions, it was found that T. gondii could exist as a protective cyst within the meat of an animal for the remainder of the animal’s life (Jacobs et al. 1960). This suggested a possible route of transmission was consuming meat containing T. gondii cyst. In addition, the domestic house cat was discovered to be the definitive host for T. gondii, and that an infective form of T. gondii, not similar to the cyst, could be found in the faeces of the cat (Hutchinson 1965). Because of the knowledge gained from studying the animal/pathogen interactions of Toxoplasmosis, humans are now directed to consume only thoroughly cooked meat, and pregnant/immunocompromised humans are directed to avoid cat faeces (CDC website 2008).
Changes in animal physiology can alter the number of pathogens shed into the environment. Research on pathogen/animal interactions found that stress hormones increase an animal’s susceptibility to infection by a zoonotic pathogen. Zoonotic Escherichia coli serotypes O157:H7 (E. coli O157:H7) adheres and colonizes pig intestinal walls when the stress molecule adrenocorticotrophic hormone (ACTH) is present, but non-zoonotic serotypes of E. coli do not adhere more (Schreiber and Brown 2005). E. coli O157:H7 is of great importance to human health. It is transmitted via faecal-oral route, and it causes severe haemorrhagic colitis and haemolytic-uremic syndrome (Lawson 2004). In addition, examination of swine faeces during stressful handling showed an increase of E. coli O157:H7 (Dowd et al. 2007). Swine are not alone in the potential increase in zoonotic shedding due to stress. The stressful transportation of cattle caused an increase shedding of Salmonella spp., another food-borne zoonotic pathogen (Barham et al. 2003). Armed with this knowledge, humans can alter their behaviour to reduce stress on livestock. This will reduce the potential exposure via food-borne transmission to consumers of the meat, and direct faecal-oral transmission to the handlers.
Developing Vaccine The study of animal immunological response to zoonotic pathogens has led to the development of vaccines. These vaccines can benefit human health in two ways: indirectly or directly. Indirectly, the vaccines are used on animals. The use of vaccines on animals in zoological pathogens reduces human exposure. Directly, vaccines could be altered for use on humans.
The study of zoological pathogen and animal interactions has led to the creation of many types of vaccines. Vaccination against zoonotic pathogens reduces human exposure. The vaccines reduce exposure in two ways: reduction of reservoir host pool, and reduction of amount of pathogen shed into the environment.
If a vaccine reduces the reservoir host pool of the pathogen around humans, it then limits the human potential exposure. A major example of this is the development of the vaccine for the Lyme disease causing pathogen, Borrelia burgdorferi. Lyme disease is tick-borne. B. burgdorferi has multiple wildlife reservoir hosts including the white-footed mouse (Peromyscus leucopus) and the white-tailed deer (Odocoileus virginianus) (Gomes-Solecki et al. 2006). As the nymph ticks feed on an infected reservoir host, they become infected with B. burgodrferi. When the nymph ticks become adults, they may feed on humans, potentially causing zoonotic transmission. Through studies of host-pathogen interactions in mice, it was discovered that there was an antigen that initiates a large specific immune response from mice (Fikrig et al. 1990). From this knowledge, an oral vaccine has been developed that reduces the amount of B. burgodrferi in wild mice substantially (Gomes-Solecki et al. 2006). It has been proposed that feed baited with this new vaccine could be spread in areas where B. burgodrferi is endemic and the wild field mice are present (Gomes-Solecki et al. 2006). This would effectively reduce the potential size of the host reservoir, thus limiting potential human exposure to zoonotic pathogens. This vaccination method could be applied to other zoonotic diseases.
Additionally vaccines can reduce the amount of pathogens shed into the environment. This method has been used with great success in the reduction of the zoonotic pathogen E. coli O157:H7. Studying the host/pathogen interactions in cattle, it was discovered that the bacterial surface protein intimin was important in intestinal colonization (Dean-Nystrom et al. 1998). Using this knowledge, a vaccine was developed that when given to cattle reduced colonization of the intestines and the amount of E. coli O157:H7 that was shed in faeces (Khare et al. 2010). This vaccine reduces the amount of bacteria present in the environment, thus limiting human exposure via direct oral contact with the environment or food contamination.
Some zoonotic pathogens have similar interactions with humans as with other animals. By studying the interactions between the pathogens and the animals, it is possible to create an animal vaccine model with which a vaccine for humans can be developed. Tuberculosis is caused by the zoonotic intracellular bacteria Mycobacterium spp. Scientist are learning a large amount about intracellular pathogens and how the animal immune responds by using multiple animal models, including bovine (Pollock et al. 2006, Van Rhijn et al. 2008). Vaccines for bovine tuberculosis, developed using knowledge gained in the aforementioned studies, provide models for human vaccines against similar intracellular pathogens (Buddle et al. 2003).
Developing Diagnostic and Epidemiological Tests A great benefit to human health from studying animal and zoonotic pathogen interactions is the development of diagnostic test that can be used in humans. Zoonotic visceral leishmaniasis is an arthropod transmitted disease caused by the protozoan parasite Leishmania infantum (Chappuis et al. 2007). Visceral leishmaniasis is fatal without treatment in both humans and canines, the animal host. It was discovered that the presence of antigen rK39 is a strong indicator of clinical visceral leishmaniasis in dogs (Goto et al. 2009). Another antigen, L. infantum cytosolic tryparedoxin peroxidise (LicTXNPx), was described and predicted to be a great indicator of both clinical and subclinical visceral leishmaniasis in dogs (Silvestre et al. 2008). A highly specific and sensitive enzyme-linked immunosorbent assay (ELISA) was developed for dogs based on those two antigens (Santarãm et al. 2010). ELISAs are rapid and can confirm the presence of an antigen within minutes. Previous techniques of diagnostics used for leishmaniasis took hours to days to confirm infections (Chappuis et al. 2007). It is predicted that this ELISA could be used in humans (Santarãm et al. 2010), showing how a diagnostic test was developed benefiting human health by studying the interaction of animal and pathogens.
Another potential use for this newly developed ELISA that would benefit humans is using it on dogs. Because the ELISA is rapid, sensitive, and specific, it will identify subclinical infections in canines. Because canines are the major reservoir host, if many dogs in an area test positive for infection, it is an epidemiological indicator that the disease is endemic in that area. This benefits humans, because it will prompt the use of proper epidemiological control mechanism.
Another way that understanding of zoonotic pathogen interactions with animals helps develop epidemiological tests is through finding sentinel animals. A sentinel species is a species that tends to develop notable signs of an infection before humans or other animals (Racloz et al. 2006). West Nile virus (Flaviviridae: Flavivirus) is a major mosquito-borne zoonotic pathogen. West Nile virus can cause mengioencephalitis in humans, and is currently of major epidemiological concern in North America where it had spread across the continent within a matter of years (Murray et al. 2010). American crows (Corvus brachyrhynchos) are very susceptible to infection from the virus pathogen (Reisen et al. 2006). Understanding this relationship between the crow and the virus has allowed epidemiologist to utilize the American crow as a sentinel species. As a sentinel species, the American crow provides an early warning system, notifying human health profession that the virus is within the area. This warning prompts the use of emergency control strategies, benefiting human health.
Conclusion Understanding zoonotic diseases is of vital importance to humans and animals alike. Zoonoses devalue livestock, harm humans, increase cost of healthcare, and impact wildlife. By studying the ways in which zoonotic pathogens interact with their animal hosts, scientists, doctors and veterinarians are able to benefit human health through reducing exposure, developing vaccines, and developing diagnostic and epidemiological tests.

Correlation of Phenotypic Traits in Maize Different Hybrids

Evaluation correlation between phenotypic traits in corn hybrids and their change trends under drought stress and non-stress conditions at flowering and grain filling stages
Rahim Mohammadian, Behnam Tahmasebpour, Peyvand Samimifar, Habib Lotfi
Abstract
To investigate the correlation of phenotypic traits in maize different hybrids, an experiment was conducted in split plot design with 3 replications under stress-free conditions and irrigation cutting treatments on flowering and grain filling stages in the experimental field of Tabriz agricultural management. Phenotypic correlation coefficients was assessed for all hybrids in drought free conditions and different levels of irrigation cutting treatments in flowering and grain filling stages, after data analysis and estimation of average characteristics of hybrids. In general, it is recommended to select hybrids likely to drought by grain row numbers and 1000 grain weight under non-stress conditions and 1000 grain weight is an appropriate criterion for above mentioned selection under irrigation cutting treatment.
Keyword: drought stress conditions, corn hybrids, phenotypic traits, grain filling stages.
Introduction
Today a large part of breeding studies is devoted to studying plant responses to water scarcity and drought stress. In Iran, plant growth and production is influenced by drought stress more than any other factor(1). In general the best way to deal with drought stress is optimal use of water and plant’s modification to increase their drought resistance that is the plant ability to desired grow and produce under stress conditions(5). We can consider plant modification and their reinforced drought resistance as an important component of desired compositional method to cope with drought. The use of existing genetic diversity is the simplest measure of plant breeding for drought resistance and other environmental stresses. In this method, different genotypes were exposed to the related stress and those which handle this situation better are selected(9). It should be mentioned that water stress on plant growth stages does not work equally; some stages are very sensitive to increased drought stress, while others are less affected(2). It is noteworthy that the phenotype of a crop is the result of interaction between many genetic and environmental factors; moreover, these different environmental factors alter the rate of correlation between yields related traits(6). Singh and Singh (8) examined the phenotypic correlation of corn different traits. There is positive phenotypic correlation between grain yields with maize characteristics like the number of grain row, the number of grain per row and 1000 grain weight. Also we observed a negative phenotypic correlation between performances with maturity and evolution parameters such as the number of the days to 50% peak flowering, the number of the days to maize 50% drying and the number of the days to 50% physiological maturity. The plant height, maize and flower crown had positive phonological correlation with the performance. The maize related parameters and crop traits showed positive correlation(8).
Shiva and Jagarnat (7) were evaluated the relationship of different traits with the plant performance and the yield per area unit separately. There was positive and significant correlation between 1000 grain weights, the number of the grain per maize, the number of the maize per plant with total of plant’s dry weight and its percentage and the percentage of dry grain weight to bush(7). Bolanos and Edmeades(3) was determined the phenotypic correlation between grain performance with other traits under stress conditions. Edmeades etal (4) used the collected data to review the effects of drought stress and found a significant correlation between the grain performances with flowering period.
Methods and Materials
In this study, two groups of ten cultivars of early and medium maturity corn hybrids were investigated according to FAO maturity groups. This experiment was conducted split plot design with 3 replications and 3 treatments in the form of randomized blocks. The main factor was irrigation different levels and sub factor was ten cultivars from two group’s maturity. Along with the performance of the experiment in the field, characteristics were measured in the treatments related to early and middle maturity and in two stress groups.
Results and discussion
The coefficients of phenotypic correlation of studied traits under non-stress conditions showed that the correlation between plant performance with 1000 grain weight and the number of the grain rows was 1% positive and significant. The most correlation is related to the number of the grain rows. It means that under non-stress conditions the plant performance is influenced by 1000 grain weight that is so important. None of the traits had significant positive or negative correlation with 1000 grain weight. The correlation of the number of the grain row with the maize height, its length and the number of the leaf under maize was 5% positive and significant. So we found that under non-stress conditions, the performance is influenced by the number of the grain row and 1000 grain weight and those are appropriate traits for the maize performance.
Table 1. The correlation coefficients of phenotypic traits in corn hybrids under non-stress conditions.
No
traits
1
2
3
4
5
6
7
8
9
10
1
Bush height
1
2
Maize height
0.52
1
3
Leave total number
0.164
0.701
1
4
Number of maize upper leave
-0.31
0.225
0.6
1
5
Number of maize under leave
0.397
0.73*
0.88*
0.158
1
6
Maize wood diameter
0.332
0.73*
0.454
0.315
0.387
1
7
Grain row number
0.106
0.541
0.193
0.132
0.142
0.324
1
8
Maize length
0.543
0.649*
0.195
-0.039
0.266
0.456
0.74*
1
9
1000 grain weight
-0.1
0.07
-0.3
-0.046
-0.354
0.153
0.683
0.41
1
10
Plant performance
-0.2
0.266
0.11
0.354
-0.084
0.339
0.85**
0.54
0.81**
1
Phenotypic correlation coefficient of irrigation cutting treatments at flowering stage showed that none of these studied traits had significant and positive correlation with the maize performance. The correlation of 1000 grain weight with the number of grains per row was negative and 5% significant. It means that the reinforcement of grain row in irrigation cutting treatment has negative impact on 1000 grain weight and reduces its weight. The irrigation cutting treatment in the flowering stage makes pollen dried and reduces pollination and fertilization and increases hollow beads percentage so it has more drops influenced by the number of grain row increase and finally reduces 1000 grain weight.
Table 2. The correlation coefficients of phenotypic traits in corn hybrids in flowering stage and irrigation cutting treatment.
No
traits
1
2
3
4
5
6
7
8
9
10
1
Bush height
1
2
Maize height
0.23
1
3
Leave total number
0.134
0.613
1
4
Number of maize upper leave
0.44
-0.179
0.214
1
5
Number of maize under leave
0.177
0.67*
0.75*
-0.483
1
6
Maize wood diameter
0.71*
0.332
0.36
0.166
0.211
1
7
Grain row number
0.069
0.044
0.001
0.008
-0.004
0.202
1
8
Maize length
0.225
0.519
0.132
-0.459
0.428
0.69
0.286
1
9
1000 grain weight
-0.122
-0.299
-0.338
0.213
-0.447
-0.583
-0.374
-0.581
1
10
Plant performance
-0.199
-0.298
-0.406
-0.172
-0.248
-0.403
0.344
-0.132
0.581
1
The under studied phenotypic traits correlation coefficients in grain filling stage and irrigation cutting treatment showed that the performance correlation of the maize with the traits like the maize wood diameter and 1000 grain weight was positive and significant and the most correlation is related to the maize wood diameter. It means that under irrigation cutting treatment, the performance is influenced by this trait and it is more important that 1000 grain weight. Also 1000 grain weight had significant positive or negative correlation with none of traits. So we can claim according there results that irrigation cutting treatment at the stage of grain filling impacts leaf photosynthesis and reduces the material transportation to the grain, so makes the performance reduced under stress free conditions. We conclude that it is possible to select 1000 grain weight resistance to drought according to the maize wood diameter under irrigation cutting treatment in grain filling stage.
Table 3. The correlation coefficients of phenotypic traits in corn hybrids in irrigation cutting treatment, in flowering stage.
No
traits
1
2
3
4
5
6
7
8
9
10
1
Bush height
1
2
Maize height
0.70*
1
3
Leave total number
0.67*
0.619
1
4
Number of maize upper leave
0.433
0.09
0.69*
1
5
Number of maize under leave
0.63*
0.76*
0.90**
0.308
1
6
Maize wood diameter
0.467
0.548
0.135
-0.074
0.22
1
7
Grain row number
0.524
0.332
0.054
0.074
0.03
0.38
1
8
Maize length
0.46
0.421
0.168
-0.105
0.29
0.17
0.84
1
9
1000 grain weight
-0.217
-0.113
-0.054
-0.275
0.08
0.35
-0.25
-0.07
1
10
Plant performance
0.352
0.318
0.054
-0.159
0.16
0.81*
0.41
0.38
0.66
1
References
Agricultural Ministry IT and statistic department, 2002,
Arzani A 1999, plants improvement (translation), forth volume, Isfahan industrial university publication
Bolanos J and Edmeades GO 1996. Midseason drought as a selection environment for tropical maize improvement . In developing drought and low nitrogen tolerant Maize . 1996 . D.F. Mexico. CIMMYT
Edmeades G, Bolanos J and Laffitte HR 1990.Selection for drought tolerance in maize adapted to the lowland tropics,CIMMYT.Mexico.D.F.
Khodabande N 1993. cereal, third print, Tehran university publication
Sarmadnia GH and Koochaki A 2007. physiological planting, second volume, Mashhad University
Shiva S and Jagarnath MK 1991. Relationship of the growth and yield component with grain yield of maize through path analysis. J.Agric.Res.42:223-225.
Singh G and singh M 1993.Correlation and path analysis in maize under mild – hills of skin. Crop Improvement .20:222-227.
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